A prediction of interfacial tension by using molecular dynamics simulation: A study on effects of cushion gas (CO2, N2 and CH4) for Underground Hydrogen Storage

Carbon Dioxide (CO2) emissions from fossil fuel consumption have caused global warming and remain challenging problems for mitigation. Underground Hydrogen Storage (UHS) provides clean fuel and replaces traditional fossil fuels to reduce emissions of CO2. Geological formations such as depleted oil/gas reservoirs, deep saline aquifers and shale formations have been recognized as potential targets to inject and store H2 into the subsurface formations for large-scale implementation of CCS and UHS. However, the presence of H2 with cushion gas at different fractions under different geo-storage conditions, which can influence Hydrogen's flow properties, was not investigated widely. Until now, studies of interfacial properties between water and a mixture of cushion gas (CO2, N2 or CH4) in the presence of H2 are very limited or unavailable data in experiments and simulations. In this study, many predictions by using molecular dynamics simulation were conducted to predict the interfacial tension (γ) for the systems of H2/CO2/H2O, H2/N2/H2O and H2/CH4/H2O at different pressures, temperatures, and fractions of cushion gases A comparison between the predicted γ results from the simulation and previous research were also made. The findings of this study indicated that γ of H2/CO2/H2O, H2/CH4/H2O, and H2/N2/H2O, as a function of pressure, temperature, and fraction of H2, decreased with increasing pressures and temperatures and increased with increasing H2% in the mixture. Additionally, an extending or new γ data in simulation for the CO2/H2/H2O, N2/H2/H2O and CH4/H2/H2O systems from this study were reported and support evaluating the stability and storage capacity of H2 combined with the cushion gas in geological formations. Furthermore, it can contribute to de-risking and proceeding safely and efficiently for the large-scale implementation of Underground Hydrogen Storage.