Casing inspection using pulsed neutron measurements

Patent metadata

Field	Value
Publication number	US-9335437-B2
Application number	US-201414325255-A
Country	US
Kind code	B2
Filing date	Jul 7, 2014
Priority date	Jul 7, 2014
Publication date	May 10, 2016
Grant date	May 10, 2016

Abstract

A method for evaluating wellbore conduit condition includes using measurements of at least one of (i) inelastic gamma rays made during emission a burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission. The at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts are characterized to estimate an amount of loss of iron in the conduit.

First claim

What is claimed is:

1. A method for evaluating wellbore conduit condition, comprising:
accepting as input to a computer measurements of at least one of (i) inelastic gamma rays made during emission a burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission;
in a computer, characterizing the at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts to estimate an amount of loss of iron in the conduit; and
displaying a parameter related to the amount of iron loss,
further comprising using measurements of inelastic gamma rays detected during the emission at at least a second location spaced apart from the at least one location and in the computer determining a ratio of inelastic gamma rays detected at the at least one location and the at least one additional location and using the ratio to estimate a condition of the conduit, wherein the estimating the condition from the ratio comprises measuring the ratio in a known undamaged section of the conduit and comparing to the ratio determined in the wellbore conduit, and
further comprising using a ratio determined from measurements of inelastic gamma rays made proximate a wall of the conduit and a ratio determined from measurements of inelastic gamma rays made proximate a center of the conduit, and in the computer comparing the ratio from proximate the wall to the ratio proximate the center to identify portions of the conduit having iron loss.

2. The method of claim 1 further comprising repeating the using measurements made at different positions along an interior of the conduit.

3. The method of claim 1 wherein the characterizing comprises comparing characterized measurements made in a known undamaged section of conduit to the measurements made within the conduit.

4. The method of claim 1 wherein the characterizing the measurements of inelastic gamma rays comprises determining in the computer an iron yield from a spectral analysis of the inelastic gamma rays.

5. The method of claim 1 wherein the characterizing the measurements of epithermal neutrons of capture gamma rays therefrom comprises in the computer estimating a neutron capture cross-section in the conduit, and estimating an iron content of the conduit from the neutron capture cross-section.

6. The method of claim 1 further comprising using measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts made proximate a wall of the conduit and made proximate a center of the conduit, and in the computer comparing the measurements made proximate the wall of the conduit to the measurements made in the center of the conduit to identify areas of the conduit subject to iron loss.

7. A method for evaluating wellbore conduit condition, comprising: (a) moving a pulsed neutron well logging instrument along an interior of a wellbore having at conduit therein; (b) emitting at least one burst of neutrons into the conduit (c) measuring at least one of (i) inelastic gamma rays made during the burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission; (d) characterizing the at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts to estimate an amount of loss of iron in the conduit; and (e) displaying a parameter related to the amount of iron loss˜ further comprising using measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts made proximate a wall of the conduit and made proximate a center of the conduit, and comparing the measurements made proximate the wall of the conduit to the measurements made in the center of the conduit to identify areas of the conduit subject to iron loss.

8. The method of claim 7 further comprising repeating (b) through (e) using measurements made at different positions along an interior of the conduit.

9. The method of claim 7 wherein the characterizing comprises comparing characterized measurements made in a known undamaged section of conduit to the measurements made within the conduit.

10. The method of claim 7 wherein the characterizing the measurements of inelastic gamma rays comprises determining an iron yield from a spectral analysis of the inelastic gamma rays.

11. The method of claim 7 further comprising using measurements of inelastic gamma rays detected during the burst at at least a second location spaced apart from the at least one location and in the computer determining a ratio of inelastic gamma rays detected at the at least one location and the at least one additional location and using the ratio to estimate a condition of the conduit.

12. The method of claim 11 wherein the estimating the condition from the ratio comprises measuring the ratio in a known undamaged section of the conduit and comparing to the ratio determined in the wellbore conduit.

13. The method of claim 12 further comprising using a ratio determined from measurements of inelastic gamma rays made proximate a wall of the conduit and a ratio determined from measurements of inelastic gamma rays made proximate a center of the conduit, and in the computer comparing the ratio from proximate the wall to the ratio proximate the center to identify portions of the conduit having iron loss.

14. The method of claim 7 wherein the characterizing the measurements of epithermal neutrons of capture gamma rays therefrom comprises estimating a neutron capture cross-section in the conduit, and estimating an iron content of the conduit from the neutron capture cross-section.

Assignees

• Schlumberger Technology Corp

Inventors

• Beekman Sicco
• Zhou Tong
• Rose David Alan
• Stoller Christian

Classifications

• G01V5/104 Primary

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

• G01V5/102 Primary

  the neutron source being of the pulsed type · CPC title

• G01V5/045

  Transmitting data to recording or processing apparatus; Recording data · CPC title

• G01V5/10

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

• G01V5/101

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