Nuclear magnetic resonance (NMR) logging has been routinely used to measure mineralogy independent porosity, irreducible water saturation, and permeability of earth formation. The T2 distribution derived from NMR logging data is often composed of several fluid components. For example T2 of clay bound water is in general less than 10ms while T2 of movable water is above 33 ms in sandstone formation. Each fluid component can be represented by a unique T2 peak in a T2 distribution. The shape of the T2 peak can be predetermined by either a Gaussian or B-Spline function. Recently we have developed a "Fluid Component Decomposition" (FCD) method that uses a set of predetermined T2 peaks as base function to perform T2 inversion with CPMG echo trains. The FCD method significantly reduces the computation time for NMR data inversion especially for multi-dimensional data sets from oil well measurements, without sacrificing the smoothness and accuracy of the inverted distributions. It also allows direct fluid typing from either raw CPMG echo data or apparent T2 distribution. We have applied FCD method for apparent heavy oil volume calculation to estimate in-situ heavy oil viscosity.
One major uncertainty of both regular and FCD T2 inversion methods is T1/ T2 ratio. Reecent study shows that T1/T2 ratio is a linear function of T2 in log-log scale. We have applied this log-log function into FCD inversion code and greatly improve the accuracy of NMR total porosity in both carbonate formation and formations with large amount of paramagnetic impurity.
