Multiscale impacts of microbial metabolism on geochemistry and hydrodynamics of underground hydrogen storage: A review

Numerous studies have explored abiotic factors affecting underground hydrogen storage (UHS) performance; however, the role of microbial metabolism remains underexplored despite its profound implications for storage security and efficiency. Subsurface microorganisms consume hydrogen, generating undesired byproducts including hydrogen sulfide and methane that compromise UHS performance. By integrating insights from molecular simulations and laboratory experiments, this review provides a focused examination of how microbial activities impact two critical domains: (i) geochemical alterations, including hydrogen consumption, impurity formation, pH shifts, and mineral evolution; and (ii) hydrodynamic disruptions, such as changes in wettability, interfacial tension, capillary pressure, and hydrogen diffusivity. This review identifies key knowledge gaps and proposes future research directions aimed at incorporating microbial factors into predictive models and engineering designs. In particular, future cross-scale studies are needed to link atomistic insights to pore-scale processes, and to connect pore-level microbial effects with reservoir-scale behavior, to improve the reliability of UHS performance assessments. • Microbial metabolism alters UHS geochemistry and flow physics. • Hydrogen consumption and impurity formation degrade gas quality. • Biofilms modify wettability, IFT, and capillary pressure. • Critical gaps in microbial risk assessment are identified. • Cross-scale models linking atomistic, pore, and reservoir scales are lacking.