Fracture Response to Cooling-Induced Stress from CO2 Injection: A Coupled EOS-Based Thermo-Hydro-Mechanical Simulation Study

Abstract Injection of cold CO2 into geological formations can induce significant thermal stresses in both reservoir and caprock, potentially leading to stress redistribution and an increased risk of fracture initiation. This study investigates the coupled effects of temperature, fluid composition, phase behavior, and fracture growth by using MF3D, a fully integrated numerical simulator incorporating non-isothermal multiphase EOS-based compositional flow, geomechanics, and dynamic fracture propagation. A numerical model was constructed based on a depleted gas-condensate field in Europe, featuring multilayer formations with contrasting properties. Simulations were conducted for CO2 injection scenarios at different temperatures (0°C, 25°C, and 75°C) under long-term operational conditions. The results indicate that lower injection temperatures lead to lower injection pressures. However, sustained cooling in the near-wellbore region causes a gradual reduction in minimum horizontal stress. In fracture-enabled simulations, cold CO2 injection triggered rapid vertical fracture growth from the initial injection depth, driven by localized thermal contraction and stress reduction. These findings suggest that models lacking proper fluid phase behavior and fracture propagation and those relying on simplified thermal formulations—such as constant heat capacity assumptions—may underestimate the mechanical risks associated with cold CO2 injection. In contrast, this study integrates dynamic fracture modeling and an EOS-based thermal formulation that captures the pressure- and temperature-dependent thermal behavior of CO2, enabling more accurate evaluation of stress redistribution and fracture growth. The proposed modeling approach offers improved reliability for designing safe and effective CO2 storage operations under thermally dynamic conditions.