Fluid flow in porous systems.

Nuclear magnetic resonance (NMR) measurements of water velocity flowing through glass bead packs with a bead diameter of 10 mm have been made using the phi echo-planar imaging (PEPI) sequence. These results indicate that for various flow rates the flow variance is proportional to the mean flow velocity in agreement with the Mansfield-Issa equation. The velocity distributions are approximately Gaussian. Investigation of the slopes of the variance vs. velocity curves as a function of slice thickness indicate some coherence effects in the connectivity of the glass bead system. An extension of an earlier intervoxel coupling model is presented, which seems to explain the observed coherence effects.