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

Long-term and large-scale H-2 storage is vital for a sustainable H-2 economy. Research in underground H-2 storage (UHS) in porous media is emerging, but the understanding of H-2 reconnection and recovery mechanisms under cyclic loading is not yet adequate. This paper reports a qualitative and quantitative investigation of H-2 reconnection and recovery mechanisms in repeated injection-withdrawal cycles. Here we use microfluidics to experimentally investigate up to 5 cycles of H-2 injection and withdrawal under a range of injection rates at shallow reservoir storage conditions. We find that H-2 storage capacities increase with increasing injection rate and range between similar to 10% and 60%. The residual H-2 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 H-2 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 H-2 injection cycles in UHS schemes. (c) 2023 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.