Abstract: An aqueous mixture is made of water, oil containing petroleum sulfonate, inorganic salt and, optionally, polymeric material wherein the polymeric material is added when it is desired to increase the viscosity of the mixture so that it is more suitable for use in certain types of oil recovery processes. The oil-to-active petroleum sulfonate ratio is adjusted to a preferred amount and oil in the petroleum sulfonate can be extracted and another oil can be added to replace the extracted oil so that the mixture has an increased tolerance to inorganic salt.

Abstract: In a post-primary oil recovery process involving the sequential addition of a saline preflush, a surfactant system comprising a surfactant, a cosurfactant and brine, the improvement comprising the addition of cosurfactant to the preflush. If desired, cosurfactant can also be added to a subsequent injected mobility buffer. The resulting system gives extraordinarily high recovery of oil.

Abstract: A series of surfactant systems is prepared at varying electrolyte concentrations, each system being mixed with oil to be displaced or its equivalent and allowed to equilibrate to determine the salinity at which the microemulsion phase has approximately equal volumes of oil and water; thereafter additional series of such surfactant systems are prepared utilizing different cosurfactants; thereafter the resulting surfactant systems are used at their optimal salinity (i.e., the salinity at which approximately equal volumes of oil and water are taken up into the microemulsion phase) to recover oil from test cores and the resulting oil recovery plotted versus the salinity to give the unique salinity at which maximum oil recovery is obtained for the particular oil-surfactant combination.

Abstract: A first and second series of aqueous surfactant-cosurfactant-electrolyte systems are prepared at varying electrolyte concentrations using, respectively, a relatively water insoluble cosurfactant and a relatively water soluble cosurfactant. The resulting systems are mixed with oil to be displaced or its equivalent and allowed to equilibrate so as to determine the salinity at which the microemulsion phases formed on said equilibration have approximately equal volumes of oil and water, thus giving the optimal salinity concentration for each surfactant-cosurfactant combination. Similar equilibrations are made using at least one surfactant system which employs a cosurfactant of intermediate water solubility. These systems are then used under the same or similar conditions to displace oil at the optimal salinity for each system and the resulting oil recovery percentage is plotted versus the salinity.

Abstract: The quantity of oil which can be economically recovered from an already waterflooded predominantly oil-wet formation is increased by passing a first solution through the formation to change the formation from its oil-wet to a water-wet state, passing a second solution having high interfacial tension with the oil through the formation to force the oil from the small pores of the formation into larger ones, and passing a third solution having a low interfacial tension between the third solution and the oil through the formation, optionally passing a mobility buffer-solution through the formation to prevent fingering or channeling, and finally passing the driving fluid through the formation.