Abstract
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.
Résumé
Le transport d'ions par diffusion dans deux milieux poreux différents est étudié en fonction de leurs saturation en fluide et mouillabilité. Un maillage selon la méthode de Boltzmann est utilisé pour modéliser la séparation de phase du mélange binaire constituant le milieu poreux. Le modèle prend en compte les effets de mouillabilité. Le transport par diffusion est ensuite évalué dans chaque phase.
Il est observé que le degré de saturation de chaque phase peut grandement affecter le transport des ions pour lesquels la diffusion est limitée à la phase mouillable ou à la phase non mouillable. Aux fortes saturations, nos estimations concernant la diffusivité sont en accord avec celles prévues par la seconde loi d'Archie laquelle est semi-empirique. Aux faibles saturations, la seconde loi d'Archie n'est plus valable lorsque les effets de percolation deviennent importants.
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Martys, N.S. Diffusion in partially-saturated porous materials. Mat. Struct. 32, 555–562 (1999). https://doi.org/10.1007/BF02480489
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DOI: https://doi.org/10.1007/BF02480489