Distributed pressure sensing

Patent metadata

Field	Value
Publication number	US-11125637-B2
Application number	US-201816624406-A
Country	US
Kind code	B2
Filing date	May 31, 2018
Priority date	Jun 19, 2017
Publication date	Sep 21, 2021
Grant date	Sep 21, 2021

Abstract

This application relates to methods and apparatus for distributed fibre optic sensing that can provide an indication of the absolute value of pressure acting on a sensing portion of a fibre optic cable. A sensor apparatus (600) has a first fibre optic cable structure (102) comprising a first optical fibre (101) and an interrogator (103) configured to perform distributed acoustic sensing on the first optical fibre (101) to provide a measurement signal from at least one sensing portion of the first optical fibre. The first fibre optic cable structure (102) is configured such that a sensitivity of a sensing portion (603, 604) to an incident pressure stimulus (ΔP1, ΔP2) depends on the ambient pressure (AP1, AP2) at the location of the respective sensing portion. A processor (104) is configured to process the measurement signal in response to an incident pressure stimulus (ΔP1, ΔP2) based on a predetermined sensitivity profile (504, 701) to determine an indication of the ambient pressure at the respective sensing portion.

First claim

The invention claimed is:

1. A distributed fibre optic sensor apparatus comprising:
a first fibre optic cable structure comprising a first optical fibre;
an interrogator configured to perform distributed acoustic sensing on the first optical fibre to provide a measurement signal from at least one sensing portion of the first optical fibre; and
a processor;
wherein the first fibre optic cable structure is configured such that, for said at least one sensing portion of the first optical fibre, a sensitivity of the sensing portion to an incident pressure stimulus depends on the ambient pressure acting on first fibre optic cable structure at the location of the respective sensing portion; and
wherein the processor is configured to process the measurement signal from said at least one sensing portion of the first optical fibre in response to an incident pressure stimulus based on a predetermined sensitivity profile to determine an indication of the value of the ambient pressure at the respective sensing portion.

2. The distributed fibre optic sensor apparatus as claimed in claim 1 wherein the processor is configured to process the measurement signal from said at least one sensing portion of the first optical fibre in response to an incident pressure stimulus which is a controlled stimulus of known magnitude.

3. The distributed fibre optic sensor apparatus as claimed in claim 2 wherein the predetermined sensitivity profile is an indication of the sensitivity of the respective sensing portion at one or more values of ambient pressure.

4. The distributed fibre optic sensor apparatus as claimed in claim 1 further comprising a second optical fibre deployed along the path of the first optical fibre, wherein:
the interrogator is configured to perform distributed acoustic sensing on the second optical fibre to provide a measurement signal from at least one sensing portion of the second optical fibre so that at least one sensing portion of the first optical fibre has a corresponding sensing portion of the second optical fibre at substantially the same location;
the second optical fibre is configured such that a sensitivity of the second optical fibre to an incident pressure stimulus has a relationship with ambient pressure that is different to that of the first sensing fibre; and
the processor is configured to process the measurement signal from a sensing portion of the first sensing optical fibre together with the measurement signal from the corresponding sensing portion of the second sensing optical fibre in response to the same incident pressure stimulus.

5. The distributed fibre optic sensor apparatus as claimed in claim 4 wherein the second optical fibre is configured such that the sensitivity of the second sensing optical fibre does not substantially vary with ambient pressure acting on the second optical fibre.

6. The distributed fibre optic sensor apparatus as claimed in claim 4 wherein said predetermined sensitivity profile is an indication of the relative sensitivity of the first and second sensing fibres to an input stimulus at one or more values of ambient pressure.

7. The distributed fibre optic sensor apparatus as claimed in claim 4 wherein the processor is configured to determine a ratio of magnitude of the measurement signal from a sensing portion of the first sensing fibre and the measurement signal from a corresponding sensing portion of the second sensing fibre.

8. The distributed fibre optic sensor apparatus as claimed in claim 1 further wherein the processor is configured to receive an indication of temperature at one or more locations along the length of the first fibre optical cable structure, wherein the predetermined sensitivity profile is indicative as to how sensitivity varies with temperature.

9. The distributed fibre optic sensor apparatus as claimed in claim 8 further comprising a fibre optic distributed temperature sensor configured to perform distributed temperature sensing on a temperature sensing optical fibre deployed along the path of the first fibre optic cable structure.

10. The distributed fibre optic sensor apparatus as claimed in claim 1 wherein the first fibre optic cable structure comprises at least one deformable strain transformer mechanically coupled to the first optical fibre and configured such that a force acting on the strain transformer in a direction transverse to the cable axis results in a deformation of the strain transformer thereby applying a longitudinal force to the first optical fibre.

11. The distributed fibre optic sensor apparatus as claimed in claim 10 wherein the first fibre optic cable structure comprises a compliant core material mechanically coupled to the first optical fibre such that a longitudinal force acting on the compliant core material induces a longitudinal strain in the at least one optical fibre.

12. The distributed fibre optic sensor apparatus as claimed in claim 11 wherein the strain transformer is stiffer than the compliant core material.

13. The distributed fibre optic sensor apparatus as claimed in claim 11 wherein the compliant core material comprises extruded nylon.

14. The distributed fibre optic sensor apparatus as claimed in claim 10 where the strain transformer comprises at least one helically coiled member or a braid member.

15. The distributed fibre optic sensor apparatus as claimed in claim 14 wherein the helix angle of said helically coiled member is of the order of 50 to 70 degrees and the diameter of said helically coiled member is in the range of 1 to 10 mm.

16. The distributed fibre optic sensor apparatus as claimed in claim 10 wherein at least one portion of the first fibre optic cable structure comprises a plurality of strain transformers, each strain transformer comprising a helically wound coiled member.

17. The distributed fibre optic sensor apparatus as claimed in claim 16 wherein at least one helically wound coiled member is wound in the opposite direction to another helically wound coiled member or is interleaved with another helically wound coiled member.

18. The distributed fibre optic sensor apparatus as claimed in claim 10 wherein the strain transformer comprises a shaped steel member wherein the volume percentage of steel of the fibre optic cable is substantially 10%.

19. The distributed fibre optic sensor apparatus as claimed in claim 1 wherein at least part of the first fibre optic cable structure is deployed within a fluid filled conduit and the processor is configured to determine an indication of the pressure of the fluid within the conduit.

20. A method of distributed fibre optic sensing comprising:
performing distributed acoustic sensing on a first optical fibre disposed within a first fibre optic cable structure to provide a measurement signal from at least one sensing portion of the first optical fibre;
wherein the first fibre optic cable structure is configured such that, for said at least one sensing portion of the first optical fibre, a sensitivity of the sensing portion to an incident pressure stimulus depends on the ambient pressure acting on first fibre optic cable structure at the location of the respective sensing portion;
the method comprising acquiring a measurement signal from at least one sensing portion of the first optical fibre in response to an incident pressure stimulus; and
processing said measurement signal based on a predetermined sensitivity profile to determine an indication of the value of the ambient pressure at the respective sensing portion.

Assignees

• Optasense Holdings Ltd

Inventors

• Godfrey Alastair

Classifications

• G01L11/025 Primary

  using a pressure-sensitive optical fibre · CPC title

• G01D5/3537

  Optical fibre sensor using a particular arrangement of the optical fibre itself · CPC title

• G01D5/35361

  using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering · CPC title

• G02B2006/12138

  Sensor · CPC title

• G02B6/4432

  with fibre reinforcements · CPC title