Numerical simulation of proppant directly entering complex fractures in shale gas

Large-scale slickwater fracturing is an important technical method for the effective development of shale gas, which generates complex fractures with fracture width of millimeters in the reservoir. It is known that the transport law of proppant in complex fractures is the premise for realizing effective propping. Taking the behavior of 70/140 mesh proppant particles commonly used in shale gas fracturing as the object,a numerical model based on the computational fluid dynamics-discrete element method (CFD-DEM) and the geometric model of the intersection of the main and secondary fractures are established. It is used to study the two-phase flow law under the conditions of different fracture widths and angles, pump displacements, and fluid viscosities. The results show that the proppant enters the secondary fracture in two ways: carried by the fluid in a suspended manner and rolling into the fracture from the sand bank surface. Particles suspended in the fracture can be transported to the distal end of the secondary fracture. Owing to the influence of the inertia force of particles, the particle flow rate entering the secondary fracture is much smaller than the fluid flow rate in the secondary fracture. As the included angle between the secondary and main fractures decreases, the fluid and particle flow rate increase, and particles can easily enter the secondary fracture. As the displacement, secondary fracture width and fracturing fluid viscosity increase, proppant particles are easier to enter secondary fractures. The absolute values of the main and secondary fracture widths become smaller, and the relative value remains the same, making it more difficult for proppant particles to enter the fractures.