Hydraulic Characterisation of Clay Rock Under Consideration of Coupled THM Properties

Abstract

Clay rock is being investigated in many countries as a potential host rock for nuclear waste repositories. Due to the state of over-consolidation and water saturation, characterisation of undisturbed rock with regard to its hydraulic and mechanical properties is a big challenge. Increased complexity is caused by temperature change in the repository of high-level waste. In situ measurement of single component, e.g. rock permeability, was conducted in the Mont Terri Rock Laboratory (CH) and the French Underground Research Laboratory Bure. Several so-called heater experiments are being carried out at different scale. The measured data including temperature, humidity, pore pressure, and deformation in various boreholes shows strong coupling effects. For interpretation of the experimental data, a numerical 3D code OpenGeoSys (OGS) was developed taking into account the strongly coupled thermal, hydraulic and mechanical processes. Because of the significant dependency of the thermal conductivity on the water saturation, the determination of the saturation state, which is again controlled by hydraulic permeability, is therefore important. The evaluated permeability from packer tests can be validated using numerical modelling. The state-dependency on the pressure, saturation and temperature is discussed.