Techniques for distributed acoustic sensing
First Claim
1. A method of determining flow speed of a fluid within a conduit comprising the steps of:
- introducing at least one acoustic stimulus into the fluid in the conduit such that a first acoustic stimulus travels in one direction in the conduit and a second acoustic stimulus travels in the opposite direction in the conduit so as to set up standing waves within the fluid;
interrogating an optical fibre deployed along the length of the conduit to provide a fibre optic distributed acoustic sensor;
monitoring the acoustic response to the first acoustic stimulus and second acoustic stimulus using said distributed acoustic sensor; and
using said acoustic response to determine the flow speed of the fluid.
1 Assignment
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Accused Products
Abstract
The application describes techniques for monitoring the rate of flow of fluid in a conduit (205) using fiber optic distributed acoustic sensing which are especially applicable to flow in oil and gas wells. The techniques also allow for calibration of the position of the channels of a fiber optic distributed acoustic sensor arranged along a fluid carrying conduit. The techniques comprise introducing a first acoustic stimulus (303) travelling in one direction and a second acoustic stimulus (304) travelling in the opposite direction. Flow of the fluid (v) results in a difference in the propagation velocity of the two acoustic stimuli. The first and second acoustic stimuli create a standing wave and the beat effect due to the flow induced wavelength variation is detected and used to determine flow rate. The acoustic stimulus may be introduced to travel through the conduit to provide the first stimulus and to reflect from the end of the conduit and travel back as the second acoustic stimulus.
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Citations
21 Claims
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1. A method of determining flow speed of a fluid within a conduit comprising the steps of:
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introducing at least one acoustic stimulus into the fluid in the conduit such that a first acoustic stimulus travels in one direction in the conduit and a second acoustic stimulus travels in the opposite direction in the conduit so as to set up standing waves within the fluid; interrogating an optical fibre deployed along the length of the conduit to provide a fibre optic distributed acoustic sensor; monitoring the acoustic response to the first acoustic stimulus and second acoustic stimulus using said distributed acoustic sensor; and using said acoustic response to determine the flow speed of the fluid. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 17, 18)
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13. A method of calibrating a distributed acoustic sensor having an optical fibre deployed along the length of a fluid carrying conduit comprising:
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introducing at least one acoustic stimulus into the fluid in the conduit such that a first acoustic stimulus travels in one direction in the conduit and a second acoustic stimulus travels in the opposite direction in the conduit so as to set up a standing wave; and determining the sensing portions of the distributed acoustic sensor which correspond to the nodes and/or antinodes of the standing wave to calibrate said distributed acoustic sensor. - View Dependent Claims (14, 15, 16)
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19. A distributed acoustic sensing apparatus capable of determining flow speed of a fluid in a conduit comprising:
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an optical source for generating radiation to be launched into an optical fibre; a detector for detecting radiation backscattered from said optical fibre; and a processor for processing said detected radiation to provide a distributed acoustic sensor;
wherein said processor is configured to process the acoustic signals to detect the acoustic response to a first acoustic stimulus travelling in one direction in the conduit and a second acoustic stimulus travelling in the other in the conduit and configures to identify sensing portions of the optical fibre which correspond to beat nodes and/or antinodes of a standing wave and determine a flow speed in said conduit based on said identified sensing portions corresponding to beat nodes and/or antinodes. - View Dependent Claims (20, 21)
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Specification