Simulations of Interfacial Tension for H2/H2S/Water and CH4/H2S/Water Systems at the Temperature of 298 K and Pressure up to 30 MPa

Abstract In 2020, hydrogen production reached around 90 million metric tons (Mt) and this is expected to keep increasing year by year toward the global net-zero target. Traditional large-scale storage methods such as the cryogenic tank and salt caverns may eventually be unable to meet local requirements. It has been suggested that depleted hydrocarbon reservoirs with a large storage volume can accommodate larger-scale hydrogen production. However, the stored gas may co-exist with residual H2S in the depleted reservoir or H2S produced by geochemical reactions with the injected gas or microorganism activity. As gas mixture composition can affect the interfacial tension (IFT) between gas and residual pore water, the dynamics and fate of injected H2 in the depleted gas reservoir may, in part, be determined by H2S effects under reservoir conditions. In this study, the interfacial tensions of H2/H2S/water and CH4/H2S/water systems were determined as a function of gas concentration at 298 K and under different pressures. The results show that gas-water IFT with different H2S concentrations decreased as pressure increased from 10 to 14.5 MPa. For pressures higher than 14.5 MPa, the effect on gas-water IFTs was relatively smaller. Furthermore, the gas-water IFTs at a relatively lower temperature of 298 K were higher than those at 343 K with different H2S concentrations under the same pressure condition. In addition, our simulation results show that even a low H2S concentration of 10% would also affect IFT when using two other types of cushion gas: CO2 and N2. The contribution of this study is to provide IFT expressions for pore water with various gas mixtures involving CH4, H2, and H2S species under different pressure and temperature conditions for hydrogen storage in depleted hydrocarbon reservoirs.