Fiber optic distributed vibration sensing with directional sensitivity

Patent metadata

Field	Value
Publication number	US-9880047-B2
Application number	US-201414898279-A
Country	US
Kind code	B2
Filing date	Jun 13, 2014
Priority date	Jun 13, 2013
Publication date	Jan 30, 2018
Grant date	Jan 30, 2018

Abstract

Methods for determining separate velocity components of an acoustic wavefield that are incident on a distributed fiber optic sensor are disclosed. A fiber optic sensor includes fiber that is spatially distributed in non-parallel planes of a three-dimensional volume having three orthogonal axes. The fiber includes a first fiber pattern that is spatially distributed within a first plane of the three-dimensional volume, and a second fiber pattern that is spatially distributed within a second plane of the volume. The fiber patterns are interrogated separately by a distributed fiber optic interrogation system. The individual responses from each pattern are combined and processed to determine separate velocity components of the acoustic wavefield relative to the orthogonal axes of the three-dimensional volume.

First claim

What is claimed is:

1. A method of determining velocity components of an acoustic wavefield incident on a distributed fiber optic sensor, comprising:
providing a distributed fiber optic sensor that is configured to provide a distributed response to an incident acoustic wavefield, the fiber optic sensor including fiber that is spatially distributed in planes of a three-dimensional volume having three orthogonal axes, the fiber including:
a first fiber pattern that is spatially distributed within a first plane of the three-dimensional volume; and,
a second fiber pattern that is spatially distributed within a second plane of the volume that is non-parallel to the first plane;

launching optical energy into the fiber optic sensor to obtain individual responses from each of the first fiber pattern and the second fiber pattern to the incident acoustic wavefield, and
processing the individual responses to determine separate velocity components of the acoustic wavefield relative to orthogonal axes of the three-dimensional volume.

2. The method as recited in claim 1 , wherein the first fiber pattern has a first effective length and a second effective length along respective orthogonal axes of the three-dimensional volume, and the second fiber pattern has a third effective length and a fourth effective length along respective orthogonal axes of the three-dimensional volume, and wherein the separate velocity components are determined based on a sum of the first effective length and the second effective length and a sum of the third effective length and the fourth effective length.

3. The method as recited in claim 1 , wherein the fiber further includes a third fiber pattern that is spatially distributed within a third plane of the volume that is non-parallel to the first plane and the second plane, and wherein launching optical energy is further to obtain an individual response from the third fiber pattern, and wherein the individual responses are processed to determine separate velocity components of the acoustic wavefield separately along each of the three orthogonal axes of the three-dimensional volume.

4. The method as recited in claim 3 , wherein the first plane, second plane and third plane are orthogonal to each other.

5. . The method as recited in claim 4 , wherein each of the first, second and third fiber patterns has an effective length ratio of approximately 1:1 in each of the orthogonal axes of the respective orthogonal planes.

6. The method as recited in claim 3 , wherein the separate velocity components are determined based on a sum of effective lengths of the first fiber pattern along orthogonal axes of the volume, a sum of effective lengths of the second fiber pattern along orthogonal axes of the volume, and a sum of effective lengths of the third fiber pattern along orthogonal axes of the volume.

7. The method as recited in claim 6 , wherein each of the first, second and third fiber patterns has a circular shape.

8. The method as recited in claim 3 , wherein dimensions of at least one of the first, second and third fiber patterns are selected so that the at least one of the first, second and third fiber patterns has a different wavenumber response than the other of the first, second and third fiber patterns.

9. The method as recited in claim 8 , wherein the dimensions of the first fiber pattern are selected so that the wavenumber response of the first fiber pattern fills a notch in the wavenumber response of at least one of the second fiber pattern and the third fiber pattern.

10. The method as recited in claim 6 , wherein at least one of the first, second and third fiber patterns has a different effective length ratio than the other of the first, second and third fiber patterns.

11. The method as recited in claim 2 , wherein the first fiber pattern is a serpentine and the second fiber pattern is a straight line.

12. The method as recited in claim 1 , further comprising providing a plurality of point sensors to monitor the acoustic wavefield at a plurality of corresponding point locations, and wherein processing includes combining responses of the point sensors to the acoustic wavefield with the individual responses of the first and second fiber patterns to determine direction of travel of the acoustic wavefield.

13. A method of determining velocity components of an acoustic wavefield incident on a distributed fiber optic sensor, comprising:
providing a distributed fiber optic sensor that is configured to provide a distributed response to an incident acoustic wavefield, the fiber optic sensor including fiber that is spatially distributed in a three-dimensional volume having three orthogonal axes, the fiber including:
a first fiber pattern that is helically wound about a tubular support structure; and
a second fiber pattern that is spatially distributed within a first plane of the three-dimensional volume;

launching optical energy into the fiber optic sensor to obtain individual responses from each of the first fiber pattern and the second fiber pattern to the incident acoustic wavefield, and
processing the individual responses to determine separate velocity components of the acoustic wavefield relative to the orthogonal axes of the three-dimensional volume.

14. The method as recited in claim 13 , wherein the fiber further includes a third fiber pattern that is spatially distributed within a second plane of the three-dimensional volume, and wherein processing determines a velocity component of the acoustic wavefield along each of the three orthogonal axes of the volume.

15. The method as recited in claim 14 , wherein the second fiber pattern is a serpentine.

16. The method as recited in claim 15 , wherein the third fiber pattern is a serpentine.

17. The method as recited in claim 16 , where a lay angle of the helically wound first fiber pattern is modulated along the length of the tubular support structure.

18. The method as recited in claim 13 , wherein the tubular support structure has a diameter that is modulated along its length.

19. The method as recited in claim 13 , wherein the tubular support structure is a mandrel made of a material having different compliances.

20. The method as recited in claim 19 , wherein the material has a first a first compliance along a longitudinal axis of the mandrel and a second compliance along a transverse axis of the mandrel.

21. The method as recited in claim 13 , further comprising deploying the fiber optic sensor in a wellbore.

22. The method as recited in claim 13 , further comprising towing the fiber optic sensor in a marine streamer.

23. A method of determining direction of travel of an acoustic wavefield, comprising:
providing a fiber optic sensor that is configured to provide a distributed response to an incident acoustic wavefield;
launching optical energy into the fiber optic sensor and detecting backscatter generated by the fiber sensor in response to the launched optical energy;
acquiring, from the detected backscatter, a data set representing strain imparted on the fiber optic sensor by the incident acoustic wavefield;
determining from the data set, a spatial gradient of the strain;
determining a polarity mask based on the spatial gradient; and
applying the polarity mask to the data set to determine direction of travel of the acoustic wavefield.

24. The method as recited in claim 23 , further comprising deploying the fiber optic sensor in a wellbore.

2

Assignees

• Schlumberger Technology Corp

Inventors

• Martin James
• Donno Daniela
• Papp Bence
• Hartog Arthur

Classifications

• 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

• G01V1/52

  Structural details · CPC title

• G01H5/00

  Measuring propagation velocity of ultrasonic, sonic or infrasonic waves {, e.g. of pressure waves} · CPC title

• G01D5/35361

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

• G01V1/226

  Optoseismic systems · CPC title