WELLBORE LEAK DETECTION SYSTEMS AND METHODS OF USING THE SAME
A leak detection system for a wellbore. The leak detection system includes: (1) at least one sensor configured to be positioned outside of a casing of the wellbore; (2) an interrogation system for sending signals to, and receiving signals from, the at least one sensor; and (3) an optical lead cable disposed between the interrogation system and the at least one sensor. A method of detecting a fluid leak in a wellbore is also disclosed.
1 . A leak detection system for a wellbore having a casing with an exterior surface, the leak detection system comprising:
at least one sensor configured to be positioned outside of the casing of the wellbore;
an interrogation system for sending signals to, and receiving signals from, the at least one sensor; and
an optical lead cable disposed between the interrogation system and the at least one sensor.
2 . The leak detection system of claim 1 wherein the at least one sensor includes a fiber optic cable configured as part of an interferometer.
3 . The leak detection system of claim 2 wherein the interferometer is a Michelson interferometer.
4 . The leak detection system of claim 2 wherein the interferometer is a Sagnac interferometer.
5 . The leak detection system of claim 2 wherein the interferometer is a Fabry-Perot interferometer.
6 . The leak detection system of claim 1 wherein the interrogator includes an optical source, an optical receiver, and a digitizer.
7 . The leak detection system of claim 1 wherein the at least one sensor includes a fiber optic cable optically divided into a series of sensing zones.
8 . The leak detection system of claim 7 wherein the fiber optic cable is optically divided into a series of sensing zones using fiber Bragg gratings written into the fiber optic cable, thereby forming a series of Fabry-Perot interferometers.
9 . The leak detection system of claim 1 wherein the at least one sensor includes at least one of an acoustic or a seismic sensor.
10 . The leak detection system of claim 1 wherein the at least one sensor includes an optical fiber and an accelerometer, the accelerometer including a fixed mandrel and a moveable mandrel, wherein the optical fiber is wrapped around the fixed mandrel and the moveable mandrel.
11 . The leak detection system of claim 1 wherein the at least one sensor is secured to the exterior surface of the casing of the wellbore.
12 . The leak detection system of claim 1 wherein the at least one sensor is embedded in a fill material outside of the casing of the wellbore.
13 . The leak detection system of claim 1 wherein the interrogator is a Rayleigh backscatter interrogator configured to process scattered intensity return signals from the at least one sensor.
14 . The leak detection system of claim 1 wherein the interrogator is a Rayleigh backscatter interrogator configured to process scattered phase return signals from the at least one sensor.
15 . A method of detecting a fluid leak in a wellbore, the method comprising the steps of:
(a) transmitting light from an interrogator to at least one sensor positioned outside of a casing of a wellbore;
(b) receiving return signals from the at least one sensor at the interrogator; and
(c) processing the return signals to determine if there is an indication of a fluid leak from the wellbore casing.
16 . The method of claim 15 further comprising the step of installing a plurality of optical fiber sensors outside the casing of the wellbore prior to step (a).
17 . The method of claim 15 wherein step (c) includes converting return optical signals into electrical signals for processing by a signal processor.
18 . The method of claim 17 wherein step (c) further includes generating an instantaneous spectrum of the electrical signals and comparing the instantaneous spectrum against a predetermined spectra related to a leak condition.
19 . The method of claim 15 further comprising the step of (d) determining a location of the fluid leak if a determination is made at step (c) that there is a fluid leak.
20 . The method of claim 19 wherein step (d) includes determining the location of the fluid leak using a Rayleigh backscatter interrogator.
21 . The method of claim 15 wherein the signals received in step (c) have been converted into phase change and light intensity change signals.
22 . The method of claim 21 wherein step (c) includes demodulating and demultiplexing the phase change and light intensity change signals.
23 . The method of claim 15 further comprising the step of installing the at least one sensor against an exterior surface of the casing of the wellbore before step (a).
24 . The method of claim 15 wherein the at least one sensor includes a plurality of sensors.
25 . The method of claim 24 wherein the at least one sensor includes a fiber optic cable configured as part of an interferometer.
26 . The method of claim 25 wherein the interferometer is a Michelson interferometer.
27 . The method of claim 25 wherein the interferometer is a Sagnac interferometer.
28 . The method of claim 25 wherein the interferometer is a Fabry-Perot interferometer.