Salinity tolerant surfactant oil recovery process

Abstract

Disclosed is an aqueous, saline surfactant-containing fluid and an oil recovery process using the fluid for recovering oil from formations containing high salinity and/or high hardness water, the fluid comprising an anionic surfactant such as organic sulfonate especially petroleum sulfonates as well as synthetic alkyl or alkylaryl sulfonates and a solubilizing co-surfactants such as an ethoxylated alcohol, alkyl phenol, or alkyl or alkylaryl thiol, or sulfated or sulfonated, ethoxylated alcohols or alkyl phenols. Optimum performance in any particular field is achieved if the ratio of primary anionic surfactant to solubilizing co-surfactant is carefully chosen so the surfactant combination exhibits borderline solubility in the particular formation brine in which the surfactants are to be employed. The concentration ratio of primary and solubilizing surfactants which results in the desired borderline solubility may be identified by preparing a number of samples in the formation water using different weight ratios of primary surfactant to solubilizing co-surfactant concentration, and visually noting the minimum co-surfactant needed to avoid separation of the surfactant fluid into separate phases, or which gives the surfactant fluid a pearlescent, a swirl-silver appearance which is characteristic of fluids having the proper balance of primary anionic surfactant and solubilizing co-surfactant.