Quantitative Study on Bed Load Proppant Transport during Slickwater Hydraulic Fracturing

Bed load proppant transport is a significant phenomenon during slickwater hydraulic fracturing. However, the mechanism of bed load proppant transport is still unclear. In the present study, the proppant transport process during slickwater hydraulic fracturing was simulated with a coupled computational fluid dynamics- (CFD-) discrete element method (DEM) model, and the mechanism of the bed load proppant transport was analyzed. A model for calculating the mass flux of the bed load layer was proposed and verified with experimental results from the literature. The results show that bed load migration is an essential mechanism of proppant transport. When the shear force of fluid acting on the surface of the sand bank reaches the critical Shields number, the proppant in the upper layer of the sand bank begins to migrate in the form of bed load. The movement of the bed load layer increases the time for the sand bank to reach the equilibrium height. In addition, the mass flux of the bed load layer significantly affects the equilibrium height of the sand bank. The mass flux of the bed load layer decreases, and the equilibrium height increases as the proppant density, proppant diameter, or rolling friction coefficient and static friction coefficient of the proppant increase, but the mass flux of the bed load layer increases, and the equilibrium height decreases as the fluid viscosity increases.