Sealing capacity of caprocks for CO₂ and H₂ storage in Illinois Basin

Permanent geological carbon dioxide (CO₂) storage is a promising pathway to mitigate the greenhouse gas levels. Recently, seasonal underground storage of hydrogen (H₂) has become of interest to fulfill energy demand uninterruptedly by periodic renewable energy supply. Caprock formations should be studied for both types of the storage to inhibit the leakage of buoyancy-driven CO₂ and H₂. Cores of two caprock representatives - Eau Claire and Maquoketa groups - are collected from CO₂ storage sites in Illinois Basin and tested for the breakthrough pressure with liquid CO₂. The direct method is time-consuming due to the necessity of achieving full saturation and stepwise injection, such that the indirect method is often utilized to estimate the breakthrough pressure via the capillary pressure-saturation curve. The comparison between the two methods indicates that the direct method provides a higher value of the breakthrough pressure. The H₂ breakthrough pressure of a given caprock is estimated by the indirect method to be approximately 2.4 times higher than that of CO₂. However, we expect that the H₂ breakthrough in very tight rock, like Maquoketa Shale, would occur through different leakage scenarios compared to CO₂ breakthrough, suggesting that direct measurements under representative in-situ conditions should be conducted.