U.S. patent application number 13/882795 was filed with the patent office on 2013-10-24 for method for enhanced oil recovery from carbonate reservoirs.
This patent application is currently assigned to ELECTRO-PETROLEUM, INC.. The applicant listed for this patent is George Chilingar, Mohammed Haroun, J. Kenneth Wittle. Invention is credited to George Chilingar, Mohammed Haroun, J. Kenneth Wittle.
Application Number | 20130277046 13/882795 |
Document ID | / |
Family ID | 46172186 |
Filed Date | 2013-10-24 |
United States Patent
Application |
20130277046 |
Kind Code |
A1 |
Haroun; Mohammed ; et
al. |
October 24, 2013 |
METHOD FOR ENHANCED OIL RECOVERY FROM CARBONATE RESERVOIRS
Abstract
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.
Inventors: |
Haroun; Mohammed; (Abu
Dhabi, AE) ; Wittle; J. Kenneth; (Williamsburg,
PA) ; Chilingar; George; (Los Angeles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Haroun; Mohammed
Wittle; J. Kenneth
Chilingar; George |
Abu Dhabi
Williamsburg
Los Angeles |
PA
CA |
AE
US
US |
|
|
Assignee: |
ELECTRO-PETROLEUM, INC.
Villanova
PA
|
Family ID: |
46172186 |
Appl. No.: |
13/882795 |
Filed: |
November 30, 2010 |
PCT Filed: |
November 30, 2010 |
PCT NO: |
PCT/US2010/058329 |
371 Date: |
July 12, 2013 |
Current U.S.
Class: |
166/248 |
Current CPC
Class: |
E21B 43/16 20130101;
E21B 43/26 20130101 |
Class at
Publication: |
166/248 |
International
Class: |
E21B 43/16 20060101
E21B043/16 |
Claims
1. A method of enhancing oil recovery from a carbonate reservoir
comprising the steps of: a. selecting an underground formation
comprising an oil-bearing carbonate reservoir; b. 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; c. 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 d.
withdrawing oil from at least one of said bore holes.
2. The method of claim 1, wherein the electrically conductive
element to which said cathode is connected is disposed in a bore
hole from which oil is withdrawn.
3. The method of claim 1 further including the step of
superimposing an AC component on the DC current to effect
decomposition of the withdrawn oil and a decrease in the viscosity
thereof.
4. The method of claim 1, wherein said formation undergoes an
acidizing pre-treatment to increase permeability of said
formation.
5. A method of fracturing an oil-bearing carbonate rock formation,
said method comprising subjecting said formation to long term
electrical stress.
6. The method of claim 5, wherein said electrical stress is applied
to said formation by means comprising: a. positioning two or more
electrically conductive elements at spaced apart locations in
proximity to said formation; and b. 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.
7. The method of claim 6, wherein said electrical stress is applied
for a time period ranging from 1 day to 12 months.
Description
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 (CaCO.sub.3) and dolomite
(CaMg(CO.sub.3).sub.2). They are anionic complexes of
(CO.sub.3).sup.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 "heavy" 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The following summary as well as the following description
will be better understood when read in conjunction with the
accompanying figures in which:
[0014] FIG. 1 is a schematic diagram of a DC electrokinetic method
for enhancing oil recovery from DC oil-bearing carbonate reservoir
in accordance with this invention;
[0015] FIG. 2 is a schematic diagram of one embodiment of a DC
electrokinetic method for enhancing oil recovery from an
oil-bearing carbonate reservoir; and
[0016] FIG. 3 is a schematic diagram of another embodiment of a DC
electrokinetic method for enhancing oil recovery from an
oil-bearing carbonate reservoir.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Referring to the figures in general, and to FIG. 1
specifically, there is shown an underground formation 11 composed
primarily of oil-bearing carbonate rock, in which the method of the
invention is practiced. A suitable carbonate reservoir may be
selected or determined using well established geologic sampling
techniques. The oil-wet or water-wet condition of the carbonate
rock present in the formation can be assessed according to the
previously reported method of Chilingar and Yen, supra. Typically,
such oil-bearing formations are found beneath the upper strata of
earth, commonly referred to as overburden, at a depth on the order
of 1,000 feet or more below the surface. Communication from the
surface 12 to the formation 11 is established through one or more
bore holes. In FIG. 1, communication from the surface 12 to the
formation 11 is established through spaced-apart boreholes 13 and
14. Borehole 13 functions as an oil-producing well, whereas the
adjacent hole 14 is a special access passage provided for the
transmission of electricity to the formation 11.
[0018] The present invention can be practiced using a multiplicity
of electrically conductive elements or electrodes in one or more
boreholes. The boreholes may be drilled in a variety of vertical,
horizontal or angular orientations and configurations. In FIG. 1,
two electrodes are disposed into vertically drilled boreholes. 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 DC electric power source 2 is connected to the first
electrode 15. The relatively negative terminal or cathode of the
power source is connected to a second electrode 16 associated with
producing well 13. Between the electrodes, the electrical
resistance of connate water 4 present 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 electrically conductive path is much
shorter than any alternative path traveling through the overburden
to "ground."
[0019] To create the electric field, a periodic voltage is produced
between the electrodes 15, 16. In one embodiment, the periodic
voltage is established using pulsed DC power. In another
embodiment, the voltage may be a DC-biased signal with a ripple
component produced under modulated AC power. See U.S. Pat. No.
6,877,556. 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 normally carried by connate formation water.
Electrical current is conducted through the formation by naturally
occurring electrolytes in the groundwater. If necessary or
desirable, aqueous electrolyte may be introduced into the formation
to modify the conductivity of the connate water. A detailed system
and procedure for injecting electrolyte solution into an
underground formation is described in U.S. Pat. No. 3,782,465. See
also, U.S. Pat. No. 5,074,986.
[0020] 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 compounds. In addition, the ripple component must
have a frequency range above about 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 about 2,000 hertz.
[0021] Referring still to FIG. 1, the steps for practicing the
method for enhancing oil recovery from a carbonate reservoir 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 the region of the formation 11 immediately
surrounding it. 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 and/or added aqueous
electrolyte, as the case may be, in the interstices of the
oil-bearing formation provides a conductive 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 formation
itself.
[0022] As current is conducted across formation 11, electrolysis in
the formation water occurs. Electrolysis generates 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 tend to cause
decomposition of 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.
[0023] 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.
[0024] 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
enhanced oil recovery may be used in conjunction with other
processes, such as electrothermal recovery or electroosmotic
treatment. For instance, electroosmotic pressure can be applied to
the oil deposit by switching to straight DC 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. See
U.S. Pat. No. 3,782,465.
[0025] 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.
Carbonate reservoirs 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.
[0026] The above-described method may be used in combination with
one or more pre-treatments to improve the permeability of the
formation. For example, the present method may be used in
conjunction with an acidizing pre-treatment. A suitable acid is
introduced into one or more borehole and an electric field is
applied, as described above, to drive the acidizing agent into the
formation. Migration of the acid is promoted by electroosmosis, but
may be assisted by other means, such as well pumping. The electric
field is effective to drive the acid into regions of the formation
that cannot readily be reached using other available
procedures.
[0027] 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. 2, 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 (anode) of high-voltage DC
electric power source 102 is connected to the first well casing
113. The relatively negative terminal (cathode) on the power source
is connected to the second well casing 114. In this arrangement,
well casing 113 acts as a cathode at the producing well, 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, or any
added aqueous electrolyte, as the case may be, 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."
[0028] The present method may include one or more electrodes placed
at ground level. See, e.g., U.S. Pat. No. 4,495,990. Referring now
to FIG. 3, an alternate oil recovery system is shown with a first
electrode 215 placed below the earth's surface (marked "E") and a
second electrode 216 is located at ground level in proximity to an
underground oil-bearing formation 211. The first electrode 215 is
disposed in a borehole 214 that penetrates the formation 211. The
first electrode 215 is located within the formation, but may be
located outside the formation, depending on the desired deployment
and range of the electric field. The second electrode 216 is
constructed on the earth's surface. By means of an insulated cable
in access hole 214, a terminal on high-voltage DC 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 contained 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.
[0029] Although not wishing to be bound by a specific theory, it is
believed that when oil-bearing carbonate rock is exposed in situ to
DC electrokinetic treatment, as described herein, the wettability
of the carbonate rock surface is altered. Specifically, the
carbonate rock surface is rendered more hydrophilic than before
electrokinetic treatment, thereby causing oil to be more easily
displaced from the rock surface, e.g., by water flooding.
[0030] The technology described herein may also be beneficially
applied to induce fracturing of an oil-bearing carbonate rock
formation by subjecting the formation to long term electrical
stress.
[0031] The fracturing method may be carried out by the steps of
positioning two or more electrically conductive elements at spaced
apart locations in proximity to the formation; and passing a
controlled amount of electric current along an electrically
conductive path through the formation, with the electric current
being 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
comprising at least one of connate formation water and an aqueous
electrolyte introduced into said formation.
[0032] Fracturing can be achieved by applying electrical stress in
the manner described above for a time period of from 1 day to about
12 months, more preferably from about 1 week to about 6 months, and
most preferably for at least 2 weeks. The electrical stress may be
applied at 2 volts/cm for the duration of the fracturing treatment,
or it may be initiated and maintained at 2 volts for a
predetermined time and thereafter reduced to a lower value, e.g., 1
volt/cm.
[0033] The following examples describe the invention in further
detail. These examples are provided for illustrative purposes only,
and should in no way be considered as limiting the invention.
[0034] In order to show the viability of the use of electrokinetics
for the production of oil from carbonate rock two tests were run in
the laboratory. One of the tests was conducted on a core taken from
a cap rock and the second on a core taken from a producing
petroleum oil reservoir.
[0035] Both cores were first saturated with formation brine and
then water flooded with 39.degree. API Light Crude oil. Normal
laboratory practice for the preparation of these cores was used in
both these tests.
[0036] Test 1 was performed on the Cap rock which had a diameter of
3.6 cm and a length of 5.5 cm. The core was placed in a sample
holder which allowed for a voltage gradient to be established
across the core and a Direct Current power supply having a variable
current control was used during the test. The measured permeability
of this rock was 5.53 mD for water and 94.3 mD to oil. The
viscosity of the oil used in this experiment was 19.5. cp. The
pressure to saturate the core with water was 40.8 psig, while the
pressure necessary to saturate the core with oil was 54.4 psig. A
voltage gradient of 2 volts/cm was imposed across the sample.
Current was applied from 0 to 244 mA. The flow of oil and water was
observed at various currents and the test established that the
lowest current at which flow could be maintained was 82 mA or at a
current density of 8.16 mA/cm. In addition to the flow established
in this low permeability core when the core was removed from the
sample holder the rock had fractured as a result of the current
passage through the core which ultimately would have increased the
permeability of the rock.
[0037] Test 2 was performed on the carbonate reservoir formation
rock core, which had a diameter of 1.8 cm and a length of 5.15 cm.
The measured permeability of this core to water was measured at
5156 mD and 4204 mD to oil. The pressure needed to saturate this
core was much lower, 0.2 psig for water and 4.6 psig to oil. The
same voltage gradient of 2 volts/cm was used in this test with a
resultant flow of water and oil being observed with a current of 18
to 21 mA.
[0038] The test results described above are summarized in the
following table.
TABLE-US-00001 Cum L D c.s.Area L/A PV Q visc. Press. K Vol cm cm2
cm2 cm-1 cc ml/min cp Psi md ml Por Vol 5.50 3.60 10.18 0.540 11.46
2 1.04 49.80 5.53 25 2.0 5.15 1.80 2.54 2.024 12.68 2 1.04 0.20
5156.70 50 4.0 5.50 3.60 10.18 0.540 12.68 2 19.504 54.40 94.93 75
5.0 5.15 1.80 2.54 2.024 12.68 2 19.504 4.60 4204.77 100 6.0
indicates data missing or illegible when filed
[0039] The results of these tests demonstrate that the use of
electrokinetics can be effective to move oil and water under a
voltage stress and current flow that will depend on the initial
permeability of the formation, the salinity of the formation and
the applied current.
[0040] A number of patent and non-patent publications are cited in
the foregoing specification in order to describe the state of the
art to which this invention pertains. The entire disclosure of each
of these publications is incorporated by reference herein.
[0041] While certain embodiments of the present invention have been
described and/or exemplified above, various other embodiments will
be apparent to those skilled in the art from the foregoing
disclosure. The present invention is, therefore, not limited to the
particular embodiments described and/or exemplified, but is capable
of considerable variation and modification without departure from
the scope of the appended claims.
[0042] Furthermore, the transitional terms "comprising",
"consisting essentially" of and "consisting of", when used in the
appended claims, in original and amended form, define the claim
scope with respect to what unrecited additional claim elements or
steps, if any, are excluded from the scope of the claim(s). The
term "comprising" is intended to be inclusive or open-ended and
does not exclude any additional, unrecited element, method, step or
material. The term "consisting of" excludes any element, step or
material other than those specified in the claim and, in the latter
instance, impurities ordinary associated with the specified
material(s). The term "consisting essentially of" limits the scope
of a claim to the specified elements, steps or material(s) and
those that do not materially affect the basic and novel
characteristic(s) of the claimed invention. All methods of
enhancing oil recovery from carbonate reservoirs that embody the
present invention can, in alternate embodiments, be more
specifically defined by any of the transitional terms "comprising",
"consisting essentially of" and "consisting of".
* * * * *