Wellbore leak detection systems and methods of using the same

Abstract

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.

What is claimed: 
     
         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.