Abstract
Interest in the hydraulic and mechanical characterization of shales has grown in recent years, because of their application in the context of energy geotechnics. In the frame of nuclear waste disposal shales are considered as host formations for the placements of nuclear waste at high depths. In the frame of hydrocarbon production they are considered as unconventional reservoirs, from which extracting natural gas. Understanding how fluids flow through shales is then a key aspect for both fields of application. This paper focuses on the analysis of the transport of water vapour through laboratory samples. After reviewing the balance and flow laws that govern the transport of fluid in unsaturated porous media, a simplified model is put forward. The model was implemented in a commercial finite element code, and it was used to reproduce the results of a literature study on wetting and drying of Opalinus Clay shale samples, imposed through the vapour equilibrium technique. Back analysis of the water content and volume strains of these specimens suggests that existing models underestimate the actual flow rate of water vapour which takes place at low suctions. The current interpretation also seems to be consistent with microstructural investigations on the interconnection between large pores of this material.
Highlights
In the last years the underground geological storage is considered the best solution for the disposal of nuclear waste produced by power plants of different countries including Switzerland, Belgium and France [1]
This study aims at gaining an insight on the transport of water vapour through unsaturated Opalinus Clay shale
In order to characterise the hydro-mechanical behaviour of the Opalinus Clay shale in [2], the coupling between the water retention and deformative response was studied performing a wetting/drying cycle with the Vapour Equilibrium Technique
Summary
In the last years the underground geological storage is considered the best solution for the disposal of nuclear waste produced by power plants of different countries including Switzerland, Belgium and France [1]. Repository systems are placed in a stable rock formation, to protect the environment and the people from the radioactive waste that they contain. Shales are studied as host rock formation, because of their sealing properties. A detailed knowledge of transport processes and mechanisms in shales is a fundamental requirement for a safe disposal. Careful attention must be payed to the mass transport phenomena occurring in the partially saturated conditions at which these materials are found. Experimental studies aim to know how the geomechanical properties of Opalinus Clay shale change with the water content, in light of engineering aspects such as the excavation and the ventilation of the tunnel or the temperature decay of the canister. Much attention has been paid to the determination of water retention behaviour of Opalinus Clay shale, e.g. Much attention has been paid to the determination of water retention behaviour of Opalinus Clay shale, e.g. [2,3]
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