A Review on Underground Gas Storage Systems: Natural Gas, Hydrogen and Carbon Sequestration

The concept of underground gas storage is based on the natural capacity of geological formations such as aquifers, depleted oil and gas reservoirs, and salt caverns to store gases. Underground storage systems can be used to inject and store natural gas (NG) or hydrogen, which can be withdrawn for transport to end-users or for use in industrial processes. Geological formations can additionally be used to securely contain harmful gases, such as carbon dioxide, deep underground, by means of carbon capture and sequestration technologies. This paper defines and discusses underground gas storage, highlighting commercial and pilot projects and the behavior of different gases (i.e., CH4, H2, and CO2) when stored underground, as well as associated modeling investigations. For underground NG/H2 storage, the maintenance of optimal subsurface conditions for efficient gas storage necessitates the use of a cushion gas. Cushion gas is injected before the injection of the working gas (NG/H2). The behavior of cushion gas varies based on the type of gas injected. Underground NG and H2 storage systems operate similarly. However, compared to NG storage, several challenges could be faced during H2 storage due to its low molecular mass. Underground NG storage is widely recognized and utilized as a reference for subsurface H2 storage systems. Furthermore, this paper defines and briefly discusses carbon capture and sequestration underground. Most reported studies investigated the operating and cushion gas mixture. The mixture of operating and cushion gas was studied to explore how it could affect the recovered gas quality from the reservoir. The cushion gas was shown to influence the H2 capacity. By understanding and studying the different underground system technologies, future directions for better management and successful operation of such systems are thereby highlighted.