Developments in core analysis by NMR measurements

For a large suite of consolidated sandstone samples low in shale content we have measured the permeability k, irreducible water saturation Swi, porosity phi, electrical-resistivity formation factor F, porosity by NMR, geometric-mean relaxation times T1g, and stretched-exponential relaxation times T1s. We find that T1g (or T1s) is the decisive parameter for the estimation of k or Swi of porous sandstones by other than direct measurements of these quantities. The additional use of phi or F brings appreciable, but not decisive, improvement. We show isovalue maps of the error factor delta, which show substantial regions of near-minimum values of delta and show basic compatibility of our estimators for permeability with different published estimators. The exponents of T1g (or T1s) in our power-law estimators and those of various published estimators for k are not very far from 2.0 if either or both of phi and F are also used in the estimators.