Molecular Dynamics Simulations of the Interfacial Tension Between Carbon Dioxide and Aqueous Solutions of the Mixed Salt

For geological CO2 storage in deep saline aquifers, the interfacial tension (IFT) between supercritical CO2 and brine plays a crucial role in determining capillary sealing efficiency and storage capacity. While previous studies have explored the impact of single-salt solutions on IFT, limited insight exists into mixed-salt brine systems under reservoir-relevant conditions. In this study, we employ molecular dynamics (MD) simulations to investigate the IFT behavior of the CO2+brine system containing mixed salts (NaCl + CaCl2) at 323 K, 90 bar, and a total salt concentration of 5.4 mol/kg. Our MD results reveal that the IFT is relatively higher for CaCl2, consistent with the experimental observations. Interestingly, in the mixed-salt system, the IFT exhibits a non-linear dependence on the Na+ ion fraction. These findings highlight the complex interplay of ionic valence and salt composition in dictating the interfacial properties and provide new insights for the accurate prediction of IFTs in mixed brine systems relevant to CO2 sequestration.