Atomistic insights into wettability and diffusion alteration by microbially-induced H2S and CH4 in underground hydrogen storage

Microbial activity in Underground Hydrogen Storage (UHS) formations leads to the production of gaseous byproducts such as hydrogen sulfide (H 2 S) and methane (CH 4 ). These impurities can alter the diffusion and interfacial properties of hydrogen, yet their individual effects on wettability and hydrogen transport under reservoir conditions remain poorly understood. In this study, molecular dynamics (MD) simulations are employed to quantify the impact of microbially-induced H 2 S and CH 4 on the interfacial and diffusive behavior of hydrogen at -quartz surfaces across pH levels of 5–9 and impurity concentrations of 10–40 vol%. The results show that the quartz surface remains strongly water-wet in all cases, with contact-angle variations limited to small shifts that do not change the wettability class. However, hydrogen diffusion decreases monotonically with increasing impurity fraction, driven by enhanced molecular crowding, with H 2 S exerting a greater mobility reduction than CH 4 . These findings demonstrate that even small compositional impurities can measurably influence hydrogen transport in UHS, demonstrating the need to consider these effects in reservoir-scale performance evaluations. • The impact of microbially induced H 2 S and CH 4 on UHS is studied using Molecular dynamics simulations • Quartz wettability remains largely unchanged in the presence of CH 4 and H 2 S impurities. • CH 4 slightly increases the contact angle, reducing water-wettability across all pH levels. • H 2 S exhibits pH-dependent behavior, leading to enhanced water-wet conditions at high pH. • Hydrogen mobility is more affected by H 2 S than CH 4 due to stronger electrostatic interactions.