Numerical Investigation of Rock Fragmentation Induced by High-Voltage Electric Pulses Under Varying Prefabricated Fracture Angles

As an innovative rock fragmentation technology, high-voltage electric pulse (HVEP) shows promise in addressing development challenges of unconventional marine oil and gas resources. To investigate the rock fragmentation mechanism of HVEP in naturally fractured reservoirs, this study establishes a multi-physics coupled “electro-mechanical-damage” numerical model considering rock heterogeneity using COMSOL Multiphysics simulation software. Driven primarily by shockwaves generated from electric pulses and incorporating the Mohr-Coulomb damage criterion, the model systematically simulates the damage evolution process in rock specimens containing prefabricated fractures at various angles (α = 0°–60°) under multiple pulse impacts. The results demonstrate that HVEP rock fragmentation is not an instantaneous penetration process under single impact, but rather a progressive fatigue damage process dominated by shockwaves. Rock damage accumulates nonlinearly with increasing discharge cycles; under α = 0° conditions, the damage increment from the third pulse is 2.38 times that of the second pulse. The prefabricated fracture angle α exerts significant nonlinear control over crack patterns and fragmentation efficiency. When α falls within the 30°–45° range, wellbore secondary cracks and main crack tips develop synergistically, forming complex fracture networks. Conversely, either insufficient (≤15°) or excessive (≥60°) angles hinder damage propagation. Under the studied parameters, optimal fragmentation occurs at α = 45°, where the total damage area after three discharges increases by 60.3% compared to the baseline case (α = 0°). This is primarily because the 45° inclination maximizes the shear-tensile composite action of shockwaves, most effectively activating wellbore damage and promoting its interconnection with main fractures.