Composition-matched inelastic or capture spectroscopy tool

Patent metadata

Field	Value
Publication number	US-9417355-B2
Application number	US-201314144871-A
Country	US
Kind code	B2
Filing date	Dec 31, 2013
Priority date	Dec 31, 2013
Publication date	Aug 16, 2016
Grant date	Aug 16, 2016

Abstract

Composition-matched downhole tools and methods for using such tools are provided. One such method includes emitting neutrons using a neutron source in the downhole tool to generate formation gamma rays in a surrounding formation. At the same time, however, some of the neutrons may interact with different parts of the downhole tool to form tool gamma rays. The gamma ray spectra of at least some of the formation gamma rays and the tool gamma rays may be detected using a gamma ray detector. The tool gamma rays from the different parts of the tool may have a substantially similar spectral shape. As such, a processor may be used to analyze the spectra of the tool gamma rays using a single tool background standard, thereby simplifying the analysis and improving the precision of the results.

First claim

The invention claimed is:

1. A method comprising:
emitting neutrons using a neutron source in a downhole tool into a surrounding formation to generate formation gamma rays, wherein some of the neutrons interact with a material of a first tool part of the downhole tool to generate first tool gamma rays and wherein some of the neutrons interact with a material of a second tool part of the downhole tool to generate second tool gamma rays;
detecting gamma ray spectra of at least some of the formation gamma rays, the first tool gamma rays, and the second tool gamma rays using a gamma ray detector, wherein the first tool gamma rays and the second tool gamma rays detected by the detector have a substantially similar spectral shape in a spectral energy range of interest; and
using a processor to analyze the spectra of the first tool gamma rays and the second tool gamma rays using a single tool background standard,
wherein the downhole tool comprises a logging-while-drilling tool, the first tool part comprises a protective cover on an outer diameter of the downhole tool, and the second tool part comprises a material lining an exterior surface of an internal drilling fluid conduit,
wherein the protective cover on the outer diameter of the downhole tool covers a first layer of a neutron-absorbing material that at least partially shields the downhole tool from penetration by neutrons from a borehole and wherein the internal drilling fluid conduit is at least partially surrounded by a second layer of the neutron-absorbing material that at least partially shields the downhole tool from penetration by neutrons from within the internal drilling fluid conduit.

2. The method of claim 1 , wherein the material of the first tool part and the material of the second tool part have substantially the same composition, thereby causing the first tool gamma rays and the second tool gamma rays detected by the detector to have the substantially similar spectral shape.

3. The method of claim 1 , wherein the protective cover on the outer diameter of the downhole tool and the internal drilling fluid conduit are both formed from a nickel alloy, thereby causing the first tool gamma rays and the second tool gamma rays detected by the detector to have the substantially similar spectral shape, wherein the substantially similar spectral shape differs substantially from a spectral shape of the formation gamma rays.

4. The method of claim 1 , wherein the material of the first tool part and the material of the second tool part comprise elements that differ from elements of the formation such that the substantially similar spectral shape of the first tool gamma rays and the second tool gamma rays differs substantially from a spectral shape of the formation gamma rays.

5. A downhole tool comprising:
a neutron source configured to emit neutrons into the geological formation to generate formation gamma rays, some of the neutrons penetrating the downhole tool to generate tool gamma rays through interactions with different components of the downhole tool;
a gamma ray detector configured to detect a spectroscopy signal of gamma ray spectra of at least some of the formation gamma rays and some of the tool gamma rays;
wherein spectra of the tool gamma rays deriving from at least two different tool parts of the downhole tool have substantially the same spectral shape to enable the spectra of the tool gamma rays to be at least partially removed from the spectroscopy signal using a single tool background standard spectrum, wherein the two tool parts of the downhole tool comprise the two tool parts most likely to produce a variable amount of tool gamma rays in different borehole or formation environments,

wherein the downhole tool comprises an external neutron shield covered by an external protective cover on an outer diameter of a collar and an internal neutron shield behind a material disposed on an interface of an internal drilling fluid conduit.

6. The downhole tool of claim 5 , wherein the external protective cover and the internal drilling fluid conduit are configured to generate tool gamma rays having substantially the same gamma ray spectra.

7. The downhole tool of claim 5 , wherein the external neutron shield and the internal neutron shield are configured to generate tool gamma rays having substantially the same gamma ray spectra.

8. The downhole tool of claim 5 , wherein the external protective cover and the internal drilling fluid conduit both comprise a common inert structural material and the internal neutron shield and the external neutron shield both comprise the same neutron-absorbing materials.

9. The downhole tool of claim 5 , wherein the external neutron shield and the internal neutron shield comprise one or more neutron-absorbing materials, wherein the neutron-absorbing materials comprise Li, enriched 6 Li, B, enriched 10 B, a borosilicate, Cd, Sm, or Gd, or any combination thereof.

10. The downhole tool of claim 5 , wherein the first tool part and the second tool part both comprise a nickel alloy.

11. The downhole tool of claim 5 , wherein the downhole tool comprises a stabilizer-mounted logging-while-drilling tool or an annular logging-while-drilling tool, or both.

12. The downhole tool of claim 5 , wherein the downhole tool comprises a mandrel logging-while-drilling tool.

13. The downhole tool of claim 5 , wherein each of the two tool parts is a different one of the following:
the tool collar;
the protective cover;
the gamma ray detector;
the material lining the exterior surface of the internal drilling fluid conduit;
a tool chassis;
a canopy of the gamma ray detector.

14. A downhole tool comprising:
a collar configured to be placed into a geological formation;
an internal drilling fluid conduit disposed within the collar;
a neutron source configured to emit neutrons into the geological formation to generate formation gamma rays, some of the neutrons penetrating the downhole tool to generate tool gamma rays through interactions with different components of the downhole tool;
a gamma ray detector configured to detect a spectroscopy signal of gamma ray spectra of at least some of the formation gamma rays and some of the tool gamma rays;
wherein spectra of the tool gamma rays deriving from at least an exterior tool part on an outer diameter of the collar and an interior tool part on the internal drilling fluid conduit have substantially the same spectral shape to enable the spectra of the tool gamma rays to be at least partially removed from the spectroscopy signal using a single tool background standard spectrum.

15. The downhole tool of claim 14 , wherein the exterior tool part and the interior tool part comprise the same material that comprises less than approximately 20% iron.

Assignees

• Schlumberger Technology Corp

Inventors

• Stoller Christian
• Haranger Fabien
• Grau James
• Miles Jeffrey
• Berheide Markus

Classifications

• G01V5/101 Primary

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

• G01V5/10

  using neutron sources {(neutron generating tubes H05H5/00; neutron sources using isotopes G21G4/00)} · CPC title

• E21B47/00

  Survey of boreholes or wells (monitoring pressure or flow of drilling fluid E21B21/08) · CPC title