Pore network connectivity anisotropy in Jurassic argillite specimens from eastern Paris Basin (France)

Physics and Chemistry of the Earth 32 (2007) 161–169 www.elsevier.com/locate/pce

Pore network connectivity anisotropy in Jurassic argillite specimens from eastern Paris Basin (France) Lionel Esteban a

c

a,b,c,*,1

, Yves Ge´raud c, Jean Luc Bouchez

a

LMTG, UMR CNRS #5563, GdR FORPRO, 14 Avenue E. Belin, 31 400 Toulouse, France b Andra – Direction Scientifique, 92298 Chatenay-Malabry Cedex, France EOST, IPGS, UMR#7516, GdR FORPRO, 1 rue Blessig, 64067 Strasbourg Cedex, France

Received 1 July 2005; received in revised form 7 November 2005; accepted 7 November 2005 Available online 18 October 2006

Abstract In order to test the feasibility of nuclear waste storage, Andra, the French radioactive waste management agency, gave us the opportunity to study preserved specimens of Jurassic clay-rich rocks from eastern Paris Basin. These rocks, deposited during the Callovian and beginning of the Oxfordian, are dark- to light-grey marls that consist mainly in a mixture of clay, calcite and silt. Magnetic susceptibility and remanence vary according to the clay/calcite/silt ratios and the mineral preferred orientations are characterized by the anisotropy of the magnetic susceptibility. A few test specimens, sampled from borehole-core #HTM 102, and coming from the base and top levels of the Callovo-Oxfordian argillite formation, were subjected to connected porosity measurements using the mercury injection technique. By imposing mercury to flow parallel to a given direction, we were able to determine the anisotropy of connectivity along the three principal magnetic susceptibility axes. We find that the clay-richest specimens have a large and sub-isotropic connected porosity which is mostly accessible through the smallest pore threshold diameters (