Petroleum production method

Claim 7

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.

Claim 8

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

Claim 9

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.

Claim 10

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.

Claim 11

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.

Claim 12

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

Claim 13

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.

Claim 14

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.

Claim 15

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.

Claim 16

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.

Claim 17

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.

Claim 18

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.

Claim 19

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.

Claim 20

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.

Claim 21

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.

Claim 22

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.

Claim 23

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.

Claim 24

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.

Claim 25

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.

Claim 26

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.

Claim 29

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

Claim 30

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.

Claim 31

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.

Claim 32

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.

Claim 33

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.

Claim 34

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.

Claim 35

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.

Claim 36

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.

Claim 37

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.