Seismic geophysical surveying
First Claim
1. A fibre optic distributed sensing apparatus for use in geophysical surveying involving stimulating an area of interest with a seismic source, said apparatus comprising:
- a source of electromagnetic radiation arranged to, in use, repeatedly launch interrogating electromagnetic radiation into an optic fibre deployed in said area of interest;
a sampling detector for sampling electromagnetic radiation back-scattered from said optic fibre; and
a processor arranged to process the back-scattered radiation to provide, for each of a plurality of longitudinal sensing portions of optic fibre, an indication of any incident acoustic signals affecting that sensing portion,wherein the sampling detector is arranged to acquire a plurality of diversity samples for each said longitudinal sensing portion from each launch of interrogating electromagnetic radiation and the processor is configured to, for each said longitudinal sensing portion;
divide said diversity samples into a plurality of diversity channels;
process each of said diversity channels to determine a measurement signal indicative of any acoustic disturbance;
correlate the measurement signal from each channel with a signal indicative of a seismic stimulus applied; and
combine the correlated measurement signals to provide an overall measurement signal for the longitudinal sensing portion.
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Accused Products
Abstract
The present invention relates to an apparatus for use in geophysical surveying. Geophysical surveying typically involves stimulating an area of interest with a seismic source (204) and detecting the response in a sensor array. The application describes a fiber optic distributed sensing apparatus having a source (112) of electromagnetic radiation for repeatedly launching interrogating electromagnetic radiation into an optic fiber (104) deployed in said of area interest, a sampling detector (116) for sampling radiation back-scattered from the fiber; and a processor (108) arranged to process the back-scattered radiation to provide, for each of a plurality of longitudinal sensing portions of optic fiber, an indication of any incident acoustic signals affecting that sensing portion. The sampling detector is arranged to acquire a plurality of diversity samples for each said longitudinal sensing portion. The processor is configured process the diversity samples in diversity channels to determine a measurement signal indicative of any acoustic disturbance; correlate the measurement signal from each channel with a signal indicative of the seismic stimulus applied; and combine the correlated measurement signals to provide an overall measurement signal for the longitudinal sensing portion. The processor may apply a quality metric to the correlated data before performing the combination based on the quality metric. By correlating the individual diversity channels with the stimulus signal prior to performing the analysis of the measurement signal for a particular longitudinal section of optic fiber, the signal to noise ratio can be improved.
16 Citations
25 Claims
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1. A fibre optic distributed sensing apparatus for use in geophysical surveying involving stimulating an area of interest with a seismic source, said apparatus comprising:
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a source of electromagnetic radiation arranged to, in use, repeatedly launch interrogating electromagnetic radiation into an optic fibre deployed in said area of interest; a sampling detector for sampling electromagnetic radiation back-scattered from said optic fibre; and a processor arranged to process the back-scattered radiation to provide, for each of a plurality of longitudinal sensing portions of optic fibre, an indication of any incident acoustic signals affecting that sensing portion, wherein the sampling detector is arranged to acquire a plurality of diversity samples for each said longitudinal sensing portion from each launch of interrogating electromagnetic radiation and the processor is configured to, for each said longitudinal sensing portion; divide said diversity samples into a plurality of diversity channels; process each of said diversity channels to determine a measurement signal indicative of any acoustic disturbance; correlate the measurement signal from each channel with a signal indicative of a seismic stimulus applied; and combine the correlated measurement signals to provide an overall measurement signal for the longitudinal sensing portion. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of distributed fibre optic sensing for geophysical monitoring, comprising:
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repeatedly launching interrogating radiation into an optical fibre deployed in an area to be surveyed whilst stimulating the area with a seismic source; sampling interrogating radiation which is backscattered from within said optical fibre; and determining any acoustic response to said stimulation for at least one longitudinal sensing portion of said optical fibre, wherein the step of determining any acoustic response comprises; taking a plurality of diversity samples corresponding to radiation backscattered from at least part of a longitudinal sensing portion of interest following each launch; dividing said plurality of diversity samples into a plurality of channels and processing said channels to determine a measurement signal indicative of the acoustic disturbance for said channel; correlating the measurement signal for each channel with a signal indicative of a seismic stimulus; and combining the correlated measurement signals for said channels into an overall measurement signal for said longitudinal sensing portion. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25)
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Specification