Method and apparatus for optical sensing
First Claim
1. A method of monitoring the position of a structure using a distributed acoustic sensor (DAS) system, the method, comprising:
- deploying a plurality of acoustic reference sources in an area in which a structure to be monitored is located;
deploying an optical fiber distributed acoustic sensor system on the structure, the optical fiber distributed acoustic sensor system comprising a sensing optical fiber that extends along the structure, the optical fiber being arranged in use to receive a pulsed optical signal, the optical fiber being configured to constrain the pulsed optical signal such that the pulsed optical signal propagates along the length of the optical fiber in a first direction, wherein the pulsed optical signal is backscattered and/or reflected along the length of the optical fiber, the backscattered and/or reflected light being constrained by the optical fiber such that the backscattered and/or reflected light propagates therealong in a second direction opposite the first direction;
emitting acoustic signals from the plurality of acoustic reference sources;
using the optical fiber distributed acoustic sensor system to detect, at a plurality of sections along the length of the sensing optical fiber, the acoustic signals emitted by the plurality of acoustic reference sources, wherein acoustic signals incident on the plurality of sections cause the optical fiber to expand and contract such that the backscattered and/or reflected light is modulated, and wherein the optical fiber distributed acoustic sensor system is configured to;
i) receive the backscattered and/or reflected light from along the length of the optical fiber; and
ii) process the received backscattered and/or reflected light to thereby detect the acoustic signals, wherein the processing comprises measuring the optical phase modulation of the backscattered and/or reflected light received from each contiguous section of optical fiber along the length of optical fiber 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 along the optical fiber in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber;
calculating relative positions of the plurality of sections along the optical fiber in dependence on the detected acoustic signals from the acoustic reference sources; and
from the calculated positions of the sections along the optical fiber, determining a position the structure.
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Abstract
Apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fiber 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. Advantages of this technique include 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.
84 Citations
13 Claims
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1. A method of monitoring the position of a structure using a distributed acoustic sensor (DAS) system, the method, comprising:
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deploying a plurality of acoustic reference sources in an area in which a structure to be monitored is located; deploying an optical fiber distributed acoustic sensor system on the structure, the optical fiber distributed acoustic sensor system comprising a sensing optical fiber that extends along the structure, the optical fiber being arranged in use to receive a pulsed optical signal, the optical fiber being configured to constrain the pulsed optical signal such that the pulsed optical signal propagates along the length of the optical fiber in a first direction, wherein the pulsed optical signal is backscattered and/or reflected along the length of the optical fiber, the backscattered and/or reflected light being constrained by the optical fiber such that the backscattered and/or reflected light propagates therealong in a second direction opposite the first direction; emitting acoustic signals from the plurality of acoustic reference sources; using the optical fiber distributed acoustic sensor system to detect, at a plurality of sections along the length of the sensing optical fiber, the acoustic signals emitted by the plurality of acoustic reference sources, wherein acoustic signals incident on the plurality of sections cause the optical fiber to expand and contract such that the backscattered and/or reflected light is modulated, and wherein the optical fiber distributed acoustic sensor system is configured to; i) receive the backscattered and/or reflected light from along the length of the optical fiber; and ii) process the received backscattered and/or reflected light to thereby detect the acoustic signals, wherein the processing comprises measuring the optical phase modulation of the backscattered and/or reflected light received from each contiguous section of optical fiber along the length of optical fiber 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 along the optical fiber in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber; calculating relative positions of the plurality of sections along the optical fiber in dependence on the detected acoustic signals from the acoustic reference sources; and from the calculated positions of the sections along the optical fiber, determining a position the structure. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A system for monitoring the position of a structure using a distributed acoustic sensor (DAS) system, the system comprising:
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a plurality of acoustic reference sources arranged to emit acoustic signals; and a distributed acoustic sensor (DAS) system, the distributed acoustic sensor system comprising a sensing optical fiber deployed such that the fiber extends along a structure to be monitored, the optical fiber being arranged in use to receive a pulsed optical signal, the optical fiber being configured to constrain the pulsed optical signal such that the pulsed optical signal propagates along the length of the optical fiber in a first direction, wherein the pulsed optical signal is backscattered and/or reflected along the length of the optical fiber, the backscattered and/or reflected light being constrained by the optical fiber such that the backscattered and/or reflected light propagates therealong in a second direction opposite the first direction, the distributed acoustic sensor system being arranged to; i) receive the backscattered and/or reflected light from along the length of the optical fiber; ii) process the received backscattered and/or reflected light to thereby detect, at a plurality of sections along the length of the sensing optical fiber, the acoustic signals emitted by the plurality of acoustic reference sources, wherein acoustic signals incident on the plurality of sections cause the optical fiber to expand and contract such that the backscattered and/or reflected light is modulated, wherein the processing comprises measuring the optical phase modulation of the backscattered and/or reflected light received from each contiguous section of optical fiber along the length of optical fiber 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 along the optical fiber in the second direction, to thereby map the received backscattered and/or reflected light to a respective section of optical fiber; iii) calculate relative positions of the plurality of sections along the optical fiber in dependence on the detected acoustic signals from the acoustic references sources; and iv) from the calculated positions of the sections along the fiber, determine a position the structure. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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Specification