Evaluation of fractal parameters of percolation model objects and natural porous media by means of NMR microscopy

Noninvasive NMR microscopy permits one to image the three-dimensional pore space of porous materials filled with a fluid. The binary representation of the geometrical structure is analysed with regard to fractal properties. T he flow pattern of percolating liquids in the presence of a stationary pres sure gradient can be visualized with the aid of NMR velocity mapping. The p ore space maintaining the transport (the backbone) can thus be distinguishe d from dead ends. The fractal parameters of the backbone turned out to be d ifferent from those of the whole pore space. Reconstructed two- or three-di mensional objects based on site-percolation or continuous swiss-cheese mode ls above the percolation threshold are compared with natural materials. The ingress of light water into a gel made with heavy water can also be visual ized using NMR microscopy. The mean-squared displacement determined in this way in the site percolation model object indicates anomalous behavior. (C) 1999 Elsevier Science B.V. All rights reserved.