Method for using neutron interaction cross section to interpret neutron measurements

Patent metadata

Field	Value
Publication number	US-9310515-B2
Application number	US-201414222397-A
Country	US
Kind code	B2
Filing date	Mar 21, 2014
Priority date	Mar 21, 2014
Publication date	Apr 12, 2016
Grant date	Apr 12, 2016

Abstract

A method for determining a petrophysical property of a formation includes detecting radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 MeV. The petrophysical property is determined from an elastic scattering cross section of the formation. The elastic scattering cross-section related to a number of detected radiation events.

First claim

What is claimed is:

1. A method for determining a petrophysical property of a formation, comprising:
receiving a number of detected radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 million electron volts (MeV);
determining an elastic scattering cross-section of the formation from the number of detected radiation events, and
determining the petrophysical property from the determined elastic scattering cross section of the formation,
wherein the detecting is performed at at least two different longitudinally spaced apart positions from a position of the imparting and the elastic scattering cross-section is determined from a ratio of the detected radiation events at each of the at least two spaced apart positions.

2. The method of claim 1 wherein the elastic scattering cross section comprises thermal neutron elastic scattering cross section.

3. The method of claim 1 wherein a thermal neutron elastic scattering cross section is determined by detecting thermal neutrons at the at least two positions.

4. The method of claim 1 wherein a thermal neutron elastic scattering cross section is determined by detecting epithermal neutrons at the at least two positions.

5. The method of claim 1 wherein a thermal neutron elastic scattering cross section is determined by detecting thermal neutron capture gamma rays at the at least two positions.

6. The method of claim 5 further comprising determining thermal neutron capture cross section of the formation and using the determined thermal neutron capture cross section to improve accuracy of the determined petrophysical property.

7. The method of claim 1 wherein the elastic scattering cross section comprises elastic scattering of neutrons having energy of at least 1 MeV.

8. The method of claim 1 wherein the radiation events comprise neutrons.

9. The method of claim 8 wherein the detected neutrons are epithermal neutrons and further comprising determining a slowing down time of neutrons by calculating a rate of detection of the epithermal neutrons with respect to time.

10. The method of claim 1 wherein the radiation events comprise gamma rays.

11. The method of claim 1 wherein the formation property comprises porosity.

12. The method of claim 11 wherein porosity is determined using the determined elastic scattering cross section, an elastic scattering cross-section of solid rock material of the formation and an elastic scattering cross section of a fluid filling the porosity.

13. The method of claim 12 wherein the fluid comprises at least one of water, oil and gas and mixtures thereof.

14. A method for determining a petrophysical property of a formation, comprising:
emitting neutrons having energy of at least 1 million electron volts (MeV) into the formation from an instrument disposed in a wellbore traversing the formations;
detecting radiation events resulting from interaction of the emitting neutrons with the formation at spaced apart position along the instrument; and
determining the petrophysical property from an elastic scattering cross section of the formation, the elastic scattering cross-section related to a number of detected radiation events,
wherein the detecting is performed at at least two different spaced apart positions from a position of the imparting and the elastic scattering cross-section is determined from a ratio of the detected radiation events at each of the at least two spaced apart positions.

15. The method of claim 14 wherein the elastic scattering cross section comprises thermal neutron elastic scattering cross section.

16. The method of claim 14 wherein the thermal neutron elastic scattering cross section is determined by detecting thermal neutrons at the at least two positions.

17. The method of claim 14 wherein the thermal neutron elastic scattering cross section is determined by detecting epithermal neutrons at the at least two positions.

18. The method of claim 14 wherein the thermal neutron elastic scattering cross section is determined by detecting thermal neutron capture gamma rays at the at least two positions.

19. The method of claim 18 further comprising determining thermal neutron capture cross section of the formation and using the determined thermal neutron capture cross section to improve accuracy of the determined petrophysical property.

20. The method of claim 14 wherein the elastic scattering cross section comprises elastic scattering of neutrons having energy of at least 1 MeV.

21. The method of claim 14 wherein the radiation events comprise neutrons.

22. The method of claim 21 wherein the detected neutrons are epithermal neutrons and further comprising determining a slowing down time of neutrons by calculating a rate of detection of the epithermal neutrons with respect to time.

23. The method of claim 21 further comprising detecting gamma rays resulting from inelastic scattering.

24. The method of claim 14 wherein the formation property comprises porosity.

25. The method of claim 24 wherein porosity is determined using the determined elastic scattering cross section, an elastic scattering cross-section of solid rock material of the formation and an elastic scattering cross section of a fluid filling the porosity.

26. The method of claim 24 wherein the fluid comprises at least one of water, oil and gas and mixtures thereof.

27. The method of claim 14 wherein the instrument is coupled to an end of an electrical cable.

28. The method of claim 14 wherein the instrument is coupled within a drilling tool assembly.

Assignees

• Schlumberger Technology Corp

Inventors

• Zhou Tong
• Stoller Christian

Classifications

• G01V5/101

  and detecting the secondary Y-rays produced in the surrounding layers of the bore hole · CPC title

• G01N33/24

  Earth materials (G01N33/42 takes precedence) · CPC title

• G01V5/107 Primary

  and detecting reflected or back-scattered neutrons · CPC title