Effect of anionic surfactant on interfacial tension and wettability of rock/water/CO2 system under geological carbon storage conditions

• SDS reduces CO 2 -brine IFT by up to 61 % at reservoir conditions. • SDS shifts wettability toward more water-wet states in quartz, sandstone and shale. • Pore-network modeling links capillary-factor reduction to higher CO 2 sweep efficiency. • First systematic IFT-wettability dataset for SDS in sandstone and shale lithologies. This study tests the hypothesis that sodium dodecyl sulfate, a commercially available anionic surfactant, can enhance CO 2 injection efficiency in geological carbon storage systems by simultaneously reducing interfacial tension and altering rock wettability. High-pressure and high-temperature experiments covered a wide range of pressure and temperature (1–12 MPa, 25–80 °C), covering from gaseous, sub-critical, to supercritical CO2 phases, and measured interfacial tensions and contact angles on quartz, Berea sandstone, and Mancos shale substrates in the absence and presence of sodium dodecyl sulfate. Results show that sodium dodecyl sulfate reduces the interfacial tension between CO 2 and brine by up to 61% at 40 °C, with reduced effectiveness at 80 °C due to increased critical micelle concentration and thermal effects on surfactant packing. Static and dynamic contact angle measurements reveal that sodium dodecyl sulfate consistently shifts wettability toward more water-wet conditions, with quartz exhibiting the greatest sensitivity and shale showing moderate change. The pore network modelling analysis demonstrates that reductions in capillary factor caused by this anionic surfactant increase CO 2 sweep efficiency. These findings highlight that sodium dodecyl sulfate can improve injectivity via interfacial tension reduction and can also enhance structural trapping by shalely caprock through wettability alteration. This study provides the first systematic experimental evidence of such effects on reservoir-relevant lithologies, sandstone as porous media and shale as caprock.