Microbiological and Geochemical Perspectives on Sustainable Dihydrogen Storage in Deep Aquifers

The successful integration of dihydrogen (H₂) as an energy vector relies on effective seasonal storage in underground facilities like deep aquifers. However, the viability of this storage remains uncertain due to the unclear behavior of indigenous microorganisms in the presence of H₂, which could influence the gas composition. While modeling can inform H₂ dynamics, reactor-scale experiments are needed for validation. In our study, we used a high-pressure reactor to simulate injecting 2% H₂ into a gas storage aquifer currently used for natural gas (CH₄, 1% CO₂), utilizing formation water and rock samples from the aquifer. Our research led to a kinetic model that analyzes the interactions among gas, water, rock, and microbial activities. We found that microorganisms consumed H₂ and caused alkalinization, which inhibited further microbial growth and respiration. This suggests that after an initial decrease in H₂ concentration, the gas storage may be stabilized in deep aquifers. Reducing CO₂ levels is vital as CO₂ can hinder alkalinization and enhance sulfate-reducing, methanogenic, and acetogenic activities. Notably, while H₂-utilizing microorganisms were predominant, both methanogens and sulfate-reducers showed significant activity. Overall, our findings provide insights into the potential for underground H₂ storage in deep aquifers, guiding future research and energy storage applications.