Laboratory‐Scale Assessment of CO₂ Sealing Potential of Heterogeneous Caprock

Abstract Geologic carbon storage is widely recognized as a critical strategy for mitigating atmospheric carbon dioxide (CO 2 ) levels, yet its effectiveness is contingent upon the integrity of caprock formations that prevent CO 2 leakage. This study investigates the sealing potential of three representative caprock formations—Eau Claire Shale, Maquoketa Shale, and Opalinus Clay—by employing a comprehensive set of experimental approaches. Laboratory assessments include permeability tests, stepwise CO 2 injection, imbibition experiments, and porosimetry‐based estimation to evaluate the sealing potential of heterogeneous geomaterials. It appears that within each formation, sand‐rich specimens exhibit significantly higher permeability and lower breakthrough pressures compared to their clay‐rich counterparts, underscoring the influence of the lithological variation. An indirect method based on pore structure analysis tends to underestimate the sealing capacity, highlighting discrepancies caused by the confinement, pore structure anisotropy, and variations in geochemical interactions. A statistical analysis based on the data set from this study and the literature reveals that CO 2 breakthrough pressure is positively correlated with the clay content, negatively correlated with the permeability and dominant pore size, and independent of its porosity. The sealing number is introduced to provide a quantitative framework for evaluating the sealing integrity of the tested caprock formations to withstand buoyant forces. This study highlights the critical role of heterogeneities in determining caprock sealing potential and emphasizes the importance of direct measurements, particularly the use of the stepwise method, for accurate assessment. Advanced imaging and geophysical monitoring, coupled with multi‐scale experiments, are recommended to enhance the reliability of heterogeneous caprock integrity assessments.