Correlation of weighted effect of different ions and surfactant composition for surfactant flood

Claim 3

A method according to claim 1 wherein said Na + weight equivalent concentration is within the range of 800 to 20,000 parts per million by weight based on the weight of water in said brine.

Claim 4

A method according to claim 2 wherein the total divalent ion concentration is less than 500 parts per million by weight and said surfactant is a petroleum sulfonate.

Claim 5

A method according to claim 1 wherein said cosurfactant is at least one of isobutyl alcohol, secondary butyl alcohol, n-butyl alcohol, n-amyl alcohol, or isoamyl alcohol and mixtures thereof.

Claim 6

A method according to claim 1 wherein said sodium equivalent concentration is such that said system is within said three-phase region.

Claim 7

A method according to claim 1 wherein said three-phase region occurs over a sodium equivalent concentration of less than 1 percentage point.

Claim 8

A method according to claim 1 wherein said sodium equivalent concentration is within the range of 800 to 20,000 parts per million, the total divalent ion concentration is less than 500 parts per million by weight based on the water in said brine, said surfactant is a petroleum sulfonate having an average equivalent weight within the range of 390 to 425, and said cosurfactant is a C 4 or C 5 alcohol.

Claim 9

A method according to claim 1 wherein an initial surfactant composition on equilibration with oil corresponding to that produced results in a system in the alpha region of said phase volume diagram and wherein said surfactant system is produced by one of (A) using a lower Na + equivalent concentration relative to said initial surfactant composition, or (B) using a surfactant system having a smaller hydrophobic portion relative to said initial surfactant composition, or (C) using a more water-soluble cosurfactant relative to said initial surfactant composition.

Claim 10

A method according to claim 8 wherein said surfactant system is produced by using a lower Na + equivalent concentration.

Claim 11

A method according to claim 8 wherein said initial surfactant composition utilized a petroleum sulfonate as a surfactant and wherein said surfactant system is produced by using a sulfonate having a lower equivalent weight.

Claim 12

A method according to claim 8 wherein said surfactant system is produced by using a more water-soluble cosurfactant than in said initial surfactant composition.

Claim 13

A method according to claim 1 wherein said initial surfactant composition equilibrated with oil corresponding to that to be produced is in the gamma region of a phase volume diagram and said surfactant system is produced by at least one of (A) using a higher sodium equivalent concentration than in said initial surfactant composition, or (B) using a surfactant having a larger hydrophobic portion than in said initial surfactant composition, or (C) using a less water-soluble cosurfactant than in said initial surfactant composition.

Claim 14

A method according to claim 12 wherein said surfactant system is produced by using a higher Na + equivalent concentration.

Claim 15

A method according to claim 12 wherein said initial surfactant composition is produced utilizing a petroleum sulfonate and wherein said surfactant system is produced by using a higher equivalent weight sulfonate.

Claim 16

A method according to claim 12 wherein said surfactant system is produced by utilizing a less water-soluble cosurfactant than that utilized in said additional surfactant composition.

Claim 17

A process for recovering oil from a subterranean oil-bearing reservoir comprising the steps of: (a) injecting into said reservoir through at least one injection well a surfactant system comprising surfactant, cosurfactant and brine composed of water and electrolyte which surfactant system is tailored to both the specific water in the formation and the specific oil in the formation to give phase behavior associated with high oil recovery on equilibration with said oil said surfactant system being prepared using brine having Na + , Ca ++ and Mg ++ with said brine having a Na + weight equivalent concentration equal to the actual Na + concentration plus the Ca ++ concentration times about 14 plus the Mg ++ concentration times about 16 so that said surfactant on equilibration with oil corresponding to that to be produced is in the three-phase region of a phase volume diagram or at least immediately adjacent said three-phase region in systems exhibiting three-phase behavior over a narrow range of salinity; (b) thereafter injecting a mobility buffer fluid behind said surfactant system; and (c) thereafter injecting a drive fluid behind said mobility buffer thus forcing said oil toward at least one recovery well.

Claim 18

A process for recovering oil from a subterranean oil-bearing reservoir comprising the steps of: (a) injecting into said reservoir through at least one injection well a surfactant system comprising surfactant, cosurfactant and brine composed of water and electrolyte which surfactant system is tailored to both the specific water in the formation and the specific oil in the formation to give phase behavior associated with high oil recovery on equilibration with said oil said surfactant system being prepared using brine having Na + , Ca ++ and Mg ++ with said brine having a Na + weight equivalent concentration equal to the actual Na + concentration plus the Ca ++ concentration times about 14 plus the Mg ++ concentration times about 16 so that said surfactant on equilibration with oil corresponding to that to be produced is in the three-phase region of a phase volume diagram or at least immediately adjacent said three-phase region in systems exhibiting three-phase behavior over a narrow range of salinity; (b) thereafter injecting a mobility buffer fluid behind said surfactant system; and (c) thereafter injecting a drive fluid behind said mobility buffer thus forcing said oil toward at least one recovery well.

Claim 19

A process for recovering oil from a subterranean oil-bearing reservoir comprising the steps of: (a) injecting into said reservoir through at least one injection well a surfactant system comprising a surfactant, cosurfactant, and brine, said surfactant system prepared by steps comprising: (1) analyzing water available for the system for Na + , Ca ++ , and Mg ++ ; and (2) forming said brine having a Na + weight equivalent concentration equal to the actual Na + concentration plus the Ca ++ concentration times about 14 plus the Mg ++ concentration times about 16, so that said surfactant on equilibration with oil corresponding to that to be produced is in the three-phase region of a phase volume diagram or at least immediately adjacent said three-phase region in systems exhibiting three-phase behavior over a narrow range of salinity; and (b) recovering said oil.

Claim 20

A process for recovering oil from a subterranean oil-bearing reservoir comprising the steps of: (a) injecting into said reservoir through at least one injection well a surfactant system comprising a surfactant, cosurfactant, and brine, said surfactant system prepared by steps comprising: (1) analyzing water available for the system for Na + , Ca ++ , and Mg ++ ; and (2) forming said brine having a Na + weight equivalent concentration equal to the actual Na + concentration plus the Ca ++ concentration times about 14 plus the Mg ++ concentration times about 16, so that said surfactant on equilibration with oil corresponding to that to be produced is in the three-phase region of a phase volume diagram or at least immediately adjacent said three-phase region in systems exhibiting three-phase behavior over a narrow range of salinity; and (b) recovering said oil.

Claim 21

A method according to claim 17 wherein said sodium equivalent concentration is within the range of 800 to 20,000 parts per million by weight based on the weight of water in said brine.

Claim 22

A method according to claim 17 wherein the total divalent ion concentration is less than 500 parts per million by weight and said surfactant is a petroleum sulfonate.

Claim 23

A method according to claim 17 wherein said three-phase region occurs over a sodium equivalent concentration of less than 1 percentage point.

Claim 24

A method according to claim 17 wherein an initial surfactant composition on equilibration with oil corresponding to that produced results in a system in the alpha region of a phase volume diagram and wherein said surfactant system produced by one of (A) using a lower Na + equivalent concentration relative to said initial surfactant composition, or (B) using a surfactant system having a smaller hydrophobic portion relative to said initial surfactant composition, or (C) using a more water-soluble cosurfactant relative to said initial surfactant composition.

Claim 25

A method according to claim 17 wherein said surfactant system is produced by using a lower Na + equivalent concentration.

Claim 26

A method according to claim 17 wherein said initial surfactant composition utilized a petroleum sulfonate as a surfactant and wherein said surfactant system is produced by using a sulfonate having a lower equivalent weight.

Claim 27

A method according to claim 17 wherein said injection of said surfactant is preceded by preflush and wherein said surfactant system is produced by using a lower Na + equivalent concentration than in said initial surfactant composition.

Claim 28

A method according to claim 17 wherein an initial surfactant composition equilibrated with oil corresponding to that to be produced is in the gamma region of a phase volume diagram and said surfactant system is produced by at least one of (A) using a higher sodium equivalent concentration relative to said initial surfactant composition, or (B) using a surfactant having a larger hydrophobic portion relative to said initial surfactant composition, or (C) using a less water-soluble cosurfactant relative to said initial surfactant composition.

Claim 29

A method according to claim 25 wherein said surfactant system is produced by using a higher Na + equivalent concentration.

Claim 30

A method according to claim 25 wherein said initial surfactant composition was produced utilizing a petroleum sulfonate and wherein said surfactant system is produced by using a higher equivalent weight sulfonate.

Claim 31

A method according to claim 25 wherein said surfactant system is produced by utilizing a less water-soluble cosurfactant than that utilized in said initial surfactant composition.