Investigation into the migration characteristics of temporary diverting agent in hydraulic fracturing of hot dry rock based on CFD-DEM coupling

Temporary plugging reorientation fracturing is one of the most promising technologies to improve the heat mining of hot dry rock, The existing numerical simulation model for the migration process of temporary plugging agent in fractures is relatively simplified, and it is difficult to accurately describe the complex flow process of a temporary plugging agent in fractures, and to capture the real movement and interaction of particles in the fracture. In order to accurately understand the migration regularity and the interaction mechanism between particles of temporary diverting agents in the hydraulic fractures of hot dry rock, the particle movement and fluid flow in the fracture are described by the Euler-Lagrange approach, through the bidirectional coupling of computational fluid dynamics (CFD) and the discrete element method (DEM),the CFD-DEM coupling model of particulate temporary diverting agents transportation in hydraulic fractures is established. Numerical results demonstrate that the main factors affecting the understanding of temporary diverting agent migration in hydraulic fractures of hot dry rock are: the carrier fluid viscosity, temporary diverting agent mass concentration, the flow state of the carrier fluid and the friction coefficient between particles.. However, the friction coefficient between particles has less influence on the interparticle interaction force in the hydraulic fracture. The friction force between particles is relatively small and it is difficult to overcome the influence of fluid flow on particle velocity. During the process of increasing the carrier fluid viscosity from 0.03mPa•s to 120mPa•s, the average velocity of the temporary diverting agents in the hydraulic fracture decreased by more than 77%, With the increase of viscosity, the increase of velocity of temporary plugging agent particles in cracks decreases gradually, and the velocity of particles at the exit and fluid flow rate decrease significantly. With an increase of the mass concentration of temporary plugging agent, the interaction force between particles increases continuously. When the transport of the temporary diverting agent reached a relatively stable state, the mass concentration doubled and, the interaction force between the particles increased by more than 44%. When the carrying fluid in the fracture shows local turbulence, the velocity of the particles and the interaction force between the particles change significantly, and the interaction between the particles increases more than 150 times compared with the normal flow condition. The research results of this paper have important theoretical and instructive significance for guiding the optimization of the dosage of temporary diverting agents.