Influence of hydrogen sulfide on gas-water interface in underground hydrogen storage: A molecular dynamics study

In this study, we investigate the dynamics of interfacial tension (IFT) between residual pore water and gas mixtures containing H2, CH4, and H2S within subsurface porous media, essential for underground hydrogen storage (UHS) systems. Utilizing molecular dynamics simulations, we established specific IFT correlations across a spectrum of H2S concentrations, ranging from 5 % to 80 %, under the conditions of 14.5 MPa and 343 K. Our results demonstrate a marked decrease in IFT, with a notable 12 % reduction observed even at a minimal H2S concentration of 5 % for H2S-H2 mixtures, contrasting with a 6 % reduction in H2S-CH4 mixtures, and reaching a saturation point at concentrations exceeding 80 %. The presence of CH4 at the interface mitigates the reduction in IFT caused by H2S, underscoring the complexity of gas interactions in subsurface storage. These insights into the molecular dynamics at the gas-water interface carry significant implications for the optimization of UHS operations, informed by the substantial variations in IFT with different H2S concentrations.