Experimental study of diffusion and relaxation of oilwater mixtures in model porous media

Fixed gradient NMR diffusion measurements have been performed on a series of porous ceramic samples containing mixtures of water and a refined oil (dodecane) using a laboratory instrument that emulates the operating characteristics of a commercial gradient NMR well logging tool. Diffusion coefficients were computed using a standard log interpretation procedure that is based on shifts in the distribution of transverse (T2) relaxation times measured as a function of interecho time. An average pore fluid ditX.rsion coefficient for partially oil-saturated samples is defined and shown to be a useful estimator of oil saturation. This saturation estimator has a potential advantage over standard NMR methods that are based on integrating relaxation time distributions because it works best at large pore sizes where light oil and water signals may not be resolved in the relaxation time distributions.