In recent times, ensuring energy security for present and future generations has become a significant challenge, prompting the search for environmentally friendly and sustainable resources. Alongside other renewable energies such as solar and wind, hydrogen emerges as a pivotal player in the ongoing energy transition, addressing the seasonal fluctuations of the former. Nevertheless, due to its low volumetric energy density, hydrogen necessitates storage at high pressures or in large volumes. Repurposing or retrofitting depleted gas fields presents a viable solution, given their ample pore volumes, established reservoir structure, existing infrastructure, and favourable pressure and temperature conditions. However, storing natural gas and hydrogen differs due to their distinct hydrodynamical properties. Consequently, a comprehensive feasibility study is essential to verify the reservoirs' suitability concerning entrapment, caprock integrity, pressure-temperature conditions, microbial activities, in-situ stresses, and fault reactivations in the context of hydrogen storage operations as this can also compensate for seasonal fluctuations in the availability of renewable energies.

Integrating all available data, both old and recent, for gas fields in Hessen to update the geological structure and generate reservoir models that capture the petrophysical characteristics. Subsequently, the reservoir model will be employed in dynamic simulation for history matching during the production phase, refining petrophysical parameters to align with pore pressure and production behaviour. Once the model is adjusted and successfully history-matched, it can be utilized for scenario testing of underground hydrogen storage (UHS). These scenarios will address diverse hydrodynamical behaviours of hydrogen, hydrogen purity, chemical reactions, types of cushion gas, and microbial activities (in-situ methanation). Outputs from the UHS scenarios, such as pore pressures, temperature, and saturations, will then be fed into the geomechanical model for stress field analysis, fault reactivation assessment, and surface displacement predictions.