Particle Transport in Fractures: A Common Problem in Enhanced Geothermal Systems and Hydraulic Fractures

Abstract

Particle transport within fractures is a common problem in hydraulic fractures and in Enhanced Geothermal Systems (EGS). In hydraulic fractures, proppant is used to keep the fractures open after the hydraulic pressure is released. Proppant concentration alters the fracturing fluid properties including dynamic viscosity and density, affecting the hydraulic fracture shape and direction especially in vertical fractures. The distribution of proppant particles over the induced fracture is crucial in maintaining the hydraulic conductivity of a fracture. In this work, a three-dimensional finite element model has been developed to simulate particle transport in fractures. Hydraulic fractures are modelled discretely as surfaces in a 3D matrix. Hydraulic fracture propagation is defined within the Linear Elastic Fracture Mechanics (LEFM) framework. Both proppant settlement and density flow are considered for movement of proppant particles in propagating vertical hydraulic fractures. The model also accounts for depth-increasing in-situ stresses. Results show that the downward movement of proppant encourages downward hydraulic fracture growth, while the depth-increasing in-situ stresses encourage the hydraulic fractures to grow upward.