Diffusion measurement in sandstone core: NMR determination of surface-to-volume ratio and surface relaxivity.

Recent theoretical work has shown that the time dependence of the effective diffusion constant in porous media contains information about the surface to pore volume ratio, the tortuosity and other petrophysical information. We have measured the effective diffusion constant in a water saturated core of Fontainebleau sandstone as a function of diffusion time. From the short time behavior, we are able to extract the surface to pore volume ratio. This value can be combined with the spin-lattice relaxation rate measured on the same core under identical conditions to yield the surface relaxivity rho = 1.6 x 10(-5)m/s. Measurements at 25.0 degrees C and 40.0 degrees C demonstrate that the effect of surface relaxation on the measured diffusion coefficient is small, as predicted by theory.