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. The flow pattern of percolating liquids in the presence of a stationary pressure gradient can be visualized with the aid of NMR velocity mapping. The pore space maintaining the transport (the backbone) can thus be distinguished from dead ends. The fractal parameters of the backbone turned out to be different from those of the whole pore space. Reconstructed two- or three-dimensional objects based on site-percolation or continuous swiss-cheese models above the percolation threshold are compared with natural materials. The ingress of light water into a gel made with heavy water can also be visualized 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.