Method and apparatus for optical sensing

• US 10,393,573 B2
• Filed: 12/05/2016
• Issued: 08/27/2019
• 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
• Primary Examiner(s): Radkowski, Peter
• Application Number:
  US15/368,954
• Publication Number:
  US 20170082484A1
• 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 fiber. 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 fiber 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. A fibre optic distributed acoustic sensing system, comprising:

an optical sensing fibre arranged in use to receive a pulsed optical signal, the optical sensing fibre being configured to constrain the pulsed optical signal such that the pulsed optical signal propagates along the length of the optical sensing fibre in a first direction, the pulsed optical signal being backscattered and/or reflected along the length of the optical sensing fibre, the backscattered and/or reflected light being constrained by the optical fibre such that the backscattered and/or reflected light propagates therealong in a second direction opposite the first direction, wherein acoustic perturbations incident along the length of the optical sensing fibre cause the optical sensing fibre to expand and contract such that the backscattered and/or reflected light is modulated;

a means for receiving backscattered and/or reflected light from along the length of the optical sensing fibre; and

a means for processing the received backscattered and/or reflected light to measure the relative phase, frequency and amplitude of the received backscattered and/or reflected light from along the length of the optical sensing fibre to detect the acoustic perturbations, wherein the relative phase, frequency and amplitude measurements taken from along the length of the optical sensing fibre are synchronised to enhance signal sensitivity, and wherein the processor is configured to measure the backscattered and/or reflected light received from each contiguous section of optical sensing fibre along the length of optical sensing fibre based on the time taken for the pulsed optical signal to propagate along the length of the optical fibre 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 fibre.

2. The system of claim 1, wherein the optical sensing fibre is a standard telecommunications fibre optic cable.

3. The system of claim 1, wherein the means for processing is further arranged to measure phase modulation of the received light at a speed of several tens of kilohertz.

4. The system of claim 1, wherein the system further comprises a means for calibrating the means for processing.

5. The system of claim 1, wherein the optical sensing fibre is deployed along a structure or in an area to be monitored.

6. The system of claim 1, wherein the optical frequency of the optical signals received by the optical sensing fibre is changed slightly to improve the sensitivity of the light backscattered and/or reflected along the optical fibre.

7. The system of claim 1, further comprising an optical modulator for generating frequency sidebands in the optical signal, and an optical filter configured to controllably select one or more of the modulation sidebands, and, thereby vary the frequency of the light input to the sensing fibre.

8. The system of claim 1, wherein the means for receiving comprises an interferometer arranged in use to the receive backscattered and/or reflected light from along the sensing optical fibre, the interferometer comprising at least two optical paths with a path length difference therebetween, the backscattered and/or reflected light interfering in the interferometer to produce interference components, and wherein the means for processing comprises plural photodetectors to measure the interference components, and a processor arranged to determine optical phase angle data therefrom.

9. A method of fibre optic distributed acoustic sensing, comprising:

inputting a pulsed optical signal to an optical sensing fibre, the pulsed optical signal being constrained by the optical sensing fibre such that the pulsed optical signal propagates therealong in a first direction, the pulsed optical signal being backscattered and/or reflected along the length of the optical sensing fibre, the backscattered and/or reflected light being constrained by the optical sensing fibre such that the backscattered and/or reflected light propagates therealong in a second direction opposite the first direction, wherein acoustic perturbations incident along the length of the optical sensing fibre cause the optical sensing fibre 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 fibre; and

processing the received backscattered and/or reflected light to measure the relative phase, frequency and amplitude of the backscattered and/or reflected light received from along the length of the optical sensing fibre to detect acoustic perturbations, wherein the relative phase, frequency and amplitude measurements taken along the length of the optical sensing fibre are synchronised to enhance signal sensitivity, and wherein the processing comprises measuring the backscattered and/or reflected light received from each contiguous section of optical sensing fibre along the length of optical sensing fibre based on the time taken for the pulsed optical signal to propagate along the length of the optical fibre 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 fibre.