In the current global race towards achieving self-sufficiency and sustainability in meeting energy demands with net-zero emissions, hydrogen has emerged as a promising solution. However, hydrogen's volumetric energy density is lower compared to conventional energy sources, and the storage conditions (pressure and temperature) for hydrogen on the surface are expensive and technically challenging.
To overcome the challenge of large-scale hydrogen storage, researchers around the world have proposed storing hydrogen in subsurface geological structures, such as salt caverns and porous reservoir rocks. While hydrogen storage in salt caverns is a more advanced concept, storing hydrogen in porous rocks such as depleted reservoirs and aquifers requires further research attention. This paper outlines a preliminary workflow for a feasibility study on the use of depleted gas reservoirs for hydrogen storage. Two different fields in Germany are used as examples to illustrate the process. One of the case study fields is still producing from the carbonates of the Zechstein Group, while the other is a decommissioned field that previously produced from unconsolidated Neogene sands. The workflow involves creating a static geological model and populating it with petrophysical parameters, followed by dynamic flow simulation for history matching. Hydrodynamical parameters for hydrogen are then introduced to simulate hypothetical storage cycles. A geomechanical model is then created incorporating the pore pressure data and material properties, to assess storage integrity, fault activity, and surface deflection in response to hydrogen filling. Overall, this workflow provides a comprehensive approach to evaluate the potential for hydrogen storage in depleted reservoirs.