On the transport properties of anisotropic networks of capillaries

Porous media such as sedimentary rocks and soils are often anisotropic in their resistance to flow of fluids, solutes, heat, and electrical current. Lattice-based calculations of the transport properties of pore networks are of considerable interest, both because of their tractability and because methods exist for the characterization of porous solids in terms of lattice model parameters. We have investigated the dependence of the anisotropy factor for different diffusive and convective transport mechanisms, on the direction-dependent connectivities and pore size distributions, using a uniaxial, anisotropic simple cubic lattice. While connectivity-induced anisotropy, due to different coordination numbers in directions parallel and perpendicular to the bedding plane, significantly affects transport coefficients in both directions, anisotropy induced by pore size distribution mainly affects the perpendicular transport coefficients.