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

Abstract

The excavation damaged zone (EDZ) of the Callovo-Oxfordian argillites can be regarded as a double-porosity media consisting of blocks of undisturbed argillites separated by cracks generated by shear or traction stresses. However, owing to hardware limitations, most of the hydraulic-gas simulations undertaken on large scales are based on an equivalent-porous-media model of the EDZ, where the fractures are not explicitly represented. The aim of this study is to improve the equivalent-porous-media model's consistency with the double-porosity flow behaviours shown by experimental data while keeping the same level of simplification. The new model has been developed through a performance assessment (PA)-like approach in two steps: a phenomenological model including explicit fractures has been designed in accordance with the actual geometrical and hydraulic understanding of the EDZ; then, the properties of the simplified model have been calibrated to comply with the hydraulic behaviour of the explicit-fracture model. This methodological approach has been used on an access gallery parallel to the main horizontal stress axis. The new equivalent-porous-media model differs from the previous one on the following three main points: the gallery EDZ has an anisotropic intrinsic permeability that is lower than previously; the same retention law is used as the undisturbed host rock; and there is a higher relative permeability for gas and water than previously.

Disposal of High-Level Nuclear Waste in Deep Horizontal Drillholes

“…This pathway is part of several subdomains referred to as (1) the engineered barrier system (EBS), which includes the waste, canister, backfill and other engineered components, such as liners and seals, (2) the geosphere, also referred to as the far field or natural barrier system, which includes the host rock and aquifers and (3) the biosphere, which is the biological environment that determines the radiation dose to the receptor [57]. Special consideration is given to the interface between the EBS and the geosphere, which consists of the damaged or disturbed zone around the excavation [58].…”

Radioactive waste confinement: clays in natural and engineered barriers – introduction

“…Bénet et al (2016) model water and gas flow through an excavation damaged zone in the Callovo-Oxfordian argillites in the framework of a single porosity model, while Smutek et al (2016) report on the gas permeability, breakthrough behaviour and re-sealing ability of Czech Ca -Mg bentonite. Finally, Jacops et al (2016) report on a study to measure diffusion coefficients of dissolved helium and argon in three potential clay host formations: Boom Clay (of relevance to the Belgian national programme), Callovo-Oxfordian Clay (of relevance to the French national programme) and Opalinus Clay (of relevance to the Swiss national programme).…”

A Numerical Investigation on the Effect of Gas Pressure on the Water Saturation of Compacted Bentonite-Sand Samples

“…Gonzalez-Blanco et al [21] simulated gas migration in a Cenozoic clay with a fully coupled hydromechanical model, which incorporated an embedded fracture permeability model. Additionally, other researchers performed a series of numerical modelling assays to determine gas migration in clayey materials [16,[22][23][24].…”