Modeling Thermal-Hydraulic-Mechanical Processes of Hydrogen Storage in Depleted Gas Reservoirs

Abstract The primary objective of this research is to develop a thermal-hydrological-mechanical (THM) simulator, which is a fully implicit, multiphase flow and multicomponent transport model, specifically designed for modeling of H2 storage processes in depleted gas reservoirs. Our modeling approach of the THM model is based on the TOUGH2-CSM simulator framework. It considers non-isothermal, multiphase-multi-component flow within a porous and fractured reservoir, by solving equations of multiphase (gas and aqueous), multi-component (H2-CH4-N2) and heat flow. It is also fully coupled with geomechanics to consider geomechanical effect on performance and safety of an H2 storing system. To validate the simulator's accuracy in incorporating in-situ phase behavior and flow and transport properties of H2 gas in reservoirs, we conduct comparisons with the National Institute of Standards and Technology (NIST) thermophysical database and laboratory experimental results. The results of our study showcase the robustness and accuracy of the THM simulator in modeling underground hydrogen storage processes in depleted gas reservoirs. We validate the model's accuracy through comparisons with the National Institute of Standards and Technology (NIST) thermophysical database and laboratory experimental results across temperatures and pressures. Our simulator is further benchmarked against existing models for pure H2 storage and validated for geomechanical calculations using Terzaghi's problem. We present an application example of the simulator to an underground hydrogen storage scenario in a depleted gas field, which demonstrates its generalized capability for modeling underground hydrogen storage processes in depleted gas reservoirs. Underground hydrogen storage can balance grid-scale energy supply and demand both short- and long-term. However, no THM numerical simulator exists for designing and optimizing such storage at reservoir scale. This paper bridges gaps in modeling hydrogen behavior in depleted gas reservoirs for storage. H2 storage provides a scalable solution for managing seasonal energy demands, utilizing existing infrastructure, and reducing CO2 emissions. The THM simulator serves as a powerful tool to optimize the design and management of H2 storage, significantly enhancing knowledge in petroleum-related energy storage technology.