Underground hydrogen storage in depleted gas fields is a potential solution for large-scale, seasonal storage of hydrogen, in support of the decarbonization of energy systems and other industrial activities. Its viability depends on the performance of the storage operations, which is influenced by the interaction between reservoir geology and operational strategies. However, general guidelines for development planning that account for geological uncertainty are still lacking. In addition, existing site screening criteria remain limited in that they do not account for how operational decisions can alter the suitability of a reservoir geology for hydrogen storage. Here, we employ a numerical model of flow and transport to evaluate a set of operational strategies in varying geological scenarios for depleted methane gas reservoirs of the Bunter Sandstone, an important formation in the North Sea. We investigate the following strategies for their impact on performance and interaction with geological features that are common in the Bunter sandstone: depletion level, injected hydrogen mass, cushion gas, well perforation, idle period, production rates, and methane reinjection. We found that depletion level, injected mass, and well perforation interact strongly with geology and are critical for site selection. The methane reinjection strategy provides pressure support that increases hydrogen production, though at the cost of purity in the long-term. Furthermore, cushion gas strategies show significant optimization potential but limited interaction with geology, whereas the duration of the idle period and target rates have low optimization potential. Based on these findings, we propose a site selection and development planning framework for underground hydrogen storage in depleted gas fields. The site selection phase introduces a novel screening criterion, the gravity–purity number, which integrates geological and operational considerations. The development phase provides criteria and guidelines for planning operational strategies, and establishes a hierarchy based on their optimization potential.

The geological storage of hydrogen is an alternative for large-scale energy storage in support of expanding renewable energy systems. The North Sea has hundreds of depleted gas fields that are potential storage sites. Robust screening procedures are necessary to select the most suitable reservoirs in terms of geology. This study investigates the geological controls on hydrogen storage in depleted natural gas fields of the Bunter sandstone, an important formation in the North Sea. Using an ensemble of geological models and numerical simulations, we assess the impact of structural features and sedimentological heterogeneities on storage performance, as measured by metrics of recovery factor and purity. Key controlling factors include depositional cycle and reservoir thickness, dip, and the lateral continuity of mudstone and aeolian sandstone layers, which mainly influence performance through gravity-driven mechanisms. Building on this insight, a modified gravity number that incorporates heterogeneities is proposed to serve as screening criterion for the selection of top-performing depleted gad fields.