COMPENSATED SIGMA CALCULATION BASED ON PULSED NEUTRON CAPTURE TOOL MEAUREMENTS

摘要

A method for determining thermal neutron decay constant for a formation includes counting radiation events corresponding to numbers of thermal neutrons with respect to time (decay spectrum) after irradiating the formation with neutrons. At least one moment of a first order of the decay spectrum or a single exponential curve to fit the decay spectrum is determined. A first apparent decay constant from the at least one moment or the single exponential curve. A second apparent decay constant is determined either by repeating the calculating a moment or exponential curve for different time segments of the decay spectrum or by using radiation events detected by at least a second radiation detector at a different spacing from a position of the irradiating than the at least a first radiation detector to determine a second apparent decay constant. A wellbore corrected thermal neutron decay constant is determined from the first and second apparent decay constants.