Comparative Salt Tolerance of Betaine Surfactants for High-Salinity EOR Applications

Betaine surfactants are widely applied in enhanced oil recovery (EOR) studies for high-salinity reservoirs owing to their amphoteric molecular structure, which provides excellent salt tolerance and environmental adaptability. In this study, erucic acid amidopropyl betaine (EAPB), dodecyl dimethyl hydroxypropyl sulfobetaine (DHSB), and octadecyl hydroxysulfobetaine (OHSB) were selected as research subjects. The effects of ionic valence and concentration on the physicochemical properties of these surfactants were investigated by systematically measuring their apparent viscosity, surface tension, and interfacial tension in various electrolyte solutions and actual oilfield water environments. The results indicate that EAPB exhibits pronounced viscoelasticity, whereas its surface and interfacial tensions are higher than those of DHSB and OHSB. Moderate concentrations of monovalent ions or trace amounts of calcium and magnesium ions promote the micellization of EAPB molecules via charge-shielding effects, thereby enhancing apparent viscosity. In contrast, barium salts and strontium salts cannot increase the apparent viscosity. Both DHSB and OHSB demonstrate stability in multivalent salt systems, maintaining surface tension values between 27.2 and 29.0 mN/m and interfacial tension at the 10-1 mN/m order of magnitude. Evaluation using oilfield water samples further confirms that EAPB, DHSB, and OHSB possess strong adaptability to complex ionic environments. This study provides an experimental foundation for developing efficient chemical flooding systems to enhance oil recovery in high-salinity reservoirs.