Study on adsorption and diffusion behaviour of multi-component system in dolomite of sulfur-containing gas storage

In recent years, depleted carbonate gas reservoirs in the Sichuan Basin have been repurposed as underground gas storage facilities for urban natural gas peak shaving, yet high concentrations of H₂S remain. To ensure safe and efficient operation, understanding the adsorption and diffusion behaviour of sulfur-containing mixed gases is critical. Current studies largely focus on single gas interactions on carbonate surfaces. This paper employs Monte Carlo and molecular dynamics simulations to construct a dolomite crystal model and predict the adsorption and diffusion behaviour of multi-component gases in nanoscale dolomite. Results indicate that as dolomite slit pore size increases, the isothermal adsorption heat of H₂S decreases while its adsorption amount increases up to a critical pore size, beyond which it rapidly stabilises. The diffusion coefficient of H₂S exhibits a linear relationship with pore size. Elevated temperatures lower the isothermal adsorption heat of CH₄ and H₂S but boost their diffusion coefficients, whereas increased pressure raises CH₄ adsorption and reduces H₂S adsorption. In multi-component systems with cushion gas injection, CO₂ dominates adsorption, and the gas diffusion order is N₂ > CH₄ > H₂S > CO₂, suggesting CO₂ as cushion gas to mitigate mixing. These findings offer theoretical insights for optimising sulfur-containing gas storage operations.