Mass Transfer & Porous Media (MTPM) - Andra

P/MTPM/31EVALUATING THE APPLICATIONOF ARCHIE’S LAWFOR ARGILLACEOUS ROCKSP. Blum 1 , M. Scheunemann 1 , L. Van Loon 2 , D. Coelho 3 , N. Maes 4 , P. Grathwohl 11. University of Tübingen, Center for Applied Geosciences (ZAG), Sigwartstr. 10, 72076 Tübingen,Germany, (philipp.blum@uni-tuebingen.de)2. Paul Scherrer Institut (PSI), CH-5232 Villingen, Switzerland, (luc.vanloon@psi.ch)3. ANDRA, 92298 Châtenay-Malabry, France, (daniel.coelho@andra.fr)4 . SCK-CEN, Boeretang 200, B-2400 Mol, Belgium, (nmaes@sckcen.be)INTRODUCTIONDiffusion is an important transport process in geological systems. Hence, for the safety assessment ofpotential radioactive waste repositories that might be build in such geological systems, effective diffusioncoefficients of various species need to be known. The effective diffusion coefficients strongly depend onporosity. Moreover, previous studies could demonstrate that the effective diffusion coefficients can beestimated using Archie’s law:D e = D aq . ε m (1)where D e is the effective diffusion coefficient, D aq is the diffusion coefficient in bulk water, ε is thetransport porosity and m represents an empirical constant depending on the type of porous medium. Boving& Grathwohl (2001) studied the diffusion of iodide (I - ) in different limestone and sandstone rocks. Theexponent m that fitted the data the best was approximately 2.2. Another study, which focused on chalk,showed that the data for various inorganic and organic compounds resulted in an exponent of around 2.4(Blum, 2000). A few studies also considered the application of Archie’s law for diffusion in argillaceousrocks. Grathwohl (1998) studied the diffusion of tetrachloroethene (TCE) in natural clays (Figure 1). Agood fit with Archie’s law was obtained using the transport-through porosity.0.250.2km5scsbavla1abenD’ = ε 3/2D’ = ε 2D’ = ε 5/20.250.2D’ = ε 3/2D’ = ε 2D’ = ε 5/2D’ = D e /D aq0.150.10.05D’ = D e /D aq0.150.10.05km5scsbavla1aben(a)00.2 0.3 0.4 0.5 0.6Porosity ( ε )0.2 0.3 0.4 0.5 0.6Transport-Through Porosity ( ε t )Figure 1: (a) Normalized diffusion coefficient (D’) of TCE versus overall porosity. (b) Normalizeddiffusion coefficient (D’) of TCE versus corrected porosity based on water adsorbed onto dry samples ata relative humidity of 98.8 %. The lines represent Archie’s law. km5: Triassic clay (Knollenmergel); scs:silty-clayey soil; bav: Jurassic clays (Opalinus Clay, Dogger α ); la1: Jurassic clay (Lias α 1); aben:activated bentonite.0(b)INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 483