A comparative study on transport and interfacial physics of H2/CO2/CH4 interacting with H2O and/or silica by molecular dynamics simulation

Underground H2 storage (UHS), i.e., injecting H2 into subsurface geological formation and its withdrawal when needed, is identified as a promising solution for large-scale and long-term storage of H2. In this study, molecular dynamics (MD) simulation was performed at a typical temperature 320 K with pressure up to 60 MPa to predict H2 transport properties and H2–H2O–rock interfacial properties, which are compared with those of CO2 and CH4. The MD results show that the CH4 profiles of property variations with pressure lie between those of H2 and CO2 and more comparable to CO2. The interaction of H2 with H2O/silica is much weaker than that of CH4 and CO2. It is found that the effect of H2 pressure on altering the water contact angle and interfacial tension is negligible under all conditions. Unlike the multi-adsorption layers of the confined CO2 and CH4, there is only one adsorption layer of H2 confined by silica nano-slit. The planar diffusion of H2 in the confined system is slower than that in the bulk system at pressures lower than 20 MPa. The data and findings of this study will be useful for modeling the multiphase flow dynamics of UHS on reservoir scale, optimizing UHS operation, and assessing the performance of a cushion gas, e.g., CO2 or CH4.