EFFECTS OF HIGH TEMPERATURE ON FRACTURE CHARACTERISTICS OF TRANSVERSELY ISOTROPIC SHALE IN DEEP RESERVOIRS

To address the evolution of fracture characteristics in high-temperature reservoirs during deep shale gas development, this study developed a numerical method for the thermal effects on shale fracture characteristics based on the discrete element method (DEM) and fundamental thermodynamic principles, and further constructed a coupled thermo-mechanical fracture model for transversely isotropic shale by explicitly incorporating bedding distribution features. The model was used to simulate fracture processes under temperatures ranging from 23 ℃ to 200 ℃, considering two bedding configurations: front and upper bedding distributions. The study systematically analyzed the synergistic effects of temperature and bedding orientation on shale fracture characteristics. The results indicate that elevated temperatures induce thermal expansion of particles and progressive bond degradation, resulting in an approximately linear decline in fracture toughness. Bedding plane distribution plays a dominant role in guiding crack paths through weak-plane effects. Shale with front beddings exhibits stronger sensitivity to both thermal and structural factors than shale with upper beddings, leading to more complex fracture modes such as deflection along bedding planes, trans-bedding propagation, and localized mixed-mode fractures. In contrast, shale with upper beddings maintains relatively higher fracture toughness and stability under low bedding angles and high temperatures. For front bedding configurations, fracture toughness becomes significantly temperature-sensitive at medium-to-high bedding angles, where thermal effects can readily trigger abrupt structural damage. Furthermore, rising temperature suppresses the development of trans-bedding shear micro-cracks while enhancing tensile micro-cracks aligned with bedding planes. This results in an increased ratio of tensile to shear micro-cracks, indicating a shift in the dominant fracture mechanism with temperature. These findings provide new insights into the thermo-mechanical responses of transversely isotropic shale and offer theoretical support for the optimization of fracturing strategies in deep shale reservoirs.