The migration mechanism of temporary plugging agents in rough fractures of hot dry rock: A numerical study

Abstract

Plugging and diverting fracturing is a promising technology that aims to enhance the heat extraction efficiency in hot dry rock. The key to the success of this technique is the formation of effective plugging zones in existing fractures. However, given the high temperature and high stress of hot dry rock, the migration and sealing mechanisms of temporary plugging agents in such reservoirs are quite different from those in conventional tight reservoirs. Using the computational fluid dynamics/discrete element method coupled method, this paper numerically investigates the migration mechanism of temporary plugging agents in rough fractures of hot dry rock. First, we construct a model of a rough fracture surface in hot dry rock by performing computerized tomography scanning. Second, we adopt the well-established theory of the joint roughness coefficient to describe the fracture surface roughness. Then a discrete phase model that considers the effect of temperature is constructed to characterize the interparticle interaction of temporary plugging agents. A bidirectional coupling algorithm between the fluid flow in the fracture and the migration of temporary plugging agent particles is adopted. Finally, the effects of key factors such as fracture wall temperature, fracture roughness, injection angle, and injection location on the migration mechanism of granular temporary plugging agents in rough fractures are analyzed in detail. The results show that fracture roughness and temperature have a significant impact on the migration process in hydraulic fractures. When the fracture surface roughness increases by 10.44 as measured by the joint roughness coefficient, the particle force and particle temperature increase by 12.0% and 37.8%, respectively. When the fracture surface temperature increases by 200 K, the particle force and particle temperature increase by 88.2% and 14.4%, respectively.