Experimental Study on the Fracture Characteristics of Shale with Natural Fractures

The mechanism of fracture formation in hydraulic fracturing of shale reservoirs essentially depends on the fracture mechanics characteristics of the rock mass. To investigate the interaction mechanism between hydraulic fractures and natural fractures during shale fracturing, semicircular disk specimens with prefabricated notches at varying angles to natural fractures were prepared. Three-point bending tests were conducted to study Fracture propagation and fracture characteristics, obtaining fracture toughness parameters under different natural fracture orientations and notch positions. Acoustic emission monitoring was employed to analyze fracture propagation patterns and deflection behavior. Key findings include: (1) Under the influence of bedding planes and natural fractures, prefabricated Fracture paths exhibit "Z-shaped" trajectories. Planar Fracture initiation occurs at low (0°, 30°) and high (90°) approach angles, while non-planar initiation dominates at intermediate angles (45° and 60°). The actual incident angle exceeds the preset intersection angle, with Fractures deflecting toward natural fractures during propagation. (2) Natural fractures cause Fracture initiation to deviate from the prefabricated notch direction, resulting in measurable initiation angle offsets. (3) As the intersection angle increases, propagation transitions from "along natural fractures" to "directly crossing natural fractures." Significant roughness contrast between prefabricated and natural fractures contributes to effective self-propping of fracture surfaces post-matrix failure. The research results have certain guiding significance for optimizing the design of shale hydraulic fracturing, regulating the interference between the fracture channels and the natural weak planes of the reservoir, as well as the communication process.