Chapter 4 - Quasistatic Discrete Element Modeling of Hydraulic and Thermal Fracturing Processes in Shale and Low-Permeability Crystalline Rocks

Abstract

A quasistatic discrete element model (DEM) has been developed and coupled with heat conduction model and network flow models to provide mechanistically based simulations of crack propagations within low-permeability heterogeneous rocks under hydraulic or thermal stimulations. For crack growth in hot brittle crystalline rocks, driven by thermal cooling, the coupled DEM–heat conduction model clearly predicts that a quasihierarchical array of subparallel cracks, oriented along the direction of the temperature gradient, is formed under small-to-moderately large thermally generated strain load conditions. The coupled DEM–network flow model enables realistic simulations of hydraulic fracturing process in low-permeability rocks with both local heterogeneity due to variations of the mineral fabric and larger-scale stratigraphic heterogeneities that can be conveniently incorporated into the model. The simulation results clearly indicate that the stratigraphic mechanical heterogeneity provides an important containment mechanism for the vertical growth of hydraulic fractures. The coupled 3D network flow and quasistatic DEM model enables a unique combination of realism and computational efficiency for the simulation of hydraulic fracturing in heterogeneous rocks.