Patent ID: 7566869

Claim:
A method of evaluating an earth formation having a fluid mixture including oil and water therein, the method comprising: irradiating the earth formation with a pulsed neutron source, the source being disposed in a borehole; measuring radiation resulting from capture of thermal neutrons by nuclei in the earth formation at at least two detectors; determining from the measurements a value of a fluid zone parameter (FZP) indicative of an oil saturation S o at at least one depth in the borehole; defining a fluid zone parameter (FZP) as a ratio of capture gamma ray measurements made by one of the at least two detectors to capture gamma ray measurements made by another of the at least two detectors; establishing values of the FZP for at least two different values of S o ; and estimating from the determined value of the FZP and the at least two established values of FZP a value of S o , the estimation being made without using any other radiation measurement.