PERCOLATION MODEL OF NUCLEAR MAGNETIC-RELAXATION IN POROUS-MEDIA

A random walk on a site percolation lattice with absorbing sites is used to simulate nuclear magnetic relaxation in a porous medium. The computed relaxation is compared to a sum of exponentials with relaxation rates proportional to the pore surface-to-volume ratios. Each isolated region of the pore space is treated as a single pore rather than as a collection of connected pores. Thus, above the percolation threshold, the pore space is essentially a single large pore. For fast diffusion this sum of exponentials gives excellent agreement with the computed results. It appears that measurements in the fast-diffusion range will give only an average surface-to-volume ratio of the pore space. © 1990 The American Physical Society.