Abstract: A process for the recovery of oil from subterranean oil reservoirs by waterflooding employing an anionic-nonionic surfactant system which is particularly suitable for use in reservoirs in which the connate waters contain a high salt content, including divalent metal salts, or which may be employed in carrying out waterfloods in which the available injection waters exhibit a relatively high salt content. The multifunctional surfactant system comprises a surface-active amide linked sulfonate anionic group and a surface-active polyethylene oxide nonionic group and may be employed in an aqueous solution having a salinity within the range of 3 to 25 weight percent. Subsequent to the injection of the aqueous solution of surfactant, an aqueous flooding medium may be injected which exhibits a salinity which is lower than the salinity of the surfactant slug.

Abstract: A surfactant waterflooding process for the recovery of oil from subterranean oil reservoirs in which a water-soluble polyalkylene oxide is employed as a sacrificial agent in order to retard adsorption of the surfactant. An aqueous pretreatment slug is injected which contains a water-soluble polyalkylene oxide sacrificial agent having a molecular weight of at least 1200. Thereafter an aqueous slug containing a surfactant exhibiting a lower molecular weight than that of the polyalkylene oxide sacrificial agent is injected. The surfactant slug may also contain a polyalkylene oxide sacrificial agent as described above. In this case, concentration of sacrificial agent in the surfactant slug normally is lower than the concentration in the pretreatment slug.