THE CHARACTERIZATION OF FLUID TRANSPORT IN A POROUS SOLID BY PULSED GRADIENT STIMULATED ECHO NMR

Pulsed magnetic field gradient stimulated echo NMR measurements are re ported for the flow and diffusion of an aqueous phase within a sample of Fontainebleau sandstone. The stimulated echo dependence on the grad ient pulse area, q, for a fixed observation time Delta, is used to der ive the displacement probability distributions, P Delta(X), where X, t he direction of the field gradient, is arranged to be parallel or perp endicular to the applied pressure gradient driving the flow. The shape of the P-Delta(X) as a function of Delta is modelled in terms of lami nar flow within a set of randomly oriented capillaries. For small Delt a, molecules remain largely within the capillaries they occupy at the beginning of the time Delta and, as a consequence, the P-Delta(X) for small Delta are dominated by the orientational distribution of the cap illaries. For larger Delta, the evolution of the P-Delta(X) is reprodu ced only when diffusion of molecules across the velocity gradients wit hin the capillaries is introduced and, in addition, the fluid transfer s between differently oriented capillaries through the action of the o verall flow.