Fabric-Dependent Hydro-Mechanical Behavior of Pre-Fractured Rocks

Abstract

Fabric and boundary conditions determine the hydro-mechanical behavior of rock masses. In this numerical study, a set of two-dimensional models are created to simulate various layered rock fabrics. The fabric varies in terms of density and relative orientation of natural fractures. The behavior of differently-structured blocky media is analyzed due to a mechanical disturbance that resembles the creation of an opening-mode discontinuity in the medium analogous to hydraulic stimulation. The response of the blocky medium is also investigated in terms of the amplitude of this idealized stimulation resembling the viscosity or flow rate of the injected fluid. The analysis is performed using the distinct element formulation, which can capture the opening and shear failure of existing discontinuities and deformations of the rock blocks globally-disturbed under high far-field stresses. The results show fundamental differences in the deformation field of rock masses with different fabrics. Local shear dilation along natural fractures and global kinematic dilation of the stimulated reservoir area are dominant mechanisms although both processes are more limited than the case of rigid block assemblies under low stresses. The amplitude of kinematic dilation differs for different fabrics, and it implies the extent of enhancement in the permeability of the rock mass.