Optimizing the Operational Efficiency of the Underground Hydrogen Storage Scheme in a Deep North Sea Aquifer through Compositional Simulations

In this study, we evaluate the technical viability of storing hydrogen in a deep UKCS aquifer formation through a series of numerical simulations utilising the compositional simulator CMG-GEM. Effects of various operational parameters such as injection and production rates, number and length of storage cycles, and shut-in periods on the performance of the underground hydrogen storage (UHS) process are investigated in this study. Results indicate that higher H2 operational rates degrade both the aquifer's working capacity and H2 recovery during the withdrawal phase. This can be attributed to the dominant viscous forces at higher rates which lead to H2 viscous fingering and gas gravity override of the native aquifer water resulting in an unstable displacement of water by the H2 gas. Furthermore, analysis of simulation results shows that longer and less frequent storage cycles lead to higher storage capacity and decreased H2 retrieval. We conclude that UHS in the studied aquifer is technically feasible, however, a thorough evaluation of the operational parameters is necessary to optimise both storage capacity and H2 recovery efficiency.