Oil–Water–Quartz Interfacial Regulation by a Temperature- and Salinity-Responsive Gemini Carboxybetaine in Low-Permeability Sandstone: A Digital-Core-Informed Case Study

The pore geometry and mineral surfaces of low-permeability sandstone constrain both surfactant transport and oil mobilization. We used micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) of Yanchang Formation sandstone from the Hua 182 block to define formulation-screening targets, then evaluated a temperature- and salinity-responsive gemini carboxybetaine (TS-CB) at oil–water and oil-aged quartz interfaces. The core had an average porosity of 12.7%, a network tortuosity of 1.8, an average fracture aperture of 18.5 μm, and a clay content of 7.5%. TS-CB had a critical micelle concentration (CMC) of 2.8 × 10−4 mol/L and reduced oil–water interfacial tension (IFT) to 1.9 × 10−2 mN/m at 0.5 wt% and 45 °C. Its apparent viscosity reached 78.5 mPa·s at 50 °C, and the contact angle on oil-aged quartz was 12.5° at 0.5 wt%. In parallel-core flooding, the total recovery increment was 16.0 percentage points, compared with 12.0 and 10.2 percentage points for OPAB and HPAB. The results link the measured interfacial and bulk-flow responses with improved recovery in the tested core system. The position and cause of flow redistribution inside the rock remain to be established by direct diagnostics.