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 T2 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.