Micellar dispersions with tolerance for extreme water hardness for use in petroleum recovery

A process for recovering petroleum from a subterranean reservoir wherein a first fluid is driven through the reservoir from an injection well to a production well by a second fluid where petroleum is produced the first fluid comprising a hydrocarbon, an aqueous fluid containing from about 1500 to 12,000 parts per million ions of calcium and/or magnesium and a surfactant system wherein the surfactant system comprises

• a first anionic surfactant having one of the following general formulas:
• R -- SO.sub.3- -- Y+
• wherein R is an alkyl radical, linear or branched, having from 5 to 25 carbon atoms, and Y is a monovalent cation such as sodium, potassium or ammonium;
• or ##STR4## wherein R and Y have the same meaning as above and a second anionic surfactant having the following general formula:
• [R' --(OCH.sub.2 CH.sub.2).sub.n -- SO.sub.4]- Y+
• wherein R' is an alkyl or alkylaryl radical, linear or branched, having from 7 to 20 carbon atoms, n is an integer from 1 to 10 and Y is a monovalent cation such as sodium, potassium or ammonium and
• a nonionic surfactant having one of the following structures:
• ##STR5## wherein R" is an alkyl radical, linear or branched, having from 5 to 20 carbon atoms, A and A' are independently selected from the group consisting of hydrogen and alkanols having from 1 to 10 carbon atoms;
• or ##STR6## wherein R'" is an alkyl radical having from 5 to 20 carbon atoms, and n' is an integer from 6 to 20 or
• R"" O(CH.sub.2 CH.sub.2 O).sub.n" H
• wherein R"" is an alkyl chain having from 5 to 20 carbon atoms and n" is an integer from 6 to 20.