Method and apparatus for inspecting well bore casing

• US 6,188,643 B1
• Filed: 10/13/1994
• Issued: 02/13/2001
• Est. Priority Date: 10/13/1994
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Stanke, Fred E., Herve, Philippe G., Liang, Kenneth K.
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US08/322,919
• Time in Patent Office: 2,315 Days
• Field of Search: 367/26, 367/28, 367/29, 367/30, 367/35, 364/422, 181/105, 736/22
• US Class Current: 367/29
• CPC Class Codes: E21B 47/00 Survey of boreholes or wells monitoring pressure or flow of drilling fluid E21B21/08
• CPC Class Codes: E21B 47/085 using radiant means, e.g. acoustic, radioactive or electromagnetic
• CPC Class Codes: G01B 17/02 for measuring thickness
• CPC Class Codes: G01V 1/48 Processing data
• CPC Class Codes: G01V 1/50 Analysing data

Abstract

An improved technique for determining the thickness of a member, especially pipe such as fluid-filled casing in an earth borehole, includes the following steps: directing a pulse of ultrasonic energy toward the inner surface of the pipe, and receiving and storing, as a function of time, signals representative of ultrasonic energy reflected from the inner surface of the pipe; determining, from the stored signals, the arrival time of the initial echo from the inner surface; determining, from the stored signals, the arrival time and the amplitude of a first candidate initial echo from the outer surface of the pipe; performing a reverse search on the stored signals to determine, from stored signals at times earlier than the arrival time of the first candidate, the arrival time and the amplitude of a second candidate initial echo from the outer surface; comparing amplitudes of the first and second candidates, and selecting, based on the comparison, one of the first and second candidates as the actual outer surface echo; and determining the thickness of the pipe from the arrival time of the actual outer surface echo and the arrival time of the inner surface echo. Using this technique, the earlier arriving candidate can be properly identified as the actual outer surface echo, even when the later arriving candidate has a greater amplitude.

Claims

1. A method for determining the thickness of a generally cylindrical member, comprising the steps of:

directing a pulse of ultrasonic energy toward the cylindrical member, and receiving and storing, as a function of time, signals representative of ultrasonic energy reflected from the member as a result of the directed pulse;

determining, from said stored signals, the arrival time of the initial echo from the front surface of the member also resulting from the directed pulse;

determining, from said stored signals, the arrival time and the amplitude of a first candidate initial echo from the back surface of said member, the first candidate initial echo also resulting from the directed pulse;

performing a reverse search on said stored signals to determine, from stored signals also resulting from the directed pulse and at times earlier than the arrival time of said first candidate, the arrival time and the amplitude of a second candidate initial echo from said back surface of the member, the second candidate initial echo also resulting from the directed pulse;

comparing amplitudes of said first and second candidates, and selecting, based on said comparison, one of said first and second candidates as the actual back surface echo; and

determining the thickness of said member from the arrival time of the actual back surface echo and the arrival time of the front surface echo.

2. The method as defined by claim 1, wherein said step of determining the arrival time of the initial front surface echo comprises determining the global peak of said stored signals having arrival times within a predetermined time period.

3. The method as defined by claim 2, wherein said first candidate initial echo is determined as the highest amplitude peak of opposite polarity to said global peak.

4. The method as defined by claim 1, wherein said second candidate is selected as the actual back surface echo if it has an amplitude of at least a predetermined fraction of the amplitude of said first candidate.

5. The method as defined by claim 2, wherein said second candidate is selected as the actual back surface echo if it has an amplitude of at least a predetermined fraction of the amplitude of said first candidate.

6. The method as defined by claim 3, wherein said second candidate is selected as the actual back surface echo if it has an amplitude of at least a predetermined fraction of the amplitude of said first candidate.

7. The method as defined by claim 6, wherein said predetermined fraction is about 0.7.

8. A method for determining the thickness of generally cylindrical pipe, comprising the steps of:

directing a pulse of ultrasonic Energy toward the inside of the pipe, and receiving and storing, as a function of time, signals representative of ultrasonic energy reflected from the inner surface of the pipe as a result of the directed pulse;

determining, from said stored signals, the arrival time of the initial echo from said inner surface also as a result of the directed pulse;

determining, from said stored signals, the arrival time and the amplitude of a first candidate initial echo from the outer surface of said pipe, the first candidate initial echo also resulting from the directed pulse;

performing a reverse search on said stored signals to determine, from stored signals also resulting from the directed pulse and at times earlier than the arrival time of said first candidate, the arrival time and the amplitude of a second candidate initial echo from said outer surface, the second candidate initial echo also resulting from the directed pulse;

comparing amplitudes of said first and second candidates, and selecting, based on said comparison, one of said first and second candidates as the actual outer surface echo; and

determining the thickness of said pipe from the arrival time of the actual outer surface echo and the arrival time of the inner surface echo.

9. The method as defined by claim 8, wherein said step of determining the arrival time of the initial inner surface echo comprises determining the global peak of said stored signals having arrival times within a predetermined time period.

10. The method as defined by claim 9, wherein said first candidate initial echo is determined as the highest amplitude peak of opposite polarity to said global peak.

11. The method as defined by claim 8, wherein said second candidate is selected as the actual back surface echo if it has an amplitude of at least a predetermined fraction of the amplitude of said first candidate.

12. The method as defined by claim 10, wherein said second candidate is selected as the actual back surface echo if it has an amplitude of at least a predetermined fraction of the amplitude of said first candidate.

13. The method as defined by claim 12, wherein said predetermined fraction is about 0.7.

14. The method as defined by claim 8, wherein said pipe is liquid-containing casing in an earth borehole.

15. The method as defined by claim 12, wherein said pipe is liquid-containing casing in an earth borehole.

16. Apparatus for determining the thickness of generally cylindrical casing in an earth borehole, comprising:

a logging device suspendible in the borehole, said logging device including;

means for directing a pulse of ultrasonic energy toward the inside of the casing, and receiving and storing, as a function of time, signals resulting from the directed pulse and representative of ultrasonic energy reflected from the inner surface of the casing;

means for determining, from said stored signals, the arrival time of the initial echo from said inner surface also resulting from the directed pulse;

means for determining, from said stored signals, the arrival time and the amplitude of a first candidate initial echo from the outer surface of said casing, the first candidate initial echo also resulting from the directed pulse;

means for performing a reverse search on said stored signals to determine, from stored signals also resulting from the directed pulse and at times earlier than the arrival time of said first candidate, the arrival time and the amplitude of a second candidate initial echo from said outer surface, the second candidate initial echo also resulting from the initial pulse;

means for comparing amplitudes of said first and second candidates, and selecting, based on said comparison, one of said first and second candidates as the actual outer surface echo; and

means for determining the thickness of said casing from the arrival time of the actual outer surface echo and the arrival time of the inner surface echo.

17. Apparatus as defined by claim 16, wherein said means for determining the arrival time of the initial inner surface echo comprises determining the global peak of said stored signals having arrival times within a predetermined time period.

18. Apparatus as defined by claim 16, further comprising means for transmitting the determined thickness to the earth'"'"'s surface for real time display of said thickness.