Pore-scale study of cyclic injection and microbial activity on H2 recovery and loss mechanisms during underground H2 storage

Underground H₂ storage (UHS) in salt caverns, deep saline formations, and depleted oil/gas reservoirs has emerged as a reliable and safe technology for storing renewable energy and reducing carbon dioxide emissions. H₂ gas, however, is one of the most important electron donors for many subsurface microorganisms. During the multiple cycles of H₂ injection and withdrawal operations, a certain amount of H₂ is permanently lost due to various physical, chemical, and biological mechanisms. Although research in UHS in porous media is evolving, our understanding of the impacts of cyclic loading and microbial activity on H₂ recovery and loss mechanisms remains inadequate.

In this study, we present recent findings from a quantitative investigation of H₂ reconnection and recovery mechanisms in repeated injection-withdrawal cycles using a microfluidic pore network simulating shallow reservoir storage conditions (30 barg). Our results reveal that H₂ storage capacities increase with higher injection rates, ranging between approximately 10% and 60%. Additionally, we observed the growth of a typical halophilic sulfate-reducing bacterium in the hydrogen-saturated pore network for 9 days. Significant H₂ loss occurred due to microbial consumption within 2 days following injection into the microfluidic device. These results may have significant implications for hydrogen recovery and gas injectivity. Microvisual experiments provide critical observations of bubble-liquid interfacial area and reaction rate that are essential to the modeling that is needed to make long-term predictions. Our results contribute to improving the selection criteria for future storage sites, ensuring optimized and efficient H₂ storage and utilization.