Diffusion in partially-saturated porous materials

The diffusive transport of ions in two classes of porous media was studied as a function of fluid saturation and wetting properties. A lattice Boltzmann method was used to model phase separation of a binary mixture, including wetting effects, in porous media. Diffusive transport is then evaluated in each separate phase. It is found that the degree of saturation of each phase can strongly affect the transport of ions that are limited to diffusing in either the wetting or non-wetting phase. At high saturations, good agreement is found between our estimates of diffusivity and that predicted by the semi-empirical Archie's second law. At lower saturations it is found that Archie's second law breaks down as percolation effects become important.