Evaluating Hydrogen Loss in Underground Storage: The Role of Microbial Activity, Mixing, and Operational Strategies

Underground hydrogen storage (UHS) is a promising solution for large-scale energy storage, yet its performance is affected by a range of physical and biochemical processes such as mixing, buoyancy, and microbial reactions. These processes interact differently under varying reservoir conditions and operational strategies, making it essential to investigate how reaction rates, injection/withdrawal (I/W) flow rates, and cycle length influence H₂ loss and purity. This study conducts a parametric analysis to examine the impact of various parameters on hydrogen consumption and microbial activity using bioreactive transport simulations incorporating methanogenic archaea (MG) and sulfate-reducing bacteria (SRB). The results suggest that environmentally realistic changes in reaction rates have a minimal effect on the overall consumption of H₂ by microbes. Although slower reactions initially display reduced consumption rates, the extended presence of the mixing zone during UHS allows sufficient time for microbial activity to equalize across all scenarios. Injecting and withdrawing the same total mass of H₂ at higher flow rates results in reduced microbial consumption and improved withdrawal efficiency. Longer injection cycles at a constant flow rate provide microbes with more substrate and time for consumption. However, relative to the total injected mass, consumption levels are lower than those in short cycles due to stronger reactant mixing. Methanogenesis is predicted to be the predominant process for microbial H₂ consumption, as SRB require significantly less H₂ to produce a unit of biomass. Nevertheless, microbial activity contributes less than 1% of the overall reduction in H₂ purity, with mixing and buoyancy effects being the main factors introducing impurities.