SONIC LOGGING FOR ASSESSING WELL INTEGRITY

• US 20150198032A1
• Filed: 01/16/2014
• Published: 07/16/2015
• Est. Priority Date: 01/16/2014
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: LEI, TING, SINHA, BIKASH K., ZEROUG, SMAINE
• Granted Patent: US 10,577,915 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: E21B 47/005 Monitoring or checking of cementation quality or level
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: G01V 1/44 using generators and receivers in the same well G01V1/52 takes precedence

Abstract

Methods are disclosed for detecting fluid in at least one annulus around at least one casing installed in a borehole traversing a formation utilizing a sonic tool. The sonic tool is activated in the borehole and the received sonic waveforms are processed to obtain a dispersion plot. A reference dispersion plot is generated using a model of the borehole where the casing is well-bonded by cement. The obtained and reference dispersion plots are compared. An indication of fluid and in some cases, the specific radial location thereof is obtained based on the signature of the obtained plot as opposed to the reference plot. The methods are effective in doubly-cased boreholes using monopole and/or dipole sources.

Claims

1. A method for detecting fluid in at least one annulus around at least one casing installed in a borehole traversing a formation, said at least one casing, said at least one annulus, said borehole and said formation having a configuration, said method comprising:

a) locating a sonic tool with a plurality of spaced receivers and at least one of a monopole sonic source and a dipole sonic source at a location in the borehole;

b) activating said sonic tool such that sonic waveforms are recorded by said plurality of spaced receivers;

c) processing said sonic waveforms to obtain a first dispersion plot that plots slowness as a function of frequency;

d) generating a reference dispersion plot that plots slowness as a function of frequency for said configuration by using a modeling tool and assuming that said at least one annulus contains cement that is well-bonded to said at least one casing;

e) comparing said first dispersion plot to said reference dispersion plot and identifying an indication of fluid in at least one of said at least one annulus at the location by locating differences between said first dispersion plot and said reference dispersion plot.

2. A method according to claim 1, wherein:

said at least one of a monopole sonic source and a dipole sonic source comprises a monopole sonic source,

said first dispersion plot includes a first Stoneley mode dispersion and said reference dispersion plot includes a reference Stoneley mode dispersion, said first Stoneley mode dispersion being slower than said reference Stoneley mode dispersion in a predetermined frequency range.

3. A method according to claim 1, wherein:

said at least one of a monopole sonic source and a dipole sonic source comprises a dipole sonic source,

said first dispersion plot includes a first flexural dispersion having a first kick-in frequency and said reference dispersion plot includes a reference flexural dispersion having a reference kick-in frequency, and said reference kick-in frequency is higher than said first kick-in frequency.

4. A method according to claim 1, wherein:

said at least one of a monopole sonic source and a dipole sonic source comprises a dipole sonic source,

said first dispersion plot includes a first flexural dispersion and said reference dispersion plot includes a reference flexural dispersion, and said first flexural dispersion being slower than said reference flexural dispersion in a predetermined frequency range.

5. A method according to claim 1, wherein:

said at least one of a monopole sonic source and a dipole sonic source comprises a dipole sonic source,

said first dispersion plot includes a Stoneley dispersion, and said reference dispersion plot includes a reference flexural dispersion, and

said method further comprises identifying said annulus as containing cement and gas between said cement and the formation.

6. A method according to claim 1, wherein:

said at least one of a monopole sonice source and a dipole sonic source comprises a monopole sonic source,

said first dispersion plot includes a Stoneley dispersion and does not include a pseudo-Rayleigh dispersion in a first identified frequency range, and said reference dispersion plot includes a Stoneley dispersion and a pseudo-Rayleigh dispersion in said first identified frequency range, and

said method further comprises identifying said annulus as containing cement and gas between said cement and the formation.

7. A method according to claim 1, where said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot includes a reference Stoneley dispersion and a reference pseudo-Rayleigh dispersion,

said first dispersion plot includes a first Stoneley dispersion and a second Stoneley dispersion, and

said method further comprises identifying said at least one of said first annulus and said second annulus as containing primarily fluid.

8. A method according to claim 7, wherein:

said first dispersion plot further includes a casing extensional dispersion, and

said method further comprises identifying said second annulus as containing primarily fluid and said first annulus as containing primarily cement.

9. A method according to claim 7, wherein:

said first dispersion plot does not include a casing extensional dispersion, and

said method further comprises identifying both said first annulus and said second annulus as containing primarily fluid.

10. A method according to claim 1, where said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot includes a reference Stoneley dispersion and a reference pseudo-Rayleigh dispersion,

said first dispersion plot includes a first Stoneley dispersion and a casing extensional dispersion, and

said method further comprises identifying said first annulus and said second annulus as containing primarily containing with at least one micro-annulus containing fluid between cement and a surface of at least one of said inner casing and said outer casing.

11. A method according to claim 1, where said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot includes a reference dipole flexural dispersion and a reference higher order flexural dispersion,

said first dispersion plot contains multiple formation flexural dispersions and no higher order flexural dispersion, and

said method further comprises identifying at least one of said first annulus and said second annulus as containing primarily fluid.

12. A method according to claim 11, wherein:

said first dispersion plot does not contain a dipole flexural dispersion, and

said method further comprises identifying said both said first annulus and said second annulus as containing primarily fluid.

13. A method according to claim 11, wherein:

said first dispersion plot contains a drill collar flexural mode, and

said method further comprises identifying said second annulus as containing primarily fluid and said first annulus as containing primarily cement.

14. A method according to claim 1, said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot includes a reference dipole flexural dispersion and a reference higher order flexural dispersion,

said first dispersion plot contains a casing flexural dispersion, and

said method further comprises identifying said first annulus and said second annulus as containing primarily cement with at least one micro-annulus containing fluid between cement and a surface of at least one of said inner casing and said outer casing.

15. A method according to claim 1, wherein:

said first dispersion plot and said reference plot show slownesses as a function of frequency over a frequency range of at least 1 kHz to 8 kHz.

16. A method according to claim 1, further comprising:

taking remedial action at the action in order to fully bond cement to said at least one casing.

17. A method according to claim 7, further comprising:

generating a first monopole waveform plot for said plurality of receivers as a function of time;

generating a reference monopole waveform plot for said configuration by using a modeling tool and assuming that said at least one annulus contains cement that is well-bonded to said at least one casing;

comparing said first monopole waveform plot and said reference monopole waveform plot to determine whether said first monopole waveform plot has extended ringing in said waveform plot relative to said reference monopole waveform plot.

18. A method according to claim 17, wherein:

if said first monopole waveform plot has said extended ringing, determining that both said first annulus and said second annulus contain primarily fluid, and

if said first monopole waveform plot does not have extended ringing, determining that said second annulus contains primarily fluid and said first annulus contains primarily cement.

19. A method according to claim 11, further comprising:

generating a first dipole waveform plot for said plurality of receivers as a function of time;

generating a reference dipole waveform plot for said configuration by using a modeling tool and assuming that said at least one annulus contains cement that is well-bonded to said at least one casing; and

comparing said first dipole waveform plot and said reference dipole waveform plot to determine whether said first dipole waveform plot has modal interference in said waveform plot relative to said reference dipole waveform plot, and if so, confirming that at least one of said first annulus and said second annulus contains primarily fluid.

20. A method for detecting the location of fluid in at least one annulus around at least one casing installed in a borehole traversing a formation, said at least one casing, said at least one annulus, said borehole and said formation having a configuration, said method comprising:

a) using a sonic tool with a plurality of spaced receivers and at least one of a monopole sonic source and a dipole sonic source in the borehole, activating the tool and processing sonic waveforms to generate a dispersion plot signature for a location in the borehole;

b) generating a reference dispersion plot signature for said configuration by using a modeling tool and assuming that said at least one annulus contains cement that is well-bonded to said at least one casing; and

c) comparing said first dispersion plot signature to said reference dispersion plot signature and identifying an indication of fluid in at least one of said at least one annulus at the location by locating differences between said first dispersion plot signature and said reference dispersion plot signature.

21. A method according to claim 20, where said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot signature includes a reference Stoneley dispersion and a reference pseudo-Rayleigh dispersion,

said first dispersion plot signature includes a first Stoneley dispersion and a second Stoneley dispersion, and

said method further comprises identifying said at least one of said first annulus and said second annulus as containing primarily fluid.

22. A method according to claim 21, wherein:

said first dispersion plot signature further includes a casing extensional dispersion, and

said method further comprises identifying said second annulus as containing primarily fluid and said first annulus as containing primarily cement.

23. A method according to claim 21, wherein:

said first dispersion plot signature does not include a casing extensional dispersion, and

said method further comprises identifying both said first annulus and said second annulus as containing primarily fluid.

24. A method according to claim 20, where said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot signature includes a reference Stoneley dispersion and a reference pseudo-Rayleigh dispersion,

said first dispersion plot signature includes a first Stoneley dispersion and a casing extensional dispersion, and

said method further comprises identifying said first annulus and said second annulus as containing primarily containing with at least one micro-annulus containing fluid between cement and a surface of at least one of said inner casing and said outer casing.

25. A method according to claim 20, where said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot signature includes a reference dipole flexural dispersion and a reference higher order flexural dispersion,

said first dispersion plot signature contains multiple formation flexural dispersions and no higher order flexural dispersion, and

said method further comprises identifying at least one of said first annulus and said second annulus as containing primarily fluid.

26. A method according to claim 25, wherein:

said first dispersion plot signature does not contain a dipole flexural dispersion, and

said method further comprises identifying said both said first annulus and said second annulus as containing primarily fluid.

27. A method according to claim 25, wherein:

said first dispersion plot signature contains a drill collar flexural mode, and

said method further comprises identifying said second annulus as containing primarily fluid and said first annulus as containing primarily cement.

28. A method according to claim 20, said configuration comprises an inner casing and an outer casing, and a first annulus between said inner and outer casings and a second annulus between said outer casing and the formation, wherein:

said reference dispersion plot signature includes a reference dipole flexural dispersion and a reference higher order flexural dispersion,

said first dispersion plot signature contains a casing flexural dispersion, and

said method further comprises identifying said first annulus and said second annulus as containing primarily cement with at least one micro-annulus containing fluid between cement and a surface of at least one of said inner casing and said outer casing.

29. A method according to claim 20, wherein:

said first dispersion plot and said reference plot show slownesses as a function of frequency over a frequency range of at least 1 kHz to 8 kHz.

30. A method according to claim 20, further comprising:

taking remedial action at the action in order to fully bond cement to said at least one casing.