Zwitterionic Surfactant-Based Silica Nanofluid for Enhanced Oil Recovery: Oil Displacement Behavior and Mechanisms

Nanomaterials have shown great potential for enhanced oil recovery in low-permeability reservoirs because of their excellent interfacial regulation capability. However, their stability and interfacial activity are challenged under extreme reservoir conditions. In this work, a silica nanofluid composed of SiO2 nanoparticles and the zwitterionic surfactant lauramidopropyl hydroxy sulfobetaine (LHSB) was prepared, and its interfacial regulation characteristics and enhanced oil recovery mechanisms were systematically investigated. The results show that the introduction of LHSB effectively improves the dispersion stability of silica nanoparticles, and the prepared nanofluid maintains good stability at temperatures up to 120 °C and salinities up to 6 wt%. The silica nanofluid exhibits excellent interfacial activity and wettability alteration capability, reducing the oil–water interfacial tension to 0.57 mN/m and decreasing the static water contact angle on the rock surface from 112° to 37°. Meanwhile, the nanofluid significantly reduces flow resistance in porous media, achieving a flow resistance reduction rate of 20%. Oil displacement experiments indicate that injection volume, injection slug number, and shut-in time all have significant effects on oil recovery performance. The optimal operating condition was determined to be 1 PV single-slug injection followed by a 12 h shut-in period, under which the oil recovery during subsequent waterflooding reached 27%. We expect that this study will provide valuable insights into nanofluid formulation design, support the efficient development of low-permeability reservoirs, and offer a theoretical basis and technical guidance for field applications.