Thermal, Hydraulic, Mechanical, and Chemical Interactions in CO2 Injection for Depleted Gas Reservoirs: A Study on Korea's CCS Project

Abstract This study evaluates containment risks driven by thermal, hydraulic, mechanical, and chemical (THMC) responses in Korea's first large-scale carbon capture and storage (CCS) project, located in a depleted gas reservoir in the East Sea. The research focuses on reservoir and caprock integrity to ensure safe, long-term CO2 storage. A full-field base model was developed to simulate the THM responses of storage and sealing formations during CO2 injection into multi-layered reservoirs using multiple wells. Chemical effects were incorporated through a 3D mechanical earth model (MEM) constructed from core analyses of CO2-treated samples, enabling simulation of rock–fluid interactions. Coupled simulations integrating chemical and thermal effects were conducted using SLB's VISAGE and INTERSECT simulators. Three simulation scenarios - base case, isothermal chemical, and thermal chemical - were analyzed. Results show predicted overburden subsidence remained below 2 cm by the end of injection. Vertical displacement was more pronounced in the isothermal case due to localized temperature effects near the injector. Throughout the project life, the stress paths of both caprock and reservoir remained below the Mohr-Coulomb failure envelope, indicating no risk of failure. This study provides practical insights into geomechanical behavior during CO2 injection in highly depleted reservoirs and contributes to the development of safe, long-term CCS operations in similar geological settings.