Chapter 8 - Grain Scale Flow of Fluid in Fractured Rocks

Abstract

This chapter develops a dual-permeability model using Universal Distinct Element Code (UDEC) to investigate the behavior of deformation and permeability of fractured rocks under loading/unloading in which both matrix flow and fracture flow are simulated. A dual-permeability model is used in this study together with the deformable and fracturing matrix model. Because of the matrix permeability that is simulated by the hydraulic conductivity of grain boundaries, this type of dual-permeability model is especially suitable for low-permeable rocks such as granites that have low porosity and tightly interlocked and bonded grains. The chapter presents a flow model where the computations determine the updated geometry of the system and yield new values of the aperture of grain boundaries and fractures and the volumes of all domains. The chapter investigates (1) the evolution or growth of fractures in response to loading, (2) the stress conditions at which originally isolated fractures are connected by newly created fractures, leading to a secondary percolation phenomenon, (3) the resulting changes in permeability because of the differences in effective mean stress, and (4) cycling loading and path-dependent behavior.