Experimental Study of the Effect of Shale Fracture Shear-Slip Behavior Under Hydraulic Pulses
摘要
Hydraulic fracturing serves as a fundamental technique for enhancing resource recovery in unconventional reservoirs such as shale gas. However, as extraction advances into deeper shale formations, conventional fracturing methods face challenges, such as limited fracture propagation and inadequate stimulated reservoir volume. Hydraulic pulse injection has emerged as a promising approach to promote complex fracture networks, though its underlying mechanisms remain incompletely understood. This study investigates deep shale gas reservoirs in the Southern Sichuan Basin through hydraulic pulse injection shear-slip experiments, comparing fracture responses under conventional monotonic and pulsed injection conditions. We systematically examine the influence of pulse parameters, including frequency, peak pressure, and waveform, on shale fracture slip behavior. Theoretical analyses based on experimental results characterize microseismic energy release patterns induced by hydraulic pulses. Key findings reveal that compared with monotonic injection, hydraulic pulse injection reduces the dynamic slip initiation pressure by 14%, suppresses the peak slip rate, and enhances cumulative shear displacement by promoting more uniform fluid distribution along the fracture surface. This enables progressive fracture slip under lower initiation pressure while reducing shear stress perturbation. Pulse parameters exhibit nonlinear control over slip behavior: increasing the peak pressure raises the dynamic slip initiation pressure by 25.1%, elevates the slip rate to 5.19 × 10–1 mm/s, and amplifies cumulative displacement by 57 times, whereas high-frequency pulses reduce the slip rate by 69.8% while improving fluid diffusion. Waveform significantly affects energy release efficiency; trapezoidal waves generate a slip rate of 4.57 × 10–2 mm/s and an energy efficiency of 0.0033 through abrupt pressure changes, while triangular waves fail to overcome the static friction threshold due to insufficient overpressure duration. These experimental and theoretical results demonstrate that optimized pulse injection parameters can simultaneously enhance fracture network complexity and regulate energy release, providing a scientific basis for improved hydraulic-fracturing design.