Secondary recovery process

Claim 1

A process for recovering hydrocarbons from a hydrocarbon-bearing formation containing acid-soluble components having at least one injection well and at least one production well penetrating the said formation and in fluid communication therewith, which comprises displacing through the formation a composition comprising an acidic aqueous polymer solution and recovering hydrocarbons through the production well, the said acidic aqueous polymer solution comprising a material selected from the group consisting of: (I) Terpolymer A consisting of repeating units of: ##STR2## (II) Terpolymer B consisting of repeating units of ##STR3## (III) Terpolymer I or II alkoxylated with about 2 to about 100 weight percent of a substance selected from the group consisting of ethylene oxide and a mixture of ethylene oxide and propylene oxide wherein in the said mixture the weight percent of ethylene oxide ranges from about 60 to about 95, the said material being dissolved in an aqueous solution of a non-oxidizing mineral acid, wherein in Terpolymer A the weight percent of vinylpyrrolidone units will vary from about 65 to about 80, the weight percent of vinyl acetate units from about 8 to about 15 with the balance being 2-acrylamido-2-methylpropanesulfonic acid, wherein in Terpolymer B the weight percent of vinylpyrrolidone units will vary from about 65 to about 80, the weight percent of hydroxyethyl acrylate units from about 8 to about 15 with the balance being 2-acrylamido-2-methylpropanesulfonic acid, wherein the said terpolymer is present in the said acidic aqueous polymer solution in a concentration of from about 0.1 to about 10 weight percent and wherein the number average molecular weight of the said terpolymer is from about 10,000 to about 2,000,000.