Surfactant oil recovery process usable in high temperature formations

Abstract

Many petroleum-containing formations contain high salinity and/or hard water and have temperatures from 150.degree. F. to 300.degree. F. Many surfactants known for oil recovery purposes may be used in either the high salinity or hard water, or in the presence of high temperature, but few surfactants or surfactant combinations are suitable for use in formations containing both high salinity water and temperatures much in excess of about 150.degree. F. An alkylpolyalkoxyalkyl sulfonate or alkylarylpolyalkoxyalkyl sulfonate, either as the sole constituent of an aqueous surfactant fluid, or as a solubilizing co-surfactant in combination with an anionic surfactant such as a petroleum sulfonate, an alkyl sulfonate, or an alkylaryl sulfonate, is effective for use in formations containing high salinity and/or hard water which are additionally at a temperature from about 70.degree.-300.degree. F. The chain length of the alkyl constituent of the alkylpolyalkoxyalkyl sulfonate or alkylarylpolyalkoxyalkyl sulfonate, as well as the number of alkoxy groups in the surfactant molecule is carefully chosen to achieve limited solubility in a solution having salinity and divalent ion concentration about equal to the formation water at a temperature about equal to the formation temperature. Such solutions are not phase stable at surface ambient temperature if the difference between the formation temperature and the surface ambient temperature is substantially greater than about 100.degree. F. It is necessary to heat the solution to completely dissolve the surfactants therein and to maintain the solution heated to a temperature within at least 100.degree. F. of the formation temperature and preferably within at least 50.degree. F. of the formation temperature when it is injected thereinto.