Comparing flows to a tunnel for single porosity, double porosity and discrete fracture representations of the EDZ

• Published in: Physics and chemistry of the earth. Parts A/B/C 2011, Vol.36 (17), p.1990-2002
• Main Authors: Hawkins, I.R., Swift, B.T., Hoch, A.R., Wendling, J.
• Format: Article
• Language: English
• Subjects: Discrete fracture network; Excavation; Excavation Damaged Zone; Fracture mechanics; Mathematical models; Modelling; Networks; Repositories; Representations; Tunnel; Tunnels (transportation); Two-phase flow
• ISSN: 1474-7065; 1873-5193
• DOI: 10.1016/j.pce.2011.07.029

► Export of data for fractured EDZs from a DFN model to a TOUGH2v2 continuum model. ► Reasonable agreement between two-phase flow for DFN and TOUGH2v2 models of an EDZ. ► An EDZ is modelled using TOUGH2v2 with and without export of data from a DFN model. ► Exporting data between models has advantages if the permeability is anisotropic. Andra is studying the feasibility of constructing a repository for radioactive waste in the Callovo-Oxfordian mudstones. The excavation of a repository leads to the formation of an Excavation Damaged Zone (EDZ) adjacent to the repository. The EDZ contains fractures and micro-fissures modifying the hydraulic properties of this region. Conventionally, porous medium representations are used to model two-phase flow around repositories. However, it is not possible to represent the detailed heterogeneity inherent to a fractured medium in such models. Conversely, discrete fracture network (DFN) models can be used to provide a direct representation of the fractures, but currently computational limitations mean that is at the expense of the representation of two-phase flow behaviour. In this study the different types of models that may be used to model two-phase flows through an EDZ to a tunnel are compared to help to determine a suitable approach for future modelling of the EDZ. In particular, calculations are performed using an approach in which the properties for a porous medium model are determined by calculation of the effective properties of a fracture network set up in a DFN model. This combined approach is examined as a possible way to improve on modelling performed using either approach alone.