Method of acoustic surveying
First Claim
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1. A system for surveying a wellbore, the system comprising:
- a distributed optical fiber sensor having;
a) a sensing optical fiber deployed along the wellbore, the wellbore having a plurality of respective acoustic propagation regions respectively corresponding to two or more of;
an interior of an inner pipe, a wall of the inner pipe, an annulus surrounding the inner pipe, and/or a casing surrounding the annulus;
b) a light source arranged to send optical pulses along the sensing optical fiber; and
c) means for processing light reflected and/or backscattered from the optical pulses as they travel along the optical sensing fiber to measure acoustic signals incident along the length of the sensing optical fiber in order to provide distributed acoustic measurements from along the length of the sensing fiber; and
a processor arranged to;
i)process the distributed acoustic measurements from along the length of the sensing fiber to obtain a plurality of distributed speed of sound measurements along the length of the sensing fiber respectively relating to the plurality of respective acoustic propagation regions; and
ii) analyze variations in the plurality of distributed speed of sound measurements and determine respective acoustic modes corresponding to the plurality of respective acoustic propagation regions in dependence thereon to thereby derive information relating to any of a surrounding rock formation, fluid in the wellbore, and/or the condition of the wellbore in dependence on the determined respective acoustic modes, wherein the analysis comprises inverting a wellbore model against the plurality of distributed speed of sound measurements in order to determine a value of one or more unknown parameters in the wellbore model.
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Abstract
The invention relates to the use of distributed optical fiber sensors for distributed acoustic sensing, and in particular, modal analysis of distributed acoustic data obtained in-well to monitoring well integrity. By determining one or more acoustic modes corresponding to distributed speed of sound measurements within the wellbore, and analyzing variations in the distributed speed of sound measurement it is possible to derive information relating to a formation and/or fluid in the wellbore.
17 Citations
18 Claims
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1. A system for surveying a wellbore, the system comprising:
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a distributed optical fiber sensor having; a) a sensing optical fiber deployed along the wellbore, the wellbore having a plurality of respective acoustic propagation regions respectively corresponding to two or more of;
an interior of an inner pipe, a wall of the inner pipe, an annulus surrounding the inner pipe, and/or a casing surrounding the annulus;b) a light source arranged to send optical pulses along the sensing optical fiber; and c) means for processing light reflected and/or backscattered from the optical pulses as they travel along the optical sensing fiber to measure acoustic signals incident along the length of the sensing optical fiber in order to provide distributed acoustic measurements from along the length of the sensing fiber; and a processor arranged to; i)process the distributed acoustic measurements from along the length of the sensing fiber to obtain a plurality of distributed speed of sound measurements along the length of the sensing fiber respectively relating to the plurality of respective acoustic propagation regions; and ii) analyze variations in the plurality of distributed speed of sound measurements and determine respective acoustic modes corresponding to the plurality of respective acoustic propagation regions in dependence thereon to thereby derive information relating to any of a surrounding rock formation, fluid in the wellbore, and/or the condition of the wellbore in dependence on the determined respective acoustic modes, wherein the analysis comprises inverting a wellbore model against the plurality of distributed speed of sound measurements in order to determine a value of one or more unknown parameters in the wellbore model. - 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 system for surveying a wellbore, the system comprising:
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a distributed optical fiber sensor having; a) a sensing optical fiber deployed along the wellbore, the well bore having a plurality of respective acoustic propagation regions respectively corresponding to two or more of;
an interior of an inner pipe;
a wall of the inner pipe, an annulus surrounding the inner pipe, and/or a casing surrounding the annulus;b) a light source arranged to send optical pulses along the sensing optical fiber; and c) means for processing light reflected and/or backscattered from the optical pulses as they travel along the optical sensing fiber to measure acoustic signals incident along the length of the sensing optical fiber in order to provide distributed acoustic measurements from along the length of the sensing fiber; the system further comprising a processor arranged to; i) process the distributed acoustic measurements from along the length of the sensing fiber to obtain a plurality of distributed speed of sound measurements along the length of the sensing fiber respectively relating to the plurality of respective acoustic propagation regions; and ii) analyze variations in the plurality of distributed speed of sound measurements and determining respective acoustic modes corresponding to the plurality of respective acoustic propagation regions in dependence thereon to thereby derive information relating to any of a surrounding rock formation, fluid in the wellbore, and/or the condition of the wellbore in dependence on the determined respective acoustic modes; wherein the analysis comprises identifying one or more features in the plurality of distributed speed of sound measurements and attributing the one or more features to one or more corresponding events, wherein identifying the one or more features comprises determining the presence and/or location of one or more discontinuities, variations, and/or relative variations between acoustic modes, in relation to speed of sound and/or amplitude corresponding to an acoustic signal.
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Specification