Numerical simulation of proppant distribution in hydraulic fractures in horizontal wells

Abstract

Since the placement of injected proppants affects fracture conductivity and fractured well productivity, it is of significant importance for fracturing design to accurately predict proppant distribution in a fracture. Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) was used to model proppant distribution in fractures in horizontal wells, and the effects of proppant diameter and density, fluid viscosity, and injection rate were investigated. The interactions between proppants and fracturing fluids were taken into account, and a contact model was used to simulate the micro-mechanical interactions between proppant particles, which can represent realistic dynamics of particle collisions. The results show that proppant motion is governed largely by the settlement and drag caused by the fracturing fluid. Settlement causes proppant dunes to form near the wellbore, while the fracturing fluid drags the proppant deeper into the fracture. The injected proppants quickly settle out of the fluid and accumulate on the fracture bottom forming proppant dune. Only when the equilibrium height of the proppant dune is reached can the later injected proppant be transported farther into the fracture. The lower and upper injection positions of the fracture were chosen to mimic vertically asymmetric fractures, and different profiles of proppant placement were observed. Three processes of overflushing, shut-down and tail-in were simulated. The overflushing can cause a large proppant-free region near the wellbore, while the tail-in process at a low injection rate can fill the injected proppant in the proppant-free region. Therefore, a composite process of overflushing and tail-in with large proppant particles at a low injection rate can improve proppant distribution in the fracture, which will greatly increase the productivity of fractured wells.