The effect of divalent cations (Ca⁺⁺ and Mg⁺⁺) on the optimal salinity and salt tolerance of petroleum sulfonate and ethoxylated sulfonate mixtures in relation to improved oil recovery

Abstract

Abstract It was demonstrated that a surfactant formulation consisting of a petroleum sulfonate and an ethoxylate sulfonate can tolerate a large amount of CaCl 2 and MgCl 2 in solution without any precipitation or phase‐separation. The stability of this surfactant formulation was not influenced significantly by the presence of divalent cations. The maximum salt concentration permissible for a stable formulation depended primarily on the ionic strength of the salt solution and not on the relative proportions of the divalent and monovalent cations. It was also observed that though the optimal salinity (Sγ) decreased upon increasing the amount of divalent cations, the interfacial tension at optimal salinity was always in the millidyne (≃10 −3 dynes/cm) range. This study has a practical application in designing the surfactant formulations for tertiary oil recovery process for reservoirs consisting of high concentrations of mono‐ and divalent cataions.