Underground hydrogen storage in a depleted gas field for seasonal storage: A numerical case study of the Tekirdag gas field

The growing attention towards hydrogen (H-2) within the energy sector recently has necessitated the development of extensive H-2 storage systems. Depleted natural gas reservoirs, which have been utilized to secure natural gas storage over an extended period, are widely regarded as a viable option for the large-scale storage of H-2. This research study presents the results of numerical simulations that were conducted to analyze the seasonal storage of H-2 in the Tekirda.g gas field, a relatively shallow-depth, low-pressure, and low-temperature gas field located in the Thrace region of Turkiye. The working gas capacity was estimated to be approximately 920 million standard cubic meters (Sm-3) under a maximum reservoir pressure of 32 bar and a minimum reservoir pressure of 10 bar. To determine the injection and withdrawal capacities of the reservoir, the H-2 ratio of the withdrawn gas, and the impact of the wells' skin factor value on these parameters, cyclic storage simulations were conducted in three distinct cases. The estimated annual injection capacities for the final storage cycles of the three cases are 372.2 million Sm-3, 276.6 million Sm-3, and 419.2 million Sm-3, and the obtained H-2 withdrawal capacities are 347.8 million Sm-3, 254.8 million Sm-3, and 393.7 million Sm-3, respectively. The differences in the H-2 ratio of recovered gas among the three cases are especially noticeable during the initial two storage cycles. Nevertheless, similar purity values were achieved for H-2 in all three cases during the last storage cycle. Based on the findings derived from the simulations, it can be inferred that depleted natural gas reservoirs offer a viable option for H-2 storage in terms of both storage capacity and H-2 purity. Although a negative skin factor value and subsequent high-rate withdrawal initially lead to a decrease in H-2 purity, this drawback gradually diminishes over time.