Simulation of shale's deformation and failure characteristics under Triaxial compression considering mineral components

To advance the design and optimization of hydraulic fracturing technology in the efficient development of shale gas, it is crucial to reveal the mechanism by which mineral composition influences the mechanical properties of shale. On the one hand, the control mechanism of mineral composition heterogeneity on shale's mechanical behavior is not clear; on the other hand, traditional experimental methods have significant limitations in characterizing the coupled mechanical effects of multi-mineral interactions. In this study, a numerical model is constructed using the combined finite-discrete element method, which considers the heterogeneity of mineral composition. Through systematic triaxial compression numerical simulations, the mechanisms by which mineral composition affects shale's strength characteristics, failure modes, and crack propagation patterns are revealed. The results show that as the mineral particle size increases, the energy transfer efficiency of the stress transmission process improves, promoting crack propagation along a single main shear fracture. In contrast, smaller particle sizes, due to enhanced interface effects, induce differential crack propagation paths, ultimately forming a conjugate X-shaped shear fracture. The heterogeneity of different mineral phases affects the stress transmission path in shale, the location where the primary fracture initiates, and the direction of fracture propagation. The critical failure displacement influences the crack propagation speed and the degree of fracture development during triaxial compression tests. The larger the critical failure displacement, the more concentrated the stress concentration in the shale sample, resulting in faster crack propagation. The interface's resistance to deformation controls the stress transmission process at the interface. The higher the interface's resistance to deformation, the more secondary crack branches form, resulting in a more complex fracture network and the sample exhibiting a more brittle behavior. This study primarily reveals the impact of mineral composition distribution on the strength characteristics, failure modes, and fracture propagation patterns of Weiyuan shale, providing theoretical support for the development of a fracture parameter optimization model based on mineral composition characteristics.