The Nuclear Magnetism Log (NML) provides a measure of the fluid content (FFI) and the thermal relaxation time (T1) for the fluid in the porous rocks penetrated by the well bore. This paper describes a method for determining the specific permeability of sandstones using the log-derivable quantities FFI and T1. The physical models and mathematical derivations which are used to relate permeability to FFI and T1 are given in detail. The results of laboratory measurements on powder packs and a large number of sandstone cores with a wide range of permeabilities are given and the permeabilities determined by this method are compared with those obtained by conventional flow methods.

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