Analysis of operating pressure and injection–production frequency on the tightness of full-stratum salt cavern hydrogen storage

Salt caverns possess superior tightness and are ideal sites for storing gases, such as natural gas and hydrogen. Compared with natural gas, hydrogen has a smaller molecular size and is more prone to leakage; therefore, the simplified stratigraphic models commonly used in previous storage studies are no longer sufficient to characterize tightness under long-term cyclic injection–withdrawal. Considering the geological conditions of the Pingdingshan area, we establish a full-stratum digital model of a salt-cavern hydrogen-storage facility and, using single-factor analysis together with response-surface-based multi-factor analysis (Response Surface Methodology, Box-Behnken Design), investigate how the minimum operating pressure, maximum operating pressure, and injection–production frequency affect tightness after 100 years of continuous operation. The results show that (1) Increasing the minimum operating pressure can not only suppress hydrogen backflow but also intensify gas leakage, thereby increasing the leakage rate. In contrast, increasing the maximum operating pressure slightly increases hydrogen leakage but reduces the overall leakage rate. (2) Increasing the injection–production frequency significantly boosts the working gas volume and reduces the hydrogen leakage rate. In this study, when the minimum operating pressure is 6.93 MPa, the maximum operating pressure is 16.17 MPa, and the annual injection-production frequency is increased to 4 times, the salt cavern meets the tightness evaluation standards. (3) Response surface analysis indicates that injection–production frequency is the most influential factor affecting hydrogen leakage, with its interaction with minimum pressure being particularly significant. Furthermore, a multivariate regression model is established to quantify the relationship between operating conditions and cumulative leakage rate, providing a theoretical basis for optimizing hydrogen storage design.