Mass Transfer & Porous Media (MTPM) - Andra

P/MTPM/41ARGILLITES THERMAL CONDUCTVITYVARIATIONS INDUCED BY SEDIMENTARY /DIAGENETIC PROCESSESAND BY MECHANICAL DECOMPRESSIONY. Géraud 1 , L. Esteban 1234 , J.L. Bouchez 2 , A. Trouiller 31. Institut de Physique du Globe de Strasbourg, UMR 7516, Université Louis Pasteur-CNRS andGdR CNRS FORPRO, 1 rue Blessig, F-67089 Strasbourg cedex ( ygeraud@illite.u-strasbg.fr )2. Univ. Toulouse, LMTG, 14 Ave E. Belin, 31400-Toulouse and GdR CNRS FORPRObouchez@lmtg.obs-mip.fr3. Andra, Parc de la Croix Blanche, 1-7 rue J. Monnet, 32290-Châtenay-Malabry(alain.trouiller@andra.fr)4. Now at Geological Survey of Canada-Pacific, 9860 West Saanich Road, Sidney, B.C., Canada,V8L 4B2 lesteban@nrcan.gc.caINTRODUCTIONAccepting the hypothesis of diffusive heat transport, thermal conductivity (TC) is a decisive parameterthat controls the geometry of the deep underground laboratory of Andra, namely the spacing between“alveoles” and the total storage volume. The optical scanning technique, initially developed by Y.Popov from the University of Moscow ( Popov et al., 1999), is used to perform thermal conductivitymeasurements. Examples obtained from argillites will be presented, showing the effect of (1)diagenetic process with calcite cementation using the mapping technique, and (2) mechanicaldecompression of samples cored at the wall of an experimental gallery using the profile technique.DIAGENETIC PROCESS WITH CALCITE CEMENTATIONUsing the optical scanning technique, TC-maps were produced with a resolution of 1 mm 2 . Mapping wasoperated on samples cored at the wall of the descending shaft along two directions: perpendicular tobedding (dashed line on the circular section of figure 1) and parallel to bedding (rectangular section). TCvalues evolve from 1.3 to 2.4 W.m -1 .K -1 , the highest ones ( > 2) being induced by calcite cement. Thisdiagenitic process seems to be independent of bedding orientation. Hence, thermal conductivitymeasurement appears to be a good indicator of calcite distribution within the argillites. Parallel to thebedding plane, clay-enriched sectors under sedimentary control seem to parallel the small K 1 axis of themagnetic anisotropy ellipsoid (Esteban et al., 2006a and b ). K 1 seems to parallel low TC values and to beperpendicular to highest TC ones. These measurements point to a mineralogical and sedimentary controlof the TC properties of the argilites. As a consequence, TC-mapping can be used as an indicator ofsedimentary and diagenetic processes in mudrocks.MECHANICAL PROCESSESProfiles were performed along cores that were drilled from the walls of the underground laboratory. Ourmeasurements show that if a mean TC could be estimated, ranging from 1.2 to 1.5 W. m -1 .K -1 , largevariations were also observed as exemplified in figure 2. Three parallel-to-core profiles were obtained onthe core surfaces. On sides of a mean TC value of 1.3 W.m -1 .K -1 , large variations could be induced by anincrease in porosity or by mineralogical variations. A damaged zone was detected with a low TC (< 1unity) at the beginning of profile 1, attributed to a high porosity zone. At the end of profile 2, pyrite grains(or framboids) were detected with high TC values (3 W.m -1 .K -1 ).INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 503