Simulation Study on Rock Fracture Mechanisms in Deep Shale Reservoirs

Deep shale contains well-developed bedding planes and a highly plastic matrix whose competition governs fracture behavior. Most Brazilian splitting simulations treat shale as linear elastic, so bedding anisotropy cannot be separated from matrix plasticity. This study addresses that question in one numerical framework: a finite element Brazilian splitting model is developed in which the Drucker–Prager criterion governs matrix plasticity and globally embedded cohesive elements represent the bedding planes and potential fracture paths. Elastic and elastoplastic responses are compared for bedding-plane angles of 0–90° and two bedding-plane strengths. Four fracture modes are identified—matrix tension, matrix shear, bedding-plane shear and bedding-plane tension. For the elastoplastic model at high bedding-plane strength, matrix tension dominates above 60°, mixed modes occur between 30° and 60°, bedding-plane shear below 30°, and bedding-plane tension near 0°. Matrix plasticity reduces microcrack number and simplifies the fracture pattern; weaker bedding planes promote shear failure and lower peak stress. The failure mode is thus governed by bedding–matrix competition, not by bedding-plane orientation alone.