Petroleum production method

• US 4,228,853 A
• Filed: 06/21/1978
• Issued: 10/21/1980
• Est. Priority Date: 06/21/1978
• Status: Expired due to Term

• Current Assignee: Harvey A. Herbert, John P. Govier
• Original Assignee: Harvey A. Herbert, John P. Govier
• Inventors: Govier, John P., Harvey, A. Herbert
• Primary Examiner(s): Novosad, Stephen J.
• Application Number:
  US05/917,730
• Time in Patent Office: 853 Days
• Field of Search: 166/248, 166/272, 166/275, 166/274, 166/65 R, 166/269, 166/268
• US Class Current: 166/248
• CPC Class Codes: E21B 17/003 with electrically conducting or insulating means E21B17/028 and E21B17/023 take precedence
• CPC Class Codes: E21B 43/121 Lifting well fluids monitoring of down-hole pump systems E21B47/008
• CPC Class Codes: E21B 43/162 Injecting fluid from longitudinally spaced locations in injection well
• CPC Class Codes: E21B 43/2401 by means of electricity
• CPC Class Codes: E21B 43/30 Specific pattern of wells, e.g. optimising the spacing of wells

Abstract

A method for electrical resistance heating of select portions of a natural underground reservoir, in a geologic formation, that contains both crude oil and water. Through selective resistance heating, oil viscosity is reduced in the select portion of the reservoir. Thus, portions which would not normally be contacted by injected fluids may be rendered susceptible to recovery by water flooding or other recovery process. Thermal expansion of heated oil also facilitates oil recovery. Resistance heating is accompanied by injection of low resistivity liquid that functions both as a conductor, through which current passes into the select portions, and as a medium for displacing oil to a production well. The low resistivity liquid also conveys convective heat, which contributes to viscosity reduction. Alternatively, the method of the invention can be used for altering the drainage pattern of a well.

Claims

1. A method for facilitating recovery of oil from a crude oil reservoir by selective electrical resistance heating of a portion of the reservoir which would normally be substantially bypassed by fluid injected into the formation in which the reservoir is located, the method comprising the steps of:

establishing a series electrical circuit for passing current through the formation along a directed path differing from the naturally predominant path of injected fluid flow, said naturally predominant path being substantially occupied by high resitivity fluid, said circuit comprising;

a source of alternating current electric power,

a first subterranean electrode electrically connected to one terminal of said source and located in or in proximity to a first well in said formation,

a second subterranean electrode electrically connected to the other terminal of said source and located in or in proximity to a second well in said formation, and

a portion of an oil reservoir in said formation that contains oil and water and is located between said electrodes substantially separate from a naturally predominant path for flow of injected fluids from an injection well through said formation but affords a current path of lesser electrical resistance between said electrodes than that along said naturally predominant path or any alternative path through the formation that is entirely outside said portion;

injecting a low resistivity liquid through an injection well into a region of said formation that forms a part of said circuit in series with said first electrode and said portion; and

passing alternating current from said power source through said circuit so as to cause selective electrical resistance heating of said portion, whereby the resistance to the flow of oil contained in said portion is reduced and oil is swept out of said portion by said low resistivity liquid.

4. A method as set forth in claim 1, 2 or 3 wherein said first well is an injection well through which said low resistivity liquid is injected.

5. A method as set forth in claim 4 wherein said high resistivity fluid is substantially fresh water.

6. A method as set forth in claim 4 wherein said high resistivity fluid comprises a fluid miscible with oil, whereby removal of oil from the low permeability layer is facilitated by the solvent action of said miscible liquid.

7. A method as set forth in claim 6 wherein said miscible high resistivity fluid is selected from the group consisting of alcohols, miscible microemulsions, liquid hydrocarbons, liquefied hydrocarbon gases, high pressure gas, rich gas, liquefied carbon dioxide, and liquefied hydrogen sulfide.

8. A method as set forth in claim 4 wherein said high resistivity fluid comprises a viscous liquid which serves as a plugging agent and impedes the subsequently injected low resistivity liquid from flowing into the high permeability layer so as to facilitate recovery from the low permeability layer through the action of the low resistivity liquid.

9. A method as set forth in claim 4 wherein said second well is a recovery well.

10. A method as set forth in claim 1, 2 or 3 wherein the resistivity of said low resitivity liquid is lower than the resitivity of said water.

11. A method as set forth in claim 1, 2 or 3 wherein low resistivity liquid is continuously injected during electrical resistance heating so that convection heating arising from penetration of heated low resistivity liquid into said portion contributes to the heating of the oil therein for reducing its viscosity and promoting its recovery.

26. A method as set forth in claim 1, 2, 3, 12, 20 or 22 wherein the recovery of oil from the selectively heated portion is promoted by the displacement of oil by gas evolved as a consequence of heating.

27. A method as set forth in claim 1, 2, 3, 12, 20 or 22 wherein selectivity of heating is enhanced by injection of a resistive fluid in a marginal zone between the portion to be heated and an adjoining region which would otherwise have sufficient conductivity to divert part of the current.

28. A method as set forth in claim 27 wherein high resistivity liquid is injected near the base of an oil zone that is to be selectively heated.

29. A method as set forth in claim 27 wherein a resistive fluid is injected near the top of an oil zone that is to be heated.

30. A method as set forth in claim 27 wherein a gas phase is generated at the top of an oil zone by allowing reservoir pressure to decline until the pressure of the oil at the top of the zone is below its bubble point.

31. A method as set forth in claim 1, 2, 3, 12, 20 or 22 wherein said low resistivity liquid is injected prior to application of current so that resistance heating power consumption is minimized in the vicinity of said first electrode and correspondingly maximized in said portion, whereby electrical energy is conserved while effecting selective electrical resistance heating.

2. A method for recovering additional oil from a geologic formation which has been subjected to a prior injection of high resistivity fluid through an injection well for recovery of oil from a recovery well to which oil has been moved by reservoir pressure and the force of said high resistivity injected fluid, the method comprising the steps of:

establishing a series electrical circuit comprising;

a source of alternating current electrical power,

a first subterranean electrode electrically connected to one terminal of said source and located in said formation in or in proximity to a first well in said formation,

a second subterranean electrode electrically connected to the other terminal of said source and located in said formation in or in proximity to a second well in said formation, and

a portion of an oil reservoir, located between said electrodes in said formation, that contains oil and salt water and has been substantially bypassed by the injection of said high resistivity fluid;

injecting a low resistivity liquid through an injection well into a region of said formation that forms a part of said circuit in series with said first electrode and said portion; and

passing alternating current from said power source through said circuit so as to cause selective electrical resistance heating of said portion, whereby the resistance to the flow of oil contained in said portion is reduced and oil is swept out of said portion by said low resistivity liquid.

3. A method for recovering additional oil from a layered crude oil reservoir having layers of unequal permeabilities in a geologic formation that has been subjected to prior injection of a high resistivity fluid through an injection well for removal of oil from the reservoir to a recovery well where it is produced, the method comprising the steps of:

establishing a series electric circuit comprising;

a source of alternating current electric power,

a first subterranean electrode electrically connected to one terminal of said source and located in said formation in or in proximity to a first well in said formation,

a second subterranean electrode electrically connected to the other terminal of said source and located in said formation in or in proximity to a second well in said formation; and

a relatively low permeability layer of a reservoir, located between said electrodes in said formation, that contains oil and salt water and has been substantially bypassed by the injection of said high resistivity fluid;

injecting a low resistivity liquid through an injection well into a region of said formation that forms a part of said circuit in series with said first electrode and said portion; and

passing alternating current from said power source through said circuit so as to cause selective electrical resistance heating of said low permeability layer, whereby the resistance to the flow of oil contained in said layer is reduced and said oil is swept out of said layer by said low resistivity liquid.

12. A pattern flooding method for recovering oil from a crude oil reservoir in a geologic formation wherein oil is recovered from a portion of a reservoir that is substantially separate from the naturally predominant path for fluid flow between any injection well and a recovery well in the pattern so that said portion normally is substantially bypassed by injected fluid, the method comprising the steps of:

establishing a series electrical circuit comprising;

a source of alternating current electrical power,

a first subterranean electrode electrically connected to one terminal of said source and located in said formation in or in proximity to a first well in said formation,

a second subterranean electrode electrically connected to the other terminal of said source and located in said formation in or in proximity to a second well in said formation, and

a portion of said reservoir that contains oil and water and is in a region substantially separate from the naturally predominant path for flow of injected fluid from any injection well to any recovery well in said pattern;

injecting through an injection well into a region of said formation that forms a part of said circuit in series with said first electrode and portion a low resistivity liquid having a resistivity less than that of the connate water in said formation; and

passing alternating current from said power source through said circuit so as to cause selective electrical resistance heating of said portion whereby the resistance to the flow of oil contained in said portion is reduced and oil is swept out of said portion by said low resistivity liquid.

13. A method as set forth in claim 12 wherein each of said first and second wells is an injection well through which said low resistivity liquid is injected.

14. A method as set forth in claim 13 wherein a pattern comprising a plurality of injection wells is disposed around a recovery well and the electrical polarity of the electrode in or in proximity to each injection well is oppposite that of the electrodes in or in proximity to the adjacent injection wells on either side thereof.

15. A method as set forth in claim 14 wherein the injection wells and recovery well are arranged in a 5-spot pattern comprising four injection wells of alternating electrode polarity at the corners of a substantially rectangular quadrilateral and a recovery well substantially in the center thereof.

16. A method as set forth in claim 14 wherein pattern flooding is commenced by injection of said low resistivity liquid at each injection well and electrical resistance heating is commenced after recovery of oil has begun from along the naturally predominant fluid flow path between the injection wells and the recovery well.

17. A method as set forth in claim 16 wherein simultaneous electrical resistance heating and low resistivity liquid injection are carried out for a period sufficient that convective heating arising from penetration of heated low resistivity liquid into said portion contributes to the heating of the oil in said portion for reducing its viscosity and promoting its recovery.

18. A method as set forth in claim 12 wherein each electrode is located in or in proximity to a production well so that said portion is located along a path between production wells that is normally bypassed by injected fluid.

19. A method as set forth in claim 18 wherein a pattern flood is carried out without application of electrical current until low resistivity liquid breaks through at a production well;

fresh water is injected at each injection well after breakthrough so that the conductance along the naturally predominant fluid flow paths between injection and production wells is sufficiently low to significantly limit the flow of current through the areas surrounding the injection wells, and current is thereafter applied in said circuit.

20. A pattern flooding method for recovering oil from a crude oil reservoir in a geologic formation, wherein oil is recovered from a portion substantially separate from the naturally predominant path for flow of injected fluid from any injection well to any recovery well and thus normally bypassed by injected fluid, the method comprising the steps of:

providing a pattern comprising a plurality of injection wells disposed about a recovery well;

establishing between each injection well and each other injection well adjacent thereto in said pattern an electrical circuit comprising;

a source of alternating current electric power,

a first subterranean electrode electrically connected to one terminal of said source and located in said formation in or in proximity to a first injection well,

a second subterranean electrode electrically connected to the other terminal of said source and located in said formation in or in proximity to an injection well adjacent to said first injection well, whereby the electrical polarity of the electrode in proximity to each injection well in said pattern is opposite that of the electrode at each said adjacent injection well on either side thereof, and

a portion of the oil reservoir, located between said electrodes and said formation, that contains oil and water and is substantially separate from the naturally predominant path for flow of injected fluid between either of said injection wells and a recovery well so that said portion would be normally bypassed by injected liquid,

injecting low resistivity liquid through said injection wells into regions of said formation that form parts of said circuit in series with said first and second electrodes, respectively, and said portion; and

passing alternating current from said power source through each circuit so as to cause selective electrical resistance heating of each said portion whereby the resistance to the flow of oil contained in each portion is reduced and oil is swept out of said portion by said low resistivity liquid.

21. A method as set forth in claim 20 wherein the injection wells and recovery well are arranged in a 5-spot pattern comprising four injection wells of alternating electrode polarity at the corners of a substantially rectangular quadrilateral and a recovery well substantially in the center thereof.

22. A method for selectively heating a relatively oil-rich portion of a crude oil reservoir in a geologic formation so as to alter the drainage pattern relative to a well in said formation and facilitate recovery of oil therefrom, the method comprising the steps of:

injecting into a relatively oil-lean portion of said reservoir adjacent said rich portion a high resistivity fluid for increasing the electrical resistivity of said lean portion;

establishing a series electric circuit comprising;

a source of alternating current power,

a first subterranean electrode electrically connected to one terminal of said source and located in said formation in or in proximity to a first well in said formation,

a second subterranean electrode electrically connected to the other terminal of said source and located in said formation in or in proximity to a second well in said formation, and

said rich portion located between said electrodes;

injecting a low resistivity liquid through an injection well into a region of said formation that forms a part of said circuit in series with said first electrode and said rich portion; and

passing alternating current from said power source through said circuit so as to cause selective electrical resistance heating of said rich portion, whereby the resistance to the flow of oil contained in said rich portion is reduced so that drainage of oil from said rich portion to a recovery well is promoted.

23. A method as set forth in claim 22 wherein said high resistivity fluid is substantially fresh water.

24. A method as set forth in claim 22 wherein said rich portion is located in the up-dip region of a dipping reservoir, connate water is located in the down-dip region thereof, a production well penetrates the oil/water interface, fresh water is injected at the production well into the water phase so as to increase the resistivity thereof, and current is thereafter applied in said circuit so as to selectively heat the oil layer and promote drainage toward the production well.

25. A method as set forth in claim 22, 23 or 24 wherein said low resistivity liquid is injected during electrical resistance heating so that convective heating arising from penetration of heated low resistivity liquid into said portion contributes to the heating of the oil therein for reducing its viscosity and promoting recovery.