Supercritical CO 2 (SC-CO 2 ) fracturing has significant potential for shale gas stimulation and CO 2 geological sequestration. However, the differentiated fracture propagation mechanisms of shale from different structural positions in complex tectonic zones under SC-CO 2 fracturing remain insufficiently understood. In this study, the Wufeng–Longmaxi Formation shale from the Anchang Syncline in northern Guizhou was selected as the research object. True triaxial SC-CO 2 fracturing experiments were conducted under simulated in-situ temperature, pressure, and three-dimensional stress conditions, and CT-based three-dimensional reconstruction was combined to quantitatively analyze the breakdown pressure, fracture morphology, and spatial connectivity characteristics of shale from the core and limb. The results show that the average breakdown pressure of the core specimens is 33.17 MPa, which is higher than that of the limb specimens at 28.51 MPa, indicating that strong tectonic compression and high in-situ stress confinement significantly increase the fracture-initiation threshold. Fractures in the core mainly propagate steadily along the direction of the maximum horizontal principal stress, with relatively simple propagation paths. In contrast, fractures in the limb are more strongly controlled by natural fractures and bedding-related weak planes, making them more prone to deflection, branching, and the formation of complex fracture networks with large dip angles. Further analysis reveals that an increase in horizontal stress difference (Δ σ h ) not only reduces breakdown pressure, but also amplifies the fracture propagation response through structural-position differences. In the core, this effect is mainly manifested by accelerated fracture initiation and penetration, whereas in the limb, it is more conducive to weak-plane activation and the formation of complex fracture networks. This study clarifies the fracture propagation behavior of SC-CO 2 fracturing in shale from different structural positions in complex tectonic zones, providing a basis for differentiated shale gas fracturing design and CO 2 sequestration evaluation.
Wang et al. (Fri,) studied this question.