Assessment of an equivalent porous medium for coupled stress and fluid flow in fractured rock

Abstract

The equivalent porous medium (EPM) for coupled stress and fluid flow in fractured rock was assessed. The assessment was focused on the contributions of the seepage-induced force to the system's equilibrium and deformation as well as fluid flux through the fractures, with the special emphasis on the inter-relations among these three aspects. Seepage-induced average stress was calculated for the EPM. And it was proved, with respect to the fluid flow system (FFS) proposed by Long et al. [Long JCS, Remer JC, Wilson CR. Witherspoon PA. Porous medium equivalents for networks of discontinuous fractures. Water Resour Res 1982;18:645-658], that the equivalence of the equilibrium contribution of the seepage-induced force is unconditionally satisfied in the EPM. The equivalence of fluid flux and seepage-induced deformation was evaluated using numerical techniques based on the FFS, in which the seepage-induced deformation was considered as 'tensile' deformation under fluid pressures. The numerical simulation results of the two cases suggest that the EPM established in terms of fluid flux based on the FFS guarantees equivalence of coupled stress and fluid flow. Also, the numerical simulation results indicate that the percolation theory can not be applied to a system with fractures of remarkably different size and hydraulic conductivity.