Macro-permeability distribution and anisotropy in a 3D fissured and fractured clay rock: ‘Excavation Damaged Zone’ around a cylindrical drift in Callovo-Oxfordian Argilite (Bure)

Abstract

factors: the large extent of chevron fractures, the assumption of constant hydraulic aperture, and the cubic law behavior based on the assumption of Poiseuille flow.The equivalent macro-permeabilities obtained in this work can be used for large scale flow modeling using any simulation code that accommodates Darcy's law with a full, spatially variable permeability tensor K ij (x).

Equivalent upscaled hydro-mechanical properties of a damaged and fractured claystone around a gallery (Meuse/Haute-Marne Underground Research Laboratory)

“…Finally, there are also numerical solvers that aim at obtaining detailed simulations of the behaviour of the porous matrix, the discrete fractures and their interactions. In some cases, these solvers use a set of local-scale effective coefficients, such as the parallel and orthogonal effective permeability of a joint embedded in a porous matrix (this concept was also used in Cañamón (2006Cañamón ( , 2009 and Ababou et al (2011) as a building block for implementing the hydraulic superposition method on larger scales). For instance, Mourzenko et al (2010) numerically solve single-phase flow in a matrix-fracture system with thousands of fractures, tens of wells and millions of elementary volumes, with local effective permeability attributed locally to the discrete joints surrounded by porous matrix.…”

“…The generalized superposition method considered in this paper goes as follows: † For hydraulic upscaling, the local Darcy and/or Poiseuille fluxes in both the permeable matrix and the cracks are superposed, and the final result is a tensorial flux/gradient law with macropermeability K ij (this problem is fully treated in Ababou et al (2011) for the same URL site and the same GMR gallery). † For mechanical upscaling, local strains are superposed, in a manner that involves both the isotropic elastic porous matrix and the strongly anisotropic elastic cracks.…”

“…The latter fractures are then numerically discretized into triangular patches before applying the generalized superposition method (see Ababou et al 2011). The statistical cracks are disc-shaped planar objects that are generated only once (single realization).…”

“…The zone of interest is the so-called excavation damaged zone (EDZ), a cylindrical annular zone around the gallery. The next section will present the study site briefly, but we also refer the interested reader to Ababou et al (2011) for more details concerning the overall objectives, the programmatic context, the URL site and some of the relevant data.…”

Modelling of water and gas flow through an excavation damaged zone in the Callovo-Oxfordian argillites in the framework of a single porosity model

“…In the DFN model, the EDZ-c is represented by small random fractures, and the EDZ-d is represented by inclined planes regularly spaced. Ababou et al (2011) used the rock matrix, the 3D geometrical structure of EDZ-c microfissures and small fractures, and the EDZ-d subvertical fractures to develop a phenomenological model. They then perform a hydraulic homogenization to define an equivalent macropermeability tensor K ij (xyz) distributed over the EDZ on a continuum model.…”