FIBER OPTIC CABLE FOR DISTRIBUTED ACOUSTIC SENSING WITH INCREASED ACOUSTIC SENSITIVITY

• US 20120111104A1
• Filed: 11/30/2011
• Published: 05/10/2012
• Est. Priority Date: 06/17/2010
• Status: Active Grant

• Current Assignee: Weatherford Technology Holdings, LLC (Weatherford International PLC)
• Original Assignee: Weatherford Technology Holdings, LLC (Weatherford International PLC)
• Inventors: Taverner, Domino, Grunbeck, John J., Dunphy, James R., Kuczma, Andrew S., Bostick, Francis X. III, Dowd, Edward M., Labella, David, Baker, Mark
• Granted Patent: US 9,255,836 B2
• Time in Patent Office: Days
• US Class Current: 73/152.16
• CPC Class Codes: E21B 47/135 using light waves, e.g. infrared or ultraviolet waves
• CPC Class Codes: G01H 9/004 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 Class Codes: G01V 2210/1429 Subsurface, e.g. in borehole or below weathering layer or mud line
• CPC Class Codes: G02B 6/02342 characterised by cladding features, i.e. light confining region
• CPC Class Codes: G02B 6/02395 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 Class Codes: G02B 6/4433 Double reinforcement laying in straight line with optical transmission element

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.

Claims

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.

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 1, wherein at least one of the one or more optical fibers have a smaller diameter compared to the standard optical fiber.

7. The fiber optic cable of claim 6, 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.

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

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

10. 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.

11. A fiber optic cable used for distributed acoustic sensing (DAS), comprising:

an outer tube comprising one or more slotted holes;

an inner tube surrounded by the outer tube; and

one or more optical fibers surrounded by the inner tube.

12. The fiber optic cable of claim 11, wherein the one or more slotted holes allow fluid ingress to enhance acoustic coupling between the inner tube and an environment of the outer tube.

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

14. 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.

15. The fiber optic cable of claim 14, 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.

16. The fiber optic cable of claim 14, further comprising local attachments to provide increased acoustic sensitivity, such as a resonant sensor mechanism to enhance coupling of acoustic signals.

17. The fiber optic cable of claim 16, wherein the resonant sensor mechanism is attached to an outer tube or an inner tube of the cable.

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

19. The fiber optic cable of claim 16, wherein the resonant sensor mechanism comprises tuned mechanical amplifiers such as Helmholtz cavity structures, tuning fork structures, or flextensional structures.

20. The fiber optic cable of claim 18, 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.

21. The fiber optic cable of claim 20, 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.

22. The fiber optic cable of claim 20, 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.

23. The fiber optic cable of claim 16, 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.

24. The fiber optic cable of claim 14, 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.

25. A method, comprising:

providing a fiber optic cable disposed along a length of a conduit, wherein the fiber optic cable has increased acoustic sensitivity; and

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

26. The method of claim 25, wherein the acoustic signals are generated from a passive source.

27. The method of claim 26, wherein the passive source is seismic or micro-seismic activity in a formation surrounding the conduit.

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

29. The method of claim 25, further comprising:

providing an acoustic energy source, wherein the acoustic energy source produces acoustic stimulation along the length of the conduit.

30. The method of claim 29, wherein the acoustic signals are generated from the acoustic energy source.

31. The method of claim 25, wherein the performing comprises:

measuring disturbances in scattered light that may be propagated within the fiber optic cable.

32. The method of claim 31, wherein the disturbances in the scattered light are due to the acoustic signals, wherein the acoustic signals may change an index of refraction or mechanically deform the fiber optic cable such that a Rayleigh scattered signal changes.

33. The method of claim 25, wherein performing acoustic sensing comprises performing acoustic sensing at one or more discrete circumference areas along the conduit.

34. The method of claim 33, wherein the fiber optic cable is wrapped in a spiral manner around the conduit at the one or more discrete circumference areas.

35. The method of claim 25, wherein the fiber optic cable comprises:

an outer tube;

an inner tube surrounded by the outer tube; and

one or more optical fibers surrounded by the inner tube.

36. The method of claim 35, wherein the outer tube comprises one or more slotted holes that allow fluid ingress to enhance acoustic coupling between the inner tube and an environment of the outer tube.

37. The method of claim 35, wherein the fiber optic cable comprises a filler material to enhance acoustic coupling between the one or more optical fibers and the inner tube.

38. The method of claim 37, wherein a fill percentage of the filler material is increased to enhance the acoustic coupling.

39. The method of claim 35, wherein the fiber optic cable comprises a filler material to enhance acoustic coupling between the inner tube and the outer tube.

40. The method of claim 35, wherein the fiber optic cable comprises an encapsulant material to enhance acoustic coupling between the outer tube and an environment surrounding the outer tube.

41. The method of claim 25, wherein performing DAS comprises:

correlating the acoustic signals to downhole conditions associated with at least one of chokes at various valve positions, gas lift valve operations, downhole pumps for artificial lift, downhole separators, subsurface safety valve (SSSV) operations, inflow of fluids from a reservoir, inflow through sand screens, inflow control devices (ICDs), gravel packing operations, downhole perforating, downhole stimulation, leak detection, and seismic and micro-seismic disturbances.

42. The method of claim 41, wherein the downhole conditions, downhole components, or an operational state of the downhole components are identified by respective acoustic signatures.

43. The method of claim 42, wherein the acoustic signatures are compared to a database of acoustic signatures to identify the downhole conditions, the downhole components, or the operational state of the downhole components.