Phase-field simulation of CO2 fracturing crack propagation in thermo-poroelastic media

Abstract

Carbon dioxide (CO₂) fracturing technology demonstrates significant potential for the development of unconventional gas resources. To elucidate the fracture propagation mechanism under CO₂ fracturing, Biot's poroelasticity theory was applied to thermo-poroelastic media, accounting for the variability of CO₂ properties. A coupled phase-field model (PFM) for CO₂ fracturing in thermo-poroelastic media was established to analyze the influence of different stress differentials on fracture propagation characteristics. This model was used to compare the evolution processes of the fracture field, displacement field, and temperature field, while examining the impact of stress and displacement evolution on microcrack development. The results indicate that for horizontal stress differences of 2 MPa and 0 MPa, the fracture propagation lengths are 0.084m and 0.169m, respectively. A smaller horizontal stress difference results in a smaller angle between fractures and more fully developed fractures. Supercritical carbon dioxide (SC-CO₂) fracturing can effectively overcome limitations imposed by stress factors on fracture propagation direction and morphology. Thermal effects from the temperature field are pronounced in the early stage of fracturing, with the temperature influence range exceeding the displacement influence range before t = 12.55s, the displacement equilibrium point. After this point, the displacement influence range surpasses the temperature influence range. During SC-CO₂ fracturing process, the displacement curve exhibits relatively small fluctuations (1.83 × 10⁻⁶ m), and a prolonged slow propagation period, indicating fully developed microcracks. In the initial stage, tensile stress concentrations form around the pores. As the fracturing fluid continues to be injected, fractures initiate and propagate, with distinct zones of tensile and compressive-shear stress concentration. Ultimately, fractures propagate continuously along the direction of shear stress concentration.