A coupled CFD-DEM approach to model particle-fluid mixture transport between two parallel plates to improve understanding of proppant micromechanics in hydraulic fractures

Abstract

Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) was used in this paper to model particle-liquid mixture transport between two parallel plates to improve the understanding of proppant micromechanics in a hydraulic fracture. The linear spring-dashpot model was used to model contact behavior between the particles in DEM code, and the interaction between the particles and fluid was coupled in the CFD code in terms of volumetric porosity and coupling force. The flow patterns and particle transport mechanisms were investigated based on which four developmental stages were divided from the beginning of injection to the formation of the final particle bank. The results show that when particles are transported in a thin fluid, they will quickly settle out of the fluid and accumulate at the bottom forming a particle dune. As the dune height increases, the flow stream is gradually hindered by the dune, and then the injected particles are vertically lifted and settle at the front of the dune. When the equilibrium height of the dune is reached, the dune develops to a bank, and then the particles injected later overshoot the bank and settle at the back side of the bank. The dune shape is significantly influenced by the erosion caused by the transported particles and flowing fluid, and the flow patterns of three-layers and two-layers are observed in different stages. Three particle transport mechanisms of settlement, fluidization and suspension, previously presented in early experimental studies, are observed in the CFD-DEM simulations. A new important transport mechanism of vorticity is also observed, which can control the motion direction of the injected particles during earlier and later injection stages.