Improving feasibility of underground hydrogen storage in aquifers: A case study based on the Mt. Simon sandstone formation in the Midwest United States

Underground hydrogen storage (UHS) in saline aquifers presents a promising solution for large-scale energy storage for the Midwestern United States because of the limit availability of depleted hydrocarbon reservoirs. This study focuses on the Manlove Field at the Mt. Simon sandstone formation, Illinois, a geological site with proven sealing capacity and known reservoir properties because of previous natural gas storage projects. We developed a three-dimensional numerical model, implemented using the TOUGH + RealGasBrine simulator, to investigate several key factors influencing UHS performance, including production strategies, well completion interval, and the cushion gas injection. The results show that the method of constant production rates can significantly reduce water production compared to constant bottom hole pressure, for the same amount of recovered H₂. Because of gravity separation effect, perforating wells in upper zones improves H₂ storage by reducing water production and achieving higher recovery efficiency. Cushion gas (nitrogen in this study) enhances recovery efficiency, mitigates H₂ leakage and dissolution, and delays water breakthrough, thereby improving the overall economic viability of UHS. However, gas mixing in both subsurface and produced stream necessitates the potential need for gas separation facilities, which remains an important consideration if large amounts of a cushion gas are injected. Lastly, the results show that the non-recoverable H₂, trapped by relative permeability hysteresis, may exceed 50 % of the injected total. This study provides insights into the design and optimization of UHS operations in aquifers using three-dimensional large-scale numerical simulations, emphasizing the key role of well completion interval and cushion gas in improving H₂ storage efficiency.