Experimental analysis of the retention behavior of shales

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2013
Article de conférence

Résumé

The analysis of the volumetric behavior and the consolidation of shales require the involved materials to be tested under high confining stresses. The paper presents the apparatuses and the techniques that have been developed recently for testing shales under high-stress conditions. An advanced oedometric cell is introduced to analyse the transition from the over- to the normally consolidated state of shales; the apparatus allows investigating the volume change behavior of shales at high vertical stress (up to 100 MPa) in controlled suction and temperature conditions. The procedure for specimen preparation is also discussed. Selected test results are presented for two shales from the northern region of Switzerland.

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Multiphysical Testing of Soils and Shales

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Significant advancements in the experimental analysis of soils and shales have been achieved during the last few decades. Outstanding progress in the field has led to the theoretical development of geomechanical theories and important engineering applications. This book provides the reader with an overview of recent advances in a variety of advanced experimental techniques and results for the analysis of the behaviour of geomaterials under multiphysical testing conditions. Modern trends in experimental geomechanics for soils and shales are discussed, including testing materials in variably saturated conditions, non-isothermal experiments, micro-scale investigations and image analysis techniques. Six theme papers from leading researchers in experimental geomechanics are also included. This book is intended for postgraduate students, researchers and practitioners in fields where multiphysical testing of soils and shales plays a fundamental role, such as unsaturated soil and rock mechanics, petroleum engineering, nuclear waste storage engineering, unconventional energy resources and CO2 geological sequestration.

Springer2012

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The involvement of shales in engineering fields such as the extraction of shale gas or the nuclear waste geological disposal is mainly driven by the low permeability and the high retention properties of these geomaterials. The high capillary forces developed in the matrix of the shales allow the fluid trapping with the consequence that the material remains saturated until significant values of suction. However, in the context of several engineering applications, the shale formations are exposed to relative humidity values which might induce changes in the degree of saturation. As a consequence, the investigation of the air entry value and of the retention behaviour of the material is of primary significance.The following paper presents an investigation on the water retention properties of shales. The experimental technique developed for such analysis is described in detail and selected results are presented. The testing methodology is based on the control of the water content and on the subsequent measurement of the total suction at equilibrium.The volumetric behaviour of the material is monitored in order to compute the retention curve in terms of degree of saturation. The results allow to identify a relationship between the air entry values and the porosity for Swiss shales.

2014

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Shales are among the most commonly considered geomaterials in current energy-related geomechanical investigations, as 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. With the aim to establish a sound protocol for shale retention behaviour analysis, this paper presents an advanced experimental methodology that takes into account the specificities of shales such as small pore size dimensions and the large variations in water potential to be applied to induce significant changes in the degree of saturation. The technique that is presented here involves 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 also used to assess the volume changes of the shale and to compute the degree of saturation. Selected test results are presented for various shale samples that have been cored at different depths. The results indicate that important features of the retention behaviour of geomaterials are fundamental aspects to be considered when analysing the retention behaviour of shales, such as the existence of main wetting and drying paths, the hysteresis domain, and the dependency of the air entry value on the void ratio.

Elsevier2014

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