Study on anionic-nonionic mixed surfactant for enhanced oil recovery in a hypersaline reservoir

Hypersaline reservoirs are characterized by high salinity and high calcium and magnesium concentration. In order to enhance oil recovery of the hypersaline reservoirs, a specialized ternary mixed surfactant system composed of nonionic alkanolamide surfactants and anionic surfactant was developed in this study. Through careful analysis and optimization, lauric acid diethanolamide (LDEA), octanoic acid diethanolamide (ODEA), and sodium dodecyl sulfonate (SDS) were identified as promising candidates for the surfactant compounding system, and formed a ternary surfactant system composed of LDEA, ODEA, and SDS with the mass ratio of 4.64 : 0.66 : 1.00. Experimental results revealed that the interfacial tension of the system was consistently below 10^-2 mN m^-1 and could even reach ultra-low levels (10^-3 mN m^-1) under conditions of calcium and magnesium ion content of 2000 mg L^-1, surfactant concentrations ranging from 0.05 to 0.3 wt%, temperature ranging from 50 to 80 °C, and salinity ranging from 20 000 to 50 000 mg L^-1. Furthermore, the mixed surfactant system exhibited favorable wetting capacity and emulsifying power. The static adsorption capacities of the mixed surfactant on oil sands were less than 2 mg g^-1. This study offered a novel strategy for the actual exploitation of reservoirs with high calcium-magnesium and high salinity.