Mechanisms of hydraulic fracture propagation in bedded shale: Insights from finite discrete element simulations

In this study, a hydro-mechanically coupled numerical model is established based on the finite discrete element method to systematically investigate the effects of the lateral pressure coefficient (λ), bedding plane weakening coefficient (R1), and mode II fracture toughness weakening coefficient (R2) on fracture propagation. The results show that: (1) when the λ approaches 1, fracture complexity is maximized for bedding angles of 0°, 45°, and 60° accompanied by a dense network of secondary fractures. At a 30° bedding angle with λ = 1, 26.3% of fractures propagate along bedding planes. In contrast, at 90°, fracture morphology becomes simpler and the proportion of lamination-parallel propagation approaches zero as λ increases. (2) When the R1 ≤ 0.3, fractures along the bedding plane exceed 20% (with 0° bedding reaching 52.3%), and shear failure dominates under high weakening conditions (R1 = 0.1). (3) When the mode II fracture toughness R2 = 0.5, the proportion of bedding parallel fractures at a 30° angle reaches 32.8%. With greater weakening (R2 = 0.7), the proportion of both tensile and shear fractures increase markedly. Gray correlation analysis indicates that mixed-mode fractures are the primary controlling factor for fractures extending along bedding planes. This study investigates the synergistic interplay among key geological and mechanical parameters affecting fracture behavior in bedding shale. The proposed numerical modeling framework provides a robust theoretical basis for optimizing fracturing design and enhancing the development of complex fracture networks, thereby offering valuable engineering guidance for improving shale gas reservoir stimulation efficiency.