Abstract
Abstract The complex ionic environment in high-salinity reservoirs can weaken surfactant adsorption at oil–water interfaces and compromise interfacial film stability, limiting the effectiveness of chemical flooding systems for residual-oil mobilization. To improve the oil-displacement performance of salt-tolerant surfactant systems, two alkyl polyether sulfonate surfactants with different alkyl chains and polyether structures (CX1 and CX2) were used to construct a mixed surfactant system. Amphiphilically modified MoS2 nanosheets were introduced to investigate their synergistic effects on interfacial behavior, wettability alteration, emulsion stability, and enhanced oil recovery performance. The results showed that the CX1/CX2 = 5:5 mass ratio exhibited favorable interfacial activity in simulated formation water containing Ca2+ and Mg2+. The addition of 0.01 wt % MoS2 further reduced the interfacial tension to 1.49 × 10–3 mN/m and increased the interfacial storage modulus and loss modulus. Meanwhile, MoS2 addition reduced water separation, inhibited droplet coalescence, and improved droplet-size distribution stability. Contact-angle measurements demonstrated enhanced wettability alteration, with the contact angle decreasing from 38.87° to 28.76° after MoS2 addition. Core-flooding experiments showed that repeated surfactant injection produced only 1.19% incremental oil recovery, whereas the surfactant–MoS2 composite system achieved an additional recovery of 6.10% with a final oil recovery of 56.10%. The enhanced oil-displacement performance was attributed to the synergistic effects of interfacial film strengthening, wettability alteration, emulsion stabilization, and residual-oil mobilization.