• Sardini, P.
• Delay, F.
• Hellmuth, K. H.
• Siitari-Kauppi, Marja
• Robinet, J. C.

Abstract

An out-difftision laboratory experiment using a non-reactive tracer was fitted using the Time Domain Diffusion (TDD) method. This rapid particle tracking method allows simulation of the heterogeneous difftision based on pore-scale images and local values of diffusivities. The superimposed porosity and mineral 2D maps act as computation grids to condition diffusion pathways. We focused on a Palmottu granite sample, in which the connected pore space has a composite microstructure with cracks linking microporous minerals and is above the percolation threshold. Three main results were achieved: (i) When compared to the fitting obtained with one coefficient (best mean square residual R = 1.6 x 10(-2)), diffusion is shown to be suitably characterised with two coefficients related to cracks and microporous minerals (best R = 6.5 x 10(-4)), (ii) rather than imposing a local apparent diffusion coefficient D, independent of the local porosity 0, a best fit is obtained by applying Archie's relationship D-a =D-0 x G with G = phi(m) to each pixel of the calculation grids (G is the geometry factor, Do is the diffusion coefficient in free fluid, and m is Archie's exponent), and (iii) the order of magnitude of the fitted diffusion coefficient or Archie's exponents (m = 0 for microcracks and m = 1.82 for microporous minerals) is physically realistic. (c) 2007 Elsevier B.V. All rights reserved.

Topics

• impedance spectroscopy
• pore
• mineral
• experiment
• simulation
• reactive
• crack
• composite
• porosity