Study on Breakthrough Pressure of <scp> H ₂ </scp> , <scp> CH ₄ </scp> , and <scp> CO ₂ </scp> in Tight Caprock for Underground Hydrogen Storage

ABSTRACT The safe construction and efficient operation of underground gas storage (UGS) facilities are of great significance for enhancing peak‐shaving capacity and ensuring national energy security. The breakthrough pressure of gas (H 2 , CH 4 , CO 2 , etc.) in caprock is a critical parameter for evaluating the sealing performance of UGS systems. In this study, typical caprock core samples, including mudstone and sandy‐mudstone, were drilled from the depleted gas reservoirs located in central and northwestern China. The experimental apparatus was developed to conduct breakthrough pressure tests on caprock samples under various temperature conditions. Breakthrough pressures of CH 4 , CO 2 , and H 2 were experimentally measured and comparatively analyzed to investigate the influencing factors. In addition, numerical simulations of gas breakthrough pressure on multicomponent gas were carried out to further explore the evolution characteristics and controlling factors of breakthrough pressures for CH 4 , CO 2 , and H 2 . The results showed that, for the same gas, the breakthrough pressure decreased with increasing temperature, and under identical temperature conditions, the values followed the order H 2 &lt; CH 4 &lt; CO 2 . The CH 4 content significantly enhanced the breakthrough pressure and the rise of the initial water saturation also led to an increase in breakthrough pressure. This study presented innovative insights into gas breakthrough pressure behavior by integrating experimental results with numerical modeling, providing theoretical support and practical guidance for subsurface hydrogen storage, natural gas storage, and CO 2 geological sequestration.