The effect of stress history on the hydraulic properties and geomechanical behavior of caprock during CO2 breakthrough

Injected CO 2 in geologic carbon storage (GCS) systems interacts with caprock formations, altering pore pressure and modifying the in-situ stress state. Understanding the geomechanical behavior of mudrocks—the most common type of caprock—is therefore essential for ensuring long-term storage integrity. As their mechanical response is strongly influenced by stress history, this study aims to systematically investigate the effects of overconsolidation ratio (OCR) on the hydraulic and geomechanical properties of kaolinite-based mudrocks using a custom-built high-pressure consolidation system. Specimens were resedimented to achieve OCR values of 1, 2, and 4, then subjected to brine and CO 2 injection to evaluate intrinsic permeability, breakthrough pressure, and deformation. Results show that increasing OCR reduces porosity and permeability due to progressive pore collapse, while increasing CO 2 breakthrough pressure by limiting the size and connectivity of preferential flow paths. Geomechanical responses differed by fluid type: brine injection increased pore pressure and caused elongation due to reduced effective stress, while CO 2 injection led to slight compaction before breakthrough and void ratio increase afterward. These findings highlight the coupled influence of stress history and multiphase flow on caprock integrity, offering practical insights for the sawfe and effective design of GCS operations. • Customized high-pressure resedimentation setup enables coupled breakthrough-deformation monitoring. • Higher OCR reduces intrinsic porosity and permeability, with both values converging. • CO 2 breakthrough pressure increases with OCR, highlighting the need for direct measurement. • Brine and CO 2 trigger distinct deformation paths for identical stress history conditions. • Results link stress history to breakthrough response relevant to seal integrity assessment.