Randomized trial investigates preloading effects on fracture behavior in shale, indicating optimization strategies for fracturing designs.
Key Points
This research aims to explore how different levels of preloading stress affect fracture initiation and propagation during hydraulic fracturing in shale formations.
Conducted hydraulic fracturing experiments on Changning shale under varying differential stresses (5, 15, and 25 MPa).
Utilized acoustic emissions (AEs) and 3D laser scanning to analyze fracture morphology and evolution.
Measured independent parameters including standard deviation (SD), θs, and Rs to evaluate fracture characteristics.
At preloading stress below 30% of uniaxial compressive strength, microcrack formation significantly increased, but macroscopic fractures were few.
Higher preloading levels reduced AE activity and breakdown pressure, inhibiting tensile microcrack formation while promoting shear and mixed-mode microcracks.
Under high preloading, fractures displayed a vertical winglike propagation pattern with smoother surfaces as stress differences increased.