Sealing Potential of Heterogeneous Caprock in Subsurface Storage
Advisor: Assistant Professor Roman Y. Makhnenko
Abstract
Caprocks with low permeability are essential for long-term containment in subsurface geoenergy systems, particularly for geologic carbon dioxide (CO2) and hydrogen (H2) storage. However, the integrity of these natural barriers can be compromised by various multiphysical processes, including capillary breakthrough, hydraulic fracturing, chemical alteration, and stress-induced deformation. Lithological heterogeneity, faults, and fractures significantly influence caprock sealing behavior under in-situ conditions. This study investigates the sealing potential of heterogeneous caprock formations – Eau Claire Shale and Maquoketa Shale from the Illinois Basin and Opalinus Clay from Switzerland – through laboratory experiments that replicate relevant stress regimes, saturation, and chemical environments. A robust experimental framework is developed to assess sealing responses in terms of CO2 breakthrough pressure, single-/multiphase permeability, unsaturated poroelasticity, and coupled hydromechanical-chemical behavior. Laboratory-scale observations are compared with in-situ observations in the underground rock laboratory, providing a proper upscaling methodology. Finally, the validated framework is extended to assess heterogeneous rock behavior under H2-water systems, highlighting effects of thin shale layers on multiphase flow and capillary response in underground hydrogen storage. These findings contribute to a comprehensive understanding of caprock integrity and provide practical guidance for site selection, risk assessment, and monitoring subsurface energy storage projects.