Study on Fracture Initiation Mechanism of Plane Perforation

Abstract

Aiming at the engineering problems of high fracture pressure, great difficulty in fracturing reconstruction, poor fracture propagation effect of conventional perforation technology and high risk of casing damage in deep shale oil reservoirs, this paper systematically studies the hydraulic fracture initiation mechanism under spiral perforation, fixed-plane perforation and plane perforation technologies by combining theoretical analysis, numerical simulation and physical simulation. Based on linear elastic fracture mechanics, a mechanical model for composite fracture initiation at perforation tips was established. The finite element method was used to analyze the influence laws of key parameters such as perforation phase angle and hole density on fracture initiation pressure, propagation morphology and casing damage. The reliability of numerical simulation results was verified by true triaxial physical model experiments, and finally the optimal process parameter scheme for plane perforation was formed. The research results show that the plane perforation technology is significantly superior to spiral perforation and fixed-plane perforation in reducing formation fracture pressure and improving fracture propagation effect; considering the fracturing effect and casing safety factor comprehensively, the optimal process parameters of plane perforation are 16 holes per meter of hole density and 30° of phase angle. Under these parameters, the formation initiation pressure is as low as 61.2 MPa, the maximum fracture width reaches 5.27 mm, and the casing Mises stress is only 551 MPa, which meets the wellbore integrity requirements. The research results can provide theoretical support and on-site guidance for the optimal design of perforation and fracturing in deep shale oil reservoirs.