Numerical modelling of the resaturation of swelling clay with gas injection

During long-term storage of radioactive waste, steel containers are corroded and this process leads to hydrogen production. An in-situ experiment has been designed by Andra, in order to analyze the influence of gas migration on the dynamics of resaturation of the bentonite plug. The competition between liquid water coming from argillite and a gas injection at both ends of the plug is studied. Predictive numerical modelling of the experiment is performed in order to support the design, with a special emphasis on the coupling between the water and gas transfers and the mechanical behaviour. can alter the good confinement between the canisters and the access gallery. The paper deals with an in-situ experiment that is currently performed by Andra in its underground laboratory at Bure. The objective of the PGZ experiment is the analysis of the dynamic of the bentonite plug resaturation, studying the competition between the liquid water coming from the host formation and a gas injection at both ends of the plug. In order to support the design of the experiment, predictive numerical simulations of the gas migration in both the host formation and the swelling clay plug are achieved, with a special emphasis on coupling between the gas transfers and the mechanical strains and stresses. The influence of damage or plasticity on the fluid transfer parameters, which can explained the preferential pathways, are not taken into account in the modelling of the experiment. In this paper, the concept of the experiment and the boundary value problem of the simulations are described in section 2. The hydro-mechanical model is then defined in section 3. In section 4 the results of the modelling are presented and analyzed, before the conclusions (section 5). 2 BOUNDARY VALUE PROBLEM The general concept of the PGZ experiment is presented on Figure 1. A 25 m long horizontal borehole is drilled in the callovo-oxfordian argillite,