Numerical Simulation of the Propagation Characteristics of a Pulse Fracture Network in Shale Reservoirs under Thermo-Hydro-Mechanical-Damage Coupling

Deep shale reservoirs feature poor physical properties and well-developed dense bedding planes. Conventional hydraulic fracturing produces limited stimulated volume and inadequate activation of natural fractures, failing to effectively boost reservoir permeability, while pulsed fracturing is a promising technique to construct complex fracture networks. The multifield coupled fracture propagation mechanism of pulsed fracturing in high-bedding-density shale remains ambiguous, and the uniformity of fracture stimulation needs optimization. This paper constructs a stress-damage-seepage-temperature four-field coupled model for pulsed fracture propagation, and systematically explores the regulating rules of pulse amplitude, frequency, and confining pressure difference on fracture evolution, considering shale bedding anisotropy. The results reveal three synchronous evolutionary stages of pulsed fracturing: initial compaction, rapid damage accumulation, and stable fracture propagation. Higher pulse amplitudes accelerate fatigue damage and branch fracture growth, and fracture network complexity negatively correlates with pulse frequency, where low-frequency pulses favor continuous seepage channels. Larger confining pressure differences raise fracture propagation resistance and restrain bedding weak plane activation. Increasing pulse amplitude, reducing frequency, and lowering confining pressure difference jointly trigger positive coupling feedback to fully activate bedding planes and form intricate fracture networks. This work offers theoretical guidance for parameter optimization of shale pulsed fracturing.