US 11,892,589 B2
Method and apparatus for enhanced formation porosity measurement using pulsed neutron source and dual-function detectors
Sheng Zhan, Houston, TX (US); and Jeremy Zhang, Houston, TX (US)
Assigned to CHINA PETROLEUM & CHEMICAL CORPORATION, Beijing (CN)
Filed by CHINA PETROLEUM & CHEMICAL CORPORATION, Beijing (CN)
Filed on Nov. 2, 2021, as Appl. No. 17/453,252.
Claims priority of provisional application 63/148,571, filed on Feb. 11, 2021.
Claims priority of provisional application 63/148,573, filed on Feb. 11, 2021.
Prior Publication US 2022/0252754 A1, Aug. 11, 2022
Int. Cl. G01V 5/10 (2006.01); G01V 5/04 (2006.01); E21B 47/017 (2012.01); E21B 49/00 (2006.01)
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
OG exemplary drawing
 
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.