Oil recovery process using a polymer slug with tapered surfactant concentration

Claim 1

A method of recovering oil from a subterranean oil-bearing formation having in communication therewith at least one injection well and at least one production well comprising: a. injecting into the formation via the injection well a slug comprising an aqueous polymer solution containing a small amount of a surfactant, b. injecting water into the formation via the injection well; and c. recovering oil from the formation via the said production well and wherein the concentration of the surfactant in the said slug is increased as the slug is injected into the said formation, and wherein the water injected in step (b) contains a small amount of a solubilizing agent selected from the group consisting of: a. a compound of the formula: ##STR7## wherein R is alkyl of from 1 to about 16 carbon atoms; wherein R' is alkylene of from 2 to 4 inclusive carbon atoms; m is an integer of from 4 to about 60, A is selected from the group consisting of hydrogen, sodium, potassium and the ammonium ion and wherein R" is selected from the group consisting of hydrogen, alkyl of from 1 to about 16 carbon atoms and --R'O(CH 2 CH 2 O) m A; b. a sulfated compound of the formula: ##STR8## wherein R, R', m and A have the same meaning as in (a) above, and R" is selected from the group consisting of hydrogen, alkyl of from 1 to about 16 carbon atoms and --R'O(CH 2 CH 2 O) m SO 3 A, and c. a sulfonated compound of the formula: ##STR9## wherein R, R' and A have the same meaning as in (a) above; wherein n is an integer of from about 4 to about 60 and R" is selected from the group consisting of hydrogen, alkyl of from 1 to about 16 carbon atoms and --R'O(CH 2 CH 2 O) n CH 2 CH 2 SO 3 A.

Claim 2

A method of recovering oil from a subterranean oil-bearing formation having in communication therewith at least one injection well and at least one production well comprising: a. injecting into the formation via the injection well a slug comprising an aqueous polymer solution containing a small amount of a surfactant, b. injecting water into the formation via the injection well; and c. recovering oil from the formation via the said production well and wherein the concentration of the surfactant in the said slug is increased as the slug is injected into the said formation, and wherein the water injected in step (b) contains a small amount of a solubilizing agent selected from the group consisting of: a. a compound of the formula: ##STR7## wherein R is alkyl of from 1 to about 16 carbon atoms; wherein R' is alkylene of from 2 to 4 inclusive carbon atoms; m is an integer of from 4 to about 60, A is selected from the group consisting of hydrogen, sodium, potassium and the ammonium ion and wherein R" is selected from the group consisting of hydrogen, alkyl of from 1 to about 16 carbon atoms and --R'O(CH 2 CH 2 O) m A; b. a sulfated compound of the formula: ##STR8## wherein R, R', m and A have the same meaning as in (a) above, and R" is selected from the group consisting of hydrogen, alkyl of from 1 to about 16 carbon atoms and --R'O(CH 2 CH 2 O) m SO 3 A, and c. a sulfonated compound of the formula: ##STR9## wherein R, R' and A have the same meaning as in (a) above; wherein n is an integer of from about 4 to about 60 and R" is selected from the group consisting of hydrogen, alkyl of from 1 to about 16 carbon atoms and --R'O(CH 2 CH 2 O) n CH 2 CH 2 SO 3 A.