DEM numerical simulation study on fracture propagation of synchronous fracturing in a double fracture rock mass

The rational choice of perforation arrangement and injection angle is of great significance to improve the efficiency of synchronous fracturing and to achieve the stimulation of the shale reservoir. In this paper, the influence of perforation angle and perforation arrangement on the crack propagation mechanism and rock failure mode of synchronous fracturing is studied based on the particle discrete element software PFC. Results show that due to the influence of the stress shadow effect, elliptical cutting cracks are produced between perforations during the synchronous fracturing. When the perforations are arranged in alignment, the fracture mode of rock mass between the perforations is single crack cutting failure under low injection angle, and double-crack cutting failure under high injection angle. Meanwhile, when the injection angle tends to the direction of maximum principal stress (θ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\uptheta$$\end{document} ≥ 60°), the fracturing effect can be greatly improved. In addition, the small perforation spacing under the high principal stress difference is more conducive to the fracturing of the central rock mass. When the perforation is staggered arrangement and the horizontal distance between the perforation centers is the perforation length, it is easy to form the intersection phenomenon of wing cracks under the high principal stress difference, which is more conducive to the realization of fracturing in the central rock mass. In addition, high injection angle is more conducive to the formation of penetrating cracks, but not easy to achieve the central rock mass fracturing. The findings of this study can help for a better understanding of crack propagation law and rock failure mode under different perforation arrangements, which can provide some theoretical guidance for the field synchronous fracturing construction.