Purity of stored hydrogen

Cushion gas is a requirement in underground hydrogen storage (UHS) to enable effective working gas production. Its volume directly affects the working gas injection and production performance. It is also a considerable upfront investment for UHS. In depleted reservoirs the remaining hydrocarbon gas may act as a cushion gas, reducing the required cushion gas volume to be added. Similarly, instead of using H₂ as a cushion gas, a cheaper option could be to use N₂, CO₂, or CH₄. However, cushion gas different to the working gas (H₂) will result in gas mixing and impurities in the produced H₂.   

  

Research questions include the performance of UHS with different cushion gases, the composition of the produced H₂ over time and over a range of production/injection cycles and production/injection rates, and the impact on costs as a result of H₂ purification. The performance of different cushion gases has been investigated numerically, but no experimental data has been published to date (to the best of knowledge). In Australia, this topic is of particular interest as many of the sites considered for UHS are depleted reservoirs with residual hydrocarbons present due to their strategic location.