Impact of geological and operational conditions on underground hydrogen storage

Transition toward renewable energies is an important step to tackle climate change and to build a sustainable energy system. Fluctuation in availability of renewable energy sources is a major issue leading to demand and supply imbalance. To solve this mismatch, surplus energy can be converted to green hydrogen (H2) through water electrolysis and be stored underground. Here we study the injection, storage, and production of H2 in a three-dimensional heterogeneous aquifer system. The goal is to understand how H2 storage is affected by vertical anisotropy ratio, temperature, injection and production period, relative permeability (kr) hysteresis, well perforation placement, and cushion gas type. For each case, we study how stored H2 is distributed in different forms: mobile, residually trapped, dissolved, and produced. We also quantify volume of extracted water. Results suggest that H2 recovery is successful if 1) the aquifer is more anisotropic and has lower temperature, 2) low density and viscosity cushion gas is injected prior to H2 storage, 3) injection and production perforations are placed at the bottom and top of aquifer, respectively, and 4) shut-in period between injection and production stages is minimized. Results demonstrate that kr hysteresis is critical to assess the amount of residually trapped H2.