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

초록

Injected CO2 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 CO2 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 CO2 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 CO2 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 safe and effective design of GCS operations.

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