On the water retention behaviour of shales

Shales are among the most considered geomaterials in current energy-related geomechanical investigations; they are involved in engineering applications such as the unconventional extraction of natural gas, CO2 sequestration and nuclear waste geological storage. A deep understanding of their behaviour with regard to variations in the degree of saturation is of primary significance for such applications. This paper illustrates the advances in the experimental analysis of the water retention behaviour of shales under non-isochoric conditions which have been recently achieved by the authors. The testing methodologies involve the direct control of the water content and the subsequent measurement of the total suction at equilibrium by a psychrometer. Furthermore, the volume change response of the material upon total suction variations can be investigated: a fluid displacement technique with a non-polar liquid is used in order to assess the volume changes of the shale samples and to compute the degree of saturation. The results highlight the important features of the retention behaviour of shales, such as the existence of main wetting and drying paths, the hysteresis domain and the scanning behaviour. Selected results are presented for three shales from the northern region of Switzerland.