Weak-Plane Activation and Non-Uniform Hydraulic Fracture Propagation in Layered Shale: Coupled Simulation and Cross-Method Comparison

Hydraulic fractures in bedding-rich shale commonly interact with natural fractures and bedding interfaces, promoting fracture diversion, height containment, and asymmetric growth between nearby initiation points. This study investigates these processes using a coupled flow-solid cohesive-zone model with 30 single-factor cases covering in situ stress differences, elastic modulus, Poisson’s ratio, matrix fracture toughness, fluid viscosity, and injection rate, together with an auxiliary two-injection-point angle model. The effective-stress framework is used to interpret weak-plane activation, while fracture initiation and mixed-mode degradation are represented by a cohesive traction-separation formulation. Increasing the in situ stress difference from 1 to 5 MPa increases fracture height from approximately 3.0 to 7.2 m while reducing width from about 4.7 to 3.5 mm. Elastic modulus, Poisson’s ratio, and matrix fracture toughness primarily influence aperture within the investigated ranges, whereas higher fluid viscosity and injection rate are associated with greater vertical extension. Cross-method comparison with RFPA2D-Flow, FDEM, phase-field, block-DEM, and CDEM studies shows consistent trends in weak-plane interaction and fracture diversion. Field-scale microseismic observations from the Guyeyouping-1 horizontal well indicate predominantly vertical fractures with interpreted full lengths of approximately 222–470 m, an average length of about 365 m, and an average left–right wing-length difference of approximately 50 m; a corresponding six-cluster simulation exhibits the same asymmetric growth tendency. Overall, the results identify stress state, weak-plane geometry, and hydraulic conditions as key controls on non-uniform fracture propagation in layered shale and provide a mechanistic basis for site-specific fracturing design within the investigated parameter ranges.