Damage Characteristics Analysis and Fractal Study of Shale With Prefabricated Fractures under Thermal-mechanical Coupling

To study the damage and failure of shale with different fracture inclination angles under uniaxial compression loading, in this work, RFPA2D-Thermal, a two-dimensional real failure process analysis software, was used for numerical simulation. Numerical simulation results show that quartz in shale mainly affects the tensile and compressive strength of shale by increasing rock brittleness. The coupling of temperature and pressure will cause lateral and volume destruction of shale, which enables the shale body to be more easily broken. Fracture inclination is the key factor affecting shale damage patterns. The failure mode of shale with low- and high-angle fractures is mainly shear failure, and the compressive strength does not vary with crack inclination. The damage mode of obliquely intersecting fractured shale is slip damage along the fracture face, the compressive strength decreases and then increases with the fracture inclination, and a minimum value exists. The acoustic emission simulation results of the damage process effectively reflect the accumulated internal damage and macroscopic crack appearance until fracture instability when the prefabricated fractured shale is subjected to uniaxial compressive loading. The crack inclinations of 0° and 120 °C corresponds to the most complex “N” shape damage mode. The crack inclinations of 30° and 60°, and the damage mode is an inverted “λ” shape.