Probing the internal field gradients of porous media

We devise a modified Carr-Purcell-Meiboom-Gill pulse sequence that allows us to probe the apparent internal field gradient distribution of a fluid-saturated porous medium as a function of the pore size. This distribution is displayed as a two-dimensional map with one axis being the field gradient, another axis being the T-2 relaxation time reflecting different pore sizes, and the vertical amplitudes being proportional to the proton population. Such a scheme of two-dimensional representation for fluid-saturated porous media can also be used for the identification of pore fluids using the contrast of their diffusion coefficients.