Note: Descriptions are shown in the official language in which they were submitted.
~35~55~
Backqround of the Invention
This invention relates to method and apparatus for
establishing an electrical field in a subsurface oil or
mineral bearing formation and establishing in response to
the electrical field a zone o electrochemical activity
resulting in electrochemical reactions with constituent
elements of the earth formation for increasing the internal
pressure of the earth formation over an area greatly
exceeding the zone of electrochemical activity~
Until fairly recent times, it was relatively easy to
find new oil reserves when a field was depleted or became
unprofitable. In many fields cnly 15%~25% of the oil in
place was actually recovered before reservoir pressure or
drive was depleted or other factors made it uneconomical to
continue to produce the field. As long as new reserves were
readily available, old fields were abandoned~ However, with
the crisis now confronting the domestic oii industry, coupled
with the fact that most of the existing on-shore oil in the
United States has already been discovered, it is obvious that
20 such known reserves must be efficiently and economically
produced.
It has been estimated that at least 50% of the known oil
reserves of the United States cannot be recovered using
conventional pumping methods. A substantial amount of this
~C~5i~7
oil is of an abnormally low gravity, and/or high viscosity,
often coupled with the fact that there is little or no
pressure in the oil-bearing formation. In the absence of
formation pressure, even oil of average viscosity and gravity
is difficult to produce without adding external energ~ to the
formation to move the oil into a producing borehole.
Accordingly, a great deal of attention has recently bean given
to various methods of secondary recovery. Water flooding has
been utilized with mixed results to attempt to increase the
natural reservoir pressure hydraulically. Thermal flooding
techniques, such as fire flooding, steam injection and ho~
water flooding have been utiliæed to alter the viscosity of
the oil and hence, enhance its flow characteristics. However,
none of these thermal techniques contributes to increasing -the
formation pressure and have been successful only in a limited
number of applications. All of the methods mentioned above
require extensive, and quite expensive, surface installations
for their utilization.
The prior art contains U.S. patents that have in-troduced
electrical currents into a subsurface oil~ or mineral-bearing
formation for the express purpose of heating the formation in
order to lower the viscosity and stimulate the flow of the oil
or mineral in the immediate area involved in tl~e heatin~
process. Examples of such patents are: 849, 524 (Baker, 1907);
2~799~641 (Bell, 1957); 2~801~090 (Hoyer, 1957); 3~428~125
(Parker, 1969); 3~507~330 (Gill, 1970); 3~547~193 (Gill, 1970);
3~605~888 (Crowson, 1971); 3~620~300 (Crowson, 1971) ~ and
3~642~066 (Gill, 1972)o All of the above patents depend in
11358557
some form on electrothermic action to enhance the flow
characteristics of the oil or an "electro osmosis" action
whereby the oil tends to flow from an electrically charged
positive region to a negatively charged region. However, none
of the above patents suggests the establishment of a zone of
electrochemical activity w~erein an electrochemica.l. reaction is
promoted with constituent elements of the formation, salt
water and oil, for increasing the internal pressure of the
formation over an area greatly exceeding the zone of
electrochemical activity~
~ ccordingly, one primary feature of the present invention
is to provide method and apparatus for establishing a zone of
electrochemical activity in a subsurface formation resulting
: in electrochemical reactions with constituent elements of the
. formation, such as salt water and oil, for generating volumes
of gas in the formation for increasing the formation pressure~
Another feature of the present invention is to provide
method and apparatus for establishiny a zone of electrochemical
activity in a subsurface formation for enhancing the flow
characteristics of oil in the formation by lower.ing the
viscosity of the oil.
Yet another feature of the present invention is to provide
method and apparatus for establishing a zone of electrochemical
activity in a subsurface formation for releasing salt water
and oil in situ from the formation matrix within the zone of
electrochemical activity and separating the oil and salt water
within the earth formation matrix by gravitational action.
Still another feature of the present invention is to
~rQ~ide method and apparatu~ blishing an electric field
within the subsurface formation wherein a plurality of
electrodes is employed, each of the elec-trodes projecting into
the formation through one of a plurality of spaced boreholes and
an insulating means is utilized for insulating each of the
electrodes from the earth structure surrounding the borehole for
preventing an electrical current path be-tween the electrode and
the earth structure and isolating the electrical current path
from the electrode into the earth formation.
Summary of the Invention
The invention in one broad aspect comprehends a method of
generating gases in-situ in a fluid-bearing earth formation
which includes the steps of establishing at least two spaced-
apart boreholes extending into a subsurface earth formation
containing oil and other aqueous li~uids, establishing an
electrical conductor in each of the boreholes in electrical
contact with the aqueous liquids in the formation, and insulate
both the conductors from substantially all earth materials other
than the materials lying within the formation to establish an
electrical path comprising the insulated conductors and the
formation materials extending therebetween. The method further
includes establishing a flow of ~.C. current across a subsurface
path consisting of the conductors and the formation materials
lying therebetween, electrochemically generating free hydrogen
gas in the subsurface formation between the boreholes, and
trapping the hydrogen gas in the formation to increase the
pressure in the formation on the oil therein.
Another aspect of the inven-tion comprehends apparatus for
increasing the formation pressure of an oil bearing subsurface
earth formation which includes at least two spaced boreholes
drilled into the earth formation containing both oll and an
~ 585S7
èlectrolyte -dispersed therein and a plurality of electrodes, one
each of which is disposed in each of the boreholes and into elect-
rical contact with the oil and electrolyte in the subsurface earth
formation. A casing of electrically insulatiny material is set
into each borehole for insulating the electrodes from substantially
all earth materials adjacent the boreholes and lying above the sub-
surface earth formation to establish an electrical circuit composed
of the insulated electrodes and the formation electrolyte. A source
of an A.C. electrical current is connected to each of the electrodes
for establishing an A.C~ current in the electrical circuit composed
of the insulated electrotrodes and the formation electrolyte lying
therebetween for electrochemically generating free gases~ at least
one constituent of which is hydrogen, in the subsurface earth for-
mation between the boreholes, and means trap the generated gases in
the formation thereby increasing the formation pressure acting on
the oil therein.
The invention further comprehends a method of increas-
ing the internal pressure in a fluid~bearlng earth formation in-
cluding the step of establishing at least two spaced apart bore-
holes extending into a subsurface earth formation containing bothoil and other aqueous liquids. A separate electrical conductor is
then disposed in each of the boreholes and into electrical contact
with the aqueous liquids in the formation. Both of the conductors
are insulated from substantially all earth materials adjacent the
boreholes and which lie above the subsurface earth formation to
establish an electrical path composed of the insulated conductors
and the formation materials extending therebetween. The method
further includes the step of establishing an A.C. flow of electric
current in the electrical path composed of the insulated conductors
and the formation materials l~ing therebetween, electrochemically
generating free hydrogen gas in the subsurface earth formation be-
tween the boreholes as a function of current intensity in the for-
mation, and trapping the free hydrogen gas in the fo~rmation to
increase the pressure in the formation on the oil therein. The zone
.~ . . .
585S7
of electrochemical activity enhances the ~low characteristics of
the oil by lowering the viscosity of the oil and the lncreased
pressures of the formation act to drive oil into a producing bore-
hole spaced from the zone of electrochemical activity. The electro-
chemical activity also releases the salt water and oil from the
earth formation matrix within the zone of electrochemical activity
and separates the oil and salt water within the earth formation
matrix by gravitational action.
The invention also com~rehends the apparatus for
accomplishing the above described method related to secondary
recovery of oil and in one preferred embodiment comprises at least
two spaced boreholes drilled into the earth formation, a ~lurality
of electrodes, one each of which is disposed ln each of the bore-
holes extending from the surface of the earth into electrical
contact with the oil and electrolyte in the subsurface earth for-
mation. Insulated casings provide for insulating the electrol~te
as noted above and a source of A.C. electrical current is connected
to each of the electrodes'for establishing an A.C. current intensity
within the subsurface earth formation for electrochemically gen-
erating free gas (one constituent being hydrogen). Means trap thegas to increase the formation pressure thereb~ facilitating for
secondary oil recovery through a producing borehole drilled into
the formation. Other means may be added to an electrode well for
cooling the casing of the well from the heat generated by the pass-
age of electrical current in the formation.
Brief Description of the Drawings
In order that the manner in which the above-recited
advantages and features of the invention are attained can be
understood in detail, a more particular description of the
invention may be had by reference to specific embodiments
thereof which are illustrated in the appended drawings, which'
drawings form a part of this specification. It is to be
` 10585S7
noted, however, that the appended drawings illustrate only
typical embodiments of the invention and therefore are not to
be considered limiting of its scope, for the invention may
admit to further equally effective embodiments.
In the drawings:
Figure 1 is a cross-sectional view illustrating a pair of
electrode well bores penetrating an oil-bearing formation for
passing electric currenk therethrough in accordance with one
embodiment o the present invention:
Figure 2 is a diagrammatic view showing one suggested
distribution of electrode wells in accordance with a second
embodiment of this invention, with the electrode wells shown
in relation to conventional oil-producing wells;
Figure 3 is a cross-sectional view illustrating a pair of
electrode well bores penetrating an oil-bearing formation
adapted or passing an electric current therethrough in
: accordance with the second embodiment of the present invention;
Figure 4 is a fragmentary detailed view of another
embodiment of the apparatus disposed in a borehole shown in
Figure 3 penetrating the oil-bearing formation;
Figure S is a diagrammatic view showing a second
suggested distribution of electrode wells in accordance with
a third embodiment of this invention with the electrode wells
: shown in relation to conventional oil-producing wells;
Figure 6 is a diagrammatic view illustrating lines of
current in a subsurface formation between a pair of electrode
wells.
Figure 7 is a diagrammakic view illustrating lines of
:~L058557
currant in a subsurface formation between three electrodes
utilizing three-phase AC current.
Figure 8 is a diagrammatic view, partly in cross-section,
illustrating a plurality of electrode well bores penetrating
an oil-bearing formation in accordance with the embodiment
illustrated in Figure 5 and illustrating the relationship
between the electrode well bores and a producing well where
the oil and salt water have been released ~rom the ormation
matrix;
Figure 9 is a diagrammatic view showing a third suggested
distribution of electrode wells in accordance with a fourth
embodiment of the invention.
Figure lO is a diagrammatic view showing a fourth
suggested distribution of electrode wells in accordance with a -
fourth embodiment of the Lnvention.
Figure 11 is~a cross-sectional view illustrating one
embodiment of the apparatus for equippiny an electxode well
bore penetrating an oil-bearing formation, appea~ng with ~gs. 6 & 7;
Figure 12 is a cross-sectional view illustrating another
embodiment o the apparatus for equipping an electrode well
bore penetrating an oil-bearing ormation;
Figure 13 is a cross sectional view illustrating yet
another embodiment of the apparatus for equipping an electrode
well bore penetrating an oil-bearing formation;
Figure 14 is a cross-sectional view illustrating still
another embodiment of the apparatus for equipping an electrode
well bore penetrating an oil-bearing formation;
Figure 15 schematically illustrates one manner in which
` ~L[35t~57
the principlas of the present invention can be applied to
produce a series of current-producing patterns for passing
electric current through an increasing area of an earth
formation, appearing with Figures 12, 16 and 17;
Figure 16 schematically illustrates the path or flow of
current in accordance with the embodiment of the invention
illustrated in Figure 2, appearing with Figures 12, 15 and 17;
Figure 17 schematically illustrates the path for flow of
current in accordance with the embodiment of the invention
illustrated in Figure 5, appearing with Figures 12, 15 and 16;
Figure 18 is a diagrammatic view, partly in cross-section,
illustrating a plurality of electrode well bores penetrating
an oil-bearing formation, a producing well bore penetrating
the oil-bearing formation, and an industrial plant utilizing
an oil-fueled energy source with the exhaust gases from the
plant being injected into the oil-bearing formation through
yet another well bore penetrating said formation,appea~ngwithFig.l.
Detailed Description o the Preferred Embodiments
For a formation or reservoir to be p.roductive, a couple
of conditions must exist. First, a pressure differential must
exist between the formation and the well boreO Energy for the
pressure differential may be supplied naturally in the form of
gas, either free or in solution, evolved under a reduction in
pressure. The energy may involve a hydrostatic head of water
behind the oil, or the water under compressionO In cases
where the natural energy forces within the formation are not
sufficient to overcome the retarding forces within the
formation or reservoir, external energy must be added.
5~3~S7
Secondly, the produced oil must be displaced by another fluid,
either gas or water.
Reservoirs are ordinarily classified according to the
type of reservoir energy that is available. The four types
are solution gas drive reservoirs, gas expansion reservoirs,
water driving reservoirs, and gravitational drainage
reservoirs. A particular reservoir may, of course, involve
more than one o these producing mechanisms.
Xn those cases where the natural energy of the reservoir
is insufficient to overcome the resistive forces such as the
forces of viscous resistance and the forces of capillary
action, external energy must be applied. To illustrate such
cases, this phenomenon is typically encountered in shallow
formations containing high viscosity oil that has little or no
reservoir energy or ormation pressure available, and in those
oil-producing formations in which the reservoir energy has been
depleted or dissipated. In this discussion, we have been
raferring to "mechanical" forces acting within the producing
formationO In a formation in which the natural energy of the
reservoir has been depleted, the mechanical forces in the
formation have reached near equilibrium and no pressure
differential is available to drive the oil from the formation
into the well bore~ In all of the cases where reservoir energy
was depleted by conventional primary production, or non-exis-
tent in the first instance~ the chemical balance of the
producing formation remains undisturbed and in virtual
equilibrium~
Artificial forces introduced into the reservoir such as
--10--
~OS8SS7
water or gas through various "pressuring" or "flood"
techniques of secondary recovery can effect a mechanical
change in the formation by way of pressure. Steam pressure is
likewise effective, with some side benefits from heat.
Combustion of some of the oil in the formation through "fire-
flooding" and heating a well bore serve to reduce the
viscosity o the oil in place and enhance flow characteristics
but lack a drive to force the oil through the formation and
into a producing well bore. However, these are primarily
mechanical forces applied and operating only on an exposed
~ace or sur~ace of the formation, and i~ some chemical or
molecular change is accomplished in the fluids in the
formation, it is limited to a localized phenomenon. The
instant invention will enhance the flow characteristics of the
oil in the formation and generate energy in the form of gas
produced in the formation for increasing the ormation
differential pressure and thus the available reservoir energyO
These factors are achieved by applying electric current to the
formation resulting in an electro-chemical action on the
fluids in the formation.
Referring now to Figure 1, there may be seen a simplified
diagrammatic illustration o a portion of a subsurface earth
formation 18 containing both oil and salt water. More
particularly, the formation 18 may be seen to have been
penetrated by three separate boreholes 10, 11 and 14. Two of
these boreholes, 10 and 11, are preferably lined with an
electrically non-conductive or insulating casing 12, whereas
the third or producing borehole 14 may be lined with
105~3S57
conventional steel casing 13. Because of the action of the
force of gravity, it will be noted that the oil in the
formation 18 will usually tend to collect in the upper
reaches or strata 19 of the formation 18, whereas the salt
water, which is heavier t~an oil, will tend to collect in
the lower portion or strata 20 o~ the formation 18 beneath
the oil. Accordingly, the electricall~ non-conductive casin~
12 in the two boreholes 10 and 11 will preferably be provided
wit~ perforations 21 at a level in the lower salt water zone
or strata 20 of the formation 18, whereas the steel casing 13
in the third well 14 will preferably have perforations 22 at an
upper level in the oil zone or strata 19 of the formation 18~
Thus, only the salt water 28 in the formation 18 will tend to
enter and at least partially~fill the casing 12 of the two
boreholes 10 and 11.
Referring again to Figure 19 it may be seen t~at a pair
of metallic electrodes 15 and 16 have been inserted to a depth
in each of the two wells 10 and 11, whereby their lower ends
are each deeply immersed in the salt water whlch is collected
in the casing 12. The upper ends of both electrodes 15 and 16
are connected by suitable leads 26 and suitable regulating and
control equipment 24 and 25 to an electrical power supply 23
by means of conductors 27. The electrical power supply 23 is
o~ appropriate size and capacity for generating electric
current that may be conducted into the contents of casing 12
and into the salt water zone 20 of the formation 1~.
Oil is a poor conductor of electricity, while salt water
disposed in a formation is a good conductorO Since an
-12-
~058557
electric current will follow the path of least resistance,
current which is applied to the electrodes 15 and 16 from the
power supply 23 will flow directly across the salt water zone
20 of the formation 18 between the two electrodes 15 and 16,
and the salt water therein will tend to be heated in
accordance with the amount of salt water which is interposed
therebetween and the magnitude of current being appLied to the
electrodes 15 and 16. The hea~ed salt water will act as a
heating element with respect to the oil in the zone or strata
19, whereby the viscosity of the oil may be decreased, thus
enhancing the flow characteristics of the oil in the formation.
The above discussion relating to Figure 1 assumes a
heating of a defined salt water strata in an oil-bearing
formation which will heat the overLying oiL strata, thereby
lowering the viscosity of the oil and improving its flow
characteristics in the formakion. However, if a natural
driving energy is not present in the reservoir or formation,
lowering the viscosity of the oil will not greatly enhance
.
oil production, since there is no formation pressure or force
available to move the oil from the formation to the bore hole.
For reasons to be hereinafter further described9 transmitting
an electric current through the formation fluids, such as salt
water of strata 20 of formation 18, will generate volumes of
gas within the formation 18 by electro-chemical action for
providing internal formation pressure to drive the oil into
; producing borehole 14 of Figure 1.
Referring now to Figures 2, 3 and 4, another embodiment
of the apparatus for secondary recovery of oil from a
~0585S7
subsurface oil-bearing earth ~ormation is disclosedO A pair
of boreholes 30 and 31 are shown penetrating the overlying
earth 34 and an oil-producing earth formation 37. Boreholes
30 and 31 are preferably lined with an electrically non-
conductive casing 35 and conventionally cemented down to the
point at which the earth 34 adjoins the oil-bearing formation
37. In the embodiment o Figure 3, the boreholes are
completed "bare~oot," that is, no casing is set in the oil-
bearing formation 37 and the borehole is left unlined. In
~igure 4, another embodiment is shown, where a steel casing
section 36 is set in the borehole in formation 37 and has
perforations 42 completed therein. Collar 43 couples the
insulating casing 35 and steel casing 36. The steel casing
36 can be anchored by a conventional cement plug 44.
; ~ pair o metal electrodes 38 and 39 are inserted one into
each o~ boreholes 30 and 31, respectively, and extend through
the insulating casing 35 into the oil-bearing formation 37 as
shown in Figure 3 or into the steel or electrically conducting
- casing section 36, as shown in Figure 4. The electrodes may
ZO be centralized within insulating casing 35 by means of packers
(not shown in Figure 3) and within the electrically conducting
casing section 36 (see Figure 4) by means o a packer 41 that
is set just below the joint of the insulating casing 35 and
the electrically conducting casing 36 for purposes to be
hereinafter further explaineda Electrical power is provided
by generator 32 and is connected to electrodes 38 and 39 by
means of conductors 40~ Suitable regulating and timing
apparatus 46 may be utilized to regulate the electric power
-14-
1~585S~
and to time the length of the application of power to the
formation, as will hereinafter be further explainedq
Formation 37 may contain many conductive elements, but
the salt water ordinarily associated with oil-bearing
formations is highly conductivè. Such salt water, called
"connate" salt water, is oten distributed throughout an oil-
bearing formation such as formation 37 because of capillary
action, in spite of gravitational forces tending to remove the
water to the bottom of the formationO The sand grains of the
oil-bearing formation matrix retain a film of salt water which,
in turn, attracts a film of oil. Although oil is a poor
conductor of electricity, the connate salt water distributed
throughout t~e formation is capable of transmitting an
electric current.
As may be seen in Figure 3~ the boreholes 30 and 31 allow
oil and salt water from formation 37 to enter the boreholes
and make contact with electrodes 38 and 39~ Upon application
of the electrical current from generator 32 to electrodes 38
and 39~ an electric current is passed between electrodes 38
and 39 through the oil-bearing formation 37 in substantial
isolation from the earth 34 above and below formation 37 by
means of the connate salt water contained within the formation
acting as an electrolyte. In the embodiment of Figure 4,
because of the effective electrical contact between the ends of
electrodes 38 and 39 within steel -casing section 36 and the
salt water within the casing and in contact with the electrode,
the effective size of the electrode is increased to the diameter
of the electricalIy conducting casing 36r
-15-
1~3585S7
The heating of the salt water within boreholes 30 and 31
or in casing section 36 by the action of the electrical
current will raise the temperature of the salt water
appreciably, often to 200 F. or greater. Often the pressures
in the borehole use several hundred psi and drive the heated
fluids from the formation up into the casing 35. These
temperatures can have a damaging effect on the non-conductive
casing 35, which can conveniently be fiherglass casing,
causing it to warp or buckle and collapse if the temperatures
rise appreciably over 200 F. In the embodiment shown in
Figure 4, the packer 41 seals the annulus between casing 36
and electrode 38 and prevents hot salt water from expanding up
into casing 35 and damaging the lower end of the casing.
In some cases it may be necessary to replenish the salt
water in electrically conducting casing 36 and in the
formation 37 surrounding casing 360 In that event, the solid
electrodes 38 and 39 shown in Figure 3 may be replaced with a
hollow tubular member acting as an electrode, such as jointed
strings of tubing. Thus salt water at the surface of the
borehole may be introduced into the conductivé casing 36 and
formation 37 through such a tubing string electrode to enhance
the electrical contact between the electrode and the formation
37.
The electrical current source 32 may conveniently be a
single-phase AC source of electric power, or it may be a
pulsed DC power source. The use of a DC power source may have
certain disadvantages, such as the high cost of obtaining a DC
source of sufficient voltage and current capacity, erosion of
-16-
~058557
the electrodes due to electrolysis, and the possibility o~
generating highly poisonous chlorine gas from the electrolysis
of salt water. However, under suitable conditions, it is
believed that DC power will be as e~fective as AC power.
When the source of electrical power is connected between
conductors 40 and electrodes 38 and 39, current will flow
through a series path comprised of conductor 40, the
resistance of the electrode 38 designated Re38, the resistance
of the water in the oil-bearing formation 37, designated Rw,
the resistance o~ the electrode 39, designated Re3g, and
conductor 40, as shown in Figure 16. The current flowing in
this circuit can be expressed mathematically as:
I = V
Re38 ~ Re39 + Rw
~,
and the power dissipated in the water will, of course, be
equal to I2RW. It will, therefore, be apparent that it is
very desirable that the resistance of the water providing a
conductive path between;electrode 38 and electrode 39 have a
high resistance as compared to the total series resistance of
the eleotrodes, Re38 + Re39. In ~act, to achleve this
relationship in some instance it may be desirable to utilize
electrodes formed of aluminum or similar material characteriæed
by a lower resistivity than steel. The current flowing through
the circuit can be controlled by varying the supply voltage
potential by means of regulating apparatus 46 or by varying
the resistivity of the waterO The power dissipated in the
water, acting as a resistor, is manifested in the ~orm of
thermal energy or heat which is in turn distributed to the
formation~ As the salt water temperature rises, the
-17-
lOS1~557
resistance of the salt water declines, t~us allowing a greater
current to flow through the formation.
The result of the flow of current between electrodes 38
and 39 through the connate water in the oil bearing formation
37 will be to produce an electric current flow throuyh the
oil-bearing earth formation 37, since the overlying or
underlying earth structures 34 are fully insulated ~rom
electrodes 38 and 39 by casing 3S. Accordingly, the electric
current flow will be substantially confined to the oil-bearing
formation 37 due to the insulation of the earth formation 34
from electrodes 38 and 39. The action of the electrical
current passing through earth formation 37 will heat the
formation due to the resistance of the salt water and because
of electrochemical reactions~with constituent elements of
earth formation 37, namely, the salt water and the oil~ will
enhance the flow characteristics of the oil within the earth
formation 37 and will provide increased internal pressure
within the formation 37 to drive the oil i.nto a producing
borehole, such as boreholes 33 in Figure 2~ remote from
electrode boreholes 30 and 31. The current will be conducted,
due to the resistance characteristics of the salt water,
through a lateral area within the earth formation 37 greater
than the area defined by the direct path between the spaced
boreholes 30 and 31~
The electrochemical action of the electrical current
will produce at least the following known phenomenao
lo Reduction in the viscosity of the oil in
the formation, thus enhancing the flow
-18-
1~58557
characteristics of the oil;
2. Generation o large volumes of gas in the
formation due to electrochemical action
with the oil and salt water in the formation;
3. Release of the oil and water from the ear~h
formation matrix, thus allowing the oil to
separate due to gravitational action to an
upper level o the formation and the salt
water to gravitate to a lower level of the
` ormation.
4. Production of heat in the formation matrix
traversed by the current as a direct result of
chemical reactions taking place with the
constLtuent elements of the formation, including
at least the salt water and the oiIO
: To reduce the visaosity of the oil, the electrical current
apparently causes an electrochemical action that changes the
: molecular structure o the oil. Of course, heat generated by
the electrical current will also alter ~he viscosity of the
: 20 oil. It is urther believed that the electrochemical action
o the electric current will increase the gravity of the oil
over a limited range of values
Tests in the ield, utilizing the two-well, single-phase
AC power installation, as shown in Figures 2 ana 3, have
- resulted in significantly elevated formation pressures, up to
: a 300 psi increase, over a large area, approximately 1,000
acres or more, as remote as 4,000-6,000 feet rom the electrode
well installationO In addition, many remote, open producing
--19~
~ C~S8~57
wells also produced a clear burning, volatile gas that it is
believed contained methane and ree hydrogen. A substantial
pressure was maintained in some of the producing wells even
after the electrode wells had been shut down for as long as
thirty days. This result was achieved after some 120,000 kw
of electrical power were injected into the producing formation.
Such production of gas within the producing formation can
provide energy within the formation to repressure the
reservoir if the natural energy of the reservoir is
insufficient to overcome the resistive forces such as the
orces of viscous resistance and the force of capillary action.
The source of the gases generated in the formation and
the reasons or its production are not fully understood at
this timeO But several explanations based on laboratory
experiments may be offeredO They are:
(a) production of free hydrogen and oxygen by
-~ electrolysis o the salt water contained in
the formation;
(b) chemical action of hydroxides, resulting from
electrolysis of the salt water, acting on the
oil in the formation;
(c) direct molecular conversion of large oil
molecules to hydrocarbon gas molecules such
as methane;
(d) release of gas molecules in solution in the
salt water present in the formation;
(e) release of solution gases by heat, such as
methane and carbon dioxide, present in the
-20-
~^~
~ C~S~5S7
oil;
() formation of hydrocarbon gases by action of
the hydrogen gases "hydrogenating" the oil;
and
(g) formation of carbon dioxide by the action
of nascent oxygen reacting with the carbon
molecules in the oil; and
(h) ormation o carbon dioxide by action o
nascent oxygen combining with carbonates
aommonly present in the salt water in some
oil-bearLng formations.
It is known that heating of oil in the formation will
release solution gases ~rom ~he oil and salt water~ Thus,
release of solution gas will~occur in the heated areas
surrounding the electrode boreholes, and release gases such as
methane gas and carbon dioxide dissolved in the oil. But the
~- large pressure increa-es encountered in the field under actual
test over widespread distances and the results of lab tests
cannot be accounted for solely on the basis of release of
solution gas by electrothermal actionO
Laboratory tests have shown that an oil and salt water
mixture will produce, under the action of an electrical
current, large volumes of free hydrogen and carbon dioxide,
and lesser volumes o free oxygen, methane, ethane, propane
and butanes pluso The free hydrogen is obviously the result
of the electrolysis of the salt water, which also produces
either free oxygen or a hydroxyl radical present in the water.
With nascent oxygen generated by electrolysis, the presence
-21-
``~
~OS85~;i7
of the carbon dioxide could be the result of (g) or (h) above.
Some of the hydrocarbon gases may be the resul~ of
"hydrogenation" of the oil by free or nascent hydrog~n as
described in (~) above.
In direct molecular conversion of a hydrocarbon molecule
chain to form molecules of hydrocarbons that remain in liquid
form and others that take the form of a gaseous hydrocarbon,
the electrical current is acting directly on the hydrocarbon
molecule to cause the conversion or breakdown for reasons not
'10 presently fully appreciated. But this phenomena could account
for a substantial part of the hydrocarbon gases produced in
the formation.
Methane is slightly soluble in water, due to a slight
attraction between methane molecules and water molecules.
~; However, lt is known that carbonates and bicarbonates present
in the water will increase the solubility of methane in the
water. In the ormation matrix, the connate water molecules
collect around methane molecules to form a cage-like film
held together by hydrogen bonds. Since the water molecules
have an unusually large dipole moment (1.8 Debye units), the
molecules rotate in response to an impressed electric fieldO
The exposed hydrogen protons of the water molecules turn
toward the negative potential of t~e electrical field. This
rotation of the water molecules in response to an electrical
field can break the hydrogen bonds between the water molecules,
thus releasing the methane molecule. This chemical action of
releasing the methane molecules trapped in the connate salt
water would also generate heat, which indicates that a heating
-22-
1C~5~35S7
effect due to chemical reactions also takes place in the
formation traversed by ~he current.
As hereinbefore mentioned, laboratory experiments have
-shown that oil will be released from sand grains under the
in1uence of an AC current, and it is believed that under
certain conditions such action will take place in a reservoir
formation. The reasons for this release o~ the oil and connate
water from the sand grains in the presence of an AC current
are not ully understood but may be the result of the rotation
of the water molecules in the connate water under influence of
~he electric field, as hereinabove described, that break
hydrogen bonds with the oil film that coats the connate water
droplet that surrounds the sand grains of the formation matrix~
Further the release of methane molecules from the connate salt
water, as above described, would also dislodge oil molecules
from the residual oil film that coats the connate water
. droplet surface, thus dislodging both the methane molecules to
~ .
foxm gas for pressurizing the formation and for freeing oil
molecules that tend to move, because of gravitational forces,
to the upper strata of the formation. The water freed of the
formation matrix would tend to gravitate to the lower portion
of the formationO Such a release of oil from the formation
matrix, and gravitating to the upper strata of the formation,
would make enhanced recovery of the oil a real possibility,
particularly in formations where water is the driving force
creating the reservoir energy~
~ ith the production of gas within the oil-producing
formation 37 ~see Figure 3), and the energy that the
-23-
~058557
production of such gas imparts to the formation, it can be
seen that the process can be utilized aither in a single
installation of a pair of boreholes as shown in Figure 2 and
Figur~ 3, or in a plurality of installations distributed
within a given field or reservoir, to restore energy to ~he
reservoir for creating a driving force for moving the oil from
the oil-bearing formation into a producing well bore. As seen
in Figure 2, a typical electrode well installation having wells
30 and 31 will cause a resulting increase in formation pressure
10 wi~hin the producing formation, thereby enhancing the recovery
of oil through producing wells 33. After substantial volumes
of gas have been generated in the producing formation and an
optimum ormation pressure is achieved, the electrode boreholes
30 and 31 may have power shut off for predetermined periods and~
only operate for selected periods of time to maintain the
desired formation pressure. Regulaking and timing apparatus
46 (see Figures 2 and 3) can be utilized to regulate the
current flow and automatically turn the currenk source off and .
on at desired intervalsO Such regulation o the current flow
can also be utilized to control pressures and temperatures in
the electrode boreholes.
In summary, a subsurface mineral bearing formation can be
- treated by establishing an electrical field within the
formation yenerally defined by a plurality of spaced electrodes
extending into the formation and by establishing in response
to said electrical field a zone of electrochemical activity in
the formation, the zone of electrochemical activity being
generally defined by the electrical field and resulting in
-24-
`: 105~35~7
electrochemlcal reactions with constituent elements of the
formation ~or increasing the internal pressure of the
formation over an area exceeding the zone of electrochemical
activity. The primary constituent elements of the earth
formation include salt water and oil. The electrochemical
reactions with the salt water and oil increase the internal
pressure of the earth formation by generating volumes o gas
within the formation and urther act to enhance the 10w
characteristics of the oil by lowering the viscosity of the
oil. In a secondary recovery operation, the oil can be
withdrawn from the formation in response to the increased
formation pressure through a producing borehole penetrating
the formation and spaced~from the zone of electrochemical
activity. Of course, oil could also be withdrawn within the
zone of electrochemical activity~
Referring now to~Figures 5 and 8t a diagrammatic view of
the distribution of three electrode wells disposed in a
triangular pattern in a field of oil-producing wells is shownO
Three electrode wells 50, 51 and 52 are shown spaced in a
triangular pattern, with electrical power supplied by source
53 and distributed to the electrodes in wells 50, 51 and 52
by conductors 55, 56 and 57, xespectively. A regulator and
timer apparatus 79 is connected to the power source for
regulating the current through the boreholes. The electrode
wells 50, 51 and 52 may be completed in the same manner as the
electrode wells 30 and 31 shown in Figures 3 and 4, and the
reference numbers in Figuxe 8 relating to the electrode
borehole 50 are identical to the reference numbers of borehole
-25-
~C~585S~
30 shown in Figures 3 and 4. In æractice, use of three-phase
AC power, with each of the thLee phases connected to one of
the electrodes of boreholes 50, 51 and 52, has been found to
be more efficient than use of single-phase AC power in a two-
well arrangement shown in Figure 2, for reasons to be further
explained. The three-well, three-phase AC electrode well
installation shown in Figures 5 and 8 will cause the same
electrochemical actions to take place in the formation 37 as
those described with respect to Figures 2-40 In actual
tests, substantial formation pressure increases were noted up
to 8,000-10,000 feet away after operation of khe three well
installation after only 40,000 kw were in~e-ted into the
producing formation. This is about one-third of the total kw
necessary to effect lesser pressure-increases in utilizing the
single~phase AC electrode installation as depicted in Figures
2 and 3.
- Referring urther to Figure 8~ a producing well bore 180
is shown having a conventional casing 181 perforated in the
upper strata 173 of formation 37 for reasons to be hereinafter
urther discussedO A tubing string 187, through which oil is
to be produced from formation 37, is disposed in the borehole
and centralized by packers 183 and 1840 Pump 188 pumps oil
through tubing 187 into a storage tank 189~
As hereinbefore discussed with relation to Figures 2 and
3~ one of the phenomena occurring as a result of the
electrochemical action of the electrical current is the
separation of the oil and water from the formation matrix and
the gravitation of the oil to an upper strata of the formation
-26-
~ 585S7
and the water to a lower strata o~ the ormationO Accordingly,
utilizing the three-well, three-phase AC power installation of
electrode boreholes 50, 51 and 52 (Fi~ure 8) the passage of
electrical current through ~ormation 37 would release oil and
salt water from tha sand matrix of formation 37, allowing the
oil to gravitate to an upper strata or level 173 while the
water would gravitate to a lower strata or level 175. If
producing well 180, remote from the electrode well installa-
tion is completed in strata or level 173, then oil recovery
would be enhanced, since no salt water from strata 175 would
be produced.
Referring now to Figures 2, 5, 6 and 7, power distribu-
tion in the earth formation can be explained. In Figure 6,
assumed lines of current flow are illustrated for the two
electrode arrangement shown in Figure 2O For simplicity all
curves are assumed to be circles~ Hence the lengths of the
current paths can be calculated from measurements of the radii
and angular lengths o~ arcsO ~ssuming the resistance to cur-
rent flow is directly proportional to khe length of the current
path, then the power dissipated can be calculated as:
P = I2R = V2
where: P is the power dissipated
I is the current
R is the resistance
V is the voltage impressed across the resistance
Substituting ~ ~length of the current path) for R:
V 2
the power at each circular arc relative to that along the
-27-
`` 1C~58557
direct line X between electrodes can be calculated.
Calculations show that greater than 50% of the power due
to the current flow will be dissipated in a circle whose
diameter is equal to the distance between the centers of the
two electrodes, as can be seen in the circle shown at A in
Figure 6, thus causing a zone within circle A of great
electrochemical acti~ity reacting with the salt water, oil
and other constituent elements of the formation. Of course,
a great amount of power will be dissipated in the formation
outside o circle A, and, correspondingly, chamical reactions
are also taking place in this greater zone~
Referring to Figure 7, a triangular spacing of electrodes
is shown as in Figure 5, with the application or three-phase
AC current to the three alectrode wells. Here three over-
lapping circles B, C and D are shown as khe greater than 50%
power dissipation zones between each of the three wells. As
can be seen by reerence to Figure 6, the three-well, three-
~` phase arrangeme~t txeats over twice the area that can betreated by a single installation of two wellsO In addition,
the overlapping zones of the power distribution circles may
enhance the electrochemical activity in those areasO thereby
enhancing the results obtainedO In field testing the spacing
between the two-well arrangement shown in Figure 2 was 100
feet while the three-well pattern shown in Figure 5 utilized a
200-foot spacing. From comparisons of Figures 6 and 7, it can
be seen that the area of formation treated by the electrical
field and the established electrochemical zone of activity
will be much larger than the area created by a two-well
-28-
`` ~05!3557
arrangement, and taking into account the increased spacing in
the three-well test, the power distribution may have been
increased by a factor of three or four or more. This can
reasonably explain why in actual field testing, as
hereinabove described, the three-well, three-phase AC
installatio~ obtained increased formation pressures over a
larger reservoir area with about a third of the pcwer required
in tha two-well single-phase AC testO
Accordingly, grea~er e~fects may result from multiple
electrode well patterns that treat as large a zone of the
formation as possible and practical. Increased spacing of the
electrodes may enhance results; however, more power will be
required to treat the formation volume as the separation of
the electrodes increases. Figure 9 illustrates a four-well
pattern in a triangular configuration with one electrode well
in the center. Electrode wells 123, 124 and 125 define the
triangular pattern and well 126 is positioned equidistant from
each of the three wells. AC or pulsed DC power is supplied
by a source 127 and is applied to wells 123, 124 and 125 by
conductors 129. ~ return path is provided by electrode well
126 and conductor 128~ In this configuration, three well-
pairs can be established with a voltage drop between well-
pairs as shown by El, E2 and E3. Figure 10 illustrates a
five-well pattern in a square or diamond configuration with
one electrode well in the center. The electrode wells 190,
191, 192 and 193 define the square or diamond pattern with
well 194 acting as the center well. A source of elactrical
power 195 is connected to electrode wells 190-lg3 by
-29-
~058557
conductors 197 and to the center electrode well 194 by means of
conductor 196. In this configuration~ four well-pairs are
established with a voltage drop between well pairs as shown
by E4, E5, E6 and E7. Obviously, other patterns having a
plurality o electrode pairs can be utilized to treat a
subsurace earth formation. The number, pattern and spacing
of the electrode wells will determine the pattern area, size
and intensity of the electrical field established and of the
electrochemical field established.
Referring now to Figure 11, another embodiment of an
electrode well apparatus is diagrammatically shown. The
apparatus may be utilized in a two-well installation, as shown
in Figures 2 and 3, or a three-well installation, as shown in
Figures S and 6. A borehole 50 is shown penetrating earth
formation 60 and oil-bearing formation 61. The borehole is
lined through the earth 60 with a non-conductive or
electrically insulàting casing 58, such as fiberglass, and is
lined in the oil-producing formation 61 by means of steel
casing section 62, ~oined to the insulating casing 58 by means
of a collar 64. The electrically conducting casing section 62
is conventionally perforated into the oil-bearing formation
61 by means of perforations 63~ A first tubing string 66 is
suspended within the insulating casing 58 and extends into
the steel casing section 62, terminating just above the lower
end o~ steel casing 62. Tubing string 66 is centralized
within the borehole 50 by means of a packer 65 which is set
just below the joint 78 of the insulated casing 58 and steel
casing section 62, for purposes which will be hereinafter
-30-
~58SS~7
further describedO A second tubing string 77 is also suspended
within casing 58, spaced from tubing string 66, and terminates
just above packer 65.
Casing 58 is sealed by means of a flanged cap or head 59
through which the tubing strings 66 ana 77 project. Tubing
string 66 acts as the electrode for the electrode well and is
energized by means o~ electrical power from a source such as
source 53 through conductor 55, as shown in Figure 5, or from
source 32 as shown in Figure 3.
As previously discussed, the heating action of the
electrical current passing through the salt water in the oil-
bearing ormation causes an increase o temperature within the
well bore. The temperatures in the immediate vicinity of the
electrode, and particularly within steel casing section 62 and
in the salt water surrounding tubing string 66, acting as the
electrode, can become quite high~ on the order of 200 F. or
higherO If the salt water within steel casing section 62
backed up into the insulating casing 58, the high temperatures
might result in damage to the insulating casing, such as
fiberglass, and damage to the borehole. Thus, packer 65 is
set just below the joint 78 between the insulating casing 58
and the steel casing 62 to insure that salt water will not
rise above packer 65 and contact the lower portion of
insulating casing 58.
- Under the pressures encountered in the well bore and the
temperatures produced by the process, the salt water within
the well bore and in the immediate surrounding area of the
oil-producing formation 61 may be reduced to steam, which is
-31-
-
J~S~3557
nct an electrical conductor. Accordingly, to enhance t~e
electrical contact between formation 61 and electrode 66, it
may be necessary to add salt water from time to time to the
borehole 50 from a salt water source 67, via piping 68 and 70
and pump 69, if necessary, through the tubing string 66 to the
interior o casing section 62. Thus, salt water can be
introduced into the interior of steel casing 62 and into the
formation 61 to maintain electrical contact with the connate
salt water in ~ormation 61. In addition, the absence of the
water conductor encourages electrical arcing which can damage
both the steel casing 62 and t~e electrode 66.
Even as hereinbefore described with packe.r 65 set to
prevent heated salt water from rising into and damaging the
lower portion of insulating casing 58, the joint 78 may still
become extremely hot because o heat conduction through casing
62 and collar 64; and to further alleviate the risk of damage
to casing 58, a system for cooling the joint 78 may be
utilized which includes filling the annular space within
casing 58 with a cooling fluid 71~ such as diesel oil or other
thin petroleums, or even water, and circulating the fluid
through tubing 77 by means o a pump 75, and piping sections
72, 74 and 76 and a cooler 730 The circulating 10w of fluid
through tubing string 77 over t~e heated joint 78 and casing
58 will cool the lower portion of fiberglass casing 58 and
maintain the temperature of the casing at an acceptable level.
~ eferring now to Figure 12, another embodiment of the
appara~us that may be utiliæed as an electrode well for use in
two-well installations such as those shown in Figures 2 and 3,
-32-
16~5855~
or in three-well installations as shown in Figures 5 and 8, is
diagrammatically illustrated~ A borehole 80 is shown
penetrating an earth formation 85 into an oil-producing
formation 86. The borehole 80 is lined with a non-conductive
or insulating casing 81, preerably fiberglass casing, through
the earth formation 85 and is l.ined in the oil-producing
~ormation 86 by means of a steel casing section 83D Steel
casing section 83 is conventionally completed utilizing
perforations 89 into the oil-producing formation 86. A string
of ~ubing 87 of smaller diameter than casing 81 is
concentrically suspended within casing 81 to a point
approximating the joinder of the earth formation 85 and the
oil-producing formation 86. Tubing 87 may either be
conventional steel tubing or may be an insulated or non-
conductive tubing. ~ string of suitable tubing 88 is
concentrically suspended:within tubing 87 and projects into
the interior of steel casing section 83 to act as an electrode
and to provide means of adding salt water to the formation, if
necessary, as previously descxibed with regard to the apparatus
shown in Figure llo Casing 81 is closed with a cap 82, and
tubing 87 is appropriately sealed to tubing 88. Packers 91
: and 92 are disposed between casing sections 83, the end of
tubing 87, and tubing 88 for centralizing and sealing the
casing section 83 from the chambers created by insulated casing
81 and the tubing 87~ as will be hereinafter further described.
Tubing 88 becomes an electrode when connected by means of
conductor 93 to an appropriate source of electrical power,
such as source 53, as shown in Figure 50 or the source of
105~35S7
electrical power 32, as shown in Figures 2 and 3. A salt
water tank 94 is connected to a pump 96 by means of piping 95,
the pump in turn being connected to tubing string 88 by means
of piping 87 for providing a means for pumping salt water into
the interior of steel casing section 83 and thence into the
formation 86 for the reasons hereinabove described with regard
to the apparatus shown in Figure 11.
Tubing 87 has perforations 90 completed just above the
area where packers 91 and 92 have been set for provlding
communication with ~he interior of tubing 87 and the interior
of casing 81~ Cooling fluid 100 is introduced into the
interior annular space of tubing 87, and can then be
circulated through tubing 87, through perforations 90, and
into the annular space of casing 81 to cause the fluid to 1OW
over the joint between insulating casing 81 and steel casing
section 83 to cool the Iower portion of casing 81 for the
purposes hereinabove described with regard to the apparatus
shown in Figure llo F1uid from tha interior of casing 81 will
be circulated through piping 101 to a cooler 102, and then
piped via piping 103 to pump 104, where the fluid is trans-
ported through piping 105 to the interior annular space 98 of
tubing 87. The cool fluid travels down the annular space 98
within tubing 87, out through perforations 90, over the lower
portion of the insulated casing 81, and returns through the
annular space 99 of casing 81 to return to the cooling means
102 via piping 101. In this way, cooling of the lower section
of the insulating casing 81 may be effectea for the purposes
hereinabove described~
-34-
~S8557
Re~erring to Figure 13, yet another apparatus embodiment
for e~uipping a well bore is shownO ~e apparatus of Figure
13 could be utilized in a two-well installation shown in
Figures 2 and 3, or in a three-well installation shown in
Figures 5 and 8. A borehole 159 is shown penetrakiny the
earth 164 into an earth ~ormation or oil-bearing ormation
165. The borehole 159 is lined with conventional steel casing
160 from the sur~ace to a lower point in the earth 164, and
then lined with an electrically non-conducting or insulating
casing section 1610 The borehole in formation 165~is lined
with an electrically conducting casing I62. Collars 163
couple casing sections 160, 161 and 162 together. A fiberglass
or other electrically insulat m g tubing 167 is suspanded in
~; borehole lS9 and centralized,and supported by packer 166.
~ Packer 166 also seals ~he annular space between tubing 167 and
; ~ casing section 161 for purposes to be hereinafter further
explained. Casing 162 has a plurality of perforations 169
disposed therein into the formation 165.
An electrode 168 of suitable material is disposed
concentrically~within tubing string 167 dcwn into formation
1650 An insulated head 170 seals casing 160 around tubing
167, ar.d a suitable~head seals tubing 167 around electrode
168. Electrical power from a suitable source is applied to
electrode 168 via conductor 171. Piping conduit 172 is
connected with the interior of tubing 167 for introducing salt
water into the borehole, if necessary, as hereinabove described
in connection with the previous embodimentsO
In this embodiment, the borehole is fully insulated with
-35-
~0585S~7
electrically insulating casing. The purpose of the fully
insulated casing of previous embodiments is to insulate the
electrode from the earth structure for preventing a direct
current path between the electrode and the earth structure
overlying the oil-bearing formation. In addition, the
insulation of the borehole is to prevent a return current path
from the electrode disposed in the earth formation back through
the borehole to said overlying earth structure. In the
embodiment of Figure 13, a direct current path from the earth
structure 164 is prevented by insulating tubing 167 and can be
enhanced by filling the annulus surrounding tubing 167 with an
insulating fluid such as oil 176. If insulating casing section
161 is of sufficient length, a return current path from the
electrode 168 in formation 165 will be effectively broken,
thereby effectively insuIating electrode 168 from a return
current path through borehole 159 into earth structurq 164.
This isolates the electrical current in formation 165 as
previously described.
During operation of the electrode well, formation fluids
will tend to back up into tubing 167, e~erting substantial
pressures on the interior of the tubing, and the addition o
oil 176 in the casing annulus can also help equalize this
pressure on the insulating tubing. Control of the current
flow through electrode 168 and formation 165 for controlling
pressure and temperature can be achieved as hereinbefore
described by appropriate regulation and/or timing equipmentO
In Figure 14 a simple embodiment of apparatus for
equipping an electrode well is shownO Borehole 200 is shown
-36-
58557
penetrating earth strata 206 and oil-bearing earth formation
207. An insulated cable 202 having an electrical insulating
jacket or co~er 203 and a conductor 204 is disposed in the
borehole. Insulating jacket 203 is skripped from the end of
the conductor 204 to e~pose the conductor throughout the earth
formation ~or acting as an eleckrode. Gravel or ot~er sui~able
porous material is packed around exposed conductor 204 in ~he
borehole portion extending into the formation 207 to permit
the electrode to have communication with formation fluids.
The borehole above formation 207 can then be filled with
insulating cement 201 to give structural support to cable 202
and to support the borehole without having to set casing. The
upper surface end of the cable 202 is connected to a suitable
source of electrical power by means of conductor 208.
Formation fluids, such as salt water and oil, wlll flow
through the porous gra~el 205 and make contact with electrode
204 for establishing the electrical fiela in the formation
207O
Referring now to Figures 5, 8 and 15, a three-electrode
well installation, as shown in Figure 5, could be effectively
patterned as shown in Figure 15 to progressively cover an
increasingly larger area and thereby both heat an increased
area of the oil-bearing formation and stimulate gas production
in the formation over a much wider area. In Figure 15, three
electrode wells 110 could be drilled and completed in a
triangular pattern shown as pattern lllo This installation
could be utilized for a predetermined period of ti~e, and then
by drilling another electrode well 110, a second triangular
` 1058557
pattern 112 could be accomplished and operated for a second
predetermined period o~ time. It is possible to exhaust some
of the formation fluids in the area defined by the electrode
well bores. However, tests demonstrata that relocation of the
electrode pattern provides new formation fluids and also moves
new fluids to old areasO By drilling additional electrode
wells 110, a series of triangular patterns 113-122 could be
accomplished, thus distributing the electrical current ~ er a
broad reservoir area.~ The gas production in the oil-bearing
formation would be enhanced, and the thermal action of the
electrical current would be distributed over a much wider
area in the reservoir oil-bearing formationO Of course, any
electrode wells 110 not being utilized as electrode wells in a
particular installation pattern may be rigged as producing
wells. In actual field tests the spacing of the three
electrode wells was 200 feet, but it is believed that much
~ larger distances may be utilized to enlarge an installation
; ~ pattern and enhance the heat generation and electrochemical
generation of gas in situ to pressure the formationO The use
of the patterning in 113-122 produces twelve injection patterns
for thirteen wells and when completed can be used for six
patterns, each four times as large as any original patternO
As hereinbefore described~ laboratory tests have re~ealed
that AC current will cause oil droplets to be released from
the sand grains of a simulated formation matrix and that
separation of the oil and water is caused by gravitational
forces that will force the oil to rise in the matrix while
water is displaced to a lower level in the matrixO It is
-38-
- ~58SS~
belie~ed tha~ under certain geological conditlons ~his same
result can be achieved in an actual reservoir formation.
Accordingly, the pattern development disclosed in Figure 15
could be especially useful to release residual oil remaining
within the reservoir pore space and allowing it to move by
gravitational force to the upper reaches of the oil-bearing
formation for enhancing production from that strata. This is
p æ ticularly true of the sugyested patterns shown in Figure 15
where broad areas of the formation could be treated simultan-
eously and successive patterns swept across a predeterminedarea to treat the formation, generate gas in situ and release
the residual oil in the formation pore space to gravitate to
the upper strata of the formation.
In discussing the three~well, three-phase AC
installations, as shown particularly in Figures 5 and 8, a
simplified circuit schematic of the system can be represented
as shown in Figure 17~ ~ith a three-phase AC source 53 (see
Figure 5) connected between electrodes 50 and 51 by conductors
55 and 56, current Ie will flow through conductor 55, tubing
electrode 50, represented by resistor Re50, through one leg of
an assumed "delta" load comprising the conductive substances
of the formation, primarily salt water, represented by
resistor RWl, and then through conductor 56. Assuming a
balanced three-phase power source and a balanced "load"
~the earth formation) then:
Vl = IeRe50 + IeResl + Iw wl
but, since Ie = ~ Iw
Vl = ~IWRe50 + ~IWRe51 + IwRwl
-39-
~ 585~7
v = Cw ~ '~Re50 ~ ~Re51 wl
I = ~1
~ (Re50 ~ Re51) ~ Rwl
However, in actual practice the "delta" load repre-
senting the oil-bearing ormation may not be balanced due to
geological variations, and ~w in the ~arious legs of the
"delta" system load then would not be balanced and the current,
Iw~ through RWl, ~w2 and Rw3 would be unequal. Whlle this is
true, loads can be balanced in the generator by creating more
resistance in the surface cables, or by changing the shape of
:
the pattern to fit resistance requirements.
Referring now to Figure 18, yet another embodiment of the
apparatus is illustrated. In Figure 18, an electrode borehole
130 is drilled through earth formation 133 and oil-bearing
formation 134 and is shown having an electrically insulating
casing 135 and a steel casing section 137 set in the oil~
bearing formation 1340 the two casing being ~oined by a collar
13&o ~A tubing string 136 is ins~erted within well bore 130
,
~ and extends into the steel casing section I37. Tubing string
: ~ :
136 is centralized by means of a packer 139 that seals the
space~within the interior of steel casing section 137 and the
interior o insulating casing 135, as hereinabove described
:
for pre~ious embodiments shown in Figures 3, 11 and 12O Of
course, the borehole 130 may be constructed alternatively as
disclosed in previous embodiments. Two additional boreholes
131 and 132 (not shown in detail) are completed to form a
triangular three-electrode well installation, as shown in
Figure 5; for instance. Of course, other multiple well
--40-
lOS#SS~
patterns could be utilized. Three-phase AC power would be
provided by a generator 140 and applied to electrodes 136,
144 and 158 of boreholes 130, 131 and 132, respectively, by
conductors 141, 142 and 143, respectively~ Three-phase ~C
power would be applied to the oil-bearing formation 134 to
produce heat and gas in situ, as hereinabove described, to
promote oil recovery. A plurality o~ producing boreholes 145,
only one of which is diagrammatically shown penetrating earth
formation 133 and the oil-bearing formation 134, would be
conventionally completed to produce oil from ormation 134.
The oil may bb produced through a tubing string 146 by various
conventional means and supplied via piping 1~7 to a pump 148
for transfer to an oil storage tank 1490 This would be
conventional production and storage to this point, assisted by
use o~ the invention to enhance oil recoveryO But in a large
reservoir, which would contain substantial oil reserves
sufficient to support an industrial plant having a need for
large volumes of fuel oil as an energy source, the exhaust or
"flue" gases from such a plant could be utilized in further
enhancing the production capabilities of the reservoir.
Assuming the industrial plant to be an electrical generating
plant utilizing oil-fired turbines, the plant could be
constructed immediately adjacent the reservoir area for
receiving the produced oil and for minimizing the distance
that the flue gases must be transported prior to use in the
reservoir. This embodiment is described in relation to an
electrical generating plant, but other industrial plants having
a high oil fuel energy need and creatin~ substantial quantities
-41-
" ~S85S7
o~ useful exhaust gases could, of course, be substituted.
Referring again to ~igure 18, the produced oil would be
transferred from the oil storage tanks 149 to the electric
generating plant 151 by means of pumps 150 for supplying the
crude oil to appropriate treating meanst if necessary (not
shown), to prepare the crude oil for iring the turbina
generators~ The oil-fired turbines would generate electrical
power ~or distribution by the generating plant in the power
company's power distribution system. The outpuk flue gases of
the oil-fired turbines would be collected at 152 and routed
khrough piping 153, pump 154 and piping 155 to a pipe or tub-
ing 157 disposed in in~ection borehole 156, as shown
penetrating the earth formation 133 and t~e oil~producing
formation 1340 In actual operation, the injection borehole
156 would be located in or adjacent the pattern of the three
electrode wells:130~ 131 and 13Z, although not so shown in
the diagrammatic illustration of Figure 18. The hot
pressurized flue gas introduced into the oil-bearing formation
134 through injection well 156 will lower the viscosity of the
oil and enhance its flow characteristicsO The flue gas from
an oil-fired turbine or engine will contain carbon monoxide
and carbon dioxide as well as other gases. The carbon dioxide
- and carbon monoxide gases, whether heated or not, will tend to
combine with the oil in the producing formation, and in so
doing combine chemically with the oil to improve its flow
characteristicsO In addition, the flue gas will orginarily be
hot (in the range of 800-1,000 F.) and will act to dissolve
tars and lower the viscosity of the oilO In addition, pumping
-42-
05~35S7
the heated flue gas back into the formation under pressure
adds to the formation pressure, thereby enhancing the
ormation driving energy.
The 1ue gas will have a considera~le BTU content since
not all o the hydrocarbons have been burned, and ~he long
term injection of the gas into khe ormation will create a
reservoir o gas having considerable BTU value that could
create a source of gas for uture reco~ery and use as a fuel.
The use of the flue gas injection process would be
ideally suited for use in an area where there is a large
reservoir of very viscous oil or sands having tar oils of
extremely low gravity and high viscosity that can be produced
by use o the invention herein described and recovered in
quantities sufficient to operate an industrial plant that, in
turn, would generate sufficient quantities of ~xhaust or flue
gases that could be returned to the oil formation or the
purposes hereinabove mentioned. As a exampleJ a one-megawatt
electrical generating plant could utilize 40,000 barrels of
oil a day produced from the oil reservoir and generate
200,000,000 cubic eet of gas a day for reinjection into the
. oil-bearing ormationO This arrangement could have particular
economic appeal to many industries dependent upon oil or
natural gas as a fuel, since natural gas is in short supply
and oil may economically be recovered by use of the electrical
processO
In addition, there are environmental benefits accruing
from the utilization of the installation and process shown in
Figure 18, since the flue gases would be returned into the
~0585S7
ground or use in enhancing recovery o~ oil and not released
into the atmosphere as a pollutant.
Although the present invention has heretofore been
described with respect to its utility in effecting the
recovery of oil, it will be apparent that the concept of the
presen~ invention is also applicable to various other uses
such as the removal o impurities from waste water and other
industrial fluids~ In one such embodiment, the liquid to be
puri~ied is collected in a vat or other container which is
charged with a brine or other suitable electrolytic solution.
A suitable alternating current may then be applied to the
terminals of two electrodes which are immersed in a spaced
apart relationship in ~he contents of the container.
Accordingly, the current passing through the eIectrolyte and
between the two electrodes will produce separation of solids
from the liquid, and these solids will then settle to the
bottom of the container as a sludge. This same process can
be used as a pre-distillation step in the purification of
water for ordinary drinking purposes, inasmuch as impurities
such as iron, gypsum and magnesium oxides may be easily
separated out in this manner before the distillation step is
performedO Combustion gases and smokes can also be removed
from air in this manner by passing the polluted air through a
chamber containing a pair of electrodes adapted to be charged
in this manner.
~ umerous variations and modifications may obviously be
made in the structure and processes herein described without
departing from the present invention. Accordingly, it should
-44-
1058SS7
be clearly understood that ~he forms of the invention herein
described and shown in the ~igures of the accompanying
drawings are illustrakive only and are not intended to limit
the scope o~ the invention.
-45-
