Advancing Hydrogen Storage in Depleted Gas Reservoirs: A Comprehensive Evaluation of Dominant Trapping Mechanisms

Abstract The utilization of depleted hydrocarbon reservoirs for Underground Hydrogen Storage (UHS) presents a promising and competitive solution for addressing large-scale hydrogen storage challenges. By repurposing existing infrastructure, UHS can provide a cost-effective and sustainable approach to integrating hydrogen storage within the energy sector. This study aims to identify and quantify the dominant trapping mechanisms that contribute to hydrogen loss during UHS, offering insights for optimizing deployment and ensuring efficient integration into the energy landscape. To achieve this objective, a real-field geological model of a depleted sandstone gas reservoir with a shale cap rock was employed. The Peng Robinson equation of state as well as the viscosity and solubility models were tuned using published hydrogen properties. Recent relative permeability, capillary pressure, and hysteresis data from the literature were also integrated into the simulations to capture the reservoir's dynamic behavior during hydrogen injection, storage, and withdrawal processes. The mechanisms examined include hydrogen residual trapping and hysteresis, diffusion in water and the formation, solubility trapping, geochemical reactions, and the impact of salinity, all of which can influence hydrogen retention and recovery efficiency. The results of this comprehensive analysis revealed that residual trapping was the most dominant mechanism, accounting for majority of the hydrogen loss. This finding emphasizes the need for precise relative permeability data to accurately model and predict reservoir performance during UHS. The geochemical loss was found to be highly dependent on rock composition, with negligible impact in sandstone reservoirs. Furthermore, diffusion in the fluid and the formation contributed to less than 3% of the total hydrogen loss, while the impact of solubility trapping was minimal. This study presents an analysis of dominant trapping mechanisms during Underground Hydrogen Storage in depleted gas reservoirs within a real-field geological model. What differentiates this study is the systematic incorporation of all loss mechanisms using a tunned fluid model, providing engineers with a more holistic understanding of UHS. The findings offer practical insights into how these factors can be optimized for improved hydrogen retention and recovery efficiency. This research is pivotal for engineers seeking data-driven methodologies and best practices in UHS. By delivering actionable knowledge, this study supports the integration of hydrogen storage into the existing hydrocarbon infrastructure, contributing to the development of a sustainable energy sector.