From CO$_2$ Sequestration to Hydrogen Storage: Further Utilization of Depleted Gas Reservoirs

Abstract

The depleted gas reservoirs can serve not only as sites for CO$_2$ sequestration but also as potential spaces for hydrogen storage. However, this process remains insufficiently investigated and thus cannot offer reliable technical support for the injection operations. In this study, a mathematical model for simulating hydrogen storage in depleted gas reservoirs was developed and numerically solved. Meanwhile, the applicability was then verified through comparison with results from previous studies. Based on this model, a detailed analysis was performed to investigate the evolution of key parameters under specific injection conditions. Finally, the effects of various factors on parameters such as hydrogen distribution and maximum pore pressure during the hydrogen injection process were thoroughly discussed. It was found that hydrogen gradually drives the CH$_4$ and CO$_2$ outward from the near-wellbore region, leading to increases in both bottom-hole pressure and pore pressure during hydrogen injection. Furthermore, as the injection progresses, the spatial extent of hydrogen distribution expands nonlinearly, and the buffering effects of CH$_4$ and CO$_2$ become prominent. Sensitivity analysis further reveals that, although low permeability-induced high pore pressure poses sealing challenges, limited hydrogen storage space within reservoir is beneficial for further hydrogen recovery. Meanwhile, a moderate increase in the injection rate can enhance storage efficiency without compromising reservoir sealing integrity. In contrast, extending the length of wellbore section used for hydrogen injection does not lead to a significant improvement in storage performance.