Patent ID: 8532929

Claim:
A method of evaluating an earth formation, the method comprising: conveying a logging tool into a borehole; using a magnet on the logging tool for applying a magnetic field to polarize nuclei in a pore space of a region of examination in the earth formation, the applied magnetic field generating an internal magnetic field gradient in the pore spaces; applying a radio frequency (RF) field to excite the nuclei; receiving nuclear magnetic resonance (NMR) signals from the excited nuclei; and estimating an intrinsic transverse relaxation time of the nuclei and a diffusion property of a fluid containing the nuclei using the received NMR signals and a model in which a measured relaxation rate is defined as a function of a diffusivity, the intrinsic transverse relaxation time, and a magnetic susceptibility contrast between a fluid in the pore spaces and a material of a matrix of the earth formation.