CPC G01V 5/102 (2013.01) [E21B 47/017 (2020.05); E21B 49/00 (2013.01); G01V 5/045 (2013.01); G01V 5/105 (2013.01)] | 16 Claims |
1. A method of evaluating downhole formation porosity, comprising:
emitting neutron pulses from a pulsed neutron tool deployed in a wellbore to irradiate earth formation surrounding the wellbore;
detecting neutrons and gamma rays using a plurality of detectors disposed in the pulsed neutron tool, wherein each detector is operable to detect neutrons and gamma rays from the formation; and
estimating a plurality of neutron porosities and a plurality of gamma-ray porosities based on data from the plurality of detectors,
wherein the estimating step comprises:
obtaining a neutron count rate and a capture gamma-ray count rate from each of the plurality of detectors;
calculating a ratio of neutron count rate and a ratio of capture gamma-ray count rate between every two of the plurality of detectors so as to obtain a plurality of ratios of neutron count rate and a plurality of ratios of capture gamma-ray count rate; and
estimating a plurality of neutron porosities using the plurality of ratios of neutron count rate and/or estimating a plurality of gamma-ray porosities using the plurality of ratios of gamma-ray count rate.
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