Preparation of Salt‐Resistant Gemini Surfactants via Ethylene Oxide Group Regulation for Enhanced Oil Recovery

Conventional anionic surfactants generally exhibit poor salt tolerance and reduced interfacial activity under high‐salinity reservoir conditions, limiting their application in enhanced oil recovery (EOR). To address this issue, a series of anionic–nonionic isotridecanol poly(oxyethylene ether) sulfonate surfactants (ES‐n, n = 3, 6, 8, and 10) and their Gemini derivatives (GES‐n) were synthesized by introducing different numbers of ethylene oxide (EO) groups. The surfactants were characterized and evaluated through critical micelle concentration (CMC), dynamic interfacial tension, salt‐tolerance, contact‐angle, and oil‐washing tests. GES‐n exhibited superior interfacial activity compared with ES‐n due to the synergistic effects of dual hydrophobic chains and spacer‐induced structural constraints. Among them, GES‐06 showed the best overall performance, with a CMC of 1.29 × 10 −5 mol L −1 and an ultralow interfacial tension of 4.15 × 10 −3 mN m −1 at a salinity of 150 g L −1 NaCl. The water contact angle decreased from 113.1° to 22.4°, and the oil‐washing efficiency reached 78.26%, significantly higher than that of ES‐06 (42.18%). Appropriate EO regulation effectively balanced hydration and hydrophobic interactions, enhancing interfacial adsorption and oil recovery performance in high‐salinity reservoirs.