Application of Carbon Dioxide as a Cushion Gas to Optimize Hydrogen Geostorage

Abstract Hydrogen is currently being considered as an alternative energy source for industries. However, hydrogen is exceedingly volatile and compressible making it challenging to move around and store at the surface. Subsurface storage of hydrogen is the critical link to hydrogen economy however, the unique properties between hydrogen and water, such as high interfacial tension (IFT) and capillary force, pose a significant risk of water intrusion in large-scale underground hydrogen storage. Therefore, this study explores the processes and impacts of employing carbon dioxide (CO2) as a cushion gas in underground hydrogen storage to enhance injection and production efficiency, achieving high recovery rates while minimizing water production. A three-dimensional (3D) reservoir model was developed to represent an artificial aquifer based on geological characteristics of a sandstone reservoir. The numerical simulations were conducted using CMG GEM to model multi-component gas–water interactions. Likewise, hydrogen injection and withdrawal cycles were simulated under various operational conditions, both with and without the presence of CO2 as a cushion gas. Key performance indicators, including hydrogen plume behaviour, pressure support, storage efficiency, and hydrogen recovery factor, were analysed. The results show that the CO2 cushion gas established a protection zone at the front of the hydrogen storage zone mainly due to low IFT, high viscosity and density. Furthermore, the use of cushion gas increased hydrogen storage capacity by 890 m3/day, significantly decreasing the water content and increased gas recovery by 83.5%. This study confirms the technical feasibility of hydrogen geostorage in artificial aquifers and highlights the potential of CO2 as an effective cushion gas. The outcomes contribute valuable insights for the design and optimization of underground hydrogen storage systems, particularly within the context of Malaysian geological settings and future hydrogen energy infrastructure development. Keywords: Carbon dioxide utilization; Hydrogen storage; CMG-GEM; Depleted oil reservoirs; Clean and affordable energy