Abstract:

To solve the problems of poor salt tolerance and insufficient interfacial activity of surfactants in chemical flooding for high-salinity reservoirs, in this work, a novel anionic-nonionic surfactant, C12P6E6PS, was designed and synthesized, and then it was blended with a laboratory-synthesized betaine-type Gemini surfactant （GCS12）. The properties of the surfactant mixture, including solubility, interfacial activity, emulsification performance, wettability-altering ability, and oil displacement efficiency, were systematically evaluated. The results showed that the mixed system with n （C12P6E6PS） /n （GCS12） of 2∶1 exhibited significant synergistic effects, achieving ultralow interfacial tension （as low as 0.007 mN/m） within the high-salinity range （150-200 g/L） and maintaining an emulsification rate of 64% even at the salinity of 12% NaCl. This system could effectively reduce the contact angle from 109° to 47.9° on rock surfaces, changing the wettability from oil-wet to water-wet and significantly decreasing the adhesion work between crude oil and rock surface. Core flooding experiments showed that the mixed system could significantly enhance the oil recovery, i.e., after flooding by water （indicative of an oil recovery of approximately 30%）, the oil recovery was further increased to 60.83%. This study might provide an efficient technical approach for chemical flooding in high-salinity low-permeability reservoirs.

Key words: anionic-nonionic surfactant, enhanced oil recovery, interfacial tension, wetting ability, compatibility