An insight on the thermo-mechanical behaviour of a shale

In recent years, several shale formations have been employed in geo-energy related engineering fields that foresee the presence of high thermal loads or significant temperature variations. Such thermal conditions are related to a need to reach great depths (several hundred of meters), as in the case of CO2 sequestration and Enhanced Geothermal System (EGS) technologies, or to the presence of thermal sources, as in the context of nuclear waste geological disposal. In addition, thermal changes can occur in shale formations through the injection of drilling and fracturing fluids at great depths, where a higher temperature with respect to the one of the injected fluid is encountered as a result of the geothermal gradient. Therefore questions are raised on the impact of temperature variations on the hydro-mechanical properties of shale formations and on the thermal response of the material in different stress conditions. The Opalinus Clay shale formation is considered as host-material for the construction of a deep geological repository for radioactive waste in Switzerland. The formation is expected to be exposed to higher temperatures relative to those found in-situ due to the disposal of the canister containing radioactive waste (Dupray et al. 2014; Gaus et al. 2014); as a consequence, the thermo-mechanical behaviour of Opalinus Clay shale must be thoroughly analysed. A devoted investigation of the thermo-mechanical behaviour of Opalinus Clay is carried out and is presented in this work.