Electro-Osmosis of Oil : Electrical Stimulation of Oil
Recovery -- Articles & patents

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**Electro-Osmosis of Oil**

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**Electrical Stimulation of
Oil Recovery**

  
It has become unarguably obvious to all but the most recidivist
technocrats ( present company excepted, of course ), that
"fracking" for natural gas is unprofitable, unsustainable,
unclean, and it is a direct cause of earthquakes. But what else
can we corporatists vampires do ?  
  
In anticipation your mindful inquiry, here is a sneak peek at the
Next Bigly Thing in Petro-Pumping : Electro-Osmosis !  
  
Water in porous material ( e.g., soil or concrete ) is attracted
to ground, to the negative electrode. This factoid is used
industrially to dewater concrete constructions at a much faster
rate.  
  
The same principle applies to oil. Not only is the migration of
molecules accelerated, but the overall energy requirements are
reduced.   
  
Electrical field treatment of oil in pipelines also minimizes
surface tension between the pipe and petroleum, thereby
accelerating delivery.  
  
In this same manner, apparently exhausted wells can be rejuvenated
in a timely manner, simply by electrically inducing the planet to
excrete still more black goo for our Needful Things.  
  
Considerable field research has been performed over several
decades to determine the parameters for electro-osmotic production
of oil. The required voltage, amperage, waveforms, and frequencies
are known, and equipment has been developed to implement the
technology.  
  


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**Contents**

  
**[Electropetroleum.com : A Vast
Opportunity a Billions of Barrels Waiting Below Us](#electropetrol)****[Wittle, et al. : Direct Electric Current
Oil Recovery (EEOR) a A New Approach to Enhancing Oil
Production](#2wittle)****[Haroun : Optimizing Electroosmotic Flow
Potential for Electrically Enhanced Oil Recovery (EEORTM)...](#3Haroun)****[Laursen : Electro-osmosis in oil
recovery : Progress report II](#4laursen)****[Al-Hamaiedh, et al. : Treatment of
oil polluted soil using electrochemical method](#5Al-Hamaiedh)****[Oilrec Trechnologies](#6OilrecTrechnologies)****[Sumatra Field Trial](#7sumatra)****[US7325604 : Method for enhancing oil
production using electricity](#8-US7325604)****[WO0303823 : Electrochemical process
for effecting redox-enhanced oil recovery](#9-wo0303823)****[US3915819 : Electrolytic oil
purifying method](#10-US3915819)****[US2013277046 : Method for
Enhanced Oil Recovery from Carbonate Reservoirs](#11-US2013277046)****[US7325604 : Method for enhancing
oil production using electricity](#12-us7325604)****[US2005161217 : Method and system
for producing methane gas from methane hydrate
formations](#13-us2005161217)****[US2799641 : Electrolytically
promoting the flow of oil from a well](#14-US2799641)****[US3417823 : Well treating process
using electroosmosis](#15-us3417823)****[US3724543 : Electro-thermal process
for production of off shore oil through on shore walls](#16-US3724543)****[US2014116683 : Method for
Increasing Bottom-Hole Formation Zone Permeability](#17-US2014116683)****[RU2132757 : Method of Removing
Hydrocarbons from Soil](#18-ru2132757)****[KR20010086551 : Purification
Method of Contaminated Soil with Petroleum Oil](#19-kr20010086551)****[RU2602615 : Method of Soil Cleaning
from Hydrocarbons](#20-ru2602615)****[KR101464878 : Remediation System
for Multi-Contaminated Soils](#21-kr101464878)****[US4645004 : Electro-Osmotic
Production of Hydrocarbons Utilizing Conduction heating of
Hydrcarbon Formations](#22-US4645004_)****[WO2012158145 : Method for
Electrokinetic Prevention of Scale Deposition in Oil Producing
Well Bores](#23-wo2012158145)**  
  


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[**http://electropetroleum.com/technology/**](http://electropetroleum.com/technology/)

**A Vast Opportunity a
Billions of Barrels Waiting Below Us**

  
Given todayas fluctuating oil prices, as well as the ever-present
politics of supply and demand, the need for further heavy oil
recovery is enormousa| as is the opportunity. Currently, there are
several hundred billion barrels of known heavy oil reserves in
North America and vast reserves elsewhere in the world. The
prevailing methods for heavy oil extraction are steam-based (which
require massive amounts of water and power), including steam
flood, cyclic steam injection, and steam-assisted gravity
drainage. However, Electro-Petroleum, Inc. (EPI) now offers a
cost-effective alternative and can recover oil in reservoirs where
steam methods cannota| and with less effect on the environment.  
  
**EEOR a Electrically Enhanced Oil Recovery SM a Highly Effective
for Heavy Oil Recovery, Cost Savings, and the Environment**  
This patented technology from Electro-Petroleum, Inc. (EPI) sets a
new standard for heavy oil recovery that requires no water and
less power to apply. The process enables low-cost recovery of
stranded oil reserves by applying electric currents to
hydrocarbons in the ground, which upgrades and mobilizes heavy
oils that are too viscous to be extracted by conventional pumping
techniques. Plus, EEOR is dramatically more environmentally
friendly than alternative heavy oil extraction techniques (such as
steam injection), which requires massive amounts of water and
power.  
  
**Breakthrough technology for heavy oil recovery using direct
current electricity.**  
  
Demonstrated ten-fold increase in production in field tests.  
More cost-effective and less capital intensive than other
secondary recovery processes.  
Ability to access oil heavy oil reserves where other technologies
cannota| without depth limitations.  
  
**Our Technology**   
EEOR a Electrically Enhanced Oil Recovery SM process involves
passing direct current (DC) electricity between cathodes (negative
electrodes) in the producing well and anodes (positive electrodes)
either at the surface or at depth.   
  
Important facts include:  
  
EEOR has demonstrated, in an 18-month field test, the ability to
increase heavy oil production ten-fold from baseline levels in a
field where other secondary oil recovery techniques were not
successful.  
  
Able to retrofit exiting wells for EEOR  
  
EEOR is able to be effective in reservoirs where steaming is
either ineffective or uneconomical  
  
Energy costs for EEOR are less than $4/barrel, and capital costs
are a fraction of steam-based methods.  
  
The 3 Mechanisms of EEOR in Heavy Oil Recovery:  
  
Electro-Chemical Upgrading, or aCold Crackinga a Oxidation and
reduction reactions break down heavy oil molecules into lighter
oil molecules, upgrading the oil in the reservoir.  
  
Electro-Kinetics or Electro-Osmosis a Oil in the reservoir
migrates toward the negative cathode, creating a drive mechanism,
or flow, towards the well.  
  
Resistance, or Joule Heating a Oil around the well bore is heated,
becoming less viscous and easier to extract.  
  
**Advantages Over Steam-Based Technologies**  
EEOR has several important advantages over competing steam-based
heavy oil recovery technologies  
No depth limitations a Steam-based methods are effective up to
approximately 2,500 feet while over 50% of US heavy oil reserves
are below 2,500 feet.  
Energy costs of less than $4 per barrel produced a Plus lower
capital costs than steaming.  
No water supply needed a And does not use a working fluid.  
Produces no greenhouse gases.  
Heat is generated directly in the reservoir a Rather than at the
surface.  
Depends upon resistivity, not permeability a And increases
apparent permeability in the reservoir.  
No athief zones.a  
Ability to add capital/infrastructure incrementally allowing for
faster cash flow break-even.  
Electro-kinetics influence produced fluid and flow.  
  
**Publications**  
  
Wittle JK and Hill DG, Use of Direct Current Electrical
Stimulation for Heavy Oil Production, Society of Petroleum
Engineers Applied Technology Workshop a Technologies for Thermal
Heavy Oil and Bitumen Recovery and Production, Calgary, Alberta,
Canada, March 14a15, 2006.  
  
Wittle JK and Hill DG, Direct Current Electrical Stimulation a A
New Approach to Enhancing Heavy Oil Production, First World Heavy
Oil Conference, Beijing, China, November 12a15, 2006.  
  
Wittle JK, Hill DG, and Chilingar GV, EEOR a Electrically Enhanced
Oil Recovery SM Using Direct Current, Oil Sands Heavy Oil
Technologies Conference, July 18-20, 2007.  
  
Wittle JK, Hill DG, and Chilingar GV, SPE-114012, Direct Current
Electrical Enhanced Oil Recovery in Heavy-Oil Reservoirs To
Improve Recovery, Reduce Water Cut, and Reduce H2S Production
While Increasing API Gravity, presented at the 2008 SPE Western
Regional and Pacific Section AAPG Joint Meeting, Bakersfield,
California, USA, March 31aApril 2, 2008.  
  


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[**http://www.tandfonline.com/doi/abs/10.1080/15567036.2010.514843?src=recsys&journalCode=ueso20**](http://www.tandfonline.com/doi/abs/10.1080/15567036.2010.514843?src=recsys&journalCode=ueso20)**http://dx.doi.org/10.1080/15567036.2010.514843****Energy Sources, Part A: Recovery, Utilization, and
Environmental Effects, Volume 33, 2011 - Issue 9** 

**Direct Electric Current Oil
Recovery (EEOR)aA New Approach to Enhancing Oil Production**  
  
**J. K. Wittle , D. G. Hill & G. V. Chilingar ( USCal)**

**Abstract**  
Based on laboratory experiments and several tests, the application
of direct electric current to enhance oil recovery appears to be a
cost-effective technology. It can be used for both heavy and light
crudes. The technology is based primarily on electrokinetics, with
coupled thermal effects.  
  


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[**https://www.onepetro.org/conference-paper/IPTC-13812-MS**](https://www.onepetro.org/conference-paper/IPTC-13812-MS)**https://doi.org/10.2523/IPTC-13812-MS****International Petroleum Technology Conference, 7-9
December, Doha, Qatar, 2009**

**Optimizing Electroosmotic
Flow Potential for Electrically Enhanced Oil Recovery
(EEORTM) in Carbonate Rock formations of Abu Dhabi Based on
Rock Properties and Composition**  
  
**Muhammad Raeef Haroun (Univ of Southern California), e tal.**

**Abstract**  
  
Among the leading emerging technologies for in-situ oil recovery
is the use of an electrokinetic technology known as electrically
enhanced oil recovery (EEORTM)i. Electrokinetic methods are
continually tested and improved both in the laboratory and in the
field to render them highly feasible for increased oil recovery.
The effectiveness of the process to enhance the flow and
production of both light and heavy crude oil from sandstone
reservoirs have been demonstrated in the laboratory by researchers
for the last four decades. Successful but limited field
applications, both in-situ and ex-situ have also been reported for
the same duration of time. There has been little work done on the
applicability of the technology to carbonate rock reservoirs,
owing to predicted high energy consumption due to low clay content
formations and high salinity environments. Yet, compared to
currently incurred high costs of conventional electrical oil
recovery which depends on joule heating of the formation ,
electroosmotic mass transport may offer a feasible option to
augment the flow of these large volumes of crude oil both onshore
and offshore.  
  
A great additional incentive is that EEORTM can be engineered as a
truly green technology, where there is no water consumption, and
no air, water, and formation pollution. The technology can be
applied with no depth limitation in-situ rendering it even more
attractive in remote operating locations as well as the
environmentally challenging ones. This paper addresses the first
attempt undertaken at the newly-established Electrokinetic
Laboratory of the Petroleum Institute in Abu Dhabi, U.A.E. to
determine the efficacy of electrokinetic technology in EEORTM
tested on field collected data samples of Abu Dhabi. The results
of the initial tests conducted on field retrieved specimens of Abu
Dhabi on-shore carbonate reservoir rock candidates from several
formations in high salinity environments that contained various
crude types are reported.  
  


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[**http://orbit.dtu.dk/en/publications/electroosmosis-in-oil-recovery(031f28aa-256b-44bb-bed2-3f5bd509cf28)/export.html**](http://orbit.dtu.dk/en/publications/electroosmosis-in-oil-recovery%28031f28aa-256b-44bb-bed2-3f5bd509cf28%29/export.html)

**Electro-osmosis in oil
recovery : Progress report II**  
 **Laursen, SA,ren; Reffstrup, Jan Otto. 1997.**

  


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[**http://www.sciencedirect.com/science/article/pii/S1110016811000184**](http://www.sciencedirect.com/science/article/pii/S1110016811000184)**https://doi.org/10.1016/j.aej.2011.01.010****Alexandria Engineering Journal, Volume 50, Issue 1, March
2011, Pages 105-110**

**Treatment of oil polluted
soil using electrochemical method**  
  
**Husam Damen Al-Hamaiedh, et al.**

**Abstract**  
  
This paper aims to investigate the effect of soil contamination by
oil on the geotechnical properties of the soil and evaluation of
the feasibility of using electrochemical method for the treatment
of the contaminated soils. The properties of contaminated soil
samples by different proportions of lubricating oil were
determined and compared with the properties of uncontaminated soil
samples to study the effect of oil contamination on soil
properties. The results showed that oil contamination caused
deleterious effects on the basic geotechnical properties of the
soil. Contaminated samples have been treated using electrochemical
treatment method. The properties of treated soil samples were
determined and compared with the properties of contaminated and
uncontaminated samples to determine the efficiency of
electrochemical treatment method. The results showed that
geotechnical properties of treated soil samples are significantly
improved. The feasibility of using electrochemical treatment
method has been prooved. Beside the ability of treating huge
amount of soil, the electrochemical treatment methods are
characterized by high efficiency and ecological safety.  
  


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[**http://www.geoox.dk/index.php/technology**](http://www.geoox.dk/index.php/technology)

**Oilrec Trechnologies / B.S.
Geoteknik**

**Technology**  
  
The QOR technology is an electro chemical based method for
electric enhanced oil recovery by inducing a low electric DC
current into the formation.  
  
In the field it`s using the existing well casing as electrode. One
setup consists of two electrodes, whereas one is an anode and the
other a cathode.  
  
The QOR Technology is based on two electro chemical processes,
namely the GeoOxidation and the Geokinetic.  
  
The GeoOxidation creates, in the formation, redox reactions, which
in steps breaks down the long chained molecules, this means that
the heavy oil is being transformed into lighter fractions. This
stage of the process is called liquefaction. Full scale test have
shown that oil with an API gravity of 15 over a period of 45 days
is changed into an API gravity of 39 to 40.  
  
The second stage of the process, Geokinetic, creates through
electro osmosis a flow of oil and water towards the cathode. Full
scale tests have shown an tenfold increase in the oil production.  
  
The QOR Technology is used in normal producing oilfields as well
as in deemed exhausted oilfields, but is specially developed for
use in fields with heavy oil and in oil sand.  
  


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[**http://www.geoox.dk/images/Sumatra\_2012.pdf**](http://www.geoox.dk/images/Sumatra_2012.pdf)

**Field Trial**

  

![sumatra1](sumatra1.JPG)

  

![sumatra2](sumatra2.JPG)

  

![sumatra3](sumatra3.JPG)

  


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**Patents**



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**US7325604**  
**Method for enhancing oil production using electricity**

  
Inventor(s):     WITTLE J K [US]; BELL CHRISTY (B2)
   
  
A method of enhancing oil production from an oil bearing formation
includes the steps of providing a first borehole in a first region
of the formation and a second borehole in a second region of the
formation. A first electrode is positioned in the first borehole
in the first region, and a second electrode is positioned in
proximity to the second borehole in the second region. A voltage
difference is established between the first and second electrodes
to create an electric field across the plugging materials. The
electric field is applied to destabilize the plugging materials
and improve oil flow through the formation.  
  
**FIELD OF THE INVENTION**  
  
The present invention relates generally to oil production, and
more particularly to a method for enhancing the production of oil
from subterranean oil reservoirs with the aid of electric current.  
  
**BACKGROUND**  
  
When crude oil is initially recovered from an oil-bearing earth
formation, the oil is forced from the formation into a producing
well under the influence of gas pressure and other pressures
present in the formation. The stored energy in the reservoir
dissipates as oil production progresses and eventually becomes
insufficient to force the oil to the producing well. It is well
known in the petroleum industry that a relatively small fraction
of the oil in subterranean oil reservoirs is recovered during this
primary stage of production. Some reservoirs, such as those
containing highly viscous crude, retain 90 percent or more of the
oil originally in place after primary production is completed.  
  
A variety of conditions in the oil-bearing formation can impede
the flow of oil through interstitial spaces in the oil-bearing
formation, limiting the recovery of oil. In many cases, formations
become damaged during the process of drilling wells into the
formation. Mud, chemical additives and other components used in
drilling fluids can accumulate around the well, forming a cake
that blocks the flow of oil into the well bore. Drilling fluids
can also migrate and accumulate in fissures in the formation,
blocking the flow of oil through the formation. Parrafins and
waxes may precipitate at the interface between the well bore and
the formation, further impeding the flow of oil into the well
bore. Sediments and native materials in the formation can also
migrate and block interstitial spaces.  
  
Numerous methods have been used to alleviate the problems
associated with plugging in oil bearing formations. Plugging is
often addressed by backflushing the well to remove mud from around
the well. Backflushing the well can consume significant time and
energy, and has limited effectiveness in unplugging areas that are
located deep within a formation and away from the well. Acidizing
the well and flushing the well with solvents are also used to
alleviate plugging, but these methods can create hazardous waste
that is expensive and difficult to dispose of. As a result, known
methods for unplugging oil bearing formations leave much to be
desired.  
  
In many cases, crude oil is extracted with high concentrations of
sulfur, polycyclic aromatic compounds (PAHs) and other compounds
that reduce the quality and value of the oil. The presence of
undesirable compounds in the oil requires subsequent processing of
the oil, increasing the time and cost of production. Therefore,
there is a great need to develop oil production methods that allow
oil to be treated while it is being extracted.  
  
**SUMMARY OF THE INVENTION**  
  
The foregoing problems are solved to a great degree by the present
invention, which uses electrodes to enhance oil production from an
oil bearing formation. A first borehole is provided in a first
region of the formation, and a first electrode is positioned in
the first borehole. A second electrode may be placed above ground
in proximity to the formation. Alternatively, the second electrode
may be installed in a second borehole. The second borehole may be
positioned in a second region of the formation, or in proximity to
the formation. A voltage difference is established between the
first and second electrodes to create an electric field across the
formation.  
  
It has been discovered that the method of the present invention
can be used to improve the condition of the oil formation and
repair damaged or plugged formations where oil flow is impeded by
drilling fluids, natural occlusions or other matter. The method
can also be applied to pre-treat oil in the formation as it is
extracted from the formation. The electric field may be applied
and manipulated to destabilize occlusions and plugging materials,
increase oil flow through the formation and improve the quality of
the oil prior to and during extraction.  
  
**DESCRIPTION OF THE DRAWINGS**  
  
[0009] The foregoing summary as well as the following description
will be better understood when read in conjunction with the
figures in which:  
  
**[0010] FIG. 1 is a schematic diagram of an improved
electrochemical method for stimulating oil recovery from an
underground oil-bearing formation;****[0011] FIG. 2 is a schematic diagram in partial sectional
view of an apparatus with which the present method may be
practiced;****[0012] FIG. 3 is an elevational view of an electrode
assembly adapted for use in practicing the present invention;****[0013] FIG. 4 is a block flow diagram of a method for
improving flow conditions and pre-treating oil in a formation;****[0014] FIG. 5 is a schematic diagram of a first alternate
electrochemical method for stimulating oil recovery from an
underground oil-bearing formation; and****[0015] FIG. 6 is a schematic diagram of a second alternate
electrochemical method for stimulating oil recovery from an
underground oil-bearing formation.**

**![US7325604a](us7325604a.JPG) ![US7325604b](us7325604b.JPG) ![US7325604c](us7325604c.JPG) *![US7325604d](us7325604d.JPG) ![US7325604e](us7325604e.JPG) ![US7325604f](us7325604f.JPG)***

**DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT**[0016] Referring to the Figures in general, and to FIG. 1,
specifically, the reference number 11 represents a subterranean
formation containing crude oil. The subterranean formation 11 is
an electrically conductive formation, preferably having a moisture
content above 5 percent by weight. As shown in FIG. 1, formation
11 is comprised of a porous and substantially homogeneous media,
such as sandstone or limestone. Typically, such oil-bearing
formations are found beneath the upper strata of earth, referred
to generally as overburden, at a depth of the order of 1,000 feet
or more below the surface. Communication from the surface 12 to
the formation 11 is established through on or more boreholes. In
FIG. 1, communication from the surface 12 to the formation 11 is
established through spaced-apart boreholes 13 and 14. The hole 13
functions as an oil-producing well, whereas the adjacent hole 14
is a special access hole designed for the transmission of
electricity to the formation 11.  
  
[0017] The present invention can be practiced using a multiplicity
of cathodes and anodes placed in boreholes. The boreholes may be
installed in a variety of vertical, horizontal or angular
orientations and configurations. In FIG. 1, the system is shown
having two electrodes installed vertically into the ground and
spaced apart generally horizontally. A first electrode 15 is
lowered through access hole 14 to a location in proximity to
formation 11. Preferably, first electrode 15 is lowered through
access hole 14 to a medial elevation in formation 11, as shown in
FIG. 1. By means of an insulated cable in access hole 14, the
relatively positive terminal or anode of a high-voltage d-c
electric power source 2 is connected to the first electrode 15.
The relatively negative terminal on the power source or cathode is
connected to a second electrode 16 in producing well 13, or within
close proximity of the producing well. Between the electrodes, the
electrical resistance of the connate water 4 in the underground
formation 11 is sufficiently low so that current can flow through
the formation between the first and second electrodes 15, 16.
Although the resistivity of the oil is substantially higher than
that of the overburden, the current preferentially passes directly
through the formation 11 because this path is much shorter than
any path through the overburden to "ground."  
  
[0018] To create the electric field, a periodic voltage is
produced between the electrodes 15, 16. Preferably, the voltage is
a DC-biased signal with a ripple component produced under
modulated AC power. Alternatively, the periodic voltage may be
established using pulsed DC power. The voltage may be produced
using any technology known in the electrical art. For example,
voltage from an AC power supply may be converted to DC using a
diode rectifier. The ripple component may be produced using an RC
circuit or through transistor controlled power supplies. Once the
voltage is established, the electric current is carried by captive
water and capillary water present in the underground formation.
Electrons are conducted through the formation by naturally
occurring electrolytes in the groundwater.  
  
[0019] The electric potential required for carrying out
electrochemical reactions varies for different chemical components
in the oil. As a result, the desired intensity or magnitude of the
ripple component depends on the composition of the oil and the
type of reactions that are desired. The magnitude of the ripple
component must reach a potential capable of oxidizing and reducing
bonds in the oil components. In addition, the ripple component
must have a frequency range above 2 hertz and below the frequency
at which polarization is no longer induced in the formation. The
waveshape of the ripple may be sinusoidal or trapezoidal and
either symmetrical or clipped. Frequency of the AC component is
preferably between 50 and 2,000 hertz. However, it is understood
in the art that pulsing the voltage and tailoring the wave shape
may allow the use of frequencies higher than 2,000 hertz.  
  
[0020] A system suitable for practicing the invention is shown in
FIG. 2. In this system, borehole 13 functions as an oil producing
well which penetrates one region 17 of underground oil-bearing
formation 11. Well 13 includes an elongated metallic casing 18
extending from the surface 12 to the cap rock 23 immediately above
region 17. The casing 18 is sealed in the overburden 19 by
concrete 20 as shown, and its lower end is suitably joined to a
perforated metallic liner 24 which continues down into the
formation 11. Piping 21 is disposed inside the casing 18 where it
extends from the casing head 22 to a pump 25 located in the liquid
pool 26 that accumulates inside the liner 24. Preferably the
producing well 13 is completed in accordance with conventional
well construction practice. The pump 25 is selected to operate at
sufficient pumping head to draw oil from adjacent formation 11 up
through metallic liner 24.  
  
[0021] Access hole 14 that contains first electrode 15 includes an
elongated metallic casing 28 with a lower end preferably
terminated by a shoe 29 disposed at approximately the same
elevation as the cap rock 23. The casing 28 is sealed in the
overburden 19 by concrete 30. Near the bottom of hole 14, a
tubular liner 31 of electrical insulating material extends from
the casing 28 for an appreciable distance into formation 11. The
insulating liner 31 is telescopically joined to the casing 28 by a
suitable crossover means or coupler 32.  
  
[0022] Below the liner 31, a cavity 34 formed in the oil-bearing
formation 11 contains the first electrode 15. The first electrode
15 is supported by a cable 35 that is insulated from ground. The
first electrode 15 is relatively short compared to the vertical
depth of the underground formation 11 and may be positioned
anywhere in proximity to the formation. Referring to FIG. 2, first
electrode 15 is positioned at an approximately medial elevation
within the oil-bearing formation 11. The first electrode may be
exposed to saline or oleaginous fluids in the surrounding earth
formation, as well as a high hydrostatic pressure. Under these
conditions, first electrode 15 may be subject to electrolytic
corrosion. Therefore, the electrode assembly preferably comprises
an elongate configuration mounted within a permeable concentric
tubular enclosure radially spaced from the electrode body. The
enclosure cooperates with the first electrode body to protect it
from oil or other adverse materials that enter the cavity.  
  
[0023] It should be noted that FIG. 2 is not to scale, and some of
the dimensions of the hole 14 and components in the hole are
exaggerated. For example, the diameter of hole 14 is shown to be
quite large in comparison to the cable 35 and other components.
The diameter of the hole 14 may be much closer to the diameter of
the cable 35. In addition, liner 31 preferably has a substantial
length and a relatively small inside diameter.  
  
[0024] Referring now to FIG. 3, a preferred assembly for the first
electrode 15 is shown. The assembly comprises a hollow tubular
electrode body 15 electrically connected through its upper end to
a conducting cable 35 and disposed concentrically in radially
spaced relation within a permeable tubular enclosure 16a of
insulating material. The first electrode 15 is preferably coated
externally with a material, such as lead dioxide, which
effectively resists electrolytic oxidation. The assembly
preferably includes means to place the internal surfaces of the
first electrode 15 under pressure substantially equal to the
external pressure to which the first electrode is exposed, thereby
to preclude deformation and consequent damage to the first
electrode. The enclosure 16a is closed at the bottom to provide a
receptacle for sand or other foreign material entering from the
surrounding formation.  
  
[0025] Referring again to FIG. 2, the first electrode 15 is
attached to the lower end of insulated cable 35, the other end of
which emerges from a bushing or packing gland 36 in the cap 37 of
casing 28 and is connected to the relatively positive terminal of
an electric power source 38. The other terminal on the electric
power source 38 is connected via a cable 42 to an exposed
conductor that acts as a second electrode 16 at the producing well
13. The second electrode 16 may be a separate component installed
in the proximity of producing well 13 or may be part of the
producing well itself. In the embodiment shown in FIG. 2, the
perforated liner 24 serves as the second electrode 16, and the
well casing 18 provides a conductive path between the liner and
cable 42.  
  
[0026] Thus far, it has been presumed that electrodes 15, 16 are
located in a formation with a suitable moisture content and
naturally occurring electrolytes to provide an electroconductive
path through the formation. In formations that do not have
adequate capillary and captive groundwater to be electrically
conductive, an electroconductive fluid may be injected into the
formation through one or both boreholes to maintain an
electroconductive path between the electrodes 15, 16. Referring to
FIG. 2, a pipe 40 in borehole 14 delivers electrolyte solution
from the ground surface to the underground formation 11.
Preferably, a pump 43 is used to convey the solution from a supply
44 and through a control valve 45 into borehole 14. Borehole 14 is
preferably equipped with conventional flow and level control
devices so as to control the volume of electrolyte solution
introduced to the borehole. A detailed system and procedure for
injecting electrolyte solution into a formation is described in
the aforementioned U.S. Pat. No. 3,782,465. See also, U.S. Pat.
No. 5,074,986, the entire disclosure of which is incorporated by
reference herein.  
  
[0027] Referring now to FIGS. 1-2, the steps for practicing the
improved method for stimulating oil recovery will now be
described. An electric potential is applied to first electrode 15
so as to raise its voltage with respect to the second electrode 16
and region 17 of the formation 11 where the producing well 13 is
located. The voltage between the electrodes 15, 16 is preferably
no less than 0.4 V per meter of electrode distance. Current flows
between the first and second electrodes 15, 16 through the
formation 11. Connate water 4 in the interstices of the oil
formation provides a path for current flow. Water that collects
above the electrodes in the boreholes does not cause a short
circuit between the electrodes and surrounding casings. Such short
circuiting is prevented because the water columns in the boreholes
have relatively small cross sectional areas and, consequently,
greater resistances than the oil formation.  
  
[0028] As current is applied across formation 11, electrolysis in
the capillary water and captive water takes place. Water
electrolysis in the groundwater releases agents that promote
oxidation and reduction reactions in the oil. That is, negatively
charged interfaces of oil compounds undergo cathodic reduction,
and positively charged interfaces of the oil compounds undergo
anodic oxidation. These redox reactions split long-chain
hydrocarbons and multi-cyclic ring compounds into lighter-weight
compounds, contributing to lower oil viscosity. Redox reactions
may be induced in both aliphatic and aromatic oils. As viscosity
of the oil is reduced through redox reactions, the mobility or
flow of the oil through the surrounding formation is increased so
that the oil may be drawn to the recovery well. Continued
application of electric current can ultimately produce carbon
dioxide through mineralization of the oil. Dissolution of this
carbon dioxide in the oil further reduces viscosity and enhances
oil recovery.  
  
[0029] In addition to enhancing oil flow characteristics, the
present invention promotes electrochemical reactions that upgrade
the quality of the oil being recovered. Some of the electrical
energy supplied to the oil formation liberates hydrogen and other
gases from the formation. Hydrogen gas that contacts warm oil
under hydrostatic pressure can partially hydrogenate the oil,
improving the grade and value of the recovered oil. Oxidation
reactions in the oil can also enhance the quality of the oil
through oxygenation.  
  
[0030] Electrochemical reactions are sufficient to decrease oil
viscosities and promote oil recovery in most applications. In some
instances, however, additional techniques may be required to
adequately reduce retentive forces and promote oil recovery from
underground formations. As a result, the foregoing method for
secondary oil recovery may be used in conjunction with other
processes, such as electrothermal recovery or electroosmosis. For
instance, electroosmotic pressure can be applied to the oil
deposit by switching to straight d-c voltage and increasing the
voltage gradient between the electrodes 15, 16. Supplementing
electrochemical stimulation with electroosmosis may be
conveniently executed, as the two processes use much of the same
equipment. A method for employing electroosmosis in oil recovery
is described in U.S. Pat. No. 3,782,465.  
  
[0031] Many aspects of the foregoing invention are described in
greater detail in related patents, including U.S. Pat. No.
3,724,543, U.S. Pat. No. 3,782,465, U.S. Pat. No. 3,915,819, U.S.
Pat. No. 4,382,469, U.S. Pat. No. 4,473,114, U.S. Pat. No.
4,495,990, U.S. Pat. No. 5,595,644 and U.S. Pat. No. 5,738,778,
the entire disclosures of which are incorporated by reference
herein. Oil formations in which the methods described herein can
be applied include, without limitation, those containing heavy
oil, kerogen, asphaltinic oil, napthalenic oil and other types of
naturally occurring hydrocarbons. In addition, the methods
described herein can be applied to both homogeneous and
non-homogeneous formations.  
  
[0032] It has been discovered that the method of the present
invention can be used to improve the condition of the oil
formation and repair damaged or plugged formations where oil flow
is impeded. The method can also be applied to pre-treat oil in the
formation as it is extracted from the formation.  
  
[0033] Referring now to FIG. 4, a method 110 for improving flow
conditions and pre-treating oil in a formation is shown in a block
diagram. The method 110 is applicable to a variety of well pump
installations that draw material from underground formations,
including oil recovery wells. The method 110 utilizes electric
current to enhance the production of oil from an oil-bearing
formation and improve the flow characteristics within the
formation. The improved flow characteristics increase the volume
of oil that is recoverable from the formation. Electric current is
also applied to modify the properties of the oil in the formation
and increase the quality of oil recovered. The decomposition of
long-chain compounds decreases the viscosity of the oil compounds
and increases oil mobility through the formation such that the oil
may be withdrawn at the recovery well. Electrochemical reactions
in the formation also upgrade the quality and value of the oil
that is ultimately recovered.  
  
[0034] The components used in the present method include many of
the same components described in U.S. patent application Ser. No.
10/279,431. The system generally includes two or more electrodes
placed in proximity of the oil bearing formation. In systems using
only two boreholes, a first borehole and a second borehole are
provided within the underground formation, or in proximity of the
underground formation. The first and second boreholes may be
drilled vertically, horizontally or at any angle that generally
follows the formation. A first electrode is placed within the
first borehole and a second electrode is placed within or in
proximity of the second borehole. Alternatively, the second
electrode may be positioned at the earth's surface. A source of
voltage is connected to the first and second electrodes. The first
and second boreholes may penetrate the body of oil to be
recovered, or they may penetrate the formation at a point beyond
but in proximity to the body of oil. A voltage difference is
applied between the electrodes to create an electric field through
the oil bearing formation.  
  
[0035] The method 110 for improving flow conditions and
pre-treating oil in an underground formation will now be described
in greater detail. A first borehole is provided in a first region
of the formation in step 120. A second borehole is provided in a
second region of the formation in step 130. A first electrode is
placed in the first borehole in step 140, and a second electrode
is placed in proximity of the second borehole in step 150. A
voltage difference is established between the first and second
electrodes to create an electric field across plugging materials
in the formation in step 160. The electric field is applied across
the plugging materials to destabilize the plugging materials in
step 170.  
  
[0036] The method of FIG. 4 may be applied in several ways to
improve flow characteristics in a formation. For example, if a mud
cake is deposited on the interface between the well bore and the
formation, an electric field may be applied to loosen and remove
the mud. A negative electrode is placed in the well bore that is
blocked by the mud cake, and the electric field is applied across
the mud cake. Formation water will can move through the well bore
interface toward the negative electrode under the influence of the
electric field. As the water moves through the interface, the
electroosmotic forces hydrate the mud and gradually dislodge the
clay from the well bore to unblock the well.  
  
[0037] The method of FIG. 4 may also be applied to remove plugging
materials from fissures within the formation. Plugging materials
may include mud or residue from drilling fluid, naturally formed
occlusions, or other matter that blocks flow of oil through the
interstitial spaces in the formation. The electrode in the well
bore may be negatively charged to draw plugging materials into the
well bore and out of the formation. Alternatively, the electrode
in the well bore may positively charged to repel and push the
plugging materials deeper into the formation.  
  
[0038] The electric field can be applied alone or in conjunction
with other techniques for unplugging formations. For example, the
present method may be used in conjunction with acidizing to
dissolve and remove clay plugging materials. An unplugging acid is
introduced into the formation, and an electrode in the formation
is positively charged. An electric field is applied to drive the
unplugging acid into the formation until the acid reaches the
plugging materials. Migration of the acid is carried out by
electroosmosis, but may be assisted by other means, such as well
pumping. The electric field may be used to drive the acid into
regions of the formation that cannot be reached through boreholes.
If desired, the voltage may be increased to impart resistive
heating and decrease viscosity of the plugging materials.
Additives may be introduced into the formation to change the
electric charge of plugging materials. Once the plugging materials
are destabilized, the formation may be backflushed to remove any
remnants or byproducts remaining in the formation. One or more
well pumps may be operated to establish suction pressure in the
well and draw the destabilized plugging materials into the well.  
  
[0039] As noted above, the present invention promotes
electrochemical reactions that upgrade the quality of the oil
being recovered. For example, the electric field may be used to
remove sulfur-containing compounds from crude, thereby improving
the quality and value of oil as it is recovered. It has been found
that superimposing a variable AC signal with a frequency between 2
Hz and 1.24 MHz on to a DC signal can induce oxidation to convert
sulfur compounds to sulfates. The sulfates tend to remain in the
formation as the oil is removed. The present invention may also be
applied to remove polycyclic aromatic compounds (PAHS) from crude
oil. Operation of the electric field to remove sulfur compounds
and PAHs may take place prior to extraction of oil, or while the
oil is being extracted. The electric field may be applied for a
specified period of time. Alternatively, the electric field may be
applied until the concentration of sulfur compounds and/or PAHs is
reduced below a predetermined limit.  
  
[0040] The present invention can be practiced using a multiplicity
of cathodes and anodes placed in vertical, horizontal or angular
orientations and configurations, as stated earlier. Referring now
to FIG. 5, an alternate system is shown with electrodes installed
in well casing 113, 114. The well casings 113, 114 extend in a
generally horizontal orientation through an oil-bearing formation
111. The relatively positive terminal or anode of a high-voltage
d-c electric power source 102 is connected to the first well
casing 113. The relatively negative terminal on the power source
or cathode is connected to the second well casing 114. In this
arrangement, well casing 113 acts a cathode producer, and well
casing 114 acts as an anode. Insulating components or breaks 120
are placed in each of the well casings 113, 114 so that
electricity flows between the horizontal sections of the casings
within the oil-bearing formation 111. Between the well casings
113, 114, the electrical resistance of the connate water in the
formation is sufficiently low so that current can flow through the
formation between the casings. Although the resistivity of the oil
is substantially higher than that of the overburden, the current
preferentially passes directly through the formation 111 because
this path is much shorter than any path through the overburden to
"ground."  
  
[0041] The present method may include one or more electrodes
placed above ground, as described earlier. Referring now to FIG.
6, an alternate system is shown with a first electrode 215 placed
below the earth's surface (marked "E") and a second electrode 216
placed above the earth's surface in proximity to an underground
oil-bearing formation 211. The first electrode 215 is installed in
a borehole 214 that penetrates the formation 211. The first
electrode 215 is positioned within the formation, but may be
positioned outside the formation, depending on the desired
position and range of the electric field. The second electrode 216
is placed on the earth's surface. By means of an insulated cable
in access hole 214, a terminal on a high-voltage d-c electric
power source 202 is connected to the first electrode 215. The
opposite terminal on the power source 202 is connected to the
second electrode 216. A voltage difference is established between
the first and second electrodes 215, 216 to create an electric
field across the formation 211. It should be noted that the second
electrode 216 may be installed at a shallow depth just beneath the
earth's surface to produce an electric field. For example, the
second electrode may be installed within fifty feet of the earth's
surface to establish an electric field across the formation.
Placing the second electrode 216 at a shallow depth below the
earth's surface may be desirable where space above ground is
limited.  
  
[0042] The terms and expressions which have been employed are used
as terms of description and not of limitation. Although the
present invention has been described in detail with reference only
to the presently-preferred embodiments, there is no intention in
use of such terms and expressions of excluding any equivalents of
the features shown and described or portions thereof. It is
recognized that various modifications of the embodiments described
herein are possible within the scope and spirit of the invention.
Accordingly, the invention incorporates variations that fall
within the scope of the following claims.  
   


---

  

**WO0303823** **Electrochemical process for effecting redox-enhanced
oil recovery**

   
A method is provided for recovering oil from a subterranean
oil-bearing formation. One or more pairs of electrodes are
inserted into the ground in proximity to a body of oil in said
formation. A voltage difference is then established between the
electrodes to create an electric field in the oil-bearing
formation. As voltage is applied, the current is manipulated to
induce oxidation and reduction reactions in components of the oil.
The oxidation and reduction reactions lower the viscosity in the
oil and thereby reduce capillary resistance to oil flow so that
the oil can be removed at an extraction well.  
  
ng earth formation, the oil is forced from the formation into a
producing well under the influence of gas pressure and other
pressures present in the formation. The stored energy in the
reservoir dissipates as oil production progresses and eventually
becomes insufficient to force the oil to the producing well. It is
well known in the petroleum industry that a relatively small
fraction of the oil in subterranean oil reservoirs is recovered
during this primary stage of production.  
  
Some reservoirs, such as those containing highly viscous crude,
retain 90 percent or more of the oil originally in place after
primary production is completed. Oil recovery is frequently
limited by capillary forces that impede the flow of viscous oil
through interstitial spaces in the oil-bearing formation.  
  
Numerous methods have been proposed for recovering additional oil
that remains the in oil-bearing formations following primary
production. These secondary recovery  
  
techniques generally involve the expenditure of energy to
supplement the expulsive forces and/or to reduce the retentive
forces acting on the residual oil. A summary of secondary recovery
techniques may be found in U. S. Patent No. 3,782, 465, the entire
disclosure of which is incorporated by reference herein.  
  
One secondary recovery technique for promoting oil recovery
involves the application of electric current through an oil body
to increase oil mobility and facilitate transport to a recovery
well. Typically, one or more pairs of electrodes are inserted
within the underground formation at spaced-apart locations. A
voltage drop is established between the electrodes to create an
electric field through the oil formation. In some processes,
electric current is applied to raise the temperature of the oil
formation and thereby lower the viscosity of the oil to facilitate
removal. Other methods use electric current to move the oil
towards a recovery well by electroosmosis. In electroosmosis,
dissolved electrolytes and suspended. charged particles in the oil
migrate toward a cathode, carrying oil molecules with them. These
methods typically use a DC potential source to generate an
electrical field across the oil-bearing formation.  
  
Oil recovery methods that utilize electrodes frequently encounter
problems affecting the quantity and quality of the recovered oil.
Systems using straight DC voltage typically operate under high
voltages and currents. In addition, systems using DC current
consume relatively large amounts of electricity with corresponding
large energy costs.  
  
**Summary of the Invention**  
  
With the foregoing in mind, the present invention provides an
improved method for stimulating oil recovery from an oil-bearing
underground formation through the use of electric current.
Electric current is introduced through a plurality of boreholes
installed in the formation. In systems using only two boreholes, a
first borehole and a second borehole are provided in the proximity
of the underground formation. The boreholes are located at
spaced-apart locations in or near the formation. A first electrode
is placed into the first borehole and a second electrode is placed
into the second borehole. A source of voltage is then connected to
the first and second electrodes.  
  
The second borehole may penetrate the body of oil in the
underground formation or be located beyond the oil body, so long
as some or all of the oil body is located between the second
borehole and the first electrode. The first and second boreholes
may penetrate the body of oil to be recovered, or they may
penetrate the formation at a point beyond but in proximity to the
body of oil.  
  
The first and second electrodes are installed in an electrically
conductive formation, such as a formation having a moisture
content sufficient to conduct electricity. A DC biased current
with a ripple component is applied through the electrodes under
conditions appropriate to create an electrical field through the
oil formation. The current is regulated to stimulate oxidation and
reduction reactions in the oil. As redox reactions occur,
long-chain compounds such as heavy petroleum hydrocarbons are
reduced to smaller-chain compounds. The decomposition of
long-chain compounds decreases the viscosity of the oil compounds
and increases oil mobility through the formation such that the oil
may be withdrawn at the recovery well. Electrochemical reactions
in the formation also upgrade the quality and value of the oil
that is ultimately recovered. The system can be used with a
multiplicity of cathodes and anodes placed in vertical, horizontal
or angular orientations and configurations.  
  


---

  

****US3915819**Electrolytic oil purifying method**

Inventor(s): BELL CHRISTY W; WITTLE JOHN K; SPEECE ARTHUR L +  
  
Sulfur is removed from liquid hydrocarbon oils such as crude oil
by subjecting a mixture of the oil and an electrolyte to a direct
current field at a relatively high current and low voltage for
causing oxidation, reduction or other electrochemical reaction of
the sulfur or sulfur-containing material enabling ready separation
and removal of the sulfur from the oil.  
  
Sulfur is removed from liquid hydrocarbon oils such as crude oil
by subjecting a mixture of the oil and an electrolyte to a direct
current field at a relatively high current and low voltage for
causing oxidation, reduction or other electrochemical reaction of
the sulfur or sulfur-containing material enabling ready separation
and removal of the sulfur from the oil.  
  
The present invention relates to the removal of sulfur from
hydrocarbon liquids, especially hydrocarbon oils such as crude
oil.  
  
It is an object of the present invention to reduce the sulfur
content of hydrocarbon liquids, particularly crude oil.  
  
It is another object of the invention to provide a process for
purifying crude oil and other hydrocarbon liquids which is readily
carried out at relatively low cost.  
  
A particular object of the invention is to provide a process of
the above type wherein the sulfur content is reduced by
electrochemical means.  
  
Other objects and advantages will become apparent from the
following description and the appended claims.  
  
With the above objects in view, the present invention in one of
its aspects relates to the method of electro-chemically removing
sulfur from hydrocarbon liquids including sulfur-containing
materials which comprises mixing the hydrocarbon liquid with an
ion-producing compound selected from the group consisting of
inorganic electrolytes and ionizing organic solvents, and
subjecting the thus obtained mixture to an electrical DC field
having a voltage in the range of about 2 to 120 volts and a
current of at least about 0.001 amperes per square centimeter, and
recovering the hydrocarbon liquid in which the sulfur-containing
materials have been substantially reduced.  
  
In general, it has been found in accordance with the invention
that the use of relatively high current at low voltages in the
electrolyte-oil mixture promotes the oxidation (or reduction, as
the case may be) of sulfur contaminants in the oil, resulting in
precipitation or volatilization of sulfur compounds which are
thereby removed from the oil mixture.  
  
As will be understood, the sulfur components in crude oil may be
of various types. It is known that the sulfur content of petroleum
may vary from less than 0.1% to 10% by weight depending upon the
source. This sulfur may be present as free sulfur, hydrogen
sulfide, mercaptans, disulfides, cyclic sulfides or thiophenes.
The present refinery methods for removal of sulfur, such as
hydro-desulfurization, require the use of relatively cumbersome
apparatus and expensive processes. The electrochemical process of
this invention, on the other hand, is a relatively simple
inexpensive desulfurization method.  
  
In the electrolysis of any particular oil-electrolyte mixture to
produce an electrochemical reaction in accordance with the
invention, under the same conditions certain sulfur compounds may
be oxidized, others may be reduced, some may be precipitated, some
may be volatilized and others may be deposited on the electrode
surfaces. From experiments carried out in the course of practicing
the invention, it appears that oxidation is the predominant
reaction, and oxidation products such as sulfonic acids and sulfur
oxides have been identified. The reduction of sulfur compounds has
been indicated by the production of H2 S volatilized during the
process.  
  
The removal or reduction of sulfur in accordance with the
principles of the invention may be carried out using various
sulfur-containing hydrocarbon liquids or oils mixed with various
ion-producing compounds. For example, hydrocarbons such as mineral
oil and crude oil from various geographical sources have been
satisfactorily treated by the electrochemical process of the
invention.  
  
The inorganic electrolyte with which the hydrocarbon liquid may be
mixed may be in the form of an aqueous solution of a salt or
alkali base in concentrations high enough to obtain an
electrically conducting system. Such solutions may contain, for
example, a salt or base such as sodium chloride, lithium chloride,
potassium chloride, strontium chloride, sodium nitrate, lithium
nitrate, potassium nitrate, sodium carbonate, potassium carbonate,
calcium carbonate, barium carbonate, sodium hydroxide, potassium
hydroxide, calcium hydroxide, and barium hydroxide.  
  
Ionizing organic solvents which may be used in combination with
the hydrocarbon liquid include methanol, benzene, nitrobenzene,
toluene, xylene, and glacial acetic acid. Many other inorganic and
organic compounds will also be found suitable for use in
practicing the present invention.  
  
In general, the electrolysis of the oil-electrolyte mixture is
carried out in a DC electrical field having a voltage in the range
of about 2 to 120 volts and a current of between .001 to 25
amperes per square centimeter, with a preferred voltage range of
about 2 to 10 volts being used in most cases. The concentration of
the ionizing compound employed in the mixture will depend mainly
on the spacing, surface area and configuration of the electrodes.
For any particular conditions, the amount of the ionizing material
used should be such as to provide a conductivity which results in
a voltage of the system in the range set forth above.  
  
The process of the present invention will be illustrated by the
following examples, it being understood that the invention is not
intended to be limited thereby. In the experiments described
below, the electrolysis was carried out in a 100 ml flask equipped
with two standard platinum electrodes. The anode was a cylinder of
platinum mesh 1/2" in diameter and 2" long. The cathode was a mesh
cylinder 13/8" in diameter and 2" long.  
  
**EXAMPLE I**  
A 43.88 gram sample of crude oil designated Fleisher Lease oil
containing 6.13% by weight of sulfur was mixed with 54.06 grams of
distilled water containing 1.08 grams of reagent grade NaOH. The
mixture, which had a pH of 10, was subjected to electrolysis
carried out in the above described reaction vessel. The mixture
was subjected to a DC electrical field of 0.100--0.175 amperes,
for a total of 64 hours. While holding the current to a maximum of
0.175 amperes during the run, the voltage varied between 25 and
200 volts. At the termination of this experiment, it was found
that the sulfur content in the oil had been reduced to 4.57%.  
  
**EXAMPLE II**  
  
A mixture of 7.14 grams of crushed limestone, 49.73 grams
distilled water, 43.03 grams of No. 6 fuel oil, and 0.48 gram
Ca(OH)2 and 38.78 grams distilled water was placed in the reaction
vessel. The mixture separated into an oil layer and water layer. A
DC current of 1 ampere was passed through the system at 15 volts
for nearly 12 hours, at which time the current had dropped to 0
and the voltage rose to 45 volts. The sulfur content in the oil
layer before the electrolysis began was found to be 0.86%, whereas
at the end of the experiment the sulfur content was 0.60%.  
  
**EXAMPLE III**  
In this experiment, 46.7 grams of No. 6 fuel oil and 4.55 grams
calcium hydroxide were added to 76.58 grams distilled water, and
the mixture was heated to reflux without stirring. A direct
current of 1 ampere at 9 volts was passed through the solution.
The current dropped to 0 within 50 minutes. At this time a
surfactant, available commercially under the name Triton X-100,
was added to the mixture, and electrolysis was again initiated at
1 ampere and 20 volts. After 4 hours and 20 minutes the voltage
had increased to 50 volts at 1 ampere. The system was allowed to
run overnight, during which time the current dropped to 0.4 ampere
and the voltage increased to 120 volts. The sulfur content of the
oil layer before the experiment was 0.86%, and after the
experiment was found to be 0.51%.  
  
**EXAMPLE IV**  
  
To a solution consisting of 92.55 grams distilled water, 0.39 gram
Ca(OH)2 and 5.7 grams limestone, there was added 38.75 grams No. 6
fuel oil cut with 10% by weight of pentane to reduce viscosity.
The system was subjected to electrolysis at an initial current of
1 ampere and 7 volts. During a period of 6 hours, the current fell
to 0 and the voltage increased to 75 volts. The sulfur content of
the oil layer was 0.86% before the experiment and was found to be
0.49% after the experiment.  
  
**EXAMPLE V**  
A solution of 1.13 grams Triton X-100, 126.83 grams water and
10.39 grams calcium hydroxide was mixed with 73.95 grams No. 6
fuel oil. The reaction mixture was heated to reflux and
electrolysis was started at 1 ampere and 20 volts. Within 2
minutes the voltage had increased to 120 volts and the current
dropped to 0.4 ampere. An additional amount of 2.14 grams Triton
X-100 was added and electrolysis continued at 1 ampere and 20
volts. After 3 hours the current had dropped to 0.4 ampere and the
voltage increased to 120 volts. Again, 2.15 grams Triton X-100 was
added and the electrolysis continued at 0.5 ampere and 120 volts.
Within 3 hours, the current dropped to 0.2 ampere and the voltage
remained at 120 volts. Before the experiment the sulfur content of
the oil layer was 0.86% and after the experiment it was 0.54%.  
  
**EXAMPLE VI**  
  
This was a control experiment which was carried out to determine
whether a reduction in sulfur content in the oil can be achieved
with a similar mixture is subjected to electrolysis at much higher
voltages.  
  
A mixture of 122.12 grams distilled water, 10.14 grams calcium
hydroxide, 4.05 grams Triton X-100 and 73.31 grams No. 6 fuel oil
was prepared and mechanically agitated for several days. At the
end of this period, the oil layer was placed in the previously
described reaction vessel and subjected to a 2000 volt per
centimeter DC potential for several hours. At the end of this
period the oil was analyzed and found to contain the same sulfur
content as the original oil content of 0.86% sulfur.  
  
**EXAMPLE VII**  
  
To a mixture of 15 ml methanol and 51.13 grams mineral oil there
was added 8cc of thiophene. This mixture was subjected to
electrolysis at 0.1 ampere and 50 volts. The resistance rapidly
increased to 30 ohms within 56 minutes and the mixture changed
from an initial colorless condition to a yellow color. Gas
collected over the reaction mixture indicated SO2 and mercaptans
were present. The electrolysis was run intermittently for 4 days.
During this time 85 ml methanol was added to maintain liquid
level. A total of 8.7 ampere hours of electricity were used.
During the last two days of operation, the gas evolved from the
reaction was found to contain formaldehyde.  
  
The inside of the reaction vessel and the stirring bar and cathode
were covered with a black deposit insoluble in carbon disulfide,
the total weight of the deposit being 0.30 gram. No deposit was
detected on the anode.  
  
Analysis of the oil layer showed that initially, prior to
electrolysis, the sulfur content was 2.30% while the final oil
layer had a sulfur content of 0.625%.  
  
**EXAMPLE VIII**  
A sample consisting of 8cc thiophene, 46.12 grams mineral oil and
46.21 grams distilled water containing 1.17 grams sodium hydroxide
was mixed and electrolyzed at 0.175 ampere and 4 volts for 15.4
ampere hours. The aqueous layer turned yellow and a gray deposit
formed on the anode, while a black deposit formed on the cathode.
A brown deposit formed and floated on top of the liquid phases. At
the end of the experiment, 42.83 grams of mineral oil, 40.00 grams
aqueous phase, 0.54 gram deposit on the anode, 1.23 gram deposit
on the cathode and 0.22 gram brown residue were found. Upon
standing several days, the oil layer turned sky blue in color. At
the start of the experiment, the oil layer had 1.24% sulfur
content, and at the end it had 0.20% sulfur. During the
experiment, the sulfur content of the aqueous layer had increased
from 0 to 2.96%.  
  
**EXAMPLE IX**  
Into the previously described reaction vessel there was introduced
46.14 grams mineral oil, 47.39 grams distilled water containing
1.13 gram calcium hydroxide and 8cc thiophene. A total of 12.86
ampere hours of DC current was passed through the system at 0.2
ampere and 7 volts. A brown solid phase began to separate from the
mixture as electrolysis proceeded. The pH of the system was
adjusted by the addition of 1.66 grams Ca(OH)2 after 8.56 ampere
hours of operation. Just prior to this addition, the generation of
gas was noted. At the start of the experiment, the oil layer had
2.71% sulfur and a pH of 12. At the end of the experiment, the oil
layer had 0.252% sulfur and the pH was 5.  
  
**EXAMPLE X**  
To a 50.37 gram sample of mineral oil was added 7.75 cc dibutyl
disulfide and 43.5 grams methanol. The mixture was electrolyzed at
0.100-0.150 amperes and 50 volts for 64.5 hours or 9.97 ampere
hours. During the run no deposits formed on the electrodes and no
color changes were noted in the mixture. At the start, the oil
layer contained 3.75% sulfur, and at the end of the experiment it
contained 2.57% sulfur.  
  
In all of the above experiments the current density of the system
was about 0.008 amperes/cm@2. As previously indicated, it is
preferable in accordance with the invention to employ a current
density of at least 0.001 amperes/cm@2 because it is economically
impractical to operate at lower current densities, while a current
density of more than 25 amperes/cm@2 is not feasible due to
erosion of the anode surface and cavitation on the electrode
surface.  
  
The Triton surfactant material mentioned in the Examples was used
to emulsify the oil so as to reduce fouling of the electrodes,
while at the same reducing the viscosity of the mixture to enhance
the electrochemical reaction.  
  
As a result of our experiments, it appeared to be preferable to
maintain the pH of the mixture at a relatively high level, i.e.,
8-12, since it appeared that the electro-chemical reaction
proceeded at a more rapid rate at such a pH level. However, it is
not intended to limit the process of the invention to mixtures of
such pH levels, since satisfactory results are obtainable at lower
pH values. In adjusting the pH by the addition of a base, it is
desirable to use compounds such as Ca(OH)2 to form insoluble
sulfur-containing compounds to facilitate the separation and
removal of these compounds from the mixture.  
  


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**US2013277046**  
**Method for Enhanced Oil Recovery from Carbonate Reservoirs**

Inventor(s): HAROUN MOHAMMED, et al.  
   
Method of using direct current (DC) electrokinetics to enhance oil
production from carbonate reservoirs The method comprising the
steps of selecting an underground formation comprising an
Oil-bearing carbonate reservoir, positioning two or more
electrically conductive elements at spaced apart locations in
proximity to said formation, at least one of said conductive
elements being disposed in or adjacent to a bore hole affording
fluid communication between the interior of said bore hole and
said formation, passing a controlled amount of electric current
along an electrically conductive path through said formation, said
electric current being produced by a DC source including a cathode
connected to one of said conductive elements and an anode
connected to another of said conductive elements, said
electrically conductive path comprising at least one of connate
formation water and an aqueous electrolyte introduced into said
formation, and withdrawing oil from at least one of said bore
holes.  
   
**BACKGROUND OF THE INVENTION**  
  
[0001] This invention relates to the use of direct current (DC)
electrokinetics to enhance oil production from carbonate
reservoirs.  
  
[0002] Carbonate formations occur naturally as sediments of
carbonate materials, especially calcite (CaCO3) and dolomite
(CaMg(CO3)2). They are anionic complexes of (CO3)<2- >and
divalent metallic cations such as calcium, magnesium, iron, zinc,
barium, strontium and copper, along with a few other less common
elements. Carbonates form within the basin of deposition by
biological, chemical and detrital processes and are largely made
up of skeletal remains and other biological constituents that
include fecal pellets, lime mud (skeletal) and microbially
mediated cements and lime mud. A main difference between
carbonates and silicious soils is that in carbonates chemical
constituents, including coated grains such as ooids and pisoids,
cement and lime mud are common, whereas they are not present in
most siliciclastic sediments. Carbonate reservoirs owe their
porosity and permeability to processes of deposition, diagenesis
or fracturing.  
  
[0003] Petroleum reservoirs in carbonate formations are porous,
permeable rock bodies that contain significant amounts of
hydrocarbons. It has been estimated that as much as 60% of the
world's oil reserves are present in carbonate reservoirs. However,
a substantial portion of these reserves is considered
unrecoverable. Among many factors that have contributed to the low
recovery rates experienced in these reservoirs, the oil-wettable
nature of carbonate rock is particularly problematic. Wettability
is generally referred to as the tendency of one fluid to spread on
or adhere to a solid surface in the presence of other immiscible
fluids. A published report of an evaluation of carbonate reservoir
rock cores obtained from all over the world showed that a vast
majority of carbonates are oil-wet. Chilingar and Yen, Energy
Sources, 7(1): 21-27 (1992).  
  
[0004] Knowledge of the wettability of reservoir rock is
important, e.g., for making an informed decision about the use of
gas injection or water flooding as an appropriate secondary oil
recovery means. A water flooding application to stimulate oil-wet
rock would be considerably less efficient than if applied to
water-wet rock.  
  
[0005] Various attempts have been made to alter the wettability
and thereby provide enhanced oil recovery from carbonate
reservoirs. One such approach involves chemically-enhanced oil
recovery from in which a surfactant is used to modify wettability
of the matrix rock to be more water-wet, as described in U.S. Pat.
No. 7,581,594. Another technique entails the use of imbibing
fluids which have the effect of modifying the concentration of
potential determining ions that influence the surface charge of
carbonate rock, so as to improve its water-wetting nature. Zhang
and Austad, Colloids and Surfactants A: Physicochemical and
Engineering Aspects, 279(1-3): 179-87 (2006). See also U.S. Pat.
No. 4,491,512.  
  
[0006] A number of methodologies have been considered for enhanced
recovery of high viscosity or aheavya oil. Low-frequency
alternating current (AC) heating has been evaluated in Canadian
heavy oil fields. Electro-magnetic (EM) and radiofrequency (RF)
induction have been proposed for near well bore heating to reduce
oil viscosity. Down-hole resistive heaters have also been
suggested for heating the near well bore reservoir rocks. The
research and development affiliates of several major oil companies
have investigated various AC, RF and down-hole heaters for
enhanced oil recovery. None of these approaches have produced
consistent results.  
  
[0007] Enhanced oil recovery has been achieved by DC electrical
stimulation. See, e.g., U.S. Pat. Nos. 6,877,556, 7,322,409 and
7,325,604, which are commonly owned with the present application.
To date, this technique has been shown to be effective in
formations composed primarily of either sandstone or
unconsolidated sand.  
  
[0008] Insofar as is known, the use of DC electrokinetics for
hydrocarbon recovery enhancement in a carbonate rock reservoir has
not previously been proposed.  
  
**SUMMARY OF THE INVENTION**  
  
[0009] In one aspect, the present invention provides an efficient
and effective method of enhancing oil recovery from a carbonate
reservoir.  
  
[0010] This method comprises selecting an underground formation
comprising an oil-bearing carbonate reservoir, positioning two or
more electrically conductive elements at spaced apart locations in
proximity to the formation, at least one of the conductive
elements being disposed in or adjacent to a bore hole affording
fluid communication between the bore hole interior and the
formation, passing a controlled amount of electric current along
an electrically conductive path through the formation and
withdrawing oil from at least one of the bore holes. The electric
current applied in carrying out this method is produced by a DC
source including a cathode connected to one of the conductive
elements and an anode connected to another of the conductive
elements, and the electrically conductive path comprises at least
one of connate formation water and an aqueous electrolyte
introduced into the formation.  
  
[0011] In another aspect, the present invention provides a method
of fracturing an oil-bearing carbonate rock formation by
subjecting the formation to long term electrical stress.  
  
[0012] The invention described herein is believed to be the first
technically feasible method using electrokinetic phenomena to
enhance oil recovery from a carbonate reservoir.  
  

![US2013277046a](us2013277046a.JPG)![US2013277046b](us2013277046b.JPG)![US2013277046c](us2013277046c.JPG)

  


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**US7325604  
 Method for enhancing oil production using electricity**  
  

A method of enhancing oil production from an
oil bearing formation includes the steps of providing a first
borehole in a first region of the formation and a second
borehole in a second region of the formation. A first
electrode is positioned in the first borehole in the first
region, and a second electrode is positioned in proximity to
the second borehole in the second region. A voltage difference
is established between the first and second electrodes to
create an electric field across the plugging materials. The
electric field is applied to destabilize the plugging
materials and improve oil flow through the formation.  
  
**FIELD OF THE INVENTION**  
The present invention relates generally to oil production, and
more particularly to a method for enhancing the production of
oil from subterranean oil reservoirs with the aid of electric
current.  
  
**BACKGROUND**  
  
When crude oil is initially recovered from an oil-bearing
earth formation, the oil is forced from the formation into a
producing well under the influence of gas pressure and other
pressures present in the formation. The stored energy in the
reservoir dissipates as oil production progresses and
eventually becomes insufficient to force the oil to the
producing well. It is well known in the petroleum industry
that a relatively small fraction of the oil in subterranean
oil reservoirs is recovered during this primary stage of
production. Some reservoirs, such as those containing highly
viscous crude, retain 90 percent or more of the oil originally
in place after primary production is completed.  
  
A variety of conditions in the oil-bearing formation can
impede the flow of oil through interstitial spaces in the
oil-bearing formation, limiting the recovery of oil. In many
cases, formations become damaged during the process of
drilling wells into the formation. Mud, chemical additives and
other components used in drilling fluids can accumulate around
the well, forming a cake that blocks the flow of oil into the
well bore. Drilling fluids can also migrate and accumulate in
fissures in the formation, blocking the flow of oil through
the formation. Parrafins and waxes may precipitate at the
interface between the well bore and the formation, further
impeding the flow of oil into the well bore. Sediments and
native materials in the formation can also migrate and block
interstitial spaces.  
  
Numerous methods have been used to alleviate the problems
associated with plugging in oil bearing formations. Plugging
is often addressed by backflushing the well to remove mud from
around the well. Backflushing the well can consume significant
time and energy, and has limited effectiveness in unplugging
areas that are located deep within a formation and away from
the well. Acidizing the well and flushing the well with
solvents are also used to alleviate plugging, but these
methods can create hazardous waste that is expensive and
difficult to dispose of. As a result, known methods for
unplugging oil bearing formations leave much to be desired.  
  
In many cases, crude oil is extracted with high concentrations
of sulfur, polycyclic aromatic compounds (PAHs) and other
compounds that reduce the quality and value of the oil. The
presence of undesirable compounds in the oil requires
subsequent processing of the oil, increasing the time and cost
of production. Therefore, there is a great need to develop oil
production methods that allow oil to be treated while it is
being extracted.  
  
**SUMMARY OF THE INVENTION**  
  
The foregoing problems are solved to a great degree by the
present invention, which uses electrodes to enhance oil
production from an oil bearing formation. A first borehole is
provided in a first region of the formation, and a first
electrode is positioned in the first borehole. A second
electrode may be placed above ground in proximity to the
formation. Alternatively, the second electrode may be
installed in a second borehole. The second borehole may be
positioned in a second region of the formation, or in
proximity to the formation. A voltage difference is
established between the first and second electrodes to create
an electric field across the formation.  
  
It has been discovered that the method of the present
invention can be used to improve the condition of the oil
formation and repair damaged or plugged formations where oil
flow is impeded by drilling fluids, natural occlusions or
other matter. The method can also be applied to pre-treat oil
in the formation as it is extracted from the formation. The
electric field may be applied and manipulated to destabilize
occlusions and plugging materials, increase oil flow through
the formation and improve the quality of the oil prior to and
during extraction.  
  
**DESCRIPTION OF THE DRAWINGS**  
  
The foregoing summary as well as the following description
will be better understood when read in conjunction with the
figures in which:  
  
**FIG. 1 is a schematic diagram of an improved
electrochemical method for stimulating oil recovery from an
underground oil-bearing formation;****FIG. 2 is a schematic diagram in partial sectional view
of an apparatus with which the present method may be
practiced;****FIG. 3 is an elevational view of an electrode assembly
adapted for use in practicing the present invention;****FIG. 4 is a block flow diagram of a method for
improving flow conditions and pre-treating oil in a
formation;****FIG. 5 is a schematic diagram of a first alternate
electrochemical method for stimulating oil recovery from an
underground oil-bearing formation; and****FIG. 6 is a schematic diagram of a second alternate
electrochemical method for stimulating oil recovery from an
underground oil-bearing formation.**

**![US7325604a](us7325604a.JPG) ![US7325604b](us7325604b.JPG) ![US7325604c](us7325604c.JPG) ![US7325604d](us7325604d.JPG) ![US7325604e](us7325604e.JPG) ![US7325604f](us7325604f.JPG)**

**DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT**  
  
Referring to the Figures in general, and to FIG. 1,
specifically, the reference number 11 represents a
subterranean formation containing crude oil. The subterranean
formation 11 is an electrically conductive formation,
preferably having a moisture content above 5 percent by
weight. As shown in FIG. 1, formation 11 is comprised of a
porous and substantially homogeneous media, such as sandstone
or limestone. Typically, such oil-bearing formations are found
beneath the upper strata of earth, referred to generally as
overburden, at a depth of the order of 1,000 feet or more
below the surface. Communication from the surface 12 to the
formation 11 is established through on or more boreholes. In
FIG. 1, communication from the surface 12 to the formation 11
is established through spaced-apart boreholes 13 and 14. The
hole 13 functions as an oil-producing well, whereas the
adjacent hole 14 is a special access hole designed for the
transmission of electricity to the formation 11.  
  
The present invention can be practiced using a multiplicity of
cathodes and anodes placed in boreholes. The boreholes may be
installed in a variety of vertical, horizontal or angular
orientations and configurations. In FIG. 1, the system is
shown having two electrodes installed vertically into the
ground and spaced apart generally horizontally. A first
electrode 15 is lowered through access hole 14 to a location
in proximity to formation 11. Preferably, first electrode 15
is lowered through access hole 14 to a medial elevation in
formation 11, as shown in FIG. 1. By means of an insulated
cable in access hole 14, the relatively positive terminal or
anode of a high-voltage d-c electric power source 2 is
connected to the first electrode 15. The relatively negative
terminal on the power source or cathode is connected to a
second electrode 16 in producing well 13, or within close
proximity of the producing well. Between the electrodes, the
electrical resistance of the connate water 4 in the
underground formation 11 is sufficiently low so that current
can flow through the formation between the first and second
electrodes 15, 16. Although the resistivity of the oil is
substantially higher than that of the overburden, the current
preferentially passes directly through the formation 11
because this path is much shorter than any path through the
overburden to "ground."  
  
To create the electric field, a periodic voltage is produced
between the electrodes 15, 16. Preferably, the voltage is a
DC-biased signal with a ripple component produced under
modulated AC power. Alternatively, the periodic voltage may be
established using pulsed DC power. The voltage may be produced
using any technology known in the electrical art. For example,
voltage from an AC power supply may be converted to DC using a
diode rectifier. The ripple component may be produced using an
RC circuit or through transistor controlled power supplies.
Once the voltage is established, the electric current is
carried by captive water and capillary water present in the
underground formation. Electrons are conducted through the
formation by naturally occurring electrolytes in the
groundwater.  
  
The electric potential required for carrying out
electrochemical reactions varies for different chemical
components in the oil. As a result, the desired intensity or
magnitude of the ripple component depends on the composition
of the oil and the type of reactions that are desired. The
magnitude of the ripple component must reach a potential
capable of oxidizing and reducing bonds in the oil components.
In addition, the ripple component must have a frequency range
above 2 hertz and below the frequency at which polarization is
no longer induced in the formation. The waveshape of the
ripple may be sinusoidal or trapezoidal and either symmetrical
or clipped. Frequency of the AC component is preferably
between 50 and 2,000 hertz. However, it is understood in the
art that pulsing the voltage and tailoring the wave shape may
allow the use of frequencies higher than 2,000 hertz.  
  
A system suitable for practicing the invention is shown in
FIG. 2. In this system, borehole 13 functions as an oil
producing well which penetrates one region 17 of underground
oil-bearing formation 11. Well 13 includes an elongated
metallic casing 18 extending from the surface 12 to the cap
rock 23 immediately above region 17. The casing 18 is sealed
in the overburden 19 by concrete 20 as shown, and its lower
end is suitably joined to a perforated metallic liner 24 which
continues down into the formation 11. Piping 21 is disposed
inside the casing 18 where it extends from the casing head 22
to a pump 25 located in the liquid pool 26 that accumulates
inside the liner 24. Preferably the producing well 13 is
completed in accordance with conventional well construction
practice. The pump 25 is selected to operate at sufficient
pumping head to draw oil from adjacent formation 11 up through
metallic liner 24.  
  
Access hole 14 that contains first electrode 15 includes an
elongated metallic casing 28 with a lower end preferably
terminated by a shoe 29 disposed at approximately the same
elevation as the cap rock 23. The casing 28 is sealed in the
overburden 19 by concrete 30. Near the bottom of hole 14, a
tubular liner 31 of electrical insulating material extends
from the casing 28 for an appreciable distance into formation
11. The insulating liner 31 is telescopically joined to the
casing 28 by a suitable crossover means or coupler 32.  
  
Below the liner 31, a cavity 34 formed in the oil-bearing
formation 11 contains the first electrode 15. The first
electrode 15 is supported by a cable 35 that is insulated from
ground. The first electrode 15 is relatively short compared to
the vertical depth of the underground formation 11 and may be
positioned anywhere in proximity to the formation. Referring
to FIG. 2, first electrode 15 is positioned at an
approximately medial elevation within the oil-bearing
formation 11. The first electrode may be exposed to saline or
oleaginous fluids in the surrounding earth formation, as well
as a high hydrostatic pressure. Under these conditions, first
electrode 15 may be subject to electrolytic corrosion.
Therefore, the electrode assembly preferably comprises an
elongate configuration mounted within a permeable concentric
tubular enclosure radially spaced from the electrode body. The
enclosure cooperates with the first electrode body to protect
it from oil or other adverse materials that enter the cavity.  
  
It should be noted that FIG. 2 is not to scale, and some of
the dimensions of the hole 14 and components in the hole are
exaggerated. For example, the diameter of hole 14 is shown to
be quite large in comparison to the cable 35 and other
components. The diameter of the hole 14 may be much closer to
the diameter of the cable 35. In addition, liner 31 preferably
has a substantial length and a relatively small inside
diameter.  
  
Referring now to FIG. 3, a preferred assembly for the first
electrode 15 is shown. The assembly comprises a hollow tubular
electrode body 15 electrically connected through its upper end
to a conducting cable 35 and disposed concentrically in
radially spaced relation within a permeable tubular enclosure
16a of insulating material. The first electrode 15 is
preferably coated externally with a material, such as lead
dioxide, which effectively resists electrolytic oxidation. The
assembly preferably includes means to place the internal
surfaces of the first electrode 15 under pressure
substantially equal to the external pressure to which the
first electrode is exposed, thereby to preclude deformation
and consequent damage to the first electrode. The enclosure
16a is closed at the bottom to provide a receptacle for sand
or other foreign material entering from the surrounding
formation.  
  
Referring again to FIG. 2, the first electrode 15 is attached
to the lower end of insulated cable 35, the other end of which
emerges from a bushing or packing gland 36 in the cap 37 of
casing 28 and is connected to the relatively positive terminal
of an electric power source 38. The other terminal on the
electric power source 38 is connected via a cable 42 to an
exposed conductor that acts as a second electrode 16 at the
producing well 13. The second electrode 16 may be a separate
component installed in the proximity of producing well 13 or
may be part of the producing well itself. In the embodiment
shown in FIG. 2, the perforated liner 24 serves as the second
electrode 16, and the well casing 18 provides a conductive
path between the liner and cable 42.  
  
Thus far, it has been presumed that electrodes 15, 16 are
located in a formation with a suitable moisture content and
naturally occurring electrolytes to provide an
electroconductive path through the formation. In formations
that do not have adequate capillary and captive groundwater to
be electrically conductive, an electroconductive fluid may be
injected into the formation through one or both boreholes to
maintain an electroconductive path between the electrodes 15,
16. Referring to FIG. 2, a pipe 40 in borehole 14 delivers
electrolyte solution from the ground surface to the
underground formation 11. Preferably, a pump 43 is used to
convey the solution from a supply 44 and through a control
valve 45 into borehole 14. Borehole 14 is preferably equipped
with conventional flow and level control devices so as to
control the volume of electrolyte solution introduced to the
borehole. A detailed system and procedure for injecting
electrolyte solution into a formation is described in the
aforementioned U.S. Pat. No. 3,782,465. See also, U.S. Pat.
No. 5,074,986, the entire disclosure of which is incorporated
by reference herein.  
  
Referring now to FIGS. 1-2, the steps for practicing the
improved method for stimulating oil recovery will now be
described. An electric potential is applied to first electrode
15 so as to raise its voltage with respect to the second
electrode 16 and region 17 of the formation 11 where the
producing well 13 is located. The voltage between the
electrodes 15, 16 is preferably no less than 0.4 V per meter
of electrode distance. Current flows between the first and
second electrodes 15, 16 through the formation 11. Connate
water 4 in the interstices of the oil formation provides a
path for current flow. Water that collects above the
electrodes in the boreholes does not cause a short circuit
between the electrodes and surrounding casings. Such short
circuiting is prevented because the water columns in the
boreholes have relatively small cross sectional areas and,
consequently, greater resistances than the oil formation.  
  
As current is applied across formation 11, electrolysis in the
capillary water and captive water takes place. Water
electrolysis in the groundwater releases agents that promote
oxidation and reduction reactions in the oil. That is,
negatively charged interfaces of oil compounds undergo
cathodic reduction, and positively charged interfaces of the
oil compounds undergo anodic oxidation. These redox reactions
split long-chain hydrocarbons and multi-cyclic ring compounds
into lighter-weight compounds, contributing to lower oil
viscosity. Redox reactions may be induced in both aliphatic
and aromatic oils. As viscosity of the oil is reduced through
redox reactions, the mobility or flow of the oil through the
surrounding formation is increased so that the oil may be
drawn to the recovery well. Continued application of electric
current can ultimately produce carbon dioxide through
mineralization of the oil. Dissolution of this carbon dioxide
in the oil further reduces viscosity and enhances oil
recovery.  
  
In addition to enhancing oil flow characteristics, the present
invention promotes electrochemical reactions that upgrade the
quality of the oil being recovered. Some of the electrical
energy supplied to the oil formation liberates hydrogen and
other gases from the formation. Hydrogen gas that contacts
warm oil under hydrostatic pressure can partially hydrogenate
the oil, improving the grade and value of the recovered oil.
Oxidation reactions in the oil can also enhance the quality of
the oil through oxygenation.  
  
Electrochemical reactions are sufficient to decrease oil
viscosities and promote oil recovery in most applications. In
some instances, however, additional techniques may be required
to adequately reduce retentive forces and promote oil recovery
from underground formations. As a result, the foregoing method
for secondary oil recovery may be used in conjunction with
other processes, such as electrothermal recovery or
electroosmosis. For instance, electroosmotic pressure can be
applied to the oil deposit by switching to straight d-c
voltage and increasing the voltage gradient between the
electrodes 15, 16. Supplementing electrochemical stimulation
with electroosmosis may be conveniently executed, as the two
processes use much of the same equipment. A method for
employing electroosmosis in oil recovery is described in **U.S.
Pat. No. 3,782,465.**  
  
Many aspects of the foregoing invention are described in
greater detail in related patents, including **U.S. Pat. No.
3,724,543, U.S. Pat. No. 3,782,465, U.S. Pat. No. 3,915,819,
U.S. Pat. No. 4,382,469, U.S. Pat. No. 4,473,114, U.S. Pat.
No. 4,495,990, U.S. Pat. No. 5,595,644 and U.S. Pat. No.
5,738,778,** the entire disclosures of which are
incorporated by reference herein. Oil formations in which the
methods described herein can be applied include, without
limitation, those containing heavy oil, kerogen, asphaltinic
oil, napthalenic oil and other types of naturally occurring
hydrocarbons. In addition, the methods described herein can be
applied to both homogeneous and non-homogeneous formations.  
  
It has been discovered that the method of the present
invention can be used to improve the condition of the oil
formation and repair damaged or plugged formations where oil
flow is impeded. The method can also be applied to pre-treat
oil in the formation as it is extracted from the formation.  
  
Referring now to FIG. 4, a method 110 for improving flow
conditions and pre-treating oil in a formation is shown in a
block diagram. The method 110 is applicable to a variety of
well pump installations that draw material from underground
formations, including oil recovery wells. The method 110
utilizes electric current to enhance the production of oil
from an oil-bearing formation and improve the flow
characteristics within the formation. The improved flow
characteristics increase the volume of oil that is recoverable
from the formation. Electric current is also applied to modify
the properties of the oil in the formation and increase the
quality of oil recovered. The decomposition of long-chain
compounds decreases the viscosity of the oil compounds and
increases oil mobility through the formation such that the oil
may be withdrawn at the recovery well. Electrochemical
reactions in the formation also upgrade the quality and value
of the oil that is ultimately recovered.  
  
The components used in the present method include many of the
same components described in U.S. patent application Ser. No.
10/279,431. The system generally includes two or more
electrodes placed in proximity of the oil bearing formation.
In systems using only two boreholes, a first borehole and a
second borehole are provided within the underground formation,
or in proximity of the underground formation. The first and
second boreholes may be drilled vertically, horizontally or at
any angle that generally follows the formation. A first
electrode is placed within the first borehole and a second
electrode is placed within or in proximity of the second
borehole. Alternatively, the second electrode may be
positioned at the earth's surface. A source of voltage is
connected to the first and second electrodes. The first and
second boreholes may penetrate the body of oil to be
recovered, or they may penetrate the formation at a point
beyond but in proximity to the body of oil. A voltage
difference is applied between the electrodes to create an
electric field through the oil bearing formation.  
  
The method 110 for improving flow conditions and pre-treating
oil in an underground formation will now be described in
greater detail. A first borehole is provided in a first region
of the formation in step 120. A second borehole is provided in
a second region of the formation in step 130. A first
electrode is placed in the first borehole in step 140, and a
second electrode is placed in proximity of the second borehole
in step 150. A voltage difference is established between the
first and second electrodes to create an electric field across
plugging materials in the formation in step 160. The electric
field is applied across the plugging materials to destabilize
the plugging materials in step 170.  
  
The method of FIG. 4 may be applied in several ways to improve
flow characteristics in a formation. For example, if a mud
cake is deposited on the interface between the well bore and
the formation, an electric field may be applied to loosen and
remove the mud. A negative electrode is placed in the well
bore that is blocked by the mud cake, and the electric field
is applied across the mud cake. Formation water will can move
through the well bore interface toward the negative electrode
under the influence of the electric field. As the water moves
through the interface, the electroosmotic forces hydrate the
mud and gradually dislodge the clay from the well bore to
unblock the well.  
  
The method of FIG. 4 may also be applied to remove plugging
materials from fissures within the formation. Plugging
materials may include mud or residue from drilling fluid,
naturally formed occlusions, or other matter that blocks flow
of oil through the interstitial spaces in the formation. The
electrode in the well bore may be negatively charged to draw
plugging materials into the well bore and out of the
formation. Alternatively, the electrode in the well bore may
positively charged to repel and push the plugging materials
deeper into the formation.  
  
The electric field can be applied alone or in conjunction with
other techniques for unplugging formations. For example, the
present method may be used in conjunction with acidizing to
dissolve and remove clay plugging materials. An unplugging
acid is introduced into the formation, and an electrode in the
formation is positively charged. An electric field is applied
to drive the unplugging acid into the formation until the acid
reaches the plugging materials. Migration of the acid is
carried out by electroosmosis, but may be assisted by other
means, such as well pumping. The electric field may be used to
drive the acid into regions of the formation that cannot be
reached through boreholes. If desired, the voltage may be
increased to impart resistive heating and decrease viscosity
of the plugging materials. Additives may be introduced into
the formation to change the electric charge of plugging
materials. Once the plugging materials are destabilized, the
formation may be backflushed to remove any remnants or
byproducts remaining in the formation. One or more well pumps
may be operated to establish suction pressure in the well and
draw the destabilized plugging materials into the well.  
  
As noted above, the present invention promotes electrochemical
reactions that upgrade the quality of the oil being recovered.
For example, the electric field may be used to remove
sulfur-containing compounds from crude, thereby improving the
quality and value of oil as it is recovered. It has been found
that superimposing a variable AC signal with a frequency
between 2 Hz and 1.24 MHz on to a DC signal can induce
oxidation to convert sulfur compounds to sulfates. The
sulfates tend to remain in the formation as the oil is
removed. The present invention may also be applied to remove
polycyclic aromatic compounds (PAHS) from crude oil. Operation
of the electric field to remove sulfur compounds and PAHs may
take place prior to extraction of oil, or while the oil is
being extracted. The electric field may be applied for a
specified period of time. Alternatively, the electric field
may be applied until the concentration of sulfur compounds
and/or PAHs is reduced below a predetermined limit.  
  
The present invention can be practiced using a multiplicity of
cathodes and anodes placed in vertical, horizontal or angular
orientations and configurations, as stated earlier. Referring
now to FIG. 5, an alternate system is shown with electrodes
installed in well casing 113, 114. The well casings 113, 114
extend in a generally horizontal orientation through an
oil-bearing formation 111. The relatively positive terminal or
anode of a high-voltage d-c electric power source 102 is
connected to the first well casing 113. The relatively
negative terminal on the power source or cathode is connected
to the second well casing 114. In this arrangement, well
casing 113 acts as a cathode producer, and well casing 114
acts as an anode. Insulating components or breaks 115 are
placed in each of the well casings 113, 114 so that
electricity flows between the horizontal sections of the
casings within the oil-bearing formation 111. Between the well
casings 113, 114, the electrical resistance of the connate
water in the formation is sufficiently low so that current can
flow through the formation between the casings. Although the
resistivity of the oil is substantially higher than that of
the overburden, the current preferentially passes directly
through the formation 111 because this path is much shorter
than any path through the overburden to "ground."  
  
The present method may include one or more electrodes placed
above ground, as described earlier. Referring now to FIG. 6,
an alternate system is shown with a first electrode 215 placed
below the earth's surface (marked "E") and a second electrode
216 placed above the earth's surface in proximity to an
underground oil-bearing formation 211. The first electrode 215
is installed in a borehole 214 that penetrates the formation
211. The first electrode 215 is positioned within the
formation, but may be positioned outside the formation,
depending on the desired position and range of the electric
field. The second electrode 216 is placed on the earth's
surface. By means of an insulated cable in access hole 214, a
terminal on a high-voltage d-c electric power source 202 is
connected to the first electrode 215. The opposite terminal on
the power source 202 is connected to the second electrode 216.
A voltage difference is established between the first and
second electrodes 215, 216 to create an electric field across
the formation 211. It should be noted that the second
electrode 216 may be installed at a shallow depth just beneath
the earth's surface to produce an electric field. For example,
the second electrode may be installed within fifty feet of the
earth's surface to establish an electric field across the
formation. Placing the second electrode 216 at a shallow depth
below the earth's surface may be desirable where space above
ground is limited.

---

  

**US2005161217** **Method and system for producing methane gas from
methane hydrate formations**

  
A system for producing gas from a gas hydrate formation includes a
first electrode and a second electrode. The first electrode is
disposed in proximity of a first region of the formation, and the
second electrode is disposed within a second region of the
formation. The second electrode is separated from the first
electrode by an electro-conductive path through the formation. An
extraction well extends within the formation and intersects the
electro-conductive path. The well comprises one or more
perforations in fluid communication with the formation. A voltage
source is connected to the electrodes and operates to produce a
voltage difference across the electrodes.; A method for extracting
gases from a gas hydrate formation includes the step of
establishing a voltage difference across two or more electrodes in
a hydrate formation to thermally react with the hydrate formation
and release gas from the formation.  
  
**CROSS-REFERENCE TO RELATED APPLICATIONS**  
[0001] This is a continuation-in part of U.S. patent application
Ser. No. 10/279,431, filed Oct. 24, 2002, which claims the benefit
of U.S. Provisional Application No. 60/335,701, filed Oct. 26,
2001, the entire disclosures of which are incorporated by
reference herein.  
  
**FIELD OF THE INVENTION**  
[0002] The present invention relates generally to the production
of natural gas, and more particularly to a method and system for
producing natural gas from gas reserves with the aid of electric
current.  
  
**BACKGROUND**  
[0003] The U.S. Department of Energy estimates that the ocean
floor and arctic permafrost regions contain several trillion cubic
feet of methane gas (also referred to as natural gas) in the form
of methane hydrates. Methane hydrates are clathrate compounds
which are inclusion complexes formed at high pressures and low
temperatures, existing as solid crystalline structures. In these
structures, methane gas molecules are surrounded or included by a
cage of water molecules. Methane hydrates are typically found on
the ocean floor in sediments which are stable at depths of
approximately 300 meters.  
  
[0004] There is increasing interest in the development of methods
to extract methane gas from formations containing methane
hydrates. The production of methane gas is viewed as one means for
lessening global dependency on oil and other fuels containing
large amounts of carbon. Efforts to increase methane gas
production are also motivated by an expanding natural gas
infrastructure and growing interest in natural gas from public
utility companies. At least one extraction technique, solvent
injection, has been proposed and tested to extract methane gas
from methane hydrates. Although solvent injection has shown
promise, the technique is difficult to apply uniformly through a
formation, and may not be suitable for deep formations. As a
result, currently proposed techniques for extracting methane gas
from methane hydrate formations leave much to be desired.  
  
**SUMMARY OF THE INVENTION**  
  
[0005] In a first aspect of the invention, a system for extracting
gases from a gas hydrate formation includes a first electrode and
a second electrode. The first electrode is disposed in proximity
to a first region of the formation, and the second electrode is
disposed within a second region of the formation. The second
electrode is separated from the first electrode by an
electro-conductive path through the formation. An extraction well
extends within the formation in proximity to the
electro-conductive path. The well comprises one or more
perforations in fluid communication with the formation. A voltage
source is connected to the first and second electrodes and
operates to produce a voltage difference across the first and
second electrodes.  
  
[0006] In one embodiment of the invention, a system includes a
first electrode in proximity to a first region of a formation
containing methane hydrates on the ocean floor. A second electrode
is disposed within a second region of the formation. The second
electrode is separated from the first electrode by an
electro-conductive path through the methane hydrate formation. An
extraction well extends within the formation in proximity to the
electro-conductive path. The well comprises one or more
perforations in fluid communication with the formation. A voltage
source is connected to the first and second electrodes and
operates to produce a voltage difference across the first and
second electrodes. Upon operation of the voltage source,
resistance in the formation causes the voltage difference between
the electrodes to generate heat energy which is sufficient to
thermally react with the methane hydrates thereby releasing
methane gas from the formation. The methane gas is formed at
elevated pressure, which drives the gas into the extraction well.
The methane gas may be recovered and stored on a barge or other
ocean vessel. Once on the barge, the gas may be used to fuel an
electric generator. Alternatively, the methane gas may be conveyed
by undersea piping to a facility on land e.g. for distribution.  
  
[0007] In a second aspect of the invention, a method for
extracting gas from a formation containing gas hydrates includes
the step of placing two or more electrodes in proximity to the
formation and drilling an extraction well into the formation. The
extraction well has one or more perforations to connect the
interior of the well with the formation. A source of voltage is
connected to the electrodes, and a voltage difference is
established across the electrodes to produce an electrical current
through the formation. The current through the formation is
adjusted to thermally react with the gas hydrates in the formation
and release gases from the gas hydrates. Gases released from the
gas hydrates are drawn into the extraction well.  
  
**DESCRIPTION OF THE DRAWINGS**  
  
[0008] The foregoing summary as well as the following description
will be better understood when read in conjunction with the
figures in which:  
  
**[0009] FIG. 1 is a schematic of a system for producing gas from
a gas hydrate formation in accordance with the present
invention.****[0010] FIG. 2 is a schematic of a system for producing gas
from a gas hydrate formation in accordance with the present
invention, where the system is employed on an ocean vessel to
extract gas from a gas hydrate formation on the ocean floor.****[0011] FIG. 3 is a schematic of an alternate system for
producing gas from a gas hydrate formation in accordance with
the present invention, where the system is employed on an ocean
vessel to extract gas from a gas hydrate formation on the ocean
floor.**

**![US2005161217a](us2005161217a.JPG) ![US2005161217b](us2005161217b.JPG) ![US2005161217c](us2005161217c.JPG)**

**DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT**  
  
[0012] Referring to the drawing figures in general, and to FIG. 1
specifically, a system 10 for producing gas from a formation
containing gas hydrates is shown in schematic form in accordance
with the present invention. The system 10 is installed in the
vicinity of a gas hydrate formation 8. Two or more electrodes,
such as a first electrode 20 and a second electrode 30, are placed
in or around the gas hydrate formation 8 and connected with a
voltage source 12. Electric current is applied between the
electrodes 20, 30 and across the gas hydrate formation 8 to
produce an electric field 40 across the hydrate formation. The
electric field 40 is applied to the formation to release gas from
the gas hydrates. The release of gas from the gas hydrates is
primarily carried out through resistive heating. The electric
field 40 gradually produces heat in the formation 8 based on
electrical resistivity of the sediments and materials in the
formation 8. As heat is generated, the temperature around the gas
hydrates increases until the hydrates are destabilized, releasing
the gas from the hydrate molecules. A gas extraction means 50 is
placed within the hydrate formation 8 to capture and convey the
released gas to a gas collection system 60.  
  
[0013] The system 10 may be used in a variety of applications to
produce gas from gas hydrate deposits. For purposes of this
description, the system 10 will be shown and described in the
context of methane gas production, with the understanding that the
invention can be applied to a variety of different gas hydrate
formations containing varying amounts of methane and other gases.
The present invention is operable in different formations of
varying compositions, and may be used for releasing and collecting
gases other than methane gas. In addition, while this description
refers to methane gas, it is understood that the gas released from
a formation will likely contain a mixture of methane gas and other
gases.  
  
[0014] The present invention can be practiced using a multiplicity
of electrodes placed in vertical, horizontal or angular
orientations and configurations. The arrangement of components in
a given installation will vary depending on the location and local
geology of the hydrate formation. As stated earlier, methane
hydrate formations have been studied in arctic permafrost regions
as well as in sediment layers on or beneath the ocean floor.
Hydrate formations may exist as large relatively flat homogeneous
formations, or may be interrupted by outcrops of non-hydrate
material. Therefore, the electrodes may be positioned in a number
of arrangements in or around the formation.  
  
[0015] Referring now to FIG. 2, a system 110 in accordance with
one embodiment of the present invention is operable to produce
methane gas from a methane hydrate formation 108 along the sea
floor. The system 110 includes a high-voltage electric power
source 112 supported above the formation. The components of system
110 may be located on land or supported on a ship, rig, barge,
vessel, or other means in proximity to the formation. In FIG. 2,
the system is shown on a barge 115. By means of an insulated cable
122, the relatively positive terminal, or anode, of the power
source 112 is connected to a first electrode 120. Depending on the
geology of the sea floor, and the proximity of the methane hydrate
formation to the sea floor surface, the first electrode 120 may be
suspended above the sea floor, rest on the sea floor or be
installed beneath the sea floor through a fissure, crevice or bore
hole that penetrates beneath the sea floor in proximity to the
hydrate formation. For purposes of FIG. 2, it will be assumed that
a significant volume of stabilized methane hydrate is exposed on
the sea floor in a substantially flat layer, allowing the first
electrode 120 to rest on the sea floor.  
  
[0016] A gas collection well 150 is drilled into the formation 108
to recover methane gas released from the formation during
operation of the system 110. The collection well 150 includes a
perforated metallic liner 151 which extends down into the
formation 108. The perforated liner 151 has one or more
perforations that connect the interior of the collection well 150
in fluid communication with the interior of the formation 108.
Since the hydrate formation 108 is exposed on the sea floor, the
liner 151 extends from the top of the well 150 into the formation.
In hydrate formations that are buried under a layer of overburden
material, the well 150 may include a solid casing that extends
through the overburden. The specific construction of the well is
not germane to the invention, and will largely depend on the
geologic conditions around the hydrate formation. Preferably, the
collection well 150 is completed in accordance with conventional
undersea drilling practices.  
  
[0017] The relatively negative terminal on the power source 112,
or cathode, is connected to a second electrode 130 placed within
the methane hydrate formation 108. The second electrode 130 may
have several forms and be positioned in the formation in several
ways. For example, the second electrode could be lowered through
large cracks or fissures in the formation. In the preferred
embodiment, the second electrode 130 is associated with the gas
collection well 150. The second electrode 130 may be a separate
component installed inside the collection well 150 or in the
proximity of the collection well. Alternatively, the second
electrode 130 may be part of the collection well 150 itself. In
the embodiment shown in FIG. 2, the perforated metallic liner 151
serves as the second electrode 130. An insulated cable 132
connects the liner 151 with the relatively negative terminal on
the power source 112. The top portion of the well 150 forms an
electro-conductive path between the insulated cable 132 and the
second electrode 130. In this arrangement, an electric field 140
is generated through the formation 108 when a voltage drop is
created across the electrodes 120, 130. The gas collection well
150 may be installed to depths of 500 meters or greater to reach
the hydrate formation.  
  
[0018] Thus far, the first electrode 120 above the formation has
been shown connected to the relatively positive terminal, or
anode, of the power source 112, and the second electrode 130
within the formation has been shown connected to the relatively
negative terminal, or cathode, of the power source. There is
nothing that precludes the first electrode 120 from being
connected to the cathode of the power source 112, and nothing to
preclude the second electrode 130 from being connected to the
anode of the power source, however. Therefore, the electrode in
the formation may be connected with either terminal of the voltage
source 112.  
  
[0019] The electrical resistance of the sediment in the formation
is sufficiently low to allow the passage of current through the
formation between the first and second electrodes 120, 130.
Although the resistivity of the formation 108 is substantially
higher than that of the seawater above the electrodes, the current
passes directly through the formation because this path is much
shorter than any path through the overlying seawater to "ground."
In the preferred embodiment, the second electrode 130 is connected
with an insulating break 153 that substantially prevents short
circuiting of current up through the well casing.  
  
[0020] To create the electric field 140 and commence resistive
heating in the formation, a voltage drop is produced across the
electrodes 120, 130. The voltage may be a straight DC voltage or a
DC-biased signal with a ripple component produced under modulated
AC power. Alternatively, the periodic voltage may be established
using pulsed DC power. The voltage may be produced using any
technology known in the electrical art. For example, voltage from
an AC power supply may be converted to DC using a diode rectifier.
The ripple component may be produced using an RC circuit.  
  
[0021] The choice of AC power or DC power depends on many
variables, and each option has advantages. One advantage of AC is
that AC systems have less potential for corrosion on the electrode
than DC. The use of AC also has limitations, including a limited
effectiveness at deeper depths. Losses in steel well casings
dissipate energy. This dissipation increases with depth, and will
typically limit the use of AC to depths of approximately 5,000
feet below the top of the well. Use of AC can be applied at
greater depths, but resistive heating may be very limited.
Therefore, for well casings and liners extending greater than
5,000 feet, straight DC power is preferable. AC power is desirable
in shallower well installations, where losses are less of a
factor.  
  
[0022] Where DC power is used to induce destabilization of methane
hydrates, the process of producing and recovering methane gas may
be enhanced through electro-osmosis and ion migration. In
addition, electrochemical reactions such as the production of
oxygen and hydrogen may assist in the production of methane.
Electrochemical reactions can also create methanol and ethane
through oxidation and reduction. The electric potential required
for carrying out thermal destabilization of methane hydrates will
vary depending on pressure and temperature conditions at the
formation, and the size of the desired electric field.  
  
[0023] Referring now to FIG. 3, a system 210 in accordance with
the present invention includes a high-voltage electric power
source 212 located on a barge 215, and a first electrode 220
incorporated into the structure of the barge. The first electrode
220 is connected to a relatively positive terminal, or anode, of
the power source 212. A gas collection well 250 is drilled into a
methane hydrate formation 208, similar to the embodiment described
above. The collection well 250 includes a perforated metallic
liner 251 which extends down into the formation 208 and serves as
a second electrode 230. An insulated cable 232 connects the liner
251 with the relatively negative terminal on the power source 212.  
  
[0024] Based on the foregoing, persons skilled in the art will
understand the advantages of system 210 over prior methods for
producing gas from gas hydrates. The first electrode 220 is
integrally connected with the barge 215, while the second
electrode 230 is a stationary electrode. The position of the first
electrode can be adjusted by navigating the barge in different
positions relative to the second electrode 230. By moving the
first electrode, the position and intensity of the electric field
can be modified. The ability to move electrodes maximizes the
range of application of the electric field. Theoretically, the
position of the field can be adjusted through an angle of up to
360 degrees around a single stationary electrode. The same
benefits may be achieved on land by mounting electrodes on
vehicles. For example, it is anticipated that the present
invention may be applied in arctic permafrost regions, with
electrodes mounted on heavy track machines or all-terrain
vehicles. The ability to reposition the electric field greatly
reduces the number of bore holes and electrodes that must be
installed, since an electric field can be applied over a
relatively large area by maneuvering a small number of electrodes
around the formation.  
  
[0025] Gas may be captured or collected using a variety of piping
arrangements in accordance with the present invention. In FIG. 2,
the well 150 is connected to a riser pipe or conduit 152 which
connects to a storage tank 160 on the barge 115. In this
arrangement, gas can be collected on the barge and transported to
shore. The conduit 152 may require special reinforcements or
materials suitable for withstanding pressures and currents
associated with deep sea installations. These structural
reinforcements and materials are generally known and therefore
will not be described in detail herein. In addition to storing the
gas on the barge 115, the gas may be used to fuel an electric
generator 170 installed on the barge. In this type of system, gas
may be piped from the extraction well into a storage tank on the
barge, and subsequently fed to a boiler to generate steam.
Electricity generated on the barge may then be exported to the
mainland by undersea cables. The gas may also be piped from the
extraction well directly to land. In FIG. 3, the well 250 is
connected to undersea piping 252 which transports the gas to a
bulk storage plant, power generator, or other facility located on
land.  
  


---

**US2799641** **Electrolytically promoting the flow of oil from a well**

  

![US2799641](us2799641a.JPG)![US2799641b](us2799641b.JPG)![US2799641c](us2799641c.JPG)

  


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**US3417823  
Well treating process using electroosmosis**

  

![US3417823a](us3417823a.JPG)![US3417823b](us3417823b.JPG)

  


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****US3724543**Electro-thermal process for production of off shore oil
through on shore walls**  


**Inventors: Bell C, Titus C**

**Abstract**  
  
The flow of oil from an undersea oil-bearing formation to an
on-shore well is induced by the steps of locating a relatively
small anode in a cavity at an approximately medial elevation of
the formation at an off-shore location preferably beyond the
reservoir of oil, injecting saline water into that cavity, raising
the electric potential of the anode with respect to a cathode in
the vicinity of an off-shore well, and withdrawing oil from the
well.  
  
Crude oil is generally recovered from an oil bearing formation
initially as a result of gas or other formation pressure forcing
the oil from the formation into a producing well from whence it is
pumped to the surface. Such a well of course must penetrate
directly into the body of oil contained in the formation and there
is consequent risk that oil under natural pressure will be
exhausted without control. To preclude or limit such uncontrolled
exhaust it is desirable that oil be moved below ground to a well
location remote from the pressurized region or to a well location
where surface conditions are such that uncontrolled exhaust may be
better controlled at least temporarily. Even where natural
pressure does not create the risk of uncontrolled exhaust it may
often be desirable to move a body of underground oil, whether
fluid or highly viscous, to a well location where production by
pumping is less expensive or more convenient than it would be
directly over the oil body in its natural location.  
  
The several techniques currently used to induce flow of
underground oil are primarily adapted to secondary recovery of oil
following primary production and may be of limited effectiveness
in treating highly viscous oils. A principal such method employs a
scavenging fluid such as air, gas, water or steam. In such
methods, however, pressure and/or temperature limitations are such
that oil flow can be induced only over short distances of the
order of several hundred feet and without directional control.  
  
Other prior art techniques for improving oil recovery involve
conducting electric current through the oilbearing strata for the
purpose of either raising the temperature of the oil by conduction
heating or controlling oil movement by electro-osmosis. The latter
is described in US Pat. No. 2,799,641 granted on July 16, 1957
to  Bell whose proposes placing two electrodes in contact
with the oil at spaced apart locations in an oil-bearing
formation. Bell teaches that electromotive force must be impressed
directly on the oil to cause electric current to flow through the
oil and postulates that the oil is induced to move by
electro-osmosis toward the cathode. Such a method, of course,
requires that both the producing well and the anode bore hole
penetrate directly into the body of oil contained in the
formation, and there is consequent risk that oil under pressures
created naturally or otherwise may exhaust through the anode hole.
  
  
The flow of oil from an undersea oil-bearing formation to an
on-shore well is induced by the steps of locating a relatively
small anode in a cavity at an approximately medial elevation of
the formation at an off-shore location preferably beyond the
reservoir of oil, injecting saline water into that cavity, raising
the electric potential of the anode with respect to a cathode in
the vicinity of an off-shore well, and withdrawing oil from the
well.  
  
Our invention relates to the production of oil from underground
oil bearing formations, and particularly to an improved
electro-thermal method for producing oil from off-shore regions of
a formation through one or more wells in an on-shore region of the
formation.  
  
Our earlier application, Ser. No. 855,637, first filed on Sept. 5,
1969, refiled on Nov. 12, 1970 Nov. 9, 1971 and now existing as a
continuing application, Ser. No. 196,917 discloses and claims
broadly an improved method for utilizing unidirectional electric
current to develop electro-kinetic and thermal driving forces in
the production of oil. In that application it is pointed out that
the method has particular utility in the secondary production of
oil from wells in which natural pressure no longer exists and to
primary or secondary production where the contained oil is highly
viscous. The present invention concerns certain improvements in
the foregoing method whereby it is rendered especially applicable
to the recovery of oil from undersea or other off-shore oil
bearing formations, whether or not the contained oil is under
natural pressure or of high viscosity.  
  
While much has been published about the phenomenom of
electro-osmosis and its more common practical applications to soil
drainage and the dehydration of wet ground, we are not presently
aware that electro-osmosis has been successfully used commercially
to transport underground oil for secondary recovery from an
existing well or for recovery at an optional location. There is
today an urgent need for improved methods of oil recovery from
fields where primary pressure has been exhausted and from tar
sands where huge quantities of highly viscous oils exist without
natural pressure adequate for recovery. Oil bearing strata located
beneath surface areas especially susceptible to pollution or
inconveniently located, as beneath a lake, gulf or ocean, present
a different problem in urgent need of solution.  
  
Accordingly, it is a general object of our invention to provide an
improved electro-thermal method for producing oil from an oil
containing earth formation through a well penetrating the
formation at a selectable point in or beyond the body of contained
oil.  
  
It is a more specific object of our invention to provide an
improved electro-kinetic method for producing oil from an
underwater oil bearing formation in a way which does not require
penetration of the contained oil body at any underwater location.  
  
In carrying out our invention in one form, we suspend an anode in
a cavity in an underground formation i.e., earth stratum in at
least a portion of which a body of oil is present. This cavity may
for example be located at the bottom of a vertical borehole
extending from the surface of the earth to a predetermined region
of the oil-bearing formation. The anode cavity is disposed at an
approximately medial elevation of the proximate region of the
formation and may penetrate the contained body of oil or lie
laterally beyond it. The relatively positive pole of a source of
high-voltage, high-power direct current is connected to the anode
(e.g., by means of an insulated cable in the anode hole), and the
other pole of the source is connected to a cathode located at or
near a well bore which penetrates the formation at a point remote
from the anode. The well bore may penetrate the contained oil body
or be located beyond it so long as some or all the oil body is
located between the well and the anode cavity. The well bore may
thus penetrate the formation at a selectable point in or near the
body of oil to be recovered.  
  
Preferably the cathode comprises a perforated metal linear in the
bottom hole of a producing well. The anode is immersed in a
hydrous electrolyte of a composition having the essential
characteristics of the connate water present in the oil-bearing
formation (hereinafter "formation water") which can be supplied
thereto through the anode hole, and its potential is raised to a
high level (i.e., 200 volts or more) with respect to the cathode.
In this arrangement the anode is in essence a point source of
heat, and the water in the cavity will be efficiently heated above
ambient to a temperature substantially hotter than 250 DEG F. The
hydrostatic pressure exerted by the column of water above the
cavity, augmented by externally imposed pressure if desired,
subjects the water in the cavity to sufficiently high pressure
(e.g., 1,000 p.s.i. and up) so that it remains in a liquid state
at its elevated temperature. The hot pressurized water surrounding
the anode is saline and thus provides a good electrical conducting
medium between the anode and the adjacent oil-bearing formation.
Due to hydrodynamic pressure and electroosmotic flow, the hot
saline water will move from the cavity in a direction toward the
producing well, and the resulting pressure and heat fronts
effectively stimulate the flow of oil in the oil-bearing
formation. Hydrogen released from the interstitial water by
electrolysis at the cathode may be absorbed by the crude oil to
beneficially increase its hydrogen content, and oxygen liberated
near the anode may unite with the oil in an oxidation process that
releases useful heat. The anode is constructed of suitable
material to resist adverse electrolytic reaction.  
  
As will be apparent from the foregoing summary, we are using
unidirectional electric current and formation water as the
prinicpal raw ingredients in a new electrothermal method of
stimulating and directing the flow of oil from known reservoirs.
These inputs are delivered to the subterranean reservoir where the
electric energy is converted to thermal energy (heat), mechanical
energy (electroosmotic movement of the formation water), and
chemical energy (hydrogeneration and oxidation of the oil) which
are effective, in combination, to increase the expulsive forces,
decrease the retentive forces acting on the oil in situ and to
direct flow of oil to a well in the cathode region. In this manner
bulk electric power can be efficiently expended to extract more
oil from existing oil fields than is otherwise practical using
conventional secondary recovery methods. Furthermore, by using our
method the number of wells usually drilled to exploit a given
reservoir may be reduced, and flexibility is provided in location
of wells relative to the location of an oil deposit. The method is
applicable regardless of the character of the oil-bearing
formation (e.g., highly viscous tarsands, oil shale deposits,
"dead" oil fields or oil under natural pressure whether or not
highly viscous). Moreover, our method can be successfully
practiced even though initially there is no oil in the particular
regions or portions of the formation where the anode hole and
well, respectively, are located, so long as a reservoir of oil is
present somewhere between anode and cathode.  
  
Our invention will be better understood and its various objects
and advantages will be more fully appreciated from the following
description taken in conjunction with the accompanying drawings in
which:  
  
**FIG. 1 is a schematic functional diagram of our improved
electro-thermal method of stimulating oil recovery from an
underground oil-bearing formation;****FIG. 2 is a diagrammatic view, partly in section, of an oil
field showing apparatus by which our method can be practiced in
one embodiment thereof;****FIG. 3 is an expanded schematic diagram of the electric
power source used in the FIG. 2 apparatus;****FIG. 4 is an enlarged fragmentary view, partially in
section, of an alternative embodiment of the tubing string shown
in the anode hole of FIG. 2 and****FIG. 5 is a diagrammatic cross-sectional representation of
an oil field illustrating the means by which our invention may
be utilized to recover oil from an underwater oil bearing
formation.**

**![US3724543a](us3724543a.JPG) ![US3724543b](us3724543b.JPG) ![US3724543c](us3724543c.JPG) ![US3724543d](us3724543d.JPG)**

Referring now to FIG. 1, the reference number 11 represents a
subterranean formation or earth stratum containing a reservoir or
body of crude oil in a porous oil-bearing medium. Typically such
oil bearing stratum formations are found beneath the upper strata
of earth, referred to generally as overburden, at a depth of the
order of 2,000 feet or more below the surface. Communication from
the surface 12 to the formation 11 is established through spaced
apart boreholes 13 and 14. The hole 13 comprises an oil-producing
well, whereas the adjacent hole 14 can be a special hole designed
for the transmission of water and electricity to the formation 11.  
  
An anode 15 is lowered through the hole 14 to a medial elevation
of the proximate region of stratum formation 11. The chamber or
cavity in the oil sand where the anode is suspended is flooded
with formation water which preferably is injected through the
anode hole under fluid pressure in excess of that existing in the
oil reservoir. In accordance with conventional practice, the
casing in the hole 14 is sealed in the overburden above the
formation 11, and the casing head is capped so that any desired
pressure may be developed.  
  
By means of an insulated cable in the anode hole 14, the
relatively positive terminal of a high-voltage (at least 200
volts) d-c electric power source is connected to the anode 15. The
negative terminal of the same source is connected to a ground
electrode in the vicinity of the well 13, as to the metallic
tubing in the producing well which thus constitutes a cathode.
Between anode and cathode, the electrical resistance of the
connate water in the oil sand is sufficiently low so that direct
current can flow through this formation from the anode 15 to the
lower regions of the producing well 13. The formation is heated
conductively by electric current passing through it. It is
believed that most of the voltage drop between the terminals of
the d-c power source is concentrated near the electrodes. By
utilizing an anode 15 of small surface area which extends
vertically for only a small portion of the vertical height of the
proximate formation 11 and raising the anode potential with
respect to the cathode to a suitably high voltage, the temperature
of the pressurized water that surrounds it can be raised to at
least several hundred degrees Fahrenheit. Thus the water is heated
and forced into the adjacent oil-bearing formation under the
pressure developed in the anode hole. The water thus absorbed is
induced to flow primarily toward the cathode well under the
applied pressure and the augmenting directional force of
electroosmosis.  
  
In the foregoing manner, heat is efficiently imparted to the oil
sand 11. This reduces the resistivity and the viscosity of the oil
therein and tends to fluidize the same. The heated oil is
entrained by the hot water and is forced under pressure toward the
producing well, as is indicated in FIG. 1 by the pointer. As the
pressure and heat fronts advance toward the producing well, the
temperature is increased in regions of the sand more remote from
the anode. Thus the entire reservoir of oil between the anode hole
14 and the producing well 13 is progressively heated, and the oil
is forced into the producing well where it is removed by ordinary
pumping means. The electrolytic action in the oil-bearing
formation may tend to hydrogenate and thereby upgrade the oil that
is removed therefrom. The operation of our process continues even
after oil migrates away from the vicinity of the anode 15, and in
fact the anode hole 14 can initially be drilled in an oil-dry
region of the formation 11 beyond the contained body or reservoir
of oil.  
  
Suitable apparatus for practicing our invention is shown in FIG.
2, and its construction and operation will now be described. As is
depicted in this figure, the borehole 13 comprises an oil
producing well which penetrates one region 17 of the underground
oil sand 11. The well 13 includes an elongated metallic casing 18
extending from the surface 12 to the cap rock 23 immediately above
the region 17. The casing 18 is sealed in the overburden 19 by
concrete 20 as shown, and its lower end is suitably joined to a
perforated metallic liner 24 which continues through the bottom
hole of the well and down to the underburden. A tubing string 21
is disposed inside the casing 18 where it extends from the casing
head 22 to a pump 25 located in the liquid pool 26 that will
accumulate inside the liner 24. Preferably the producing well 13
is drilled and constructed in accordance with common practices in
the art, and it operates in the usual manner to withdraw or pump
from the bottom hole 26 the mixture of oil and water that flows
therein from the adjacent reservoir 11. Our invention is intended
to stimulate the flow of that mixture into the producing well 13,
thereby promoting the recovery of oil from the formation 11.  
  
In accordance with our invention, another borehole 14 penetrates
the oil sand 11 at a region 27 thereof horizontally-spaced from
the region 17 with which the producing well 13 communicates. This
borehole provides ingress to the region 27 for the anode 15 and
for water. While a conventional producing well like the well 13
could be modified for this purpose, we have illustrated in FIG. 2
a borehole 14 comprising a special "anode hole" which will next be
described.  
  
The anode hole 14 includes an elongated metallic casing 28 whose
lower end is terminated by a shoe 29 disposed at approximately the
same elevation as the cap rock 23, and as usual this casing is
sealed in the overburden 19 by concrete 30. Near the bottom of the
hole a tubular liner 31 of insulating material extends from the
casing 28 for an appreciable distance into the oil sand 11. The
insulating liner 31 is telescopically joined to the casing 28 by a
suitable tubular crossover means or coupler pipe 32. Preferably
the space between the exterior wall of the liner 31 and the
surrounding oil sand 11 is packed by high-temperature concrete 33.
Although shown out of scale in FIG. 2 to simplify the drawing,
actually, for reasons explained hereinafter, the liner 31 should
have a substantial length and a relatively small inside diameter.  
  
Below the liner 31, a cavity 34 is formed in the oil sand 11, and
in this cavity there is an exposed, cylindrical electroconductive
body comprising the anode 15 supported by a cable 35 which is
insulated from ground. The anode 15 is relatively short compared
to the depth of the proximate region of the oil sand (e.g.,
substantially less than one-half the depth of region 27), and it
is positioned at an approximately medial elevation in this region.
For example, if the region 27 were about 100 feet deep, the center
of the anode would be disposed approximately 50 feet below the cap
rock 23. (Obviously the vertical dimensions of the formation 11,
the anode 15, and liner 31, and the cavity 34 have been
foreshortened in FIG. 2 for the sake of drawing simplicity).  
  
The anode 15 is attached to the lower end of the insulated cable
35 whoseother end emerges from a bushing or packing gland 36 in a
cap 37 at the top of casing 28 and is connected to the positive
pole (+) of an electric power source 38. Preferably the cable 35
is clamped for support at spaced intervals on a tubing string 40
which is disposed in the casing 28. The lower section 41 of this
tubing string, which section extends axially through the liner 31,
is made of insulating material whereby there is no metal in the
zone between the anode 15 and the casing shoe 29 except for the
conductor inside the insulated cable 35.  
  
The negative pole (-) of the electric power source 38 is connected
via a cable 42 to an uninsulated conductor or electrode in the
producing well 13. As is shown in FIG. 2, the perforated liner 24
itself conveniently serves as this electrode (the cathode), and
the well casing 18 provides a conductive path between the cathode
and the cable 42. If desired a ground electrode other than the
well casing but also in the vicinity of the well 13 may be used as
cathode. More details of the electric power source 38 will be
explained below in connection with the description of FIG. 3.  
  
The tubing string 40, 41 in the anode hole 14 conveniently serves
as a duct for delivering water from the surface 12 down the hole
to the vicinity of the anode 15. Preferably a pump 43 at the
surface is used to drive this water from a suitable reservoir 44
through a control valve 45 and into the upper section 40 of the
tubing string. The injected water fills the cavity 34 where it is
subjected to a high pressure (e.g., in the order of 1,000 p.s.i.
or more) due to the hydrostatic head plus additional pressure
externally imposed thereon by the pump 43, and it therefore can
flow from the cavity into the surrounding region 27 of the oil
sand 11. As is the case in known water flooding practice, the
apparatus is arranged and operated so as to control the volume
flow of water as desired.  
  
The resistivity of the bottom hole water will be relatively low
due to its saline content. While salts will probably diffuse
therein from the adjacent formation 11, we presently prefer to
inject electroconductive water from the surface. A slightly saline
solution having a resistivity of approximately 1,000
ohm-centimeters or less is suitable for this purpose, it being
understood that the degree of resistivity is not critical. In
addition to being electroconductive, the injected water should
have the proper mix of metal salts and other colloidal matter to
make it compatible with the native formation 11. This will
minimize or prevent swelling of certain clays which may be in the
formation, thereby avoiding any severe reduction in permeability
of the formation. In oil fields where natural formation water is
readily available, it is preferable that such water be injected
into the anode hole 14, thereby to minimize any disturbance to the
chemical balance of the underground formation. Alternatively,
surface water could be chemically treated to produce an equivalent
hydrous electrolyte, i.e., a fluid of a composition having the
essential characteristics (electroconduction and deflocculation
properties) of the formation water. In either case, the injection
water can also be treated if desired with chemical additives which
have other beneficial affects such as enhancing oil production
under the influence of the electric fields and current which will
be present in the formation 11 between the anode 14 and the
cathode 24.  
  
From the foregoing it will be seen that a supply of formation
water (or equivalent) is maintained about and in contact with the
anode 14. Injecting the water from the surface, by a process of
regulated flow (see below), ensures that the anode is continuously
immersed in a pressurized pool of this fluid. The pool of fluid
surrounding the anode constitutes an electroconductive path
between this electrode and the adjacent oil sand. If necessary to
prevent collapse of the walls of the cavity 34, the anode can also
be surrounded by an inert porous medium such as glass beads or
coarse sand having more than approximately 10 percent openings. A
desirable alternative is to dispose both the anode 15 and the
outlet of the water duct 41 inside a tubular container or basket
having sidewalls of porous, insulating material, whereby a
backflow of oil and sand is effectively prevented and the stream
of injected water is directed over a substantial portion of the
surface of the anode body before dispersing to the adjacent region
27 of the formation 11.  
  
In practicing our improved method of stimulating oil recovery, an
electric potential is applied to the anode 15 so as to raise its
voltage, with respect to the remote region 17 of the formation 11
where the producing well 13 is located, to a relatively high level
(i.e., of the order of several hundred to several thousand volts).
Consequently current will flow through the formation 11 between
the anode 15 and the producing well 13. The connate water in the
intersticies of the oil sand initially provides a path for this
current, and its temperature is raised thereby. Interstitial water
typically constitutes only on the order of 15 percent of the
formation 11 by volume, and the resistance of the conducting path
through this formation will be much higher than that of the mass
of saline water which immediately surrounds the anode 15 in the
cavity 34. Nevertheless, because the current density in these
conducting media is highest next to the relatively small surface
area of the anode and decreases as an exponential function of the
distance (radius) therefrom, a high percentage of the voltage drop
between the anode and the ground is expected to be concentrated
near the interface of the water mass and the adjoining
oil-saturated region of the formation 11. As a result, a great
deal of electric power dissipates in the vicinity of this
interface, and the temperature of the pressurized water around the
anode 15 will be raised appreciably. We contemplate a power input
of the order of 25 to 1,000 kilowatts or more, which may heat the
water in the cavity 34 to a temperature substantially in excess of
250 DEG Fahrenheit. This hot water is maintained in a liquid state
by appropriately regulating both its temperature and its pressure.
For example, the hydrostatic pressure of a 2,000 foot column of
water exceeds 900 p.s.i., and at this pressure water remains
liquid to approximately 530 DEG F.  
  
It should be noted at this point that the vertical column of
saline water above the cavity 34 will not form a short circuit
between the anode 15 and the metallic casing 28 of the anode hole
14. This is because the water column is confined in a long, narrow
space having a relatively small cross-sectional area. The
dimensions of the insulating liner 31 through which the water is
injected are selected so that the resistance of the confined
water, if measured between the top of the anode 15 and the lower
end of the casing 28, will be appreciably higher than the
resistance of the conducting path through the oil sand between
anode and cathode. Due to its close proximity to the source of
heat, the bottom part of the insulating liner 31 is adventageously
made of high-temperature material.  
  
Within the underground formation 11, the temperature of the oil
regionadjoining the pressurized hot water in the cavity 34 is
elevated by this source of heat, whereby both the viscosity of the
oil and the resistivity of the oil bearing sand are reduced. As
hot oil recedes from the anode 15, more conductive saline water
fills the vacated space in the porous media. The heat dissipated
per unit volume of saline water will decrease near the anode where
the resistivity of the water has decreased due to the temperature
increase. Thus a heat front advances toward the cathode and behind
it displaced oil is replaced by hot injected water. Because a
substantial portion of the impressed unidirectional voltage
appears at this advancing interface heat is continuously generated
electrically in the immediate vicinity of the front to maintain
the action.  
  
In operation, our invention causes a stream of hot water and oil
to flow in the formation 11 toward the producing well 13. This
stream is driven by water injected into the anode hole 14, and it
is guided toward the cathode by electro-osmosis. The latter effect
can be attributed to a net movement of ions in the interstitial
water under the influence of a unipolarity field. This
electro-osmotic motive force supplements applied water pressure in
the region between electrodes and promotes a migration of heating
water from the cavity 34 through the porous oil sand to the
producing well 13. In a given medium the volume flow of water due
to electro-osmosis depends on the magnitude of current being
conducted. Because the sand particles in the native formation 11
are predominantly water wet and because the residual oil tends to
adhere, by interfacial tension, to the contiguous water film on
these particles, this electro-osmotic mode of transporting water
through the capillaries and crevices of the oil sand is
particularly effective in achieving the desired result of
transferring heat and motion to the residual oil.  
  
Some of the electric energy supplied to the electrodes in our
invention will be utilized to liberate hydrogen from the water in
the pool 26 at the bottom of the producing well 13. This
electro-chemical action is well known as electrolysis. Because the
formation 11 is not homogeneous, there are anomalies in its
conductivity that form a series of local anodes and cathodes
between the main electrodes 15 and 24. Consequently, hydrogen and
other gases will be electrolytically released throughout the
formation. Some of the gasses, such as chlorine, will chemically
react to form certain beneficial acids which promote formation of
appropriate porosity and fluid flow in the oil sand. The union of
hydrogen and warm oil may partially hydrogenate the oil that is
extracted from the formation 11 thereby improving the grade and
the value of the recovered oil. Furthermore, the unipolarity
electric field between the main electrodes may raise the peak
kinetic energy of mobile charged particles in some areas of the
underground formation to a sufficiently high level to produce
fractional distillation and further upgrading of the oil in situ.
Gasses thus liberated and not absorbed or reacted may accumulate
in higher strata and develop pressure which supplements other
forces driving oil toward the well 13.  
  
In the cavity 34 electrolytic action contributes to a hostile
environment for the anode 15 and associated parts of the apparatus
disposed at the bottom of the anode hole. In operation oxygen and
other corrosive gases and chemicals are liberated at the anode.
Electrolytic action will tend to deplate or consume certain
positively energized metals. Therefore care should be exercised in
designing the anode 15 so that its surface, which is the only
exposed conductor in the bottom of the anode hole 14, will resist
both chemical and galvanic corrosion.  
  
To ensure a sound mechanical and electrical connection between the
cable 35 and the anode 15 under the foregoing difficult conditions
and in the high-pressure ambient at the contemplated depth of the
anode hole, it is believed desirable that the cable be inserted,
as by a threaded conducting plug connection, into a recess in the
anode. The lower section of the cable and the juncture of the plug
and the anode should then be covered with insulation which has
adequate dielectric strength and is impervious to oxygen and other
deleterious chemicals. There is a possibility that a high pressure
differential between the exterior surface and the interior recess
of the anode may damage the anode. To protect the interior surface
of the anode it is desirable to fill any voids in the anode recess
with suitable high gravity electroconductive liquid and to close
the recess with a pressure-equalizing seal. The exterior surface
of the anode body should be the only part of the apparatus from
which current enters the surrounding saline water, and it is
resistant to chemical attack and deplating.  
  
An electric power supply suitable for energizing the anode 15 has
been shown in FIG. 3. The availability of three-phase a-c
high-voltage service is assumed, and in FIG. 3 this service is
illustrated symbolically at 60. The high voltage is fed to the
primary windings of a power transformer 61 through a conventional
circuit breaker 62 which is equipped with an operating mechanism
63 for opening and closing the primary circuit on command. The
secondary circuit of the power transformer 61 is connected to a
controlled converter which is constructed and arranged to apply
across the conductors 35 and 42 a unipolarity output voltage of
controllable magnitude. The illustrated converter comprises an
adjustable autotransformer 64 in series with a high-power
rectifier 65. The average magnitude of its output voltage can be
varied from a few hundred volts to thousands of volts. This can be
done manually or, if desired, automatically by suitable means well
known in the pertinent electrical art.  
  
In operation, the load on the power supply 38 is expected to vary
after the anode 15 is first energized. The resistivity of the
saline water tends to decrease with increasing temperature in the
formation 11. The presently preferred mode of controlling the
electric power and water inputs of our process will now be
explained. The magnitude of current in the cable 35 is regulated
by suitably adjusting or programming the applied voltage. In this
way the electric current between anode and cathode can be held at
a desirable preset level. To prevent excessive heating of the
anode itself, the electroconductive fluid supplied through the
anode hole 14 is suitably controlled so as to vary the value of
its volume rate of flow as a function of the electric energy
dissipated underground. This can be accomplished, for example, by
employing appropriate means for controlling the rate of flow of
the injected fluid in accordance with the product of the magnitude
of applied voltage and the magnitude of anode-to-cathode current,
whereby the desired rate of fluid flow is determined by the amount
of input power. As the input power increases, so does the quantity
of injected fluid thereby beneficially increasing the cooling
effect on the anode 15. A maximum pressure override should also be
provided to prevent excessive underground pressure which might
fracture the formation 11.  
  
For optimum utilization of the input power without excessive
heating, it may be desirable to open the circuit breaker 62 for a
certain interval or intervals of time during which oil can
continue flowing in the oil-bearing formation due to the energy
retained therein. If and when the primary circuit is deenergized,
a low-voltage (e.g., 12 volts) positive bias is preferably
maintained on the anode 15 to minimize adverse galvanic action in
the anode hole, and toward this end a battery 66 is connected in
series with an isolating diode 67 across the output terminals of
the rectifier 65. To recharge the battery 67, it is connected to a
conventional battery charger 68 which is coupled to a suitable
source 69. This positive bias means, which is not our joint
invention, is more fully described and is claimed by C.H. Titus
and H.N. Schneider in a copending patent application Ser. No.
117,488 filed on Feb. 22, 1971 assigned to the assignee of the
present invention.  
  
It may be advantageous to reverse from time to time the
unipolarity voltage applied between the cables 35 and 42. Toward
this end, suitable reversing means is optionally provided. By way
of example, FIG. 3 shows a polarity reversing switch 70 between
the rectifier 65 and the cables, with the position of this switch
being controlled as desired by an associated mechanism 71.
Ordinarily the reversing cycle would be asymmetrical so that there
is a net electroosmotic movement of water through the oil sand in
the direction of the producing well 13. The reactance of the cable
35 in the anode hole 14 will not seriously impede the flow of
current through this path so long as either direct current or
low-frequency reversible current is being supplied. In view of
these alternative modes of practicing our invention, the terms
"d-c" and "unipolarity" are meant herein to apply to quantities
whose direction of influence can be reversed during or after a
cycle of operation of our process without reducing to zero the
average influence of the quantity in that direction during that
cycle.  
  
When our process is operated in either the discontinuous power
mode or the reverse polarity mode described in the preceding two
paragraphs, respectively, it is possible to use the anode hole as
a producing well for extracting oil from the proximate region 27
of the formation 11. Furthermore, it is possible to use our
invention to recover oil from a subterranean formation in a
push-pull fashion where there is only a single borehole
communicating with the surface of the ground.  
  
FIG. 4 shows an alternative arrangement for joining the two
sections 40 and 41 of the tubing string in the anode hole 14. In
FIG. 4 the lowest part of the upper section 40' of the tubing
string is secured in side-by-side relation to the top part 41' of
the lower section, and these parts are respectively provided with
registering slots 70 and 71 which permit the injected water to
flow from the section 40' into part 41'. The bottom of section 40'
is closed by a suitable plug 72 as shown. The top of part 41' is
provided with a packing gland for admitting the cable 35. As is
shown in FIG. 4, this gland includes cooperating threaded sleeves
73 and 74 between which the shoulders of a pair of tubular metal
clamps 75 and 76 are captured. The insulated cable 35 passes
vertically through this assembly, and its lower portion is
therefore disposed inside the lower section of the tubing string.
At an elevation below what is shown in the fragmentary view of
FIG. 4, the metal part 41' is connected to an insulating tube, and
the metal clamp 75 is terminated. There are two principal
advantages of this "Zee" assembly. It protects the cable 35 from
damage during installation of the anode 15, and it directs the
injected water around the lower portion of the cable 35 and
directly over the top of the anode 15 for improved cooling of the
surfaces of these conductors. The Zee assembly is more fully
described and is claimed by C.H. Titus and H. N. Schneider in U.S.
Pat. No. 3,674,912 filed Feb. 22, 1971 and assigned to the same
assignee as is the present application.  
  
At FIG. 5 we have illustrated schematically a modified form of
apparatus whereby our invention may be practiced in a particular
embodiment made available when all or a portion of the reservoir
of oil in an oil bearing formation lies under a body of water, and
in particular under saline water, as offshore under the sea. In
the embodiment there illustrated the earth structure including an
oil bearing formation 11 is shown in substantially the same manner
as at FIG. 2 except that part of stratum formation 11 lies under a
body of seawater 80. At FIG. 5 the anode hole 14 is located in a
region 27' of the stratum formation 11 which is laterally
contiguous to but beyond the body or reservoir of oil 81 contained
in the formation and below an off-shore area of the earth's
surface. The electric power source 38 and pump 43 associated with
the anode hole are mounted on a sea platform 82 and the anode hole
casing 28 extends to the platform.  
  
The water inlet to the pump 43 is shown connected to the seawater
80 as a supply reservoir, but it will be understood that other
appropriate sources of water for injection may be used, as
described heretofore. If seawater is used it may require certain
chemical additives of the type previously mentioned, but due to
its accessibility to an offshore anode hole it is to be preferred.
Use of seawater in an offshore anode region offers the further
advantage that hydrostatic pressure of the sea itself may be used
in place of the pump 43 to supply the added pressure required to
inject water at the anode cavity. To illustrate such a water
supply source we have shown two water inlet valves 85 and 86
located on the anode casing 14 at different depths beneath the
surface of the sea 80. A selected one of these valves may be
opened (with the pump shut down) to admit sea water at a desired
pressure to the anode cavity. Any desired number of such inlet
valves may be provided at different pressure levels.  
  
The producing well 13 at FIG. 5 is shown in an onshore location
with metal liner 24 electrically connected to ground and through a
cable 42 to the negative terminal of the d-c supply source 38, as
at FIG. 2. While this well is shown as penetrating the oil body
81, it will now be understood that if desired it may be located
initially beyond the body of oil 81 between the electrodes.  
  
In summary it will be seen that we have marshalled a number of
different forces toward the desired end of efficiently utilizing
bulk electric power to increase the amount and the value of oil
extracted from underground reservoirs. While most useful in
combination, all of these forces do not necessarily have to be
employed in concert to obtain satisfactory results.  
  
In spite of the high potential contemplated at the anode 15, the
voltage gradient near the surface 12 of the ground will be small
or negligible. Therefore our invention can be practiced safely.
Where necessary, conventional cathodic protection can be used to
retard corrosion of underground pipe lines, if any, in the
vicinity of the surface.  
  


---

  

**US2014116683**

**Method for Increasing Bottom-Hole Formation
Zone Permeability**  

**FIELD**  
  
[0002] The invention is related to the well services in
oil-field industry, particularly, to the methods for
increasing permeability of a near-wellbore zone of a formation
by stimulation of a fluid inflow into a wellbore.  
  
**BACKGROUND**  
[0003] A stimulation of a fluid inflow into a wellbore is
required to recover and improve the near-wellbore zone
filtration characteristics, basically through improved
permeability of the near-wellbore zone and reduced fluid
viscosity. Among the most efficient methods of the stimulation
of fluids' influx from a formation are acid treatment and
formation hydraulic fracturing (see, for example, V.I.
Kudinov, Osnovy neftegazopromyslovogo dela ( Foundations of
Oil and Gas Formation Industry), Moscow, 2005, pp. 428-429).
Acid treatment and formation hydraulic fracturing enable
stimulation of a fluid inflow into a wellbore by creating
high-permeable paths for the fluid inflow into the wellbore
hereby the selection of a specific treatment method and a
quality of the works completed are critical for the efficiency
of the future well operation. Thus, incorrectly performed
fluid inflow stimulation may, for example, result in the need
to completely stop the future wellbore operation. To intensify
the fluid inflow during the matrix treatment and formation
hydraulic fracturing various liquid and solid chemicals are
injected into a wellbore. Thus, during hydraulic fracturing
various substances are injected into a wellbore under large
pressure which results in cracks in the rock. To prevent a
closure of the cracks in the rock solid particles are injected
into the wellbore using a viscous gelapropping agent
(proppant). Due to high viscosity of the gel the crack becomes
low-permeable and to improve its permeability, as a rule,
reverse recirculation is used. To reduce the gel viscosity
different chemicalsabreakersaare added to the solution and,
when penetrating the formation, they can reduce the gel
viscosity. The chemicals being added are, as a rule,
expensive, but not always efficient. Besides, engineers
normally are not able to impact the breakers' activity after
the chemicals have been injected into the wellbore. Therefore,
among the key disadvantages of the existing methods for
increasing the near-wellbore zone permeability are high costs,
low speed and inability to monitor the reaction speed after
the chemicals have been injected into the wellbore.  
  
[0004] The proposed method provides for increased reliability
and efficiency of stimulating a fluid inflow into a wellbore,
enhanced speed of stimulating with simultaneous reduction of
the risk of incorrect performing thereof as well as reduced
costs.  
  
**SUMMARY**  
  
[0005] The method comprises carrying out a stimulation of a
fluid flow into a wellbore comprising injecting chemical
substances into a targeted zone of a formation and applying an
electric field to the targeted zone of the formation.  
  
[0006] The stimulation of the fluid flow into the wellbore is
an acid formation treatment or a hydraulic fracturing of the
formation.  
  
[0007] Additional magnetic, thermal, acoustic treatment or a
combination of thereof can be applied to the targeted zone of
the formation zone during the stimulation.  
  
[0008] The electric filed can be applied by electrodes. At
least one of the electrodes is disposed in the wellbore on the
level of the targeted zone.  
  
[0009] One of the electrodes can be disposed in the wellbore
on the level of the targeted zone and the other electrode can
be disposed on the surface.  
  
[0010] One of the electrodes can be disposed lower than the
targeted zoned of the formation while the other can be
disposed higher than the targeted zone of the formation being
treated.  
  
[0011] Casings and tubing can be used as the electrodes.  
  
**BRIEF DESCRIPTION OF THE DRAWINGS**  
  
[0012] The invention is explained by a drawing ( FIG. 1)
showing a system providing an electric impact onto a formation
in which stimulation of the fluid inflow is performed.  
  

![US2014116683](us2014116683a.JPG)

  
**DETAILED DESCRIPTION**  
  
[0013] The proposed method is based on applying an electric
field to a formation in which stimulation of a fluid inflow is
performed. The effect of the electrical stimulation depends on
physical parameters of the formation and is determined by
positioning of electrodes, value and frequency of the electric
field being created as well as a power of a power supply being
used. The electric impact causes enhancement of
physico-chemical processes in the formation and in space
inside a wellbore during the stimulation of a fluid inflow
into the wellbore. Thus, for example, the electric field
causes the appearance of electric currents as well as an
electro-kinetic, phenomena like electroosmosis or
electrophoresis. These phenomena result in the motion of
charged particles and the fluid and therefore result in the
intensification of current physico-chemical processes.
Additional application of magnetic field promotes additional
motion of the charged particles. Extra temperature heating
also causes the intensification of physico-chemical processes
in the area being heated through intensification of the
substances' thermal diffusion. Additional acoustic impact
using a sound-emitting device also enhances the
physico-chemical processes due to additional oscillations of
the particles caused by the sound wave passage. Hereby any of
the impacts above may be applied locally or directionally
which enables intensification of the physico-chemical
processes (such as chemical reaction speed) in the required
area.  
  
[0014] A system that allows to create an electric field inside
a wellbore and a formation is shown on FIG. 1 where 1 is a
current and voltage generator, 2aelectrodes connected to the
current and voltage generator 1, 3aa targeted zone of the
formation in which stimulation of a fluid inflow is performed,
chemicals have been injected into this targeted zone 3. For
creating the electric field different combinations of
electrodes positioning in the wellbore are possible, but at
least one of the electrodes should be disposed in the wellbore
at the level of the targeted zone 3 being treated. The other
electrode may be located in an adjacent wellbore (see FIG. 1
a) or on the surface (see FIG. 1 b). The electrodes may also
be disposed in the wellbore above and below the targeted zone
3 being treated (see FIG. 1 c). Casings and tubings may also
be used as electrodes. A source of magnetic field can be
placed into the wellbore at the level of the targeted zone 3
being treated. If a sound emitting device and/or a thermal
heater is used they also can be disposed in the wellbore at
the level of the targeted zone 3 being treated. Different
components of the instruments used may be located both on the
same device and on different and their power may be supplied
by a cable or by batteries or accumulators.  
  
[0015] As an example, three series of experiments were
conducted in order to check the feasibility of described
method. These experiments were carried out at room temperature
22A deg C. (72A deg F.). For the first experiment 750 ml of YF130LGD
gel was prepared and put into a tank with plane electrodes
attached thereto. The electrodes were connected to a standard
power generating unit with AC output of 100V at I50 Hz. The
distance between the electrodes was about 10 cm. After 15
minutes, only a slight gel destruction near the surface of the
electrode was observed. That can be a result of local
temperature increase up to 80A deg C. (180A deg F.) near the
electrodes. The temperature was measured immediately after
power was off.  
  
[0016] For the second experiment two samples of YF130LGD
hydraulic-fracture gel were prepared (500 ml each) and 2 g of
J218 breaker was added to each gel sample. J218 breaker
concentration for YF130LGD gel destruction is about 10
pounds/1000 gallons (1,2 kg/m3) that is two times lower than
for carrying out this experiment. But it should be mentioned
that the breaker operation temperature range is 52-107A deg C.
(125-225A deg F.), moreover, the breaker is activated by adding
special chemical catalysts. One sample of the prepared gel
with the breaker portion was placed into a tank without
electrodes and thoroughly mixed. The other sample was placed
into the system with electrodes. After 7 minutes of AC
applying it was detected that almost all gel (90%) in the tank
under voltage was destroyed (the gel viscosity reduced to
water viscosity value). In the tank without AC application
only 10-15% gel was destroyed. During the second experiment
the temperature value was 95A deg C. (200A deg F.) on the electrodes
and 35A deg C. (95A deg F.) in the centre of the tank after 7 minutes
of the AC impact.  
  
[0017] The third experiment was performed to prove that at
high temperatures there will be no gel destructions. For this
purpose 500 ml of YF130LGD gel mixed with 2 g of J218 breaker
was prepared and placed into a pre-heated tank, and then into
an oven at 100A deg C. (210A deg F.). After 15 minutes of the
temperature action destruction of maximum 25-30% of gel was
noted.  
  
[0018] Comparing the results of electrical field and
temperature impact in presence of breaker, the advantage of
the electrical field impact for the gel destruction becomes
evident.

  


---

****RU2132757****   
**Method of Removing Hydrocarbons from Soil**  

FIELD: oil pollution removal. SUBSTANCE:
central and peripheral electrodes are plunged into soil at
area to be cleaned and voltage gradient between electrodes is
created. Then, nonpolluting liquid carrier is fed into the
surface region around central electrode, which carrier moves
under electroosmosis effect from central electrode toward
peripheral electrodes and displaces hydrocarbons in soil that
are removed from peripheral electrodes. As liquid carrier,
water with pH 9 prepared by cavitation effect or water with pH
5,5 prepared by heating is utilized. Utilization of water
taken from bed in oil and gas deposit development is possible.
EFFECT: enhanced cleaning efficiency due to accelerated
movement of liquid carrier and reduced voltage gradient on
electrodes.  
  
A method for cleaning sand from petroleum products is known
(as. USSR N 1629102, MKI 5: B 03 V 5/00, C 01 B 33/12, pub.
23.02.91 y. Bul-N-7-analogue.), Including sand treatment with
an aqueous solution of hydrofluoric acid with a concentration
of 0.5-2.0% by weight, with a ratio of the mass of solid soil
to the liquid reagent as 1: (2-6) for 30 minutes.  
  
The main disadvantage of this method is sand treatment with a
chemical reagent, for neutralization it is necessary to add
additional reagents and remove the reaction products of these
reagents, which entails additional economic costs and does not
increase the ecology of the cleaned sandy soil.  
  
The closest in technical essence to the proposed invention is
the method for removing contaminated soil (U.S. Patent No.
5,415,7774 A, MKI 6: B 01 D 61/56, published, ISM, No. 001,
No. 10, 1996, p. 34 - prototype ), Including immersion in the
soil on the cleared area of aathe central and peripheral
electrodes, the creation of a voltage gradient between them,
feeding the non-contaminating carrier fluid to the zone
adjacent to the central one, moving the carrier fluid under
the effect of the electroosmotic effect between the
electrodes, displacing the carrier liquid of the contaminated
Material from the soil to the peripheral electrodes and the
removal of contaminated material from the latter.  
  
This method is more ecological than the analogue. However, the
motion of pure carrier fluids of the water type under the
action of the electroosmotic effect is not intensive, and it
is further slowed down when the carrier fluid displaces such
impurities as viscous hydrocarbons such as oil, engine oil and
the like. Especially large resistance to the displacement of
the carrier fluid with hydrocarbons occurs in the cold season,
when the viscosity of the latter increases. Therefore, to
ensure the movement of the carrier fluid and viscous
hydrocarbons, it is necessary to maintain a high voltage
gradient, on the order of 380-500 V, depending on the soil
structure, which leads to high energy costs and makes this
method ineffective.  
  
The purpose of the invention is to increase the efficiency of
soil purification from hydrocarbons by accelerating the
movement of the carrier fluid and reducing the voltage
gradient at the electrodes.  
  
The aim is achieved by the fact that in a method for purifying
soil from hydrocarbons including immersion in the soil on the
cleaning portion of the central and peripheral electrodes,
creating between the first and second voltage gradients,
feeding into the region adjacent to the central electrode not
contaminating the carrier fluid, Carrier under the action of
the electroosmotic effect from the central electrode to the
peripheral electrode, displacement of hydrocarbon from the
soil by the carrier fluid and their removal from the
peripheral electrodes, as Carrier liquids use water in which
the pH is changed to 9 by applying cavitation to it, or up to
5.5 by heating.  
  
The use of water as the carrier fluid, in which the pH is
changed to 9, by applying it to cavitation, or up to 5.5 by
heating, has made it possible to increase the efficiency of
soil purification at any temperatures without the use of
chemical reagents and their neutralization.  
  
The Applicant does not know how to purify soils that use water
as the carrier fluid, in which the pH is changed to 9,
influencing it by cavitation, or up to 5.5 by heating.  
  
**In Fig. 1 is a graph of the pH change of distilled and
fresh water, depending on the time of action of cavitation.****In Fig. 2 is a plot of the pH of water versus its
temperature.****In Fig. 3 is a flow diagram of an installation for
implementing a method for cleaning soil from hydrocarbons.**  

![RU2132757a](ru2132757a.JPG)![RU2132757b](ru2132757b.JPG)

  
The proposed method for cleaning soil from hydrocarbons is as
follows.  
  
Due to the action of cavitation, the water molecules
dissociate into H + and OH- ions. H + ions partially leave the
liquid phase, and OH- ions accumulate in the latter, raising
the pH of the water. In Fig. 1 is a graph of the pH change of
distilled water and fresh water taken from different sources 2
and 3, depending on the time of action of the cavitation.
Water with an elevated pH has a high surface activity and has
high detergent properties.  
  
Such water in contact with hydrocarbons - destroys the viscous
surface film of hydrocarbons and intensively flushes them from
the soil; - increases the dynamics of mixing of leachable
hydrocarbons with them and forms an emulsion, which has a
small hydraulic and low electrical resistance.  
  
These properties increase the mobility in the soil of the
formed liquid system (emulsion) under the action of the
electroosmotic effect, which ultimately leads to a reduction
of the voltage between the electrodes to 60 V and the cost of
electricity and, as a consequence, to an increase in the
efficiency of the method for cleaning the soil of
hydrocarbons.  
  
When the water is heated, its pH decreases and, as a result,
its electrical conductivity increases. In Fig. 2 is a plot of
the pH of water versus its temperature. As the pH of the water
decreases, the solubility of hydrocarbons in it increases.  
  
Such water when in contact with hydrocarbons - reduces their
surface tension and viscosity; - forms a mobile electrically
conductive emulsion.  
  
These properties intensify the joint movement of water with
hydrocarbons in the soil under the effect of the
electroosmotic effect from the central electrode to the
peripheral, which, as a consequence, leads to a decrease in
the voltage between the electrodes to 60 V and the reduction
of electricity costs and increases the efficiency of the
method for cleaning the soil of hydrocarbons.  
  
The proposed method for cleaning soil from hydrocarbons is
similar in its intensity to methods for cleaning soil using
chemical reagents such as surfactants with pH 9 and acids pH
5.5.  
  
However, this method is environmentally friendly, does not
require additional costs for chemical reagents and for their
neutralization.  
Compared with the prototype, this method is more effective
than the prototype for energy costs in 6-7 times.  
[3]  
  
The method can be implemented with the apparatus shown in FIG.
3. The installation consists of immersed in the soil in the
cleaning area 1 of the central 2 and peripheral 3 electrodes,
a water supply nozzle 4, a pump 5 serving to remove water from
the peripheral electrodes with hydrocarbons, a separator 6 for
separating water and hydrocarbons, a container 7 with a nozzle
Venturi 8 and heater 9, a pump 10 for injecting water into the
nozzles 4 and a Venturi nozzle 8. The separator 6 and the tank
7 are connected by a pipeline through the water with a check
valve 11. The container 7 is additionally connected to the
nozzle 4 by a high-pressure water supply pipe 12 with a pH of
5.5.  
  
An example of the execution of the method. Water with a
temperature of 17 A deg C, having a pH of 7.4, is supplied by a
pump 10 from the tank 7 to the Venturi nozzle 8 at a speed of
30 m / s. The pressure of water flowing through the diffuser
of the Venturi 8 nozzle is reduced to 2 x 103 Pa. This causes
cavitation of water. The cavitated liquid re-enters the vessel
7. The water is cavitated in this manner for 520 s, after
which the water in the vessel has a pH of 9. The obtained
surface active water by the pump 10 is fed through the nozzle
4 to the region adjacent to the central electrode 2. A voltage
gradient of 60 V is created between the central and peripheral
electrodes. Surface-active water with pH 9 under the action of
the electroosmotic effect moves from the central electrode 2
to the peripheral 3. At the same time, it contacts
hydrocarbons that pollute the soil, destroys their surface
film and intensively flushes them from the soil.
Surface-active water with pH 9 with hydrocarbons forms an
emulsion that enters the peripheral electrodes 3, from where
it is removed by pump 5 and fed to separator 6.  
  
In the separator 6, the emulsion is divided into water at the
bottom and hydrocarbons located at the top of the separator 6.
The separated water enters the tank 7 through the check valve
11. The separated hydrocarbons are sent to storage tanks.  
  
The described cycle is repeated until the hydrocarbons are
completely removed from the soil. The process of cleaning the
soil with surface active water obtained by cavitation is
energetically beneficial at soil temperatures above 0oC.  
  
In the case of soil cleaning with a temperature below 0oC from
hydrocarbons, this water is used with water at pH 5.5, which
is obtained by heating to 240oC in tank 7 using a heater 9.
When the water in the tank 7 is heated, the pressure rises to
3.5 MPa. Under this pressure, water with a pH of 5.5 is fed,
bypassing the pump 10, via the line 12 through the nozzle 4 to
the work area 1. Further process of soil purification from
hydrocarbons is carried out in a similar manner to the process
described above.

---

****KR20010086551****   
**Purification Method of Contaminated Soil with
Petroleum Oil**  

PURPOSE: A purification method of contaminated
soil with petroleum oil is provided, which can purify
contaminated soil by generating radical oxidant such as
hydroxide radical using metal peroxide such as calcium
peroxide and magnesium peroxide in the presence of a catalyst
of iron and by transferring the radical to contaminated area
in soil by electroosmosis. The method does not need any
excavation and transportation of soil and can remove more than
99 % of contaminants. CONSTITUTION: The system comprises the
followings: (i) an acrylic box (10) which has an anode chamber
(16a) and a cathode chamber (16b) at both sides of the box
(10); (ii) anode chamber (16a) that is made of anode diaphragm
(15a), in which an anode (11a) is inserted and to which
discharge line of an electrode liquid supplement tank (18) is
inserted; and (iii) a cathode chamber (16b) that is made of
cathode diaphragm (15b), in which a cathode (11b) is inserted
and to which discharge line of an electroosmosis liquid
storage tank (19) is connected.  
  

![KR20010086551 a](kr20010086551a.JPG)![KR20010086551b](kr20010086551b.JPG)![KR20010086551c](kr20010086551c.JPG)

  


---

****RU2602615****  
**Method of Soil Cleaning from Hydrocarbons**  

FIELD: ecology.SUBSTANCE: invention relates to
environmental protection, namely to reclamation of lands,
contaminated with hydrocarbons (oil products), decontamination
of soil from pesticides using phenomenon of electric osmosis.
Method of cleaning soil from oil products and pesticides using
electroosmosis consists in immersing of central and peripheral
electrodes into soil at section, undergoing cleaning, creation
of non-uniform electric field between central and peripheral
electrodes, supplying of non-contaminating carrier fluid into
area adjoining central electrode, movement of carrier fluid
under action of electroosmotic effect from central electrode
to peripheral ones, removal of dirt beyond contaminated
section, displacement of contaminants from soil by carrier
fluid and removal thereof from peripheral electrodes,
non-uniform electric field intensity value is set within
50-110 kV/m, before supplying carrier fluid soil is milled
into particles of 1.0 mm in depth of 20-25 cm. Milled soil is
mixed with carrier fluid to concentration of 1:6. Fluidized
layer is created by device in depth of 10-12 cm with supply of
compressed air of pressure 1-2 ATM. Proposed device comprises
central electrode and system of peripheral electrodes,
submerged into soil cleaning section, nozzle for carrier fluid
supply and removal of fluid, containing contaminants, from
cleaning section. Central electrode is made in form of rod
with cross section in form of polygon with concave sides.
System of peripheral electrodes is composed by separate rods.
Rods are connected by wire conductors with sharp-pointed
elements on them, point of which is directed to central
electrode. Ahead of nozzles for supply of carrier fluid
dispenser is placed. Above system of peripheral electrodes
device for creation of fluidized layer is located, including
central r-shape pipeline with compressor, connected via
control valve with system of radial pipelines, at end of each
of which nozzles are located, submerged into soil for depth of
10-12 cm.EFFECT: proposed method of soil cleaning from
hydrocarbons and pesticides and device for it provide maximum
effect of soil cleaning.  
  
The invention relates to the protection of the environment, in
particular to the reclamation of soils contaminated with
hydrocarbons (oil products), the neutralization of soil from
pesticides using the phenomenon of electroosmosis.

With the expansion of the use of pesticides, a number of
negative consequences were identified: pollution of soils
and water sources, accumulation of residues of chemicals
in food. In soil, pesticides decay as a result of both
physical-chemical processes and microbiological
decomposition. Remnants of pesticides in the soil are
washed out by storm and soil waters, gathering in natural
reservoirs, polluting them, as well as surrounding land.

The problem of clearing lands and soils for agricultural
purposes, the disposal of excess pollutants, especially
those stored in the open way, is especially urgent for
modern ecology. Currently, in the technology of
agricultural production, herbicides have spread, as well
as organochlorine pesticides: fusid-forte, zenkor,
chistoplan, puma-super.

  

A method
for cleaning a capillary-porous medium contaminated with
oil and oil products is known, by introducing a solution
of oil-oxidizing microorganisms into the cleaning zone,
introducing an electroconductive liquid, passing an
electric current to create an electroosmosis (RU 96115094
A, IPC B09C 1/10, publ. 27.11.1998).

  

There is a
known method for restoring contaminated soils contaminated
with different in composition and properties
(heterogeneous), including applying a material for
purification from contaminants to the heterogeneous soil
area, passing a constant electric current between the
electrodes within the contaminated heterogeneous soil,
applying a hydraulic gradient across the contamination
area (RU 2143954 C1, IPC B09C 1/08, publ. 10.01.2000).

The disadvantage of the above analogs is the laboriousness
of their application and the insufficient degree of soil
purification from contamination.

  

The closest
analogue of the method adopted as a prototype is a method
for cleaning the soil, including immersion in the soil on
the cleaned portion of the central and peripheral
electrodes, creating a voltage gradient between the
central and peripheral electrodes, feeding into the region
adjacent to the central electrode not contaminating the
carrier fluid , Displacement of the carrier fluid under
the effect of the electroosmotic effect from the central
electrode to the peripheral electrode, displacement of the
hydrocarbon carrier from the soil, removal x of the
peripheral electrodes, creating an uneven electric field
between the central and peripheral electrodes (RU 2508954
C1, IPC B09C 1/00, publ. 10.03.2014).

The disadvantage of the prototype is the insufficient
degree of soil purification from hydrocarbons, since
cleaning with the use of electroosmosis is carried out in
an insufficiently strong uneven electric field, as well as
the lack of effective cleaning from pesticides.

A device is
known for applying a method for cleaning from
contamination of a capillary-porous medium, comprising a
chamber for placing a cleaned medium with electrodes
connected to a DC source, a container with a liquid to be
cleaned and a container for the spent liquid (RU 2106432
C1, MPC <6> C25C 1/22 , Publ. 10.03.1998).

  

A plant
for processing soils and soils is known (RU 2330734 C1,
IPC B09C 11/00, publ. 10.08.2008), containing a hopper
with a stirring device, with a device for transporting
liquid therefrom to the overflow tank and a device for
removing solid inclusions, a washing liquid supply system,
a vibrator.

The disadvantage of the above-mentioned analogue devices
is also the insufficient degree of soil purification from
pollution.

The
closest to the proposed device for implementing the method
adopted for the prototype is a device comprising a central
electrode and a peripheral electrode system immersed in
the soil, a nozzle for supplying the carrier liquid, pumps
for injecting liquid into the nozzles and removing the
contaminating liquid from the Cleaning zone, the central
electrode is made in the form of a rod, the cross section
of which is a polygon with concave sides (RU 2508954 C1,
IPC B09C 1/00, publ. 10.03.2014).

The disadvantage of the prototype is the ineffective
cleaning of the soil from hydrocarbons (oil products) and
the lack of purification from pesticides.

The task of the proposed method and device for its
implementation is to increase the degree of soil
purification from hydrocarbons (petroleum products), as
well as soil cleaning from pesticides.

The technical result of the application of the method for
cleaning the soil from hydrocarbons and pesticides is
achieved by including immersion in the soil on the
cleanable portion of the central and peripheral
electrodes, creating an uneven electric field between the
central and peripheral electrodes, feeding a non-polluting
liquid to the region adjacent to the central electrode
Carrier, the transport of the carrier fluid under the
effect of the electroosmotic effect from the central
electrode to the peripheral electrode, displacement from
the soil by liquid-n And, in contrast to the prototype,
the magnitude of the uneven electric field strength is set
in the range of 50-110 kV / m, preliminary before feeding
the carrier liquid, the soil is ground by means of a
standard ripper in the form of a disk cutter to the
particle size 1.0 mm at a depth of 20-25 cm, the ground
soil is mixed with the carrier fluid to a concentration
controlled by a doser of 1: 6, by means of an additionally
installed device, a fluidized bed is formed with a depth
10-12 cm with the supply of compressed air at a pressure
of 1-2 atm.

The technical result of using a soil cleaning device for
hydrocarbons and pesticides is achieved by including a
central electrode in the form of a rod with a
cross-section in the form of a polygon with concave sides
immersed in the soil, and a system of peripheral
electrodes made of individual rods, Liquid carrier, pumps
for injecting liquid into the nozzles and removing the
contaminating liquid from the cleaning zone, in contrast
to the prototype, a system of peripheral electrodes of soy
The foam is interconnected by wire conductors with pointed
elements attached to them, the point of which is directed
to the central electrode, a dispenser is installed in
front of the carrier liquid injectors, and a device for
creating a fluidized bed is installed above the peripheral
electrode system, including a central L- Connected through
a distributor with a system of radial pipelines, at the
end of each of which there are nozzles immersed in the
soil to a depth of 10-12 cm.

The state of the art does not know the effect of the new
set of features of the claimed method and device on the
achievement of a new technical result - cleaning the soil
of pesticides, which makes it possible to conclude that
the technical solutions meet the criteria of "novelty" and
"inventive level".

Soil cleaning from hydrocarbons and pesticides is as
follows. On the area to be cleaned, a voltage gradient is
created between the central and peripheral electrodes, the
magnitude of the uneven electric field strength is set
within 50-110 kV / m, fed to the region adjacent to the
central electrode, the carrier fluid, the carrier fluid is
transported by the electroosmotic effect from Central
electrode to the peripheral, are displaced from the soil
with the help of a carrier fluid and remove oil from
peripheral electrodes.

Prior to supplying the carrier fluid to increase the
degree of soil purification from hydrocarbons and
pesticides, the soil is ground by means of a standard
ripper in the form of a disk cutter to a particle size of
1.0 mm at a depth of 20-25 cm. The depth of soil grinding
depends on the depth of penetration of pesticides, and
this is determined by the depth of plowing, and by the
technology of processing different crops an average of
10-12 cm. To create a fluidized bed to a depth of 10-12
cm, it is necessary to grind the contaminated soil with a
ripper, respectively, to a depth of two times as much,
which is 20-25 cm.

If the particle size is larger than 1.0 mm, then in the
formation of a fluidized (boiling) layer of soil
consisting of water droplets and air bubbles, the
particles will soon be sedimented and settle on the site
without sufficient purification. In the event that the
particle size is less than 1.0 mm, the particles will
migrate in the water-air phase.

The crushed soil particles are mixed with the carrier
fluid to a concentration of 1: 6, which is determined by
the flow of water through the circulating pump for
supplying the carrier liquid and the dispenser. If the
concentration of soil particles in the liquid phase is
more than 1: 6, a suspension between the solid and liquid
phase is not formed. Conversely, if the concentration of
soil particles in the liquid phase is less than 1: 6, then
in the resulting suspension the soil particles will not be
sufficient to implement the method.

If the compressed air pressure is less than 1-2 atm, the
formed fluidized bed can not penetrate to a depth of 10-12
cm, if the compressed air pressure is more than 1-2 atm,
the depth of the fluidized bed will be greater than 10-12
cm, which will lead to Increased consumption of compressed
air and energy costs for its production.

The efficiency of soil purification from hydrocarbons and
pesticides increases due to physical processes occurring
during the interaction of the fluidized bed with the
uneven electric field of the indicated tension, which
occur as follows.

It is known that when the carrier liquid is saturated with
air in a ratio of 1: 6 (in our case), air bubbles are
created in the liquid phase. Under the influence of an
uneven electric field between the sharpened elements of
the peripheral electrodes and the central electrode, air
bubbles align along the lines of force of the field, then
they elongate along the lines of force and decrease in the
transverse direction. Compression of a bubble in the
transverse direction means that compressive forces act
near its equator. In this case, the air bubble behaves
like a dielectric, the field inside it is slightly
distorted. Further, it increases in all directions with
the formation of a primary streamer that flies out of its
tip (Korobeinikov SM The role of bubbles in the electrical
breakdown of liquids. Thermophysics of High Temperatures,
1998, No. 3, pp. 362-367, 1998, No. 4, p. 541-547). The
streammer is an ionized channel, obtained by overlapping
individual electron avalanches occurring in its path.

The formation of streamers is accompanied by shock waves,
whose center is the origin of the streamers, that is, the
tip of the bubble. When the streamer channel develops, the
surface of the bubbles turns to be charged, a volume
discharge develops over the surface of the bubbles as a
result of the action of the streamers in a two-phase
medium (a mixture of water and soil), ozone and a number
of active particles are generated, including the OH
radical, atomic oxygen, Formed ozone decomposes
pesticides, up to the mineralization. In addition, the
hard ultraviolet radiation of the plasma takes place.
Also, during the development of electrical breakdown, a
powerful shock wave is formed, which has an additional
disinfection effect on the soil.

It is known that the electric field E of a charged
cylinder of radius r is determined by the formula (1)
(Koshkin NI Handbook on elementary physics .- M .: Nauka,
1980):

  

Where k is
the coefficient of proportionality, k = 8.9875 \* 10
<9> m / F;

Q -
electric charge, q = 2,3467 \* 10 <-2> Cl;

R is the
radius of the cleaning zone;

I is the
permittivity of the medium.

It is
known that, depending on the amount of humus, the amount
of water, the viscosity of the soil, the permittivity of
the soil is Iu = 19.2; 23.8; 26.7; 41,2 (Bobrov PP,
Belyaeva TV Experimental check of the model of complex
dielectric permittivity of soils and viscosity of soil
moisture. // Natural sciences and ecology. Yearbook of the
Omsk GPU. 2002. - p. 29-33).

  

The
results of calculating the electric field strength from
formula (1) for r = 10 m are given in Table. 1.

  
**Table 1**  

Calculations
show that for a given range from 19.2 to 41.2 changes in
the dielectric permittivity of the soil, the electric
field strength ranges from 50 to 110 kV / m.

In Fig. 1 is a schematic diagram of an apparatus for
carrying out a process for cleaning soil from hydrocarbons
and pesticides; FIG. 2 is a device for creating a
fluidized bed.

**FIG. 1 is a schematic diagram of an apparatus for
carrying out the method,   
FIG. 2 shows a fluidized bed apparatus**

![RU2602615](ru2602615a.JPG)![RU2602615b](ru2602615b.JPG)

  
The scheme of the device (Figure 1) shows: the cleaning
zone 1, immersed in the soil of the cleaning zone, the
central electrode (anode) 2, the peripheral electrode
system (cathodes) 3, the injector 4 for feeding the
carrier fluid, the dispenser 5 for creating a controlled
liquid concentration A pump 7 for removing liquid
containing oil products from the peripheral electrodes, a
pump 6 for injecting the carrier liquid into the injector
4 through a dispenser 5, a pump 9 for evacuating
contaminants containing petroleum products and pesticides
from the perforated pipe 8.

The system of peripheral electrodes is made of individual
rods 3 connected with each other by wire conductors 11
(fig.2) with pointed elements 10 on it, the point of which
is directed to the central electrode. For grinding the
soil, use a standard ripper in the form of a disk cutter.
A device 12 for creating a fluidized bed is provided above
the peripheral electrode system including a central
L-shaped conduit 13 with a compressor 14 connected through
a distributor 15 to a system of radial conduits 16 at the
end of which are installed injectors 17 for supplying
compressed air into the fluidized bed immersed in the soil
To a depth of 10-12 cm.

The proposed method for cleaning the soil is carried out
using the device as follows.

A serial ripper in the form of a disk mill cuts the soil
to a particle size of 1.0 mm. In soil crushed to a depth
of 20-25 cm, the pump 6 is fed through a nozzle 4 with a
carrier fluid.

Turn on the pumps 6 and 7. The ground soil is then mixed
with the carrier fluid by means of a pump 6 and a
dispenser 5 to a concentration of 1: 6. Electrodes 2 and 3
are supplied with a voltage, the value of which is set
within 50-110 kV / m, as a result, an uneven electric
field is created between the protrusions of the central
electrode and the pointed elements. The carrier fluid
under the effect of the electroosmotic effect flows from
the central electrode 2 to the peripheral electrode system
3, sorbing oil products or pesticides in its path, then
the impurities are removed by the pump 7.

The fluidized bed using the device is constructed as
follows. From the compressor 14, compressed air is
injected through a central L-shaped conduit connected
through a distributor 15 and a system of radial conduits
16 with injectors 17 at a pressure of 1-2 atm. And air
bubbles appear. In this case, under the influence of an
uneven electric field between the sharpened elements of
the peripheral electrodes 3 and the central electrode 2,
air bubbles are aligned along the lines of force. Further
on, at the tip of the bubble, the formation of a streamer
takes place, which flies into the cleaning zone. As a
result of the action of streamers in a two-phase medium,
ozone and a number of active particles are generated (OH
radical, atomic oxygen, etc.). The ozone formed decomposes
pesticides up to their mineralization.

As a
result, the degree of soil purification from hydrocarbons
(oil, oil, fuel oil, etc.) and pesticides rises to 98-99%.

  


---

****KR101464878****  
**Remediation System for Multi-Contaminated Soils**

An aspect of the present invention provides a remediation
system for complexly contaminated soil using a combined
chemical oxidation and soil flushing method by electrokinetic
remediation that increases the remediation efficiency of
complexly contaminated soil as a treatment region is formed by
hydrogen peroxide inserted into one side of a soil cell from
an anode cell to induce the oxidation and decomposition of oil
contaminants and the oil contaminants are oxidized and
decomposed by being flushed and adsorbed by an anionic surface
active agent inserted into the other side of the soil cell
from a cathode cell to be moved into the treatment region. The
remediation system for complexly contaminated soil using a
combined chemical oxidation and soil flushing method by
electrokinetic remediation according to an embodiment of the
present invention comprises: a soil cell complexly
contaminated by oil contaminants and heavy metal contaminants;
an anode cell having an anode inserted into one side of the
soil cell; a cathode cell having a cathode inserted into the
other side of the soil cell to be separated from the anode by
a certain distance; a hydrogen peroxide supply cell connected
to the anode cell to supply hydrogen peroxide to one side of
the soil cell; a first anionic surface active agent supply
cell connected to the cathode cell to supply a first anionic
surface active agent to the other side of the soil cell; and a
power supply device for flushing and adsorbing oil
contaminants via electric ion movement using the first anionic
surface active agent to be moved from the cathode to the
treatment region while simultaneously forming the treatment
region, which is defined by the flowing distance of hydrogen
peroxide, so that oil contaminants can be oxidized and
decomposed as hydrogen peroxide is moved from the anode to the
cathode via electroosmosis by supplying power to the anode and
the cathode.

![KR101464878a](kr101464878a.JPG)![KR101464878b](kr101464878b.JPG)

---

**US4645004**  
**Electro-Osmotic Production of Hydrocarbons Utilizing
Conduction Heating of Hydrocarbon Formations**  
  

An electro-osmotic method for the production
of hydrocarbons utilizes in situ heating of earth formations
having substantial electrical conductivity. A particular
volume of an earth formation is bounded with a waveguide
structure formed of respective rows of discrete elongated
electrodes in a dense array wherein the active electrode area
and the row separation are chosen in reference to the deposit
thickness to avoid heating barren layers. Electrical power is
applied at no more than a relatively low frequency between
respective rows of electrodes to deliver power to the
formation while producing relatively uniform heating thereof
and limiting the relative loss of heat to adjacent regions to
less than a predetermined amount. At the same time the
temperature of the electrodes is controlled near the
vaporization point of water to maintain an electrically
conductive path between the electrodes and the formation. A
heat sink is provided by supplying aqueous liquid electrolyte
to space between the electrodes and the adjacent formation,
thereby maintaining the temperature thereat no greater than
about the boiling point of water and maintaining a conductive
path between said formation. A d.c. polarized potential is
applied to enhance flow of reservoir fluid into a preselected
row of electrodes, and collected reservoir fluids are removed
from the electrodes in the preselected row.

**BACKGROUND OF THE INVENTION**  
This invention relates generally to the exploitation of
hydrocarbon-bearing formations having substantial electrical
conductivity, such as tar sands and heavy oil deposits, by the
application of electrical energy to heat the deposits. More
specifically, the invention relates to the delivery of
electrical power to a conductive formation at relatively low
frequency or d.c., which power is applied between rows of
elongated electrodes forming a waveguide structure bounding a
particular volume of the formation, while at the same time the
temperature of the electrodes is controlled.  
  
Materials such as tar sands and heavy oil deposits are
amenable to heat processing to produce gases and hydrocarbons.
Generally the heat develops the porosity, permeability and/or
mobility necessary for recovery. Some hydrocarbonaceous
materials may be recovered upon pyrolysis or distillation,
others simply upon heating to increase mobility.  
  
Materials such as tar sands and heavy oil deposits are
heterogeneous dielectrics. Such dielectric media exhibit very
large values of conductivity, relative dielectric constant,
and loss tangents at low temperature, but at high temperatures
exhibit lower values for these parameters. Such behavior
arises because in such media ionic conducting paths or layers
are established in the moisture contained in the interstitial
spaces in the porous, relatively low dielectric constant and
loss tangent rock matrix. Upon heating, the moisture
evaporates, which radically reduces the bulk conductivity,
relative dielectric constant, and loss tangent to essentially
that of the rock matrix.  
  
It has been known to heat electrically relatively large
volumes of hydrocarbonaceous formations in situ. Bridges and
Taflove U.S. Pat. No. Re. 30,738 discloses a system and method
for such in situ heat processing of hydrocarbonaceous earth
formations wherein a plurality of elongated electrodes are
inserted in formations and bound a particular volume of a
formation of interest. As used therein, the term "bounding a
particular formation" means that the volume is enclosed on at
least two sides thereof. The enclosed sides are enclosed in an
electrical sense with a row of discrete electrodes forming a
particular side. Electrical excitation between rows of such
electrodes established electrical fields in the volume. As
disclosed in such patent, the frequency of the excitation was
selected as a function of the bounded volume so as to
establish a substantially nonradiating electric field which
was confined substantially in the volume. The method and
system of the reissue patent have particular application in
the radio-frequency heating of moderately lossy dielectric
formations at relatively high frequency. However, it is also
useful in relatively lossy dielectric formations where
relatively low frequency electrical power is utilized for
heating largely by conduction. The present invention is
directed toward the improvement of such method and system for
such heating of relatively conductive formations at relatively
low frequency and to the application of such system for
heating with d.c.  
  
**SUMMARY OF THE INVENTION**  
For electrically heating conductive formations, it is
desirable to utilize relatively low frequency electrical power
or d.c. to achieve relatively uniform heating distribution
along the line. At low frequency, it is necessary that
conductive paths remain conductive between the subsurface
electrodes and the formation being heated. It is also
desirable to heat the formation as fast as possible in order
to minimize heat outflow to barren regions. This presents
certain inconsistent requirements, as fast heating requires a
large amount of heat at the electrodes, and the resultant high
temperatures boil away the water needed to maintain the
conductive paths. On the other hand, if the heating proceeds
slowly, excessive temperatures leading to vaporization of
water and consequent loss of conductivity are avoided, but
there is economically wasteful loss of heat to the barren
formations in the extended time needed to heat the deposit of
interest.  
  
It is a primary aspect of the present invention to provide
compromises to best meet such disparate requirements in the in
situ heating of earth formations having substantial
conductivity. A waveguide structure as shown in the reissue
patent is emplanted in the earth to bound a particular volume
of an earth formation with a waveguide structure formed of
respective rows of discrete elongated electrodes wherein the
spacing between rows is greater than the distance between
electrodes in a respective row and in the case of vertical
electrodes substantially less than the thickness of the
hydrocarbonaceous earth formation. Electrical power at no more
than a relatively low frequency is applied between respective
rows of the electrodes to deliver power to the formation while
producing relatively uniform heating thereof and limiting the
relative loss of heat to adjacent barren regions to less than
a tolerable amount. At the same time the temperature of the
electrodes is controlled near the vaporization point of water
thereat to maintain an electrically conductive path between
the electrodes and the formation. A d.c. polarized potential
is applied to enhance flow of reservoir fluid toward at least
one preselected electrode.  
  
A waveguide electrical array which employs a limited number of
small diameter electrodes would be less expensive to install
than an array using more electrodes but would result in excess
electrode temperature and nonuniform heating and consequently
inefficient use of electrical power. On the other hand, a
dense array, that is, one in which the spacing s between rows
is greater than the distance d between electrodes in a row,
would be somewhat more costly, but would heat more uniformly
and more rapidly and, therefore, be more energy efficient.  
  
A key to optimizing these conflicting factors is to control
the temperature of the electrodes and the resource immediately
adjacent the electrodes by properly selecting the deposit gas
pressure, heating rates, heating time, final temperature,
electrode geometry and positioning and/or cooling the
electrodes.  
  
These and other aspects and advantages of the present
invention will become more apparent from the following
detailed description, particularly when taken in conjunction
with the accompanying drawings.  
  
**BRIEF DESCRIPTION OF THE DRAWINGS****FIG. 1 is a vertical sectional view, partly
diagrammatic, of a preferred embodiment of a system for the
conductive heating of an earth formation in accordance with
the present invention, wherein an array of electrodes is
emplaced vertically, the section being taken transversely of
the rows of electrodes;****FIG. 2 is a diagrammatic plan view of the system shown
in FIG. 1;****FIG. 3 is an enlarged vertical sectional view, partly
diagrammatic, of part of the system shown in FIG. 1;****FIG. 4 is a vertical sectional view, partly
diagrammatic, of an alternative system for the conductive
heating of an earth formation in accordance with the present
invention, wherein an array of electrodes is emplaced
horizontally, the section being taken longitudinally of the
electrodes;****FIG. 5 is a vertical sectional view, partly
diagrammatic of the system shown in FIG. 4, taken along line
5--5 of FIG. 4;****FIG. 6 is a vertical sectional view comparable to that
of FIG. 4 showing an alternative system with horizontal
electrodes fed from both ends;****FIG. 7 is a plan view, mostly diagrammatic, of an
alternative system comparable to that shown in FIG. 3, with
cool walls adjacent electrodes;****FIG. 8 is a vertical sectional view, partly
diagrammatic of the system shown in FIG. 7, taken along line
8--8 of FIG. 7;****FIG. 9 is a set of curves showing the relationship
between a time dependent factor c and heat loss and a
function of deposit temperature utilizing the present
invention;****FIG. 10 is a set of curves showing the temperature
distribution at different heating rates when heat is
delivered to a defined volume;****FIG. 11 is a set of curves showing the relationship
between time and temperature at different points when a
formation is heated by a sparse array;****FIG. 12 is a set of curves showing the relationship
between time and temperature at different points when a
formation is heated in accordance with the present invention
with electrode diameters of 32 inches; and****FIG. 13 is a set of curves showing the relationship of
time and temperature at the same points as in FIG. 12 in
accordance with the present invention with electrode
diameters of 14 inches.**

**![US4645004a](us4645004a.JPG) ![US4645004b](us4645004b.JPG) ![US4645004c](us4645004c.JPG) ![US4645004d](us4645004d.JPG) ![US4645004e](us4645004e.JPG)**

  
**DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS**  
FIGS. 1, 2 and 3 illustrate a system for heating conductive
formations utilizing an array 10 of vertical electrodes 12,
14, the electrodes 12 being grounded, and the electrodes 14
being energized by a low frequency or d.c. source 16 of
electrical power by means of a coaxial line 17. The electrodes
12, 14 are disposed in respective parallel rows spaced a
spacing s apart with the electrodes spaced apart a distance d
in the respective rows. The electrode array 10 is a dense
array, meaning that the spacing s between rows is greater than
the distance d between electrodes in a row. The rows of
electrodes 12 are longer than the rows of electrodes 14 to
confine the electric fields and consequent heating at the ends
of the rows of electrodes 14.  
  
The electrodes 12, 14 are tubular electrodes emplaced in
respective boreholes 18. The electrodes may be emplaced from a
mined drift 20 accessed through a shaft 22 from the surface 24
of the earth. The electrodes 12 preferably extend, as shown,
through a deposit 26 or earth formation containing the
hydrocarbons to be produced. The electrodes 12 extend into the
overburden 28 above the deposit 26 and into the underburden 30
below the deposit 26. The electrodes 14, on the other hand,
are shorter than the electrodes 12 and extend only part way
through the deposit 26, short of the overburden 28 and
underburden 30. In order to avoid heating the underburden and
to provide the power connection, the lower portions of the
electrodes 14 may be insulated from the formations by
insulators 31, which may be air. The effective lengths of the
electrodes 14 therefore end at the insulators 31.  
  
FIGS. 4 and 5 illustrate a system for heating conductive
formations utilizing an array 32 of horizontal electrodes 34,
36 disposed in vertically spaced parallel rows, the electrodes
34 being in the upper row and the electrodes 36 in the lower
row. The upper electrodes 34 are preferably grounded, and the
lower electrodes 36 are energized by a low frequency or d.c.
source 38 of electrical power. The electrodes 34, 36 are
disposed in parallel rows spaced apart a spacing s, with the
electrodes spaced apart a distance d in the respective rows.
The electrode array 32 is also a dense array. The upper row of
electrodes 34 is longer than the lower row of electrodes 36 to
confine the electric fields from the electrodes 36. The
electrodes 34 extend beyond both ends of the electrodes 36 for
the same reason. Grounding the upper electrodes 34 keeps down
stray fields at the surface 24 of the earth.  
  
The electrodes 34, 36 are tubular electrodes emplaced in
respective boreholes 40 which may be drilled by well known
directional drilling techniques to provide horizontal
boreholes at the top and bottom of the deposit 26 between the
overburden 28 and the underburden 30. Preferably the upper
boreholes are at the interface between the deposit 26 and the
overburden 28, and the lower boreholes are slightly above the
interface between the deposit 26 and the underburden 30.  
  
FIG. 6 illustrates a system comparable to that shown in FIGS.
4 and 5 wherein the array is fed from both ends, a second
power source 42 being connected at the end remote from the
power source 38.  
  
FIGS. 7 and 8 illustrate a system comparable to that of FIGS.
1, 2 and 3 with an array of vertical electrodes. In this
system the rows of like electrodes 12, 14 are in spaced pairs
to provide a low field region 44 therebetween that is not
directly heated to any great extent.  
  
The deposit thickness h and the average or effective thermal
diffusion properties determine the uniformity of the
temperature distribution as a function of heating time t and
can be generally described for any thickness of a deposit in
the terms of a deposit temperature profile factor c, such that  
c=kt/(h/2)@2  
  
where k is the thermal diffusivity. FIG. 9 presents a curve A
showing the relationship between the factor c and the portion
of a deposit above 80% of the temperature rise of the center
of the deposit for a uniform heating rate through the heated
volume. Note that at c=0.1, about 75% of the heated volume has
a temperature rise greater than 80% of the temperature rise of
the center of the heated volume.  
  
FIG. 10 illustrates the heating profiles for three values of
the factor c as a function of the distance from the center of
the heated volume, the fraction of the temperature rise that
would have been reached in the heated volume in the absence of
heat outflow. Note that where c=0.1 or c=0.2, the total
percentage of heat lost to adjacent formations is relatively
small, about 10% to 15%. Where low final temperatures, e.g.,
less than 100 DEG C., are suitable, c up to 0.3 can be
accepted, as the heat lost, or extra heat needed to maintain
the final temperature, is, while significant, economically
acceptable. FIG. 9, curve B, showing percent heat loss as a
function of the factor c, shows percent heat loss to be less
than 25% at c=0.3. On the other hand, if higher temperatures
(e.g., about 200 DEG C.) are desired to crack the bitumen,
then higher central deposit temperatures above the design
minimum are needed to process more of the deposit, especially
if longer heating times are employed. Moreover, the heat
outflows at these higher temperatures are more economically
disadvantageous. Thus a temperature profile factor of c less
than about 0.15 is required. In general the heating rate
should be great enough that c is less than 30 times the
inverse of the ultimate increase in temperature AT in degrees
celsius of the volume:  
c.ltoreq.0.3(100/.DELTA.T)  
  
The lowest values of c are controlled more by the excess
temperature of electrodes and are discussed below.  
  
The electrode spacing distance d and diameter a are determined
by the maximum allowable electrode temperature plus some
excess if some local vaporization of the electrolyte and
connate water can be tolerated. In a reasonably dense array,
the hot regions around the electrodes are confined to the
immediate vicinity of the electrodes. On the other hand, in a
sparse array, where s is no greater than d, the excess heat
zone comprises a major portion of the deposit.  
  
FIG. 11 illustrates a grossly excessive heat build-up on the
electrodes as compared to the center of the deposit for a
sparse array. In this example row spacing s was 10 m,
electrode spacing d 10 m, electrode diameter a 0.8 m, and
thermal diffusivity 10@-6 m@2 /s, with no fluid flow.  
  
FIG. 12 shows how the electrode temperature can be reduced by
the use of a dense array. In this example row spacing s was 10
m, electrode spacing d 4 m, electrode diameter a 0.8 m, and
thermal diffusivity 10@-6 m@2 /s, with no fluid flow.  
  
FIG. 13 illustrates the effect of decreasing the diameter of
the electrodes of the dense array of FIG. 12 such that the
temperature of the electrode is increased somewhat more
relative to the main deposit. In this example row spacing s
was 10 m, electrode spacing d 4 m, electrode diameter a 0.35
m, and thermal diffusivity 10@-6 m@2 /s, with no fluid flow.
The region of increased temperature is confined to the
immediate vicinity of the electrode and does not constitute a
major energy waste. Thus, varying the electrode separation
distance d and the diameter of the electrode a permit
controlling the temperature of the electrode either to prevent
vaporization or excessive vaporization of the electrolyte in
the borehole and connate water in the formations immediately
adjacent the electrode.  
  
The electrode spacing d and diameter a are chosen so that
either electrodetemperature is comparable to the vaporization
temperature, or if some local vaporization is tolerable (as
for a moderately dense array), the unmodified electrode
temperature rise without vapor cooling will not significantly
exceed the vaporization temperature.  
  
The means for providing water for both vaporization and for
maintenance of electrical conduction is shown in the drawings,
particularly in FIG. 3 for vertical electrodes and in FIG. 4
for horizontal electrodes. As shown in FIG. 3, a reservoir 46
of aqueous electrolyte provides a conductive solution that may
be pumped by a flow regulator and pump 47 down the shaft 22
and up the interior of the electrodes 12 and into the spaces
between the electrodes 12 and the formation 26. A vapor relief
pipe 48, together with a pressure regulator and pump 50
returns excess electrolyte to the reservoir 46 and assures
that the electrolyte always covers the electrodes 12.
Similarly, a reservoir 52 provides such electrolyte down the
shaft 22, whence it is driven by a pressure regulator and pump
53 up the interior of the electrodes 14 and into the spaces
between the electrodes 14 and the formation 26. In this case
the electrodes are energized and not at ground potential. The
conduits 54 carrying the electrolyte through the shaft 22 are
therefore at the potential of the power supply and must be
insulated from ground, as is the reservoir 52. The conduits 54
are therefore in the central conductor of the coaxial line 17.
The electrodes 14 have corresponding vapor relief pipes 56 and
a related pressure regulator and pump 58.  
  
As shown in FIG. 4, electrolyte is provided as needed from
reservoirs 60, 61 to the interior tubing 62 which also acts to
connect the power source 38 to the respective electrodes 34,
36, the tubing being insulated from the overburden 28 and the
deposit 26 by insulation 64. The electrolyte goes down the
tubing 62 to keep the spaces between the respective electrodes
34, 36 and the deposit 26 full of conductive solution during
heating. The tubing to the lower electrode 36 may later be
used to pump out the oil entering the lower electrode, using a
positive displacement pump 66.  
  
In either system, the electrolyte acts as a heat sink to
assure cool electrodes and maintain conductive paths between
the respective electrodes and the deposit. The water in the
electrolyte may boil and thereby absorb heat to cool the
electrodes, as the water is replenished.  
  
The vaporization temperature is controlled by the maximum
sustainable pressure of the deposit. Typically for shallow to
moderate depth deposits the gauge pressure can range from a
few psig to 300 psig with a maximum of about 1300 psig for
practical systems. The tightness of adjacent formations also
influences the maximum sustainable vapor pressure. In some
cases, injection of inert gases to assist in maintaining
deposit pressure may be needed.  
  
Another way to keep the electrodes cool is to position the
electrodes adjacent a reduced field region on one side of an
active electrode row. This reduces radically the heating rate
in the region of the diminished field, thus creating in effect
a heat sink which radically reduces the temperature of the
electrodes, in the limiting case to about half the temperature
rise of the center portion of the deposit.  
  
As shown in FIGS. 7 and 8, in the case of vertical arrays,
pairs of electrodes 12, 14 can be installed from the same
drift and the same potential is applied to each pair, thus the
regions 44 between the pairs become low field regions. By
proper selection of heating rates and pair separation, it is
possible to control the temperature of the electrode at
slightly below that for the center of the deposit. The
thickness of the cool wall region 44 can be sufficiently thin
that the cool wall region can achieve about 90% of the maximum
deposit temperature via thermal diffusion from the heated
volume after the application of power has ended.  
  
As shown in FIGS. 4, 5 and 6 in the case of a horizontally
enlarged biplate, a nearly zero field region exists on the
barren side of the row of grounded upper electrodes 34 and a
nearly zero field region exists on the barren side of the row
of energized electrodes 36. Such low field regions act as the
regions 44 in the system shown in FIGS. 7 and 8.  
  
The arrangement of FIGS. 4, 5 and 6 with the upper electrodes
grounded is superior to other arrangements of horizontal
electrodes in respect to safety. No matter how the biplate
rows are energized and grounded (such as upper electrode
energized and lower electrode grounded, vice versa or both
symmetrically driven in respect to ground) leakage currents
will flow near the surface 24 that may be small but
significant in respect to safety and equipment protection.
These currents will create field gradients which, although
small, can be sufficient to develop hazardous potentials on
surface or near-surface objects 68, such as pipelines, fences
and other long metallic structures, or may destroy operation
of above-ground electrical equipment. To mitigate such
effects, ground mats can be employed near metallic structures
to assure zero potential drops between any metallic structures
likely to be touched by anyone.  
  
These safety ground mats as well as electrical system grounds
will collect the stray current from the biplate array. These
grounds then serve in effect as additional ground electrodes
of a line. Leakage currents between the grounding apparatus at
the surface and the biplate array also heat the overburden,
especially if the uppermost row is excited and the deposit is
shallow. Thus biplate arrays, although having two sets of
electrodes of large areal extent, also implicitly contain a
third but smaller set of electrodes 68 near the surface at
ground potential. Although this third set of electrodes
collects diminished currents, the design considerations
previously discussed to prevent vaporization of water in the
earth adjacent the other electrodes must also be applied.  
  
The near surface ground currents are minimized if the upper
electrodes 34 are grounded and the lower electrodes 36 are
energized. Also the grounded upper electrodes 34 can be
extended in length and width to provide added shielding. This
requires placing product collection apparatus at the potential
of the energized lower set of electrodes by means of isolation
insulation. However, this arrangement reduces leakage energy
losses as compared to other electrodes energizing
arrangements. Such leakage currents tend to heat the
overburden 28 between the row of upper electrodes 34 and the
above-ground system 68, giving rise to unnecessary heat
losses.  
  
Short heating times stress the equipment, and therefore, the
longest heating times consistent with reasonable heat losses
are desirable. This is especially true for the horizontal
biplate array. The conductors of an array in the biplate
configuration, especially if it is fairly long, will inject or
collect considerable current. The amount of current at the
feed point will be proportional to the product of the
conductor length l, the distance d between electrodes within
the row, and the current density J needed to heat the deposit
to the required temperature in time t. Thus the current I per
conductor becomes at the feed point (assuming small
attenuation along the line):  
I=(J) (l) (d) ##EQU1## where  
  
.sigma. is the conductivity of the reservoir and
joules-to-heat is the energy required to heat a cubic meter to
the desired temperature. Thus the current carrying requirement
of the conductors at the feed points is reduced by increasing
the heat up time t as determined by the maximum allowable
temperature profile factor c and deposit thickness h. Further,
making the array more dense, that is, decreasing d, also
reduces the current carrying requirements as well as
decreasing l. If conductor current at the feed point is
excessive, heat will be generated in the electrode due to I@2
R losses along the conductor. The power dissipated in the
electrode due to I@2 R losses can significantly exceed the
power dissipated in the reservoir immediately adjacent the
electrode. This can cause excessive heating of the electrode
in addition to the excess heat generated in the adjacent
formation due to the concentration of current near the
electrode. Thus another criterion is that the I@2 R conductor
losses not be excessive compared to the power dissipated in
the media due to narrowing of the current flow paths into the
electrodes. Also the total collected current should not exceed
the current carrying rating of the cable feed systems.  
  
Another cause of excess temperature of the electrodes over
that for the deposit arises from fringing fields near the
sides of the row of excited electrodes. Here the outermost
electrodes (in a direction transverse to the electrode axis)
carry additional charges and currents associated with the
fringing fields. As a consequence, both the adjacent reservoir
dissipation and I@2 R longitudinal conductor losses will be
significantly increased over those experienced for electrodes
more centrally located. To control the temperature of these
outermost electrodes, several methods can be used, including:
(1) increasing the density of the array in the outermost
regions, (2) relying on additional vaporization to cool these
electrodes, and (3) the enlarging the diameter of these
electrodes. Some cooling benefit will also exist for the
cool-wall approach, especially in the case of the vertical
electrode arrays if an additional portion of the deposit can
be included in the reduced field region near the outermost
electrodes. Applying progressively smaller potentials as the
outermost electrodes are neared is another option.  
  
In the case of the biplate array, especially if it extends a
great length into the deposit, such as over 100 m, special
attention must be given to the path losses along the line. To
alleviate the effects of such attenuation, the line may be fed
from both ends, as shown in FIG. 6. At the higher frequencies,
these are frequency dependent and are reduced as the frequency
is decreased. Perhaps not appreciated in earlier work, is that
there is a limit to how much the path attenuation can be
reduced by lowering the frequency. The problem is aggravated
because, as the deposit is heated, it becomes more conducting.  
  
A buried biplate array or triplate array exhibits a path loss
attenuation .alpha. of  
.alpha.=8.7[(R+j.omega.L)(G+j.omega.C)]@1/2 dB/m  
  
where  
  
R is the series resistance per meter of the buried line, which
includes an added resistance contribution from skin effects in
the conductor, if present,  
  
L is the series inductance per meter of the buried line,  
  
G is the shunt conductance over a meter for the line and is
directly proportional to .sigma., the conductivity of the
deposit,  
  
C is the shunt capacitance over a meter for the line. Where
conduction currents dominate, G>>j.omega.c, so that the
attenuation .alpha. becomes  
.alpha.=8.7[(R+j.omega.L)(G)]@1/2 dB/m  
  
If the frequency .omega. is reduced, j.omega.L is radically
reduced, R is partially decreased (owing to a reduction in
skin effect loss contribution) and G tends to remain more or
less constant. Eventually, as frequency .omega. is decreased,
R>>j.omega.L, usually at a near zero frequency
condition, so that  
.alpha.=8.7[(R)(G)]@1/2 dB/m  
  
If thin wall steel is used as the electrode material,
unacceptable attenuation over fairly long path lengths could
occur, especially at the higher temperatures where conductance
G and conductivity .sigma. are greater. If thin walled copper
or aluminum is used for electrodes (these may be clad with
steel to resist corrosion), the near zero-frequency
attenuation can be acceptably reduced so that  
.alpha.l=8.7[(R)(G)]@1/2 (l).ltoreq.2dB  
  
for the single end feed of FIG. 4 and less than 8 dB for the
double end feed of FIG. 6.  
  
When d.c. power is applied, advantage may be taken of
electro-osmosis to promote the production of liquid
hydrocarbons. In the case of electro-osmosis, water and
accompanying oil drops are usually attracted to the negative
electrodes. The factors affecting electro-osmosis are
determined in part by the zeta potentials of the formation
rock, and in some limited cases the zeta potentials may be
such that water and oil are attracted to the positive
potential electrodes.  
  
Electro-osmosis can also be used to cause slow migration of
the reservoir water toward one of the sets of electrodes
preferentially. This preferential migration will be toward the
cathode for typical reservoirs. However, depending upon the
salinity of the reservoir fluids and the mineralogy of the
reservoir matrix, the net movement under application of d.c.
can be toward the anode. Remote ground can be used as an
opposing electrode to facilitate this. This can be used to
replenish conductivity in formations around the desired
electrodes of sets of electrodes by resaturating the formation
using reservoir fluids. This will permit resumption of
heating.  
  
In some cases, the presence of water fills the available pore
spaces and thereby suppresses the flow of oil. Also in the
case of a heavy oil deposit, influx of water from the lower
reaches of the deposit may reach the producing electrodes such
as electrodes 36 (FIG. 6). Therefore, in some cases it may be
desirable to place a potential onto both sets of electrodes
34, 36 such that water is drawn away from the array. This may
be done by modifying the source 38 such that the ground
electrode array 68 near the surface is placed at a negative
potential with respect to the entire set of deep electrodes
34, 36.  
  
D.C. power applied for electro-osmosis can cause anodic
dissolution of the metal electrodes, and hence, it will be
preferable to keep the d.c. power levels just high enough to
cause migration of fluids. Such required d.c. power can either
be added as a bias to a.c. power which provides the bulk of
the energy required to heat the formation or be applied
intermittently.  
  
While the use of electro-osmotic effects to enhance recovery
from single wells or pairs of wells has been described, the
employment of the dense array offers unique features
heretofore unrecognized. For example, in the case of a pair of
electrodes widely separated, the direct current emerges
radially or spherically from the electrode. The radially
divergent current produces a radially divergent electric
field, and since the electro-osmotic effect is proportional to
the electric field, the beneficial effects of electro-osmosis
are evident only very near the electrode. Furthermore, the
amount of current which can be introduced by an electrode is
restricted by vaporization consideration or, if the deposit is
pressurized, by a high temperature coking condition which may
plug the producing capillary paths. On the other hand, with
the arrangement of the present invention, the large electrode
surface area and the controlled temperature below the
vaporization point allows substantially more d.c. current to
be introduced. Further, the effects of electro-osmosis are
felt throughout the deposit, as uniform current flow and
electric fields are established throughout the bulk of the
deposit. Thus an electro-osmotic fluid drive phenomenon of
substantial magnitude can be established throughout the
deposit which can substantially enhance the production rates.  
  
Further, electrolyte fluids will be drawn out of the
electrodes which are not used to collect the water. Therefore,
means to replace this electrolyte must be provided.  
  
Production of liquid hydrocarbons using electro-osmosis can
also be practiced in combination with conventional recovery
techniques such as gravity drainage. Electro-osmosis can be
used to increase the rate of production of liquid hydrocarbons
by gravity drainage. For example, the polarity of the
electrode rows shown in FIG. 5 can be so chosen such that
reservoir water will slowly move toward the upper row of
electrodes 34. This will cause a simultaneous increase in
saturation of hydrocarbons toward the bottom row of electrodes
36. The rate of flow of hydrocarbons toward these bottom
electrodes 36 is directly proportional to the permeability of
the formation near the electrodes to flow of hydrocarbons.
This in turn increases with increase in hydrocarbon
saturation. Thus, the rate of hydrocarbon production can be
increased by forcing the reservoir water to move toward the
upper part of the formation by electro-osmosis.  
  
Although various preferred embodiments of the present
invention have been described in some detail, various
modifications may be made therein within the scope of the
invention.  
  
Several methods of production are possible beyond the unique
features of electro-osmosis. Typically, the oil can be
recovered via gravity or autogenously generated vapor drives
into the perforated electrodes, which can serve as product
collection paths. Provision for this type of product
collection is illustrated in FIG. 4, where a positive
displacement pump 66 located in the lowest level of electrode
36 can be used to recover the product. Product can be
collected in some cases during the heat-up period. For
example, in FIG. 4 the reservoir fluids will tend to collect
in the lower electrode array. If those are produced during
heating, those fluids can provide an additional or substitute
means to control the temperature of the lower electrode. On
the other hand, it may not be desirable to produce a deposit,
if in situ cracking is planned, until the final temperature is
reached.  
  
Various "hybrid" production combinations may be considered to
produce the deposit after heating. These could include
fire-floods, steam floods and surfactant/polymer water floods.
In these cases, one row of electrodes can be used for fluid
injections and the adjacent row for fluid/product recovery.  
  
In contrast with polarizing the electrodes so as to suppress
the production of water, the electro-osmotic forces can be
used as a drive mechanism which exists volumetrically
throughout the deposit for a fluid replacement type flood. The
principal benefits of using the electro-osmotic drive in
conjunction with the electrode arrays discussed here is that
the volumetric drive can be maintained without excessive heat
being developed near the electrode or without excessive
electrolysis as might occur in a simple five-spot well
arrangement.  
  
The fluids injected at the electrodes can contain surfactants
such as long chain sulfonates or amines or polymers such as
polyacrylamides. The presence of surfactants will reduce the
interfacial tension between the injected fluids and the liquid
hydrocarbons and will help in recovering the liquid
hydrocarbons. Addition of polymers will increase the viscosity
and cause an improvement in sweep efficiency. The applied d.c.
power can act as the driving force for the migration of fluids
toward the other set of eIectrodes, whereby the accompanying
liquid hydrocarbons can be produced along with the drive
fluid.  
  
The foregoing discussion, for simplicity, has limited
consideration to either vertical or horizontal electrode
arrays. However, arrays employed at an angle with respect to
the deposit may be useful to minimize the number of drifts and
the number of boreholes. In this case, the maximum row
separation s is chosen to be midway between the vertical or
horizontal situation, such that if largely vertical, the row
separation s is not much greater than that found for the true
vertical case. On the other hand, if the rows are nearly
horizontal, then a value of s closer to that chosen for a
horizontal array should be used.

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****WO2012158145****  
**Method for Electrokinetic Prevention of Scale
Deposition in Oil Producing Well Bores**  

Method of using direct current (DC)
electrokinetics to alleviate and prevent scale deposition in
and around well bores, e.g., the well bores of oil producing
wells.  
  
**FIELD OF THE INVENTION**  
The present invention relates generally to the prevention of
mineral scale deposition in a well bore, and more particularly
to a method for electrokinetically preventing mineral scale
deposition in oil well bores with the aid of DC electric
current.  
  
**BACKGROUND OF THE INVENTION**  
  
The waterflood, a secondary enhanced oil recovery
process/<11> is a simple, low cost, and proven approach
for pressure maintenance and for driving oil towards a
production well.  
  
Though initial waterflooding attempts were used to rectify
plugged wells or casing leaks, the apparent benefits led to
broader applications <pl>. Waterflood efficiency depends
on oil viscosity, permeability, wettability, structural
considerations, uniformity of reservoir rock, and type of
flood<[2]>. The volume of liquid produced partly
determines the volume of water required for
injection<111>. For economic reasons nearby seawater is
commonly used, where available, as the injection water type to
save money on water transportation. The mixing of incompatible
injection seawater and formation water frequently produces
mineral scale deposits, one of the most significant and costly
problems encountered in oilfield operations <[3> Water
flooding operations conducted in the Abu Dhabi oilfields often
result in the formulation of BaS04, CaS04 and SrS04 deposits.
The S04<2"> and Ba<2+> ion content in both
seawater and formation water, respectively, can easily reach
the solubility product (Ks) causing accumulation of BaS04
scale on surface and subsurface equipment. This is recognized
as a major cause of formation damage in production or
injection wells. Inorganic scale contributes to wear,
corrosion, and flow restriction, resulting in a decrease of
oil and gas production. This scale also deposits in downhole
pumps, tubing, casing, flow lines, heaters, treaters, tanks
and other production equipment and facilities<131>.
Barium sulfate (BaS04) scale is among the toughest to remove
either by mechanical or chemical means. BaS04 is typically
removed by mechanical tools that involve abrasion, such as
gauge cutters, nipple brushes and spinning wash tools.
Chemical removal methods utilizing ethylenediaminetetraacetic
acid (EDTA) are also available<[3>  
  
Unfortunately, current scale inhibitor applications incur high
costs due to conventional chemical dissolution. Scale
inhibitor treatment is limited by its "squeeze efficiency"
into the formation, which results in limited penetration as
well as quick consumption in the reservoir. A squeeze usually
involves the application of pump pressure to force a treatment
fluid or slurry into a planned treatment zone (Schlumberger
Oilfield Glossary). The problem is that scale inhibitors do
not move deeply into the reservoir, hence only a small volume
can be squeezed before being rapidly consumed. A need exists
for a new methodology to prevent scale formation which is both
economical and effective.  
  
While electrically enhanced techniques for promoting oil
recovery are known, including those described in United States
Patent Nos. 5,614,077 and 7,325,604, such techniques have not
been applied in the fashion described herein for preventing
mineral scale deposits.  
  
**SUMMARY OF THE INVENTION**  
  
The method of the invention involves the application of
electrokinetics for mitigating mineral scale formation. In one
embodiment, the present invention provides an electrokinetic
method for preventing mineral scale deposition in an oil well,
having a well bore in fluid communication with an oil-bearing
formation in which water and positively and negatively charged
scale-forming species are present. The method comprises the
steps of:  
  
a) positioning at least one first electrode adjacent to a well
bore;  
  
b) positioning at least one second electrode at a location
spaced apart from the first electrode and within electrical
current conducting proximity of the first electrode;  
  
c) applying a potential difference between the first
electrode(s) and the second electrode(s) using a direct
current (DC) power source, the potential difference producing
an electrical current flow between the first electrode(s) and
the second electrode(s), whereby the positively charged
scale-forming species are caused to migrate toward one of the
first and the second electrode(s), and the negatively charged
scale-forming species are caused to migrate toward the other
of the first and second electrode(s). In an aspect of this
method, the potential difference is applied such that the
first electrode(s) serves as one or more cathodes and the
second electrode(s) serves as one or more anodes.  
  
In another aspect of this method, at least one of the
positively and negatively charged scale-forming species is
introduced into the formation from an external source such as
waterflooding. When waterflooding is the source of the
scale-forming species, the method may be performed using an
electrically conducting aqueous solution, e.g., a prepared or
manmade aqueous salt solution, or alternatively, an aqueous
solution selected from the group consisting of seawater,
groundwater, surfacewater, and wastewater.  
  
In a further aspect of the method, the positively and
negatively charged scale-forming species include at least one
alkaline earth metal ion and sulfate or carbonate ions.  
  
In still a further aspect of the electrokinetic method,
multiple cathodes are positioned in the vicinity of the well.
Additionally, multiple anodes may be positioned at locations
spaced apart from the cathodes and beyond the well, and in
preferred installations the number of anodes exceeds the
number of cathodes.  
  
In yet another embodiment, the present invention provides an
electrokinetic method for preventing mineral scale deposition
in an oil well, and the vicinity of the well, with the well
having a well bore in fluid communication with an oil-bearing
formation in which water and positively and negatively charged
scale-forming species are present, the method comprising the
steps of:  
  
a) positioning at least one cathode adjacent to the well bore;  
  
b) positioning a plurality of anodes at a location spaced
apart from the at least one cathode and within electrical
current conducting proximity of the at least one cathode,
wherein the number of anodes exceeds the number of cathodes;  
  
c) applying a potential difference between the at least one
cathode and each individual anode of the plurality of anodes;
whereby electrical current flow between the at least one
cathode and each individual anode of the plurality of anodes
causes the positively charged scale-forming species to migrate
toward the at least one cathode, and the negatively charged
scale-forming species to migrate toward each individual anode
of the plurality of anodes.  
  
In another aspect, the method further comprises the step of
providing a switch between the at least one cathode and each
individual anode of the plurality of anodes, wherein the
switch is adapted to be opened to interrupt application of the
potential difference between the at least one cathode and each
individual anode of the plurality of anodes, or closed to
apply the potential difference between the at least one
cathode and each individual anode of the plurality of anodes.  
  
In a further aspect of the method of the invention, the step
of applying a potential difference between the at least one
cathode and each individual anode of the plurality of anodes
further comprises the step of providing a DC power source
between the at least one cathode and each individual anode of
the plurality of anodes.  
  
The method described herein is believed to be the first use of
direct current to prevent scale deposition in a well bore in
fluid communication with an oil bearing formation. The
electrokinetic method for preventing scale deposition
described herein may be categorized as a green technology,
since there is no water consumption, and no air, water, or
formation pollution. The technology can be applied without
depth limitations in situ, thereby making it an attractive
option in remote or environmentally challenging operating
locations.  
  
**BRIEF DESCRIPTION OF THE DRAWINGS**  
The following description will be more easily understood when
read in conjunction with the accompanying figures in which:  
  
**FIGURES 1A-C are circuit diagrams representing cathode and
an anode configurations where the number of anodes exceeds
the number of cathodes.****FIGURE 2 is a graphical representation of the pressure
across the core versus time in experiment 1 of Example 1.****FIGURES 3A-C are a set of graphs showing the barium
concentration profiles of the experiments in Example 1 ;
Figure 3A is a graphical representation of the concentration
profile of barium found in the tested electrode
configuration (++--) for all tested salinity and****composition waters against the blank at the five
strategic sampled positions across the 18 cm sand specimen
of Example 1; Figures 3B-C are graphs representing the
concentration profile of barium remaining after application
of DC current; where Figure 3B includes the average of
experiments 1 and 10 in addition to experiments 2, 5, 8 -
seawater/formation composition water (SW/FW) and 11 of
Experiment 1; and Figure 3C includes experiments 5, 8, 9 and
12 of Example 1. FIGURE 4 is a graph of the current across
the core as a function of time for experiment 2 of Example
1.****FIGURES 5A-C are a set of graphs showing current as a
function of time across the core for several experiments of
Example 1 ; Figure 5A is a graph of the current across the
core as a function of time for experiment 3 of Example 1;
Figure 5B is a graph of the current across the core as a
function of time for experiment 5 of Example 1 ; and Figure
5C is a graph of the current across the core versus time for
experiment 8 of Example 1.****FIGURES 6A-C are a set of graphs showing pressure as a
function of current across the core for several experiments
of Example 1; Figure 6A is a graph of the pressure versus
current for experiment 2 of Example 1 ; Figure 6B is a graph
of the pressure as a function of current for experiment 3 of
Example 1 ; and Figure 6C is a graph of the pressure as a
function of current for experiment 8 of Example 1.****FIGURE 7 is a graph of the standardized concentration
profile of barium with and without DC current - No salinity
and actual seawater/formation composition water (SW/FW) of
Example l(see Table 3).****FIGURE 8 is a graphical representation of the change in
permeability with respect to the pore volume in the blank
experiment of Example 2.****FIGURE 9 is a schematic illustration of a consolidated
sand cell shown, in cross-section, with an electrode
positioned at each of the production water outlet and the
sea water inlet.****FIGURES 10A-B are schematic illustrations of the
electrokinetic cell utilized in****Example 2; Figure 10A is a schematic illustration of a
consolidated sand cell showing, in cross- section, the
distribution of anodes and cathodes in a first configuration
(AAACC), and Figure 10B is a schematic illustration of a
consolidated sand cell shown, in cross-section, a
distribution of anodes and cathodes in the second
configuration (AAAAC).****FIGURE 11 is a graphical representation of the effect
of pH on BaS04 solubility.****FIGURES 12 A-F are a set of graphs showing permeability
as a function of pore volume for several experiments of
Example 2; Figure 12A is a graphical representation of
permeability reduction with respect to the pore volume in
experiment 5 of Example 2; Figure 12B is a graphical
representation of permeability reduction with respect to the
pore volume in experiment 6 of Example 2; Figure 12C is a
graphical representation of permeability reduction with
respect to the pore volume in experiment 7 of Example 2;
Figure 12D is a graphical representation of permeability
reduction with respect to the pore volume in experiment 8 of
Example 2; Figure 12E is a graphical representation of
permeability reduction with respect to the pore volume in
experiment 9 of Example 2; and Figure 12F is a graphical
representation of permeability reduction with respect to the
pore volume in experiment 10 of Example 2.**  
![WO2012158145a](wo2012158145a.JPG) ![WO2012158145b](wo2012158145b.JPG) ![WO2012158145c](wo2012158145c.JPG) ![WO2012158145d](wo2012158145d.JPG) ![WO2012158145e](wo2012158145e.JPG) ![WO2012158145f](wo2012158145f.JPG) ![WO2012158145g](wo2012158145g.JPG) ![WO2012158145h](wo2012158145h.JPG) ![WO2012158145i](wo2012158145i.JPG) ![WO2012158145j](wo2012158145j.JPG) ![WO2012158145k](wo2012158145k.JPG)

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