Systems and methods for determining clean inelastic and capture spectra

Patent metadata

Field	Value
Publication number	US-11774630-B2
Application number	US-202117199979-A
Country	US
Kind code	B2
Filing date	Mar 12, 2021
Priority date	Mar 12, 2021
Publication date	Oct 3, 2023
Grant date	Oct 3, 2023

Abstract

A method for obtaining nuclear measurement data includes measuring a burst gate source intensity. The method also includes measuring at least one of burst gate neutron count rate or a capture gate neutron count rate at a neutron detector arranged proximate a gamma ray detector. The method further includes determining, based at least in part on the burst gate source intensity and at least one of the burst gate neutron count rate or the capture gate neutron count rate, a normalized neutron count rate. The method also includes determining at least one of an inelastic spectrum or a capture spectrum. The method includes determining based at least in part on the normalized neutron count rate, at least one of a corrected inelastic spectrum or a corrected capture spectrum.

First claim

The invention claimed is:

1. A downhole nuclear measurement tool, comprising:
a housing;
a neutron source, arranged within the housing;
a first detector positioned at a distance away from the neutron source, the first detector receiving backscatter radiation, from a formation, in response to neutron emission from the neutron source, and the first detector being a gamma ray detector; and
a second detector, positioned radially outward from and circumferentially surrounding at least a portion of the first detector, the second detector receiving the backscatter radiation, the second detector being a neutron detector, wherein the backscatter radiation at the second detector corresponds to a neutron flux incident on the first detector.

2. The downhole nuclear measurement tool of claim 1 , wherein the second detector is a diamond neutron detector.

3. The downhole nuclear measurement tool of claim 2 , wherein the second detector includes a layer, of a material different from diamond, having thermal neutron sensitivity.

4. The downhole nuclear measurement tool of claim 1 , wherein the second detector is configured to detect both fast neutrons and thermal neutrons.

5. The downhole nuclear measurement tool of claim 1 , wherein the second detector is formed from a plurality of second detector sections, the plurality of second detector sections being segmented over a portion of a circumference of the first detector, the plurality of second detector sections at least partially surrounding the first detector.

6. The downhole nuclear measurement tool of claim 1 , wherein the second detector is thinner than the first detector.

7. A method for obtaining nuclear measurement data, comprising:
measuring at least one of a burst gate neutron count or a capture gate neutron count at a neutron detector arranged circumferentially around a gamma ray detector;
obtaining at least one of an inelastic spectrum or a capture spectrum; and
determining, based at least in part on a correction factor, at least one of a corrected inelastic spectrum or a corrected capture spectrum.

8. The method of claim 7 , further comprising:
determining the correction factor, based at least in part on at least one of the burst gate neutron count or the capture gate neutron count.

9. The method of claim 7 , wherein determining the corrected inelastic spectrum comprises:
determining an inelastic spectrum correction; and
removing the inelastic spectrum correction from the inelastic spectrum.

10. The method of claim 7 , wherein the neutron detector has fast neutron sensitivity.

11. The method of claim 7 , further comprising:
obtaining the capture spectrum; and
determining a corrected total spectrum; and
determining, based at least in part on the corrected total spectrum and the corrected capture spectrum, the corrected inelastic spectrum.

12. The method of claim 7 , wherein determining the corrected capture spectrum comprises:
determining a capture spectrum correction; and
removing the capture spectrum correction from the capture spectrum.

13. The method of claim 7 , further comprising:
determining, based at least in part on the corrected inelastic spectrum or the corrected capture spectrum, a formation property.

14. A system for formation evaluation, comprising:
a tool body;
a neutron source positioned within the tool body, the neutron source emitting neutrons into a formation;
a gamma ray detector;
a neutron detector surrounding at least a portion of the gamma ray detector and arranged between the gamma ray detector and at least a portion of the tool body; and
a control system, having a memory and a processor, the memory storing instructions that, when executed by the processor, cause the processor to:
determine, based at least in part on first neutron detector data, a burst gate neutron count;
determine, based at least in part on second neutron detector data, a capture gate neutron count;
determine a burst gate correction factor; and
determine a corrected inelastic spectrum, based at least in part on the burst gate correction factor and a capture spectrum.

15. The system of claim 14 , wherein the instructions, when executed by the processor, further cause the system to:
determine, based at least in part on the burst gate correction factor, a total spectrum correction; and
determine a corrected total spectrum.

16. The system of claim 14 , wherein the instructions, when executed by the processor, further cause the system to:
determine a capture gate correction factor;
determine, based at least in part on the capture gate correction factor, a capture spectrum correction; and
determine a corrected capture spectrum.

17. The system of claim 14 , wherein the corrected inelastic spectrum is a difference between a corrected total spectrum and a scaled corrected capture spectrum.

18. The system of claim 14 , wherein the neutron detector comprises:
a diamond detector; and
a layer having thermal neutron sensitivity.

Assignees

• Baker Hughes Oilfield Operations Llc

Inventors

• Inanc Feyzi
• Vasilyev Maxim
• Anniyev Toyli
• Esfandiari Ezzatollah

Classifications

• G01V5/104 Primary

  and detecting secondary Y-rays as well as reflected or back-scattered neutrons · CPC title

• G01V5/105 Primary

  the neutron source being of the pulsed type · CPC title