Numerical modeling of supercritical CO₂ fracture propagation in shale formations under in-situ stress

This study presents a numerical investigation of fracture propagation in shale formations induced by supercritical carbon dioxide (SC-CO₂) using a coupled thermo–hydro–mechanical (THM) model implemented in COMSOL Multiphysics. The model evaluates the influence of key operational and geological parameters, including injection mass flux (0.002–0.006 kg/(m²·s)), rock mechanical properties (Young’s modulus: 14.85–27 GPa; tensile strength: 10–16 MPa), and in-situ stress conditions (isotropic: 15–20 MPa; anisotropic stress differentials up to 18 MPa), on fracture initiation, propagation behavior, and pressure response. The results demonstrate that the distinct thermophysical properties of SC-CO₂—including pressure- and temperature-dependent viscosity and density, together with Joule–Thomson effects—significantly influence fracture development compared with conventional water-based fracturing. SC-CO₂ reduces breakdown and propagation pressures by 18.24–23.63% and 25.61–34.73%, respectively, under the tested reservoir conditions. Increasing injection mass flux increases the pressure required for fracture initiation and enlarges the stimulated damage area. Rock mechanical properties also play a critical role: increasing tensile strength raises both breakdown and propagation pressures, while changing Young’s modulus from 14.85 to 27 GPa produces only a modest pressure response and alters fracture morphology under otherwise identical conditions. In-situ stress conditions govern both pressure requirements and fracture orientation, with higher confinement increasing the required pressure and stress anisotropy promoting directional fracture growth. These findings highlight the potential of SC-CO₂ as an efficient stimulation fluid for unconventional shale reservoirs and provide mechanistic guidance for optimizing fracturing design.