Injection fluids comprising anionic surfactants and alkoxylated alcohols and the use of such fluids in chemical enhanced oil recovery processes

A method for chemical enhanced oil recovery from a subterranean formation that is penetrated by at least one injection well and one production well, comprising:

• i) injecting into an injection well a surfactant formulation such that said surfactant formulation contacts crude oil present in said subterranean formation to lower the interfacial tension of said crude oil to ultralow values at or below 10−2 mN/m, said surfactant formulation being able to lower interfacial tension values in temperatures from 25° C. up to 70° C. and in brines with from 4% up to 15% total dissolved solids, at least a portion of said dissolved solids being divalent cations, said surfactant formulation comprising at least
• a) an anionic salt of an alkyl alkoxylated sulfate, wherein said alkyl alkoxylated sulfate has a molecular structure as shown in [I]:
• wherein
• R is a linear, branched or mixture of linear and branched alkyl group having from 10 to 20 carbon atoms,
• n=4-15,
• m=0-10,
• M+is an alkali metal ion, an alkanolamine ion, an alkyl amine ion or an ammonium ion;
• and
• b) a non-ionic alcohol ethoxylate, wherein said alcohol ethoxylate has a molecular structure as shown in [II]:
• wherein
• R1 is a linear, branched or mixture of linear and branched alkyl group having from 8 to 24 carbon atoms,
• y=20-100,
• recovering oil from the subterranean formation from a production well.