Impact of CO2 -Induced Geochemical Alteration on The Mechanical Integrity of Reservoir and Caprock in Saline Aquifers

Abstract

Rising carbon dioxide (CO₂) emissions accelerate the deployment of Carbon Capture and Storage (CCS) in saline aquifers, yet the quantitative integration of geochemical alteration and geomechanical response remains limited, particularly in assessing effective stress and the fracture-pressure margin. This study addresses this gap using a fully coupled geochemistry–geomechanics workflow in CMG-GEM that links mineral reactions, petrophysical evolution, and geomechanical response with global (Sobol) sensitivity analysis. A homogeneous sandstone reservoir at a depth of 1200 m, with an initial porosity of 0.18 and permeability of 200 mD, undergoes 10 years of CO₂ injection followed by 500 years of post-injection monitoring. The results show that mineral dissolution modifies reservoir properties, while pore pressure increases from 11.8 to 15.8 MPa, corresponding to an 18–20% reduction in effective stress. With an estimated fracture pressure of 19.0 MPa, the resulting safety margin is 3.2 MPa (safety ratio of 1.20), indicating stable conditions without caprock failure. Pressure is the dominant sensitivity parameter, contributing 59% of the sensitivity. These findings provide a quantitative basis for evaluating safe injection-pressure conditions and prioritizing pressure management in long-term CO₂ storage and monitoring strategies.