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

The adsorption behaviors of methane(CH 4), hydrogen(H 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 H 2 and mixed gases(H 2 and CH 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 H 2 lacks a pressure point for adsorption equilibrium below 100 MPa at ambient temperature(298K). The competitive adsorption dynamics between H 2 and CH 4 on kerogen models demonstrate that CH 4 exhibits stronger selectivity at lower pressures. Yet, this selectivity diminishes compared to H 2 as system pressure increases, indicating turning points in pressure buildup with kerogen maturity. Additionally, the presence of pre-loading H 2 O molecules reduces the adsorption capacity of mixed gases, particularly affecting CH 4 more than H 2. This study offers profound insights into the effect of kerogen maturity and moisture content on the interaction between H 2 /CH 4 and kerogen at a microscopic scale. • Hydrogen adsorption fits the Langmuir model poorly. • Methane and hydrogen have the same preferred adsorption sites. • Hydrogen can become a more selective adsorbent in high-pressure conditions. • Water reduces hydrogen adsorption non-significantly compared with methane. • Hydrogen-accessible volume resists water harm on adsorption. [ABSTRACT FROM AUTHOR]