Patent ID: 8607865

Claim:
A process for mineral oil extraction by means of Winsor type III microemulsion flooding, in which an aqueous surfactant formulation comprising at least one ionic surfactant, for the purpose of lowering the interfacial tension between oil and water to <0.1 mN/m, is injected through at least one injection borehole into a mineral oil deposit, and crude oil is withdrawn from the deposit through at least one production borehole, wherein the surfactant formulation comprises at least one surfactant of the general formula R 1 —O-(D) n -(B) m -(A) l —XY − M + , where R 1 is a linear or branched, saturated or unsaturated, aliphatic and/or aromatic hydrocarbon radical having 8 to 30 carbon atoms, A is ethyleneoxy, B is propyleneoxy, and D is butyleneoxy, is from 0 to 99, m is from 0 to 99 and n is from 1 to 99, X is an alkyl or alkylene group having 0 to 10 carbon atoms, M + is a cation, and Y − is selected from the group of sulfate groups, sulfonate groups, carboxylate groups and phosphate groups, where the A, B and D groups may be distributed randomly, alternatingly, or in the form of two, three, four or more blocks in any sequence, the sum of 1+m+n is in the range from 3 to 99 and the proportion of 1,2- butylene oxide, based on the total amount of butylene oxide, is at least 80%.