Method and apparatus for optical sensing
First Claim
1. An apparatus, comprising:
- a distributed acoustic sensor (DAS) system having a fibre optic cable deployed along a pipe to be monitored, wherein the fibre optic cable is arranged in use to receive an input optical signal and propagate the received optical signal along its length, the distributed acoustic sensor system being configured to;
i) receive light backscattered and/or reflected from along the fibre optic cable as the optical signal travels therealong, the light being backscattered and/or reflected in dependence on acoustic signals incident along the length of the fibre optic cable causing the fibre optic cable to expand and contract; and
ii) process the received light to determine the relative optical phase modulation along at least one section of the fibre optic cable, and determine acoustic signals incident along the pipe therefrom;
wherein the fibre optic cable is deployed along the pipe such that at at least one portion of the pipe the cable is wrapped around the pipe whereby to increase the spatial resolution of the DAS in the at least one portion.
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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.
41 Citations
12 Claims
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1. An apparatus, comprising:
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a distributed acoustic sensor (DAS) system having a fibre optic cable deployed along a pipe to be monitored, wherein the fibre optic cable is arranged in use to receive an input optical signal and propagate the received optical signal along its length, the distributed acoustic sensor system being configured to; i) receive light backscattered and/or reflected from along the fibre optic cable as the optical signal travels therealong, the light being backscattered and/or reflected in dependence on acoustic signals incident along the length of the fibre optic cable causing the fibre optic cable to expand and contract; and ii) process the received light to determine the relative optical phase modulation along at least one section of the fibre optic cable, and determine acoustic signals incident along the pipe therefrom; wherein the fibre optic cable is deployed along the pipe such that at at least one portion of the pipe the cable is wrapped around the pipe whereby to increase the spatial resolution of the DAS in the at least one portion. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of distributed acoustic sensing, comprising:
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determining acoustic signals incident along a pipe to be monitored using a distributed acoustic sensor (DAS) system having a fibre optic cable deployed along the pipe, whereinthe determining comprises; i) inputting an optical signal to the fibre optic cable, the optical signal being propagated along its length; ii) receiving light backscattered and/or reflected from along the fibre optic cable as the optical signal travels therealong, the light being backscattered and/or reflected in dependence on acoustic signals incident along the length of the fibre optic cable causing the fibre optic cable to expand and contract; and iii) processing the received light to determine the relative optical phase modulation along at least one section of the fibre optic cable, and determining acoustic signals incident along the pipe therefrom; wherein the fibre optic cable is deployed along the pipe such that at at least one portion of the pipe the cable is wrapped around the pipe whereby to increase the spatial resolution of the DAS in the at least one portion.
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Specification