Hydrogen storage in depleted gas reservoirs with carbon dioxide as a cushion gas: Exploring a lateral gas separation strategy to reduce gas mixing
Harri Williams, Niklas Heinemann, Ian L. Molnar, Fernanda M. L. Veloso, Toni Gladding, Tarek L. Rashwan
Abstract
Large-scale H 2 storage in depleted hydrocarbon reservoirs offers a practical way to use existing energy infrastructure to address renewable energy intermittency. Cushion gases often constitute a large initial investment, especially when expensive H 2 is used. Cheaper alternatives such as CO 2 or in-situ CH 4 can reduce costs and, in the case of CO 2 , 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 estimations of CO 2 storage and H 2 withdrawal, ( ii ) macro-scale fluid dynamics, and ( iii ) the effects of gas mixing trends on H 2 purity. The results underscore key trade-offs between CO 2 storage volumes and H 2 withdrawal and purity. • A numerical simulation of H 2 storage in a laterally extensive depleted gas reservoir. • Cushion and working gases were laterally separated to limit gas mixing. • An assessment of CO 2 , CH 4 , and H 2 cushion gas on H 2 working gas capacity and purity. • There is a trade-off between CO 2 storage volumes and H 2 working gas capacity. • Residual CH 4 and H 2 cushion gas reduced H 2 –CO 2 mixing.