Geological controls on Underground Hydrogen Storage in depleted gas fields

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 gas fields.