Large Scale Physical Modeling of Shale Fracture Propagation Under Different Controllable Shock Wave and Perforation Operation Schemes

Abstract

To address the relatively high near-wellbore fracture-initiation resistance and the tendency of hydraulic fractures to propagate along a dominant path under conventional perforation-based hydraulic fracturing, three large-scale hydraulic-fracturing experiments were conducted using a 10,000-ton ultra-large true-triaxial hydraulic-fracturing physical simulation system to investigate the effects of different controllable shock-wave–perforation operation schemes on shale fracture initiation and propagation. Natural shale outcrop blocks from the Jimsar shale oil reservoir, each measuring 2.0 m × 2.0 m × 1.0 m, were used. Three operation schemes were investigated: conventional perforation–hydraulic fracturing, shock wave–perforation–hydraulic fracturing, and perforation–shock wave–hydraulic fracturing. Post-fracturing fracture observations, three-dimensional fracture reconstruction, and wellhead-pressure responses were jointly analyzed to characterize fracture initiation and propagation under the different operation schemes. The results showed that, under conventional perforation–hydraulic fracturing, fracture propagation was dominated by a principal fracture, with only limited secondary fractures, and the wellhead breakdown pressure reached 21.2 MPa. After breakdown, the pressure remained at a relatively high level and exhibited sustained fluctuations, indicating large and continuously varying fracture-propagation resistance. When one 100 kJ shock was applied before perforation, several large-scale dominant fracture surfaces developed, and the breakdown pressure decreased to 6.6 MPa, representing a reduction of 68.9% relative to the conventional case. The post-breakdown pressure gradually stabilized, indicating reduced variation in fracture-propagation resistance. When two successive 100 kJ shocks were applied after perforation, fractures propagated in multiple directions with more pronounced bending, deflection, and branching. The breakdown pressure further decreased to 4.6 MPa, 78.3% lower than that of the conventional case. Fractures continued to propagate under relatively low pressure, followed by a late-stage pressure increase. The dynamic disturbance induced by controllable shock waves altered the near-wellbore stress distribution and rock-failure conditions, reduced hydraulic-fracture initiation resistance, and modified subsequent fracture-propagation paths. These results reveal the coupled mechanism of near-wellbore stress redistribution and dynamic fracture propagation induced by controllable shock-wave–perforation operations, and provide experimental support for fracture-initiation control and optimization of integrated stimulation parameters in the Jimsar shale oil reservoir.