Capillary Sealing Efficiency Analysis of Caprocks: Implication for Hydrogen Geological Storage

In hydrogen geological storage, capillary sealing efficiency analysis of caprocks is very important for containment security. In this work, the H2 wettabilities of three shales and one evaporite under various pressures (0.1, 5, 10, 15, and 20 MPa), temperatures (298 and 353 K), and organic acid concentrations (10(-9) to 10(-2) mol/L) were measured using the tilted plate method, and their effects on the capillary sealing efficiency of the caprocks were analyzed. Furthermore, two oil shales were tested to see the effect of their total organic content (TOC) on the wettability at two different pressure (5 and 15 MPa) and temperature (323 and 353 K) values since the TOC dramatically varies in shales and can significantly influence the wetting characteristics and, thus, the sealing efficiency. The results of this study indicate that the H2 wettability of the caprocks increased with pressure, organic acid concentration, and TOC but decreased with temperature. However, the sealing efficiency and H-2 column height of the caprocks decreased with all the varying parameters but increased with temperature for oil shales. Furthermore, small pore sizes (i.e., r = 5 nm as a typical value for this study) and evaporites (e.g., gypsum) have the most efficient conditions for sealing for increased storage capacity. Overall, this work provides a deep understanding of the sealing efficiency of caprocks, which will aid in the successful implementation of hydrogen geo-storage and its associated structural trapping capacities.