Effect of carbon dioxide on the water/n-decane interfacial properties under reservoir conditions by Molecular Dynamics

Carbon dioxide introduces additional complexity into petroleum reservoir interaction, influencing both improved oil recovery (IOR) and carbon capture and storage (CCS) strategies. Its presence affects interfacial tension (IFT), capillary forces, viscosity, oil mobility, and the adsorption of surface-active components. We investigated the effect of pressure on the interfacial tension between n-decane and water in the presence of CO₂ using Molecular Dynamics simulations. N-decane was chosen as a model oil to isolate fundamental interfacial mechanisms under reservoir conditions. An all-atom force field was applied, combining a modified flexible EPM2 for CO₂, SPC/E for water, and OPLS for n-decane. The CO₂ concentrations in the systems were adjusted based on its experimentally reported solubilities in both water and n-decane. The simulated IFT decreased with increasing pressure, consistent with experimental trends, due to progressive accumulation of CO₂ in the interfacial region, whereas the interfacial tension of the CO₂-free water/n-decane system exhibits negligible pressure dependence. The proposed methodology provides a robust molecular-level framework for analyzing interfacial phenomena under high-pressure reservoir conditions. The future work will extend this approach to systems containing multivalent ions and surface-active species under reservoir conditions, aiming to support the design of optimized injection fluids to improve oil recovery.