Assessment of stress-induced evolution of permeability tensor in rock mass containing discrete fracture network

The work presented in this paper is focused on the assessment of equivalent permeability, and its stress-induced evolution, in fractured rock mass. A procedure is proposed for specifying the eigenvectors/eigenvalues of permeability tensor based on the notion of a fabric tensor. The approach involves a series of mesoscale simulations of fluid flow for a given discrete fracture network and determining the best-fit approximation to the spatial distribution of directional permeability that represents a scalar fabric descriptor. In order to specify the stress-induced evolution law for the permeability tensor, a set of ‘virtual data’ is generated based on a mechanical analysis that takes into account the changes in fracture aperture and onset/activation of new fractures. The proposed evolution law relates the principal values/directions of permeability operator to those of the stress tensor through a polynomial expression that incorporates the value of the failure function as an independent variable. The results of a numerical study are presented for a fracture pattern mapped from the south-west region of the Bristol Channel Basin. The hydraulic and mechanical analyses for the rock mass are carried out using a constitutive law with embedded discontinuity (CLED), in which the permeability and stiffness operators in the domain adjacent to the discontinuity both incorporate a length scale parameter.