Hydro-mechanical Behaviour of Reconstituted and Intact Shales

Abstract

The geo-energy sector is nowadays bringing ahead advanced technologies such as shales gas extraction, CO2 sequestration and nuclear waste geological storage, where the exploitation of shale formations is considered. Due to the great depth involved in the mentioned applications and to the difficulties in retrieving intact samples, reconstituted shale specimens are often adopted for hydro-mechanical testing. Reconstituted and intact shales may substantially differ in their hydro-mechanical behaviour due to the particular structure of the natural material; such peculiar structure is the result of diagenesis and burial history. This paper presents and experimental campaign aimed at (i) characterizing the role of diagenesis for Opalinus Clay shale from the northern region of Switzerland and (ii) understanding how representative the behaviour of reconstituted material is respect to the one of the natural shale. The investigation program comprises a series of low and high-pressure oedometric tests. The results of the tests on the reconstituted material are compared to those on the intact one and the major aspects related to the effect of structure on the geomechanical behaviour have been highlighted. Particular attention is given to the compressibility, swelling response, permeability and secondary consolidation of the material at the reconstituted and intact states.