Microfluidic hydrogen storage capacity and residual trapping during cyclic injections: Implications for underground storage

Long-term and large-scale H2 storage is vital for a sustainable H2 economy. Research in underground H2 storage (UHS) in porous media is emerging, but the understanding of H2 reconnection and recovery mechanisms under cyclic loading is not yet adequate. This paper reports a qualitative and quantitative investigation of H2 reconnection and recovery mechanisms in repeated injection-withdrawal cycles. Here we use microfluidics to experimentally investigate up to 5 cycles of H2 injection and withdrawal under a range of injection rates at shallow reservoir storage conditions. We find that H2 storage capacities increase with increasing injection rate and range between ∼10% and 60%. The residual H2 saturation is in the same range between cycles (30–40%), but its distribution in the pore space visually appears to be hysteretic. In most cases, the residually trapped H2 reconnects in the subsequent injection cycle, predominantly in proximity to the large pore clusters. Our results provide valuable experimental data to advance the understanding of multiple H2 injection cycles in UHS schemes.