Fiber optic cable for distributed acoustic sensing with increased acoustic sensitivity

Patent metadata

Field	Value
Publication number	US-9255836-B2
Application number	US-201113307765-A
Country	US
Kind code	B2
Filing date	Nov 30, 2011
Priority date	Jun 17, 2010
Publication date	Feb 9, 2016
Grant date	Feb 9, 2016

Abstract

Methods and apparatus for performing Distributed Acoustic Sensing (DAS) using fiber optics with increased acoustic sensitivity are provided. Acoustic sensing of a wellbore, pipeline, or other conduit/tube based on DAS may have increased acoustic sensitivity through fiber optic cable design and/or increasing the Rayleigh backscatter property of a fiber's optical core. Some embodiments may utilize a resonant sensor mechanism with a high Q coupled to the DAS device for increased acoustic sensitivity.

First claim

The invention claimed is:

1. A fiber optic cable used for distributed acoustic sensing (DAS), comprising:
an outer tube;
an inner tube surrounded by the outer tube; and
one or more optical fibers surrounded by the inner tube, wherein the one or more optical fibers have increased acoustic sensitivity compared to a standard optical fiber, wherein at least one of the one or more optical fibers have a smaller diameter compared to the standard optical fiber, and wherein, upon application of pressures created by acoustic waves, the smaller diameter provides for increased response of the fibers when compared to the standard optical fiber.

2. The fiber optic cable of claim 1 , wherein at least one of the one or more optical fibers comprise:
a core;
a cladding surrounding the core; and
a fiber coating surrounding the cladding.

3. The fiber optic cable of claim 2 , wherein at least one of the one or more optical fibers further comprise holes lengthwise within the cladding.

4. The fiber optic cable of claim 3 , wherein the holes enhance strain sensitivity of the one or more optical fibers compared to the standard optical fiber.

5. The fiber optic cable of claim 3 , wherein the holes are arranged such that pressures created by acoustic waves are focused on the core.

6. The fiber optic cable of claim 2 , wherein the fiber coating comprises graded layers with at least one of different materials or different thicknesses.

7. The fiber optic cable of claim 2 , wherein a modulus of the fiber coating is modified to have the increased acoustic sensitivity.

8. The fiber optic cable of claim 1 , wherein fiber composition of at least one of the one or more optical fibers are modified to have the increased acoustic sensitivity.

9. A fiber optic cable used for distributed acoustic sensing (DAS), comprising:
an outer tube comprising one or more slotted holes in a body of the outer tube;
an inner tube surrounded by the outer tube; and
one or more optical fibers surrounded by the inner tube.

10. The fiber optic cable of claim 9 , wherein the one or more slotted holes allow fluid ingress from an outer environment of the outer tube towards the inner tube to enhance acoustic coupling between the inner tube and the environment of the outer tube.

11. The fiber optic cable of claim 9 , wherein the inner tube comprises a corrosion-resistant material.

12. A fiber optic cable used for distributed acoustic sensing (DAS), comprising:
one or more sensing regions along a length of the cable having a first acoustic sensitivity; and
one or more segments having a second acoustic sensitivity, connecting the one or more sensing regions, wherein the first acoustic sensitivity is greater than the second acoustic sensitivity.

13. The fiber optic cable of claim 12 , wherein each of the one or more sensing regions have different acoustic signatures to distinguish at least a first sensing region from a second sensing region.

14. The fiber optic cable of claim 12 , further comprising local attachments to provide increased acoustic sensitivity, wherein the local attachments include a resonant sensor mechanism to enhance coupling of acoustic signals.

15. The fiber optic cable of claim 14 , wherein the resonant sensor mechanism is attached to an outer tube or an inner tube of the cable.

16. The fiber optic cable of claim 14 , wherein the resonant sensor mechanism is attached to one or more fibers within an inner tube of the cable.

17. The fiber optic cable of claim 16 , wherein the resonant sensor mechanism is spliced into a signal path of at least one of the one or more of fibers using input and output pigtails on waveguide components contained within the resonant sensor mechanism.

18. The fiber optic cable of claim 17 , further comprising a cane waveguide coupled to the resonant sensor mechanism, wherein the cane waveguide is spliced into a fiber path using the input and output pigtails.

19. The fiber optic cable of claim 17 , further comprising a fiber waveguide coupled to the resonant sensor mechanism, wherein the fiber waveguide is spliced into a fiber path using the input and output pigtails.

20. The fiber optic cable of claim 14 , wherein the resonant sensor mechanism comprises tuned mechanical amplifiers such as Helmholtz cavity structures, tuning fork structures, or flextensional structures.

21. The fiber optic cable of claim 14 , wherein the local attachments are interrogated using an acoustic energy source in a tone burst mode so as to enable signal processors to conduct non-crosstalking measurements of individual local attachments.

22. The fiber optic cable of claim 12 , wherein at least one of the one or more sensing regions are clamped along a length of a conduit, to couple pressures created by acoustic waves generated along the length of the conduit with the cable.

23. A method, comprising:
providing a fiber optic cable disposed along a length of a conduit, wherein the fiber optic cable comprises:
an outer tube comprising one or more slotted holes in a body of the outer tube;
an inner tube surrounded by the outer tube; and
one or more optical fibers surrounded by the inner tube; and

performing distributed acoustic sensing (DAS) along the length of the conduit by receiving acoustic signals using the fiber optic cable.

24. The method of claim 23 , wherein the acoustic signals are generated from a passive source.

25. The method of claim 24 , wherein the passive source is seismic or micro-seismic activity in a formation surrounding the conduit.

26. The method of claim 24 , wherein the passive source is flow in or around the conduit.

27. The method of claim 23 , further comprising:
providing an acoustic energy source, wherein the acoustic energy source produces acoustic stimulation along the length of the conduit.

28. The method of claim 27 , wherein the acoustic signals are generated from the acoustic energy source.

29. The method of claim 23 , wherein the performing comprises:
measuring disturbances in scattered light propagated within the fiber optic cable.

30. The method of claim 29 , wherein the disturbances in the scattered light are due to the acoustic signals, wherein the acoustic signals change an index of refraction or mechanically deform the fiber optic cable such that a Rayleigh scattered signal changes.

31. The method of claim 23 , wherein performing acoustic sensing comprises performing acoustic sensing at one or more discrete circumference areas along the conduit.

32. The method of claim 31 , wherein the fiber optic cable is wrapped in a spiral manner around the conduit at the one or more discrete circumference areas.

33. The method of claim 23 , wherein the one or more slotted holes allow fluid ingress from an outer environment of the outer tube towards the inner tube to enhance acoustic coupling between the inner tube and the environment of the outer tube.

34. The method of claim 23 , wherein the fiber optic cable comprises a filler material to enhance acoustic coupling between the one or more optical fibers and the inner tube.

35. The method of claim 34 , wherein a fill percentage of the filler material is increased to enhance the acoustic coupling.

36. The method of claim 23 , wherein the fiber optic

Assignees

• Taverner Domino
• Grunbeck John J
• Dunphy James R
• Dowd Edward M
• Kuczma Andrew S
• Bostick Iii Francis X
• Labella David
• Baker Mark
• Weatherford Technology Holdings Llc

Inventors

• Taverner Domino
• Grunbeck John J
• Dunphy James R
• Dowd Edward M
• Kuczma Andrew S
• Bostick Iii Francis X
• Labella David
• Baker Mark

Classifications

• G02B6/02342

  characterised by cladding features, i.e. light confining region · CPC title

• G02B6/4433

  Double reinforcement laying in straight line with optical transmission element · CPC title

• E21B47/135

  using light waves, e.g. infrared or ultraviolet waves · CPC title

• G02B6/02395

  Glass optical fibre with a protective coating, e.g. two layer polymer coating deposited directly on a silica cladding surface during fibre manufacture (G02B6/02052, G02B6/02057, G02B6/024, G02B6/032, G02B6/105, G02B6/14 take precedence; coating on fibre gratings G02B6/02104; multilayer core or cladding G02B6/036; reinforcing splice joints G02B6/2558; optical cables, i.e. comprising protective structures external to the protective coating such as a jacket or plural coated optical fibres G02B6/44; coating of glass to obtain optical fibres C03C25/104) · CPC title

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title