An Insight into the Fluid Retention Capabilities of Shales

SUMMARY The hydro-mechanical behaviour of shales is becoming one of the most important issues in modern geomechanics, largely driven by petroleum industries (i.e., the extraction of shale gas), the sequestration of CO2 and the nuclear waste geological storage. In any such application, a deep understanding of the hydro-mechanical behaviour of the involved materials is of primary significance. The water retention mechanisms play a major role in either fluid trapping due to the capillary forces present in low permeability formations or in the resaturation of shale formations after desaturation. The paper presents different experimental methodologies that have been developed by the authors for the analysis of the retention behaviour of shales. They involve the direct control of the shale water content and the subsequent measurement of the suction at equilibrium by a psychrometer. A fluid displacement technique with a non-polar liquid is then used to assess the volume changes and compute the degree of saturation. Selected test results are presented for two shales from the northern region of Switzerland. Introduction Growing interest toward the geomechanical behaviour of shales is nowadays observed mainly due to the fields of application in which this material has been involved in the recent years such as petroleum industries, nuclear waste storage and sequestration of CO2. In any such application, a deep understanding of the hydro-mechanical behaviour of shales is of primary significance. The water retention mechanisms play a major role in either fluid trapping due to the capillary forces present in low permeability formations, as in the case of shale gas reservoir, or in the resaturation of shale formations after ventilation, as in the case of deep geological repositories. This paper presents an advanced experimental technique that have been recently developed by the authors for testing the water retention behaviour of shales as well as the main obtained results on 2 different shales. Different testing procedures are conceived for the determination of the wetting and of the drying paths of the shale water retention curves; the methodologies are based on the direct control of the shale water content and on the subsequent measurement of the total suction at equilibrium by a psychrometer. The swelling/shrinkage of shale is related to suction, or the degree of saturation variations; in order to investigate the volume change response of the material upon total suction variations a fluid displacement technique with a non-polar liquid is used. The technique allows to assess …