Abstract

Many petroleum formations contain water having high salinity and/or high concentrations of divalent ions such as calcium or magnesium dissolved therein, and are additionally at temperatures from about 70° F. to about 300° F. Most surfactants suitable for use in oil recovery operations are either ineffective in high salinity or high hardness waters, or cannot tolerate the higher temperatures encountered in many such formations. A water-external phase emulsion, microemulsion or micellar dispersion containing a water soluble alkylpolyalkoxyalkylene sulfonate or alkylarylpolyalkoxyalkylene sulfonate and a water-insoluble polyethoxylated aliphatic alcohol (including alkanols) or polyethoxylated alkylphenol nonionic surfactant is an effective fluid for flooding in formations containing water whose salinity is from 70,000 to 220,000 parts per million total dissolved solids and also having temperatures as high as 300° F. The fluid is phase stable over a wide range of formation temperatures and water salinities and hardness values.