Characterization of fluid distributions in porous media by NMR techniques

Nuclear magnetic resonance (NMR) spin‐lattice relaxation measurements are used to investigate pore structures and fluid phase distributions in porous media. A new method for estimating relaxation time distribution functions from measured relaxation data is presented using a B‐spline basis to represent the distribution function and Tikhonov regularization to stabilize the estimation problem. Surface relaxivity, which is required to convert relaxation time distributions to pore‐size distributions of fluid phase distributions at partial saturations, is determined using pore volume‐to‐surface‐area ratios estimated by NMR diffusion measurements. This approach was validated by analyzing certain model porous media with known pore volume‐to‐surface‐area ratios. The method is demonstrated by determining pore‐size and fluid phase distributions of sandstone and carbonate samples, as well as by comparing the pore‐size distributions of chalk samples obtained by this methodology with those estimated by mercury porosimetry.