Molecular dynamics simulation of interfacial tension of the CO2-CH4-water and H2-CH4-water systems at the temperature of 300 K and 323 K and pressure up to 70 MPa

Subsurface geologic formations such as depleted hydrocarbon reservoirs, deep saline aquifers and shale formations have been considered promising targets for carbon dioxide and hydrogen storage. A solid understanding of the interfacial properties of multiphase systems, including binary (pure gas-water) and ternary (gas mixtures and water), is vital to assess for reliability and storage capacity of the geological formations. However, most previous experimental and simulation studies for interfacial properties have mainly focused on binary systems at low-medium pressure. Only a few experimental and simulation studies investigated the interfacial tension at high pressure (above 20 MPa) for the CO2-CH4-H2O system, and no simulation data are available for the H2-CH4-H2O system. In this study, Molecular dynamics simulations were used to predict the interfacial tension (γ) for both the binary and ternary system at 300 K and 323 K for a wide pressure range (1.0 to 70 MPa). The study was first conducted for the binary systems (H2O-CO2; H2O-CH4 and H2OH2) and then followed by the ternary systems (CO2-CH4-H2O and H2-CH4-H2O). The γ results were also validated with previous studies by comparing them to experimental and simulation data. The findings of this study indicated that γ data of binary and ternary systems decreased with increasing pressure and temperature. However, at high pressure (above 50 MPa), the γ data at 300 K and 323 K showed a plateau or changed very slightly, apparently not depending significantly on temperature. Furthermore, at a fixed pressure, determined γ values for the ternary system (H2-CH4-H2O) are constantly larger than for the CH4-H2O and CO2-CH4-H2O systems. The results provide extending or new γ data in simulation for the binary and ternary systems and contribute to evaluating the stability and long-term viability of various key Carbon Capture and Storage (CCS) and Underground Hydrocarbon Storage (UHS) related processes in support of the large-scale implementation of a hydrogen economy.