H2 storage with CO2 cushion gas in aquifers: Numerical simulations and performance influences in a realistic reservoir model

This paper presents the results of comprehensive numerical simulations utilizing the GEM modelling tool from Computer Modelling Group (CMG) to investigate the feasibility of seasonal Underground Hydrogen Storage (UHS) using CO2 as the cushion gas in a realistic aquifer with a well-defined geological structure. The primary focus of the study is to address the challenge of efficiently recovering pure hydrogen (H2) in UHS, as the contamination and recovery of the cushion gas significantly impact the economic viability of the project. The research aims to analyse and understand how various parameters, including operational, geological, and reservoir-related factors (e.g., injection and production rates, heterogeneity, gas solubility, etc.), influence the performance of the H2 storage system, with the ultimate goal of identifying optimal storage scenarios. The study evaluates the performance of a single injection and withdrawal well positioned at the summit of the anticline. The results highlight that the amount of recovered H2 progressively increases with successive withdrawal cycles. Several parameters are found to influence the quality and quantity of the gas produced at this site, with geological heterogeneities playing a crucial role in attenuating up-coning effects. Notably, short-period cycles lead to an enhanced Hydrogen Productivity Index, while the production rate significantly impacts the quality of the produced gas and the mixing zone extent and location. The findings of this work demonstrate that H2 storage can be achieved with reasonable gas recovery parameters. However, it is important to note that no geochemical considerations have been incorporated into this analysis.