ABSTRACT

This paper presents the results of a laboratory investigation of the thermomechanical behaviour of anisotropic rock. The tests were performed on natural (Tournemire shale) using special triaxial cell able to control and to go to high temperature. The range of temperatures that were investigated is from 20 C° to 250 C°. (20, 100, 150, 200 and 250 C°), and the range of confining pressures is from 0 MPa to 20MPa. (0, 5, 10, and 20 MPa). The influence of temperature on their mechanical behaviour was investigated for drained tests. Anisotropic elastic response and plastic deformation have been investigated. It seems that, the thermomechanical behaviour of the Tournemire shale is anisotropic and strongly depends on confining pressure and loading orientation at the applied temperature. Hydrostatic compressibility tests (in the perpendicular orientation θ = 90°) allowed to present the thermal effect on the mechanical behaviour of this rock. In this range of temperatures, the deformability and strength of this rock were found also to be strongly dependent of temperature.

1 INTRODUCTION

Many underground works, such as chemical and nuclear waste storage, oil boreholes, injection and production activity, are located in anisotropic rocks and based on the study of thermomechanical behaviour. The design and stability analysis of such structures require knowledge of the deformation and failure of these rock materials. A large number of experimental investigations involving the laboratory tests have been performed. However, most of experimental data reported in the literature is obtained from the tests carried out between the ambient temperature (20 C°) and (100 C°), especially for the clay (Behrooz 2003; Campanella 1968; Cekerevac 2004; De Bruyn 1996; Delage 2000; Del Olmo 1996; Hueckel 2002; Imbert 2005). For a higher temperature, few experimental results are available in the literature; this may be due to the technical difficulties in the experimental works.

The group of sedimentary rocks, termed shales, represents a particular interest in oil industry. Experimental investigations are still necessary to have a better understanding of the thermomechanical behaviour of these materials. In the oil industry, the exploitation of heavy oil by the technical injection of vapour at high temperature, the rocks of the reservoir are subjected to coupled thermal and hydromechanical efforts. So it is necessary to study the thermo-mechanical behaviour of these materials subjected to variations of temperature in order to study the mechanical stability of the petroleum reservoirs.

The object of this study consists in carrying out new experimental study of the thermomechanical behaviour of the saturated stiff shales subjected to high temperatures (until 250 C°) and to compressive stresses. The main aim was to carry out extensive laboratory experiments on the thermomechanical behaviour of Tournemire shale. The emphasis is given to investigating thermal effect on the elastic response, plastic flow and failure behaviour of the shale. Experimental results presented here provide a data base for the development of thermoelastoplastic modelling and failure criteria.

2 EXPERIMENTAL STUDIES

For the sake of realize this experimental laboratory investigation performed on Tournemire shale.

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