Pore-Scale Investigation of Caprock Integrity in Underground Hydrogen Storage

Abstract This study investigates the sealing capacity of shale caprocks for underground storage of hydrogen (H2) utilizing mercury intrusion capillary pressure (MICP) data of caprock samples. The research explores the influence of capillary forces on gas leakage through caprocks and evaluates the effectiveness of caprocks in confining H2 and CO2. Results indicate that the interfacial tension between H2 and water/brine is significantly higher than that between CO2 and water/brine, leading to greater column heights for H2 (ranging from 59 to 667 meters) compared to CO2 (ranging from 20 to 500 meters). Additionally, the study reveals that thicker caprock layers significantly reduce the rate of gas leakage, with CO2 exhibiting higher mass leakage rates due to its larger molar mass and lower interfacial tension compared to H2. Furthermore, while the capillary bundle model estimates higher leakage rates, the pore network model, accounting for the shielding effect of small channels, predicts lower leakage rates, demonstrating its potential for more accurate estimations. The findings highlight the potential of shale caprocks as effective barriers for H2 and CO2 storage, emphasizing the importance of capillary forces and caprock thickness in mitigating gas leakage.