Sensitivity Analysis of Microbial Reaction Rate Models for Underground Hydrogen Storage

This study investigates the sensitivity of microbial reaction rate models in the context of underground hydrogen storage (UHS), with a focus on methanogenesis reactions that consume hydrogen and produce methane. Five different kinetic models are evaluated: Arrhenius, Single Monod, Dual Monod, and their modified counterparts incorporating environmental corrections for pH, temperature, and salinity. A batch simulation was conducted using 1 kg of water and 10 moles of H2 at 60 °C in a Bentheimer sandstone matrix containing 2% dolomite. Results show four distinct pH phases driven by microbial activity and mineral interactions. Initially, methanogenesis disrupts equilibrium, followed by dolomite dissolution that buffers the system. Once dolomite is depleted, calcite dissolves without buffering capacity, leading to a pH rise and eventual microbial decline. The study finds that bicarbonate, not hydrogen, is the rate-limiting substrate under batch conditions, explaining the similar behavior of Single and Dual Monod models. However, the Arrhenius model fails to capture early microbial growth or respond to pH shifts. The results highlight the importance of including environmental feedback in kinetic formulations. Future work will extend this analysis to dynamic, spatially-resolved (1D and 2D) simulations to capture heterogeneity in real reservoir conditions.