Repurposing Natural Gas Storage Fields for Hydrogen Storage: Design of Cushion Gas

Facilities across Europe, previously used for storing natural gas are increasingly being considered for re-purposing for H2 storage. This is because re-purposing can lead to significant reductions in infrastructure costs. However, the impact of remaining hydrocarbons on the storage/withdrawal performance of H2 is not yet clear and must be better understood for effective management of this process. In this study, a representative aquifer, which was historically used for storing natural gas, is examined for underground H2 storage. With the use of full-compositional simulations at the field scale, we analysed the key factors influencing fluid mixing between H2 and the remaining natural gas, which drives the H2 purity during back production. In addition, we tested different operational strategies, such as varying the injection timing of the cushion gas and the volume ratio between cushion gas and working gas, with the aim of improving the H2 recovery performance. A certain amount of sacrificial H2 is necessary to sustain the quality of the back-produced gas when repurposing the natural gas storage field for H2 storage. The timing of the injection of such sacrificial H2 also plays an important role in driving recovery performance.