A numerical investigation on the utilization of a depleted natural gas field for seasonal hydrogen storage: A case study for Degirmenkoy gas field

The growing interest in hydrogen (H-2) within the energy sector has necessitated the development of alternative storage systems for H-2. Depleted natural gas reservoirs, currently utilized for large-scale natural gas storage, are also seen as a feasible choice for storing H-2. This study presents the results of numerical simulations to assess the applicability of utilizing the Degirmenkoy gas field for underground hydrogen storage. The Degirmenkoy gas field is onshore and depleted in the Thrace region of Turkiye. Cyclic storage simulations were run in four distinct scenarios to assess the reservoir's injection and withdrawal capacities and the H-2 ratio of the withdrawn gas from the reservoir. If the injection and withdrawal flow rates are 1.5 million Sm-3/day (250.0 thousand Sm-3/day/well), a constant flow rate can be achieved on almost all days of the injection and withdrawal periods, and annual average H-2 injection and withdrawal capacities were estimated as 221.5 million Sm-3 and 177.7 million Sm-3, respectively. Besides, H-2 ratio of the withdrawn gas increased as storage cycles repeated and average H-2 ratio increased to 88% in the last cycle. On the other hand, in the simulations performed with constant bottom hole pressure (BHP), both injection and withdrawal flow rates are quite variable during injection and withdrawal periods and peak flow rates at the beginning of each period is higher during H-2 storage as compared to natural gas. Nevertheless, in both cases the flow rate gradually diminished and eventually ceased before the related period ended. Hence, it can be inferred that conducting storage operations with a steady flow rate, as opposed to a constant BHP, is deemed more suitable for the field under investigation due to the stability of flow rate. As a result, depleted natural gas reservoirs are considered a suitable option for H-2 storage in large-scale, especially for applications without the need to obtain pure H-2, considering their storage, injection, and withdrawal capacities.