Sweep improvement in enhanced oil recovery

Claim 2

A process, including sweep improvement, for recovering oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, wherein said fluid flows through regions of least flow resistance, contacting oil therein and displacing it toward a production well, and producing such displaced oil from said production well, (b) monitoring the displacing fluid/displaced oil ratio and discontinuing the injection of displacing fluid when the volume of displaced fluid-to-volume of displaced oil produced reaches a predetermined value, (c) injecting an aqueous slug comprising a mixed surfactant of (1) at least one surfactant foaming agent selected from the group consisting of anionic, non-ionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, said aqueous slug flowing through regions of least flow resistance, comparable to the flow pattern of the displacing fluid, (d) resuming injection of the displacing fluid, such that the newly-injected displacing fluid contacts and disperses throughout the aqueous mixed system slug, generating foam, and wherein the sum of the values of the characteristics of foam quality and foam stability of the foam generated by said mixed surfactant system exceeds the sum of the values of the characteristics of foam quality and foam stability of the foams formed by the action of the individual components (1) and (2) above, based on the concentration by weight of the components employed, with the foam resulting from the interaction of the displacing fluid and the aqueous mixed surfactant system producing an increase in flow resistance to said displacing fluid in regions previously having least flow resistance, such that said displacing fluid flows through regions which prior to the generation of foam had a higher flow resistance than the resistance of the regions of least flow resistance referred to in part (c), above, thus contacting and displacing additional quantities of oil toward a production well and improving the sweep efficiency of the process, and, (e) recovering the displaced oil from said production well.

Claim 3

The method of claim 1, wherein the displacing fluid is selected from the group consisting of carbon dioxide, nitrogen, air, methane, ethane, propane, butane, hydrogen sulfide, flue gas, and steam.

Claim 4

The method of claim 1, wherein the ratio of the displacing fluid slug volume to the aqueous slug volume varies from about 100:1 to about 1:1.

Claim 5

The method of claim 1, wherein, in the mixed surfactant system, the weight ratio of surfactant foaming agent to lignosulfonate foaming agent varies from about 10:1 to about 1:10.

Claim 6

The method of claim 1, wherein, in the aqueous slug, concentration of the mixed surfactant system varies from about 0.01% (w/v) to about 10% (w/v).

Claim 7

The method of claim 1, wherein the displacing fluid is selected from carbon dioxide, nitrogen, and air.

Claim 8

The method of claim 1, wherein the ratio of the displacing fluid slug volume to the aqueous slug volume varies from about 20:1 to about 1:1.

Claim 9

The method of claim 1, wherein, in the mixed surfactant system, the weight ratio of surfactant foaming agent to lignosulfonate foaming agent varies from about 4:1 to about 1:4.

Claim 10

The method of claim 1, wherein, in the aqueous slug, the concentration of the mixed surfactant system varies from about 0.1% (w/v) to about 10% (w/v).

Claim 11

A process, including sweep improvement, for recovering oil from a subterranean oil-bearing formation comprising: (a) injecting a displacing fluid selected from the group consisting of carbon dioxide, nitrogen, and air into a subterranean oil-bearing formation through an injection well, such that the displacing fluid flows through regions of least flow resistance, contacting oil and displacing it toward a production well and producing said displaced oil from a production well, (b) monitoring the displacing fluid/displaced oil volume ratio and discontinuing the injection of displacing fluid when this ratio reaches a predetermined value, (c) injecting an aqueous slug comprising a mixed surfactant of (1) at least one foaming agent selected from the group consisting of anionic, nonionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, wherein the sum of the properties of foam quality and foam stability of a foam generated from said mixed surfactant system exceeds the sum of the properties of foam quality and foam stability generated by the action of the individual components (1) and (2), based on the concentration by weight of the components employed, said aqueous slug flowing through regions of least flow resistance, comparable to the flow pattern of said displacing fluid, and wherein (A) in the mixed surfactant system, the weight ratio of surfactant foaming agent/lignosulfonate foaming agent varies from about 4:1 to about 1:4, and (B) in the aqueous slug, the concentration of the mixed surfactant system varies from about 0.1% w/v to about 10% w/v, (d) injecting displacing fluid, wherein the newly-injected displacing fluid contacts and disperses throughout the aqueous mixed surfactant slug, generating foam, said foam resulting in an increase in flow resistance in the regions previously at least flow resistance such that the displacing fluid flows through regions which prior to the generation of the foam had a higher flow resistance than the resistance of the regions of least flow resistance referred to in part (c), above, contacting and displacing additional oil toward a producing well, thus improving sweep efficiency, and wherein the ratio of displacing fluid slug volume/aqueous slug volume varies from about 20:1 to about 1:1, and (e) recovering the displaced oil from a producing well.

Claim 12

A process, including sweep improvement, for recovering oil from a subterranean oil-bearing formation comprising: (a) injecting a displacing fluid selected from the group consisting of carbon dioxide, nitrogen, and air into a subterranean oil-bearing formation through an injection well, such that the displacing fluid flows through regions of least flow resistance, contacting oil and displacing it toward a production well and producing said displaced oil from a production well, (b) monitoring the displacing fluid/displaced oil volume ratio and discontinuing the injection of displacing fluid when this ratio reaches a predetermined value, (c) injecting an aqueous slug comprising a mixed surfactant of (1) at least one foaming agent selected from the group consisting of anionic, nonionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, wherein the sum of the properties of foam quality and foam stability of a foam generated from said mixed surfactant system exceeds the sum of the properties of foam quality and foam stability generated by the action of the individual components (1) and (2), based on the concentration by weight of the components employed, said aqueous slug flowing through regions of least flow resistance, comparable to the flow pattern of said displacing fluid, and wherein (A) in the mixed surfactant system, the weight ratio of surfactant foaming agent/lignosulfonate foaming agent varies from about 4:1 to about 1:4, and (B) in the aqueous slug, the concentration of the mixed surfactant system varies from about 0.1% w/v to about 10% w/v, (d) injecting displacing fluid, wherein the newly-injected displacing fluid contacts and disperses throughout the aqueous mixed surfactant slug, generating foam, said foam resulting in an increase in flow resistance in the regions previously at least flow resistance such that the displacing fluid flows through regions which prior to the generation of the foam had a higher flow resistance than the resistance of the regions of least flow resistance referred to in part (c), above, contacting and displacing additional oil toward a producing well, thus improving sweep efficiency, and wherein the ratio of displacing fluid slug volume/aqueous slug volume varies from about 20:1 to about 1:1, and (e) recovering the displaced oil from a producing well.

Claim 15

The method of claim 11, wherein the weight ratio of the surfactant foaming agent to the lignosulfonate foaming agent is about 1:1.

Claim 16

The method of claim 11, wherein the volume of the aqueous slug of the volume surfactant system is about 5 vol.% of the pore volume of the area from which the oil is to be displaced.

Claim 19

An enhanced oil recovery method, including sweep improvement, for the recovering of oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, displacing oil from said formation toward a production well and collecting said displaced oil from the production well, (b) monitoring the displacing fluid/displaced oil ratio and discontinuing the injection of displacing fluid when said ratio reaches a predetermined value, (c) injecting, into said formation through said injection well, an aqueous slug comprising a mixed surfactant of (1) at least one surfactant foaming agent selected from the group consisting of anionic, non-ionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, said aqueous slug flowing through regions at least flow resistance, comparable to the flow pattern of the displacing fluid, (d) resuming injection of the displacing fluid into the formation through the injection well, thus forming foam and displacing oil in the formation toward a production well, and, (e) recovering the displaced oil from said production well.

Claim 20

An enhanced oil recovery method, including sweep improvement, for the recovering of oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, displacing oil from said formation toward a production well and collecting said displaced oil from the production well, (b) monitoring the displacing fluid/displaced oil ratio and discontinuing the injection of displacing fluid when said ratio reaches a predetermined value, (c) injecting, into said formation through said injection well, an aqueous slug comprising a mixed surfactant of (1) at least one surfactant foaming agent selected from the group consisting of anionic, non-ionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, said aqueous slug flowing through regions at least flow resistance, comparable to the flow pattern of the displacing fluid, (d) resuming injection of the displacing fluid into the formation through the injection well, thus forming foam and displacing oil in the formation toward a production well, and, (e) recovering the displaced oil from said production well.

Claim 21

The method of claim 15, wherein the weight ratio of the surfactant foaming agent to the lignosulfonate foaming agent is about 1:1.

Claim 22

An enhanced oil recovery method, including sweep improvement, for the recovering of oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, contacting and displacing oil from said formation toward a production well, and producing said displaced oil from the production well, (b) monitoring the displacing fluid/displaced oil ratio produced at the production well, and discontinuing the injection of displacing fluid when said ratio reaches a predetermined value, (c) injecting, into said formation through said injection well, an aqueous slug comprising a mixed surfactant system of (1) at least one surfactant foaming agent selected from the group consisting of anionic, non-ionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, (d) resuming injection of the displacing fluid into the formation through the injection well, wherein the sum of the properties of foam quality and foam stability of a foam generated from said mixed surfactant system exceeds the sum of the properties of foam quality and foam stability generated by the action of the individual components (1) and (2), based on the concentration by weight of the components employed, and, (e) recovering the displaced oil from said production well.

Claim 23

An enhanced oil recovery method, including sweep improvement, for the recovering of oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, contacting and displacing oil from said formation toward a production well, and producing said displaced oil from the production well, (b) monitoring the displacing fluid/displaced oil ratio produced at the production well, and discontinuing the injection of displacing fluid when said ratio reaches a predetermined value, (c) injecting, into said formation through said injection well, an aqueous slug comprising a mixed surfactant system of (1) at least one surfactant foaming agent selected from the group consisting of anionic, non-ionic, and amphoteric surfactants having foam-producing characteristics, and (2) a lignosulfonate foaming agent, (d) resuming injection of the displacing fluid into the formation through the injection well, wherein the sum of the properties of foam quality and foam stability of a foam generated from said mixed surfactant system exceeds the sum of the properties of foam quality and foam stability generated by the action of the individual components (1) and (2), based on the concentration by weight of the components employed, and, (e) recovering the displaced oil from said production well.

Claim 32

An enchanced oil recovery method including sweep improvement for the recovery of oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, displacing oil from said formation toward a production well, and collecting said displaced oil from the production well, (b) monitoring the displacing fluid/displaced oil ratio, and discontinuing the injection of displacing fluid when said ratio reaches a predetermined value, (c) injecting, into said formation through said injection well, an aqueous slug comprising: (1) at least one foaming agent selected from the group consisting of anionic, nonionic, and amphoteric surfactants having foam-producing characteristics, (2) a lignosulfonate foaming agent, and (3) reservoir brine, (d) resuming injection of the displacing fluid into said formation through said injection well and displacing oil in said formation toward a production well, and, (e) recovering the displaced oil from the production well.

Claim 33

An enchanced oil recovery method including sweep improvement for the recovery of oil from a subterranean oil-bearing formation, comprising: (a) injecting a displacing fluid into said formation through an injection well, displacing oil from said formation toward a production well, and collecting said displaced oil from the production well, (b) monitoring the displacing fluid/displaced oil ratio, and discontinuing the injection of displacing fluid when said ratio reaches a predetermined value, (c) injecting, into said formation through said injection well, an aqueous slug comprising: (1) at least one foaming agent selected from the group consisting of anionic, nonionic, and amphoteric surfactants having foam-producing characteristics, (2) a lignosulfonate foaming agent, and (3) reservoir brine, (d) resuming injection of the displacing fluid into said formation through said injection well and displacing oil in said formation toward a production well, and, (e) recovering the displaced oil from the production well.