Modeling of flow characteristics in 3D rough rock fracture with geometry changes under confining stresses

Abstract

A series of fracture geometries of an artificially tensile fractured sandstone, measured during the hydraulic tests at increasing confine stresses, were adopted to build 3D fracture models. At each stress level, four groups of flow simulations with increasing injection flow rates were conducted, to examine how voids and contact alterations due to stress changes affect the flow characteristics within the fracture. The results show that the simulated normalized apparent transmissivity matched well with that measured from hydraulic tests, and both them decreases nonlinearly with increasing confine stress. The alterations in fracture geometries due to stress changes increase the heterogeneities of flow characteristics in 3D fractures, including flow rates, streamlines, water pressure. The streamlines become more channeled with observable tortuosity under high stress. The stress induced increase in contact and the occurrence of eddy flow enhance the non-linearity of pressure drop. The decrease of both apertures and sharp geometries under high stress reduces the range of eddy flows, which delays the occurrence of significant inertial effects and results in the increase of critical Reynolds numbers. These features are demonstrated well using an idealized 3D representative geometric including both the asperity contacts and voids.