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 effe ctive diffusion constant in porous media contains information about th e surface to pore volume ratio, the tortuosity and other petrophysical information. We have measured the effective diffusion constant in a w ater saturated core of Fontainebleau sandstone as a function of diffus ion time. From the short time behavior, we are able to extract the sur face to pore volume ratio. This value can be combined with the spin-la ttice relaxation rate measured on the same core under identical condit ions to yield the surface relaxivity rho = 1.6.10(-5) m/s. Measurement s 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.