Method and Apparatus for Optical Sensing

• US 20190331523A1
• Filed: 07/11/2019
• Published: 10/31/2019
• Est. Priority Date: 05/27/2009
• Status: Active Grant

• Current Assignee: Silixa Limited
• Original Assignee: Silixa Limited
• Inventors: Farhadiroushan, Mahmoud, Parker, Tom Richard, Shatalin, Sergey
• Granted Patent: US 11,079,269 B2
• Time in Patent Office: Days
• CPC Class Codes: E21B 47/002 by visual inspection
• CPC Class Codes: E21B 47/0025 generating an image of the borehole wall using down-hole measurements, e.g. acoustic or electric
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35306 using an interferometer arrangement
• CPC Class Codes: G01D 5/35325 using interferometer with two arms in reflection, e.g. Mickelson interferometer
• CPC Class Codes: G01D 5/35335 Aspects of emitters or receivers used by an interferometer in an optical fibre sensor arrangement using multiple sensor devices using multiplexing techniques G01D5/35383
• CPC Class Codes: G01D 5/35358 using backscattering to detect the measured quantity
• CPC Class Codes: G01D 5/35364 using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering
• CPC Class Codes: G01D 5/35377 Means for amplifying or modifying the measured quantity
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01F 1/66 by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
• CPC Class Codes: G01F 1/661 using light
• CPC Class Codes: G01F 1/662 Constructional details
• CPC Class Codes: G01F 1/666 by detecting noise and sounds generated by the flowing fluid
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• 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: G01M 11/085 the optical fiber being on or near the surface of the DUT
• CPC Class Codes: G01M 11/331 by using interferometer
• CPC Class Codes: G01M 3/24 using infrasonic, sonic, or ultrasonic vibrations
• CPC Class Codes: G01M 5/0058 : of elongated objects, e.g. pipes, masts, towers or railways
• CPC Class Codes: G01M 5/0066 : by exciting or detecting vibration or acceleration vibration testing of structures G01M7/00
• CPC Class Codes: G01M 5/0091 : by using electromagnetic excitation or detection
• CPC Class Codes: G01V 1/226 : Optoseismic systems
• CPC Class Codes: G01V 1/40 : specially adapted for well-logging

Abstract

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

Claims

1-10. -10. (canceled)

11. An apparatus for monitoring seepage along a dam or a dyke, the apparatus comprising:

an optical fiber sensing system; and

an acoustic source located in use within a body of fluid contained by the dam or dyke, or within the dam or dyke itself;

wherein the optical fiber sensing system is arranged in use to measure a strength of an acoustic signal generated by the acoustic source, and to determine areas of seepage in the dam or dyke based thereon;

wherein the optical fiber sensing system is arranged in use to detect a louder acoustic signal in areas of seepage, wherein areas of seepage provide low acoustic impedance paths for acoustic wave transmission.

12. An apparatus according to claim 11, wherein the optical fiber sensing system is a distributed acoustic sensor system, the system including an optical sensing fiber deployed in use to monitor the dam or dyke, and an interferometer arranged to receive backscattered light from along the optical sensing fiber, the interferometer comprising at least two optical paths with a path length difference therebetween, the backscattered light interfering in the interferometer to produce interference components, the DAS system further comprising plural photodetectors to measure the interference components, and a processor arranged to determine optical phase angle data therefrom.

13. An apparatus of claim 12, wherein the interferometer further comprises an optical coupler arranged to introduce a relative phase shift between the interference components.

14. An apparatus of claim 12, wherein the interferometer further comprises an optical amplifier arranged to amplify the received backscattered light to produce an amplified light signal.

15. An apparatus of claim 14, wherein the interferometer further comprises an optical filter to filter out the out of band Amplified Spontaneous Emission (ASE) noise generated by the optical amplifier from the amplified light signal.

16. An apparatus according to claim 11, wherein the optical fiber sensing system is a distributed acoustic sensor system, the system including an optical sensing fiber deployed in use to monitor the dam or dyke, and an interferometer arranged to receive reflected light from along the optical sensing fiber, the interferometer comprising at least two optical paths with a path length difference therebetween, the reflected light interfering in the interferometer to produce interference components, the DAS system further comprising plural photodetectors to measure the interference components, and a processor arranged to determine optical phase angle data therefrom.

17. An apparatus of claim 16, wherein the interferometer further comprises an optical coupler arranged to introduce a relative phase shift between the interference components.

18. An apparatus of claim 16, wherein the interferometer further comprises an optical amplifier arranged to amplify the received reflected light to produce an amplified light signal.

19. An apparatus of claim 18, wherein the interferometer further comprises an optical filter to filter out the out of band Amplified Spontaneous Emission (ASE) noise generated by the optical amplifier from the amplified light signal.

20. An apparatus of claim 16, wherein the interferometer is further arranged to receive backscattered light from along the optical sensing fiber.

21. An apparatus according to claim 11, wherein the optical fiber sensing system comprises an optical source configured to output a pulsed optical signal.

22. An apparatus according to claim 11, wherein the optical fiber sensing system comprises an optical sensing fiber deployed in use along the dam or dyke, the optical sensing fiber being arranged in use to receive a pulsed optical signal, the pulsed optical signal being constrained by the optical sensing fiber such that it propagates therealong in a first direction, the pulsed optical signal being backscattered and/or reflected along the length of the optical sensing fiber, the backscattered and/or reflected light being constrained by the optical sensing fiber such that it propagates therealong in a second direction opposite the first direction, wherein acoustic perturbations generated by the acoustic signal of the acoustic source incident along the length of the optical sensing fiber cause the optical sensing fiber to expand and contract such that the backscattered and/or reflected light is modulated.

23. An apparatus according to claim 22, wherein the optical fiber sensing system comprises a means for receiving the backscattered and/or reflected light from along the length of the optical sensing fiber.

24. An apparatus according to claim 23, wherein the means for receiving comprising optical componentry.

25. An apparatus according to claim 23, wherein the optical fiber sensing system comprises a means for processing the received backscattered and/or reflected light to measure the phase, frequency and amplitude data of the received backscattered and/or reflected light to provide quantitative measurements of the acoustic perturbations incident along the length of the fiber to thereby measure a strength of the acoustic signal generated by the acoustic source, wherein the processing comprises measuring the backscattered and/or reflected light received from each contiguous section of optical sensing fiber along its length based on the time taken for the pulsed optical signal to propagate along the length of the optical fiber in the first direction, and the time taken for the backscattered and/or reflected light to propagate back in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber.

26. An apparatus according to claim 25, wherein the means for processing comprises a plurality of photodetectors and a processor.

27. A method of monitoring seepage along a dam or dyke using an optical fiber sensing system, the method comprising:

measuring an acoustic signal generated by an acoustic source located within the body of fluid contained by the dam or dyke, or within the dam or dyke itself, wherein the optical fiber sensing system measures a strength of the acoustic signal; and

determining areas of seepage in the dam or dyke based on the measured acoustic signal, wherein the optical fiber sensing system detects a louder acoustic signal in areas of seepage, wherein areas of seepage provide low acoustic impedance paths for acoustic wave transmission.

28. A method according to claim 27, wherein the optical fiber sensing system comprises an optical sensing fiber deployed along the dam or dyke, and wherein the method further comprises:

transmitting a pulsed optical signal into the optical sensing fiber, the pulsed optical signal being constrained by the optical sensing fiber such that it propagates therealong in a first direction, the pulsed optical signal being backscattered and/or reflected along the length of the optical sensing fiber, the backscattered and/or reflected light being constrained by the optical sensing fiber such that it propagates therealong in a second direction opposite the first direction, wherein acoustic perturbations generated by the acoustic signal of the acoustic source incident along the length of the optical sensing fiber cause the optical sensing fiber to expand and contract such that the backscattered and/or reflected light is modulated;

receiving the backscattered and/or reflected light from along the length of the optical sensing fiber; and

processing the received backscattered and/or reflected light to measure the phase, frequency and amplitude data of the received backscattered and/or reflected light to provide quantitative measurements of the acoustic perturbations along the length of the optical sensing fiber to thereby measure the strength of the acoustic signal generated by the acoustic source.

29. A method according to claim 28, wherein the processing comprises measuring the backscattered and/or reflected light received from each contiguous section of optical sensing fiber along its length based on the time taken for the pulsed optical signal to propagate along the length of the optical fiber in the first direction, and the time taken for the backscattered and/or reflected light to propagate back in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber.

30. A dam or dyke comprising:

an optical fiber sensing system; and

an acoustic source located within a body of fluid contained by the dam or dyke, or within the dam or dyke itself;

wherein the optical fiber sensing system is arranged to measure a strength of an acoustic signal generated by the acoustic source, and to determine areas of seepage in the dam or dyke based thereon;

wherein the optical fiber sensing system is arranged to detect a louder acoustic signal in areas of seepage, wherein areas of seepage provide low acoustic impedance paths for acoustic wave transmission.