Interaction Propagation Behavior and Control Mechanisms of Hydraulic Fractures Under Conditions of High-Angle Natural Fractures

Natural fractures in fractured buried-hill reservoirs exhibit complex spatial distributions and strongly control hydraulic fracture network morphology and stimulation effectiveness. This study investigates the BZ19-6 gas field (Bozhong 19-6 gas field), a fractured buried-hill reservoir, using true triaxial hydraulic fracturing experiments and three-dimensional discrete lattice simulations to clarify hydraulic fracture propagation under high stress contrast and highly inclined natural fractures. The effects of natural fracture inclination, stress–fracture angle, and cementation strength on fracture interaction and propagation are analyzed. An interaction-state classification and a differentiated stimulation zoning scheme are proposed. Results show that natural fracture activation decreases with increasing inclination, but this effect weakens when inclination exceeds about 50°. For highly inclined fractures (80°), increasing the stress–fracture angle promotes a transition from natural fracture activation to hydraulic fracture penetration. Strong interaction and cooperative propagation occur at 45–75°, favoring complex fracture networks. Cementation strength controls the post-intersection failure pathway: weakly cemented fractures promote activation, deflection, and branching, whereas strongly cemented fractures favor direct penetration. Overall, hydraulic fracture propagation is governed by competition between natural fracture reactivation and intact rock failure. The proposed classification and zoning method provides guidance for predicting fracture propagation and optimizing hydraulic fracturing in naturally fractured reservoirs.