On the impact of proppants shape, size distribution, and friction on adaptive fracture conductivity in EGS

Abstract

Enhanced Geothermal Systems (EGS) rely on efficient water circulation through fracture networks to maximize heat extraction. In the presence of fractures with large apertures, the working fluid naturally tends to localize in the fractures with the shortest and least-resistance path between the injection and production wells. Such occurrences leave enormous amounts of unrecovered heat and can shorten the duration of an EGS project. Tuning the hydraulic conductivity of each fracture based on the surrounding formation temperature may provide a solution for short-circuiting and result in uniform heat production from each fracture within the EGS. However, no technology currently exists to do so. In this paper, we aim to investigate the effectiveness of using a novel proppant whose size is temperature dependent. The proposed proppant shrinks or expands based on the local temperature to control the fluid flow in each fracture. Through particle-scale modeling, the impact of the shape, size, and friction coefficient of such proppants on the proppant permeability is systematically investigated using discrete element methods (DEM), finite element methods (FEM), and Lattice Boltzmann Methods (LBM). Particle-scale analysis shows that small proppants with slightly irregular shapes yield a higher increase in permeability and thus higher heat production from EGS. In addition, a high friction coefficient yields a higher proppant permeability. The results of particle-scale analysis are used as an input to field-scale analysis. Field-scale results show a 103.46% improvement in the heat extraction efficiency from EGS after 50 years of production when such a temperature-sensitive proppant is adopted. Thermal breakthroughs occur at a later time when temperature-sensitive proppant is used compared to conventional proppant.