Phenomenal study of microbial impact on hydrogen storage in aquifers: A coupled multiphysics modelling

Underground hydrogen storage (UHS) has been considered as an integral part of energy transition from fossil fuels to renewable sources. Porous aquifers can serve as typical sites for this purpose due to their worldwide distribution and huge storage capacity. However, the diverse microbial species that inhabit the aquifers are known to be able to catalyze in-situ biochemical reactions within the hosting rock. These reactions can normally lead to microbial consumption of hydrogen, microbial clogging of pore space and thus affect hydrogen injection and withdrawal rates as reported in the literature. So far, these phenomena have been widely reported but rarely quantified. In this study, we build a coupled hydrological-mechanical-chemical-biological (HMCB) multiphysics model to simulate these microbe-related processes during UHS in aquifers. The model consists of a complete set of partial differential equations to describe: (1) rock deformation; (2) water-hydrogen two-phase flow; (3) microbes and dissolved hydrogen transport; (4) mineral dissolution/precipitation; and (5) microbial activities involving adsorption/desorption and growth/decay. All these processes are linked together through the porosity/permeability models which consider the joint impacts of microbial clogging, mineral dissolution/precipitation and effective stress. This multiphysics model is verified against laboratory biochemical reaction data and microbial transport data. Then, the verified model is used to investigate the impacts of iron-reduction bacteria (IRB) activities on UHS in aquifers. Based on the simulation results, it can be concluded that (1) hydrogen saturation at the top surface of the aquifer is the greatest while microbial activities surrounding the injection well is stimulated the most; (2) microbial activities influence the initial few cycles of hydrogen injection and withdrawal but the impacts gradually diminish with the dissolution of Fe₂O₃; (3) hydrogen recovery efficiency is degraded due to the combined effects of hydrogen consumption, water production and microbial clogging with the microbial clogging impact being the most significant; and (4) effective stress impacts aquifer permeability throughout UHS operations while microbial clogging influences it in the initial few cycles. For mineral dissolution/precipitation, the impact can be neglected.