Molecular simulation to understand the effect of methane concentration and moisture contents on hydrogen adsorption in kerogens

The adsorption behaviors of methane(CH4), 4 ), hydrogen(H2), 2 ), and their mixtures are crucial for estimating the underground hydrogen storage(UHS) capacity in depleted shale gas reservoirs. In this study, we developed four formulated kerogen models, each representing different maturation levels of type II kerogen molecules via utilizing molecular dynamics (MD) methodologies. We investigated the adsorption characteristics of pure H2 2 and mixed gases(H2 2 and CH4) 4 ) on these kerogen models with varying gas components(0.5:0.5 to 0.9:0.1) and moisture content(0-3.0 wt percentage) through grand canonical Monte Carlo(GCMC) simulations. Our findings reveal that pure H2 2 lacks a pressure point for adsorption equilibrium below 100 MPa at ambient temperature(298K). The competitive adsorption dynamics between H2 2 and CH4 4 on kerogen models demonstrate that CH4 4 exhibits stronger selectivity at lower pressures. Yet, this selectivity diminishes compared to H2 2 as system pressure increases, indicating turning points in pressure buildup with kerogen maturity. Additionally, the presence of pre- loading H2O 2 O molecules reduces the adsorption capacity of mixed gases, particularly affecting CH4 4 more than H2. 2 . This study offers profound insights into the effect of kerogen maturity and moisture content on the interaction between H2/CH4 2 /CH 4 and kerogen at a microscopic scale.