Numerical modelling of the effects of permeability contrasts on underground hydrogen storage in sandstone reservoirs

Hydrogen is an energy carrier that can balance the divergent variations in seasonal energy demand and energy supply from renewables. Underground hydrogen storage in porous formations, such as depleted gas sandstone reservoirs or saline aquifers, provides the capacities needed for large-scale, long-duration energy balancing. This paper reports on the fundamental behaviour of hydrogen in a model reservoir setup, involving a two-phase (H2, water) system and a two well (injector, producer) setup placed at different depths in the reservoir. We specifically focus on the impact of natural heterogeneities, and associated permeability contrasts, on flow and efficacy of hydrogen injection and production. We found that positioning the wells, both injector and producer, at the top of the reservoir facilitates the highest hydrogen production. We also found that permeability contrasts of three to four orders of magnitude significantly affect hydrogen flow; however, factors affecting the pressure gradient also need to be considered. These factors include compartmentalisation, the behaviour of co-existing fluids and the localised pressure gradient created by the hydrogen plume. Our research underlines the need to understand the architecture of the whole reservoir, from seismic to sub-seismic scales, not just the zones surrounding the wells and pathways in-between, as this controls capacity, pressure fluctuations and informs operational management decisions.