Gas migration properties through a bentonite/argillite interface

Among diversified industrial uses, see for instance Koch [Koch, Appl. Clay Sci., (21) 2002], and following positive in situ experiments, compacted bentonite blocks are potential candidates for sealing nuclear waste repositories, thanks to their swelling ability in a wet environment.As requested by Andra (French Agency for Nuclear Waste Management) and complementarily to in situ experiments, an original experimental laboratory set-up was designed in order to reproduce the introduction and swelling of bentonite plugs inside an argillite host rock. Once the argillite/bentonite interface is established, an increase in storage tunnel gas pressure is simulated and the interface gas migration pressure (or gas critical pressure) is evaluated. More precisely, a first experimental set-up provides bentonite swelling pressure and kinetics (i.e. mainly hydraulic cut-off, time to reach asymptotic swelling pressure and value of asymptotic swelling pressure) at given initial compaction and saturation rate. This phase is preparatory to reproducing the introduction and subsequent swelling of a bentonite plug inside the argillite host rock, which uses a similar test rig. Experimental results of water permeability and gas critical pressure are provided for MX80 compacted bentonite associated to Bure Callovo-Oxfordian argillite.