Hydrogen Storage in Depleted Gas Reservoirs with Carbon Dioxide as a Cushion Gas: Exploring a Lateral Gas Seperation Strategy to Reduce Gas Mixing
Abstract
Large-scale H2 storage in depleted hydrocarbon reservoirs offers a practical way to use existing energy infra structure to address renewable energy intermittency. Cushion gases often constitute a large initial investment, especially when expensive H2 is used. Cheaper alternatives such as CO2 or in-situ CH4 can reduce costs and, in the case of CO2, integrate within carbon capture and storage systems. This study explored cushion and working gas dynamics through numerically modelling a range of storage scenarios in laterally extensive reservoirs – such as those in the Southern North Sea. In all simulations, the cushion and working gases were separated laterally to limit contact surface area, and therefore mixing. This work provides valuable insights into (i) capacity estima tions of CO2 storage and H2 withdrawal, (ii) macro-scale fluid dynamics, and (iii) the effects of gas mixing trends on H2 purity. The results underscore key trade-offs between CO2 storage volumes and H2 withdrawal and purity