Experimental investigation and physics-informed modeling of CO₂-brine interfacial tension under reservoir conditions

Interfacial tension (IFT) critically governs multiphase flow, mass transfer, and wettability within natural and engineered water systems. Understanding its behavior is essential for assessing fluid interactions and CO₂ migration during geological carbon sequestration. However, accurate quantification of CO₂-brine IFT under in-situ reservoir conditions remains challenging due to the coupled effects of pressure, temperature, salinity, and ionic composition. In this study, a data-driven predictive framework integrating pendant-drop experiments with an extensive literature database was developed to characterize CO₂-brine IFT under realistic subsurface conditions. Experiments were conducted at 313.15–363.15 K and 7.5–17 MPa using formation water from the South China Sea, complemented by 3,409 data points compiled from previous studies for model training and validation. A Bayesian-optimized XGBoost model achieved excellent agreement with measured data (R² = 0.985), capturing nonlinear dependencies beyond conventional empirical correlations. SHAP analysis identified pressure as the primary factor influencing IFT, followed by temperature and ionic composition, and revealed distinct temperature-dependent variations even at constant pressure. These results provide advance insights into the water-phase interfacial processes governing CO₂ transport and trapping, while the proposed framework offers a scalable, transferable approach for rapid IFT estimation across diverse subsurface and water-energy systems.