UHS Microfluidic Investigation of Hydrogen-Methane Mixtures at 58.6 bar and 20–50 °C

Hydrogen storage in depleted gas reservoirs has gained attention as a large-scale option for intermittent green energy. Few experimental studies have investigated the influence of its native natural gas on the storage process. We investigate the influence of methane on UHS through microfluidic experiments with pre-blended and port-injection mixtures at 58.6 bar and 20–50 °C. Our drainage results indicate a positive correlation between front stability and capillary number. A wider range of pores is invaded with increasing methane content. In-situ mixing exerts a negative effect on storage capacity (as high as 13 %) and flow connectivity. Conversely, a higher withdrawal efficiency is observed for hydrogen, with one-third of the remaining ganglia occupying pore corners and parts of pores. Presence of methane in the mixtures increases the percentage of multiple pore-spanning ganglia from 1.6 % to 23–25 % at the end of imbibition. While the presence of methane can enhance connectivity, the process of in-situ mixing may reduce storage capacity, indicating a complex effect on the overall UHS process which required further investigation especially over higher-pressure conditions. • Microfluidic study for hydrogen, methane, and 50 % mixtures. • Up to 21 % higher storage capacity with increasing methane content. • In-situ mixing of hydrogen and methane impairs storage capacity up to 13 %. • Higher gas trapping (10 %) with increasing hydrogen content. • Increasing temperature halves withdrawal efficiency.