Barrier flow diagnostics through differential mapping

Abstract

A method of abandoning a wellbore can include obtaining a first sample data set within a wellbore, wherein the first sample data set is a sample of an acoustic signal originating within the wellbore; determining a plurality of frequency domain features of the first sample data set; identifying a fluid flow location within the wellbore using the first plurality of frequency domain features; setting a barrier at or above the fluid flow location; obtaining a second sample data set above the barrier, wherein the second sample data set is a sample of an acoustic signal originating within the wellbore above the barrier; determining a second plurality of frequency domain features of the second sample data set; and identifying that a fluid flow rate or flow mechanism at the fluid flow location has been reduced or eliminated and/or identifying another fluid flow location using the second plurality of frequency domain features.

1 . A method of abandoning a wellbore, the method comprising:
 obtaining a first sample data set within a wellbore, wherein the first sample data set is a sample of an acoustic signal originating within the wellbore;   determining a first plurality of frequency domain features of the first sample data set;   identifying a first fluid flow location within the wellbore using the first plurality of frequency domain features;   setting a first barrier at or above the first fluid flow location;   obtaining a second sample data set within the wellbore above the first barrier, wherein the second sample data set is a sample of an acoustic signal originating within the wellbore above the first barrier;   determining a second plurality of frequency domain features of the second sample data set; and   identifying that a fluid flow rate or fluid flow mechanism at the first fluid flow location has been reduced or eliminated and/or identifying a second fluid flow location within the wellbore using the second plurality of frequency domain features.   
     
     
         2 . The method of  claim 1 , further comprising:
 setting a second barrier at or above the second fluid flow location; and   substantially blocking fluid flow from the first fluid flow location and the second fluid flow location using the first barrier and the second barrier.   
     
     
         3 . The method of  claim 1 , wherein at least one of the first sample data set or the second sample data set is representative of the acoustic signal across a frequency spectrum. 
     
     
         4 . The method of  claim 1 , wherein obtaining the first sample data set comprises:
 obtaining a baseline acoustic signal data set while the wellbore is shut in;   obtaining a baseline fluid flow log using the baseline acoustic signal data set;   inducing a pressure differential within the wellbore;   obtaining a flowing acoustic signal data set while inducing the pressure differential;   obtaining a flowing fluid flow log using the flowing acoustic signal data set; and   subtracting the baseline fluid flow log from the flowing fluid flow log.   
     
     
         5 . The method of  claim 4 , wherein the wellbore comprises one or more tubular strings and one or more annuli disposed between at least one of: i) two adjacent tubular strings of the one or more tubular strings, ii) a tubular string of the one or more tubular strings and a formation, or iii) both i and ii, and wherein inducing the pressure differential comprises releasing a fluid from an annulus of the one or more annuli. 
     
     
         6 . The method of  claim 4 , wherein the baseline acoustic signal data set is a time averaged acoustic data set. 
     
     
         7 . The method of  claim 1 , wherein the first barrier comprises a bridge plug, a packer, a cement plug, or a combination thereof. 
     
     
         8 . The method of  claim 1 , wherein the first fluid flow location, the second fluid flow location, or both the first fluid flow location and the second fluid flow location comprise: a location of flow from a formation into the wellbore, a location of flow between the formation and an annulus between a tubular string and the wellbore wall, or a location of flow between annuli formed between a plurality of tubular strings in the wellbore. 
     
     
         9 . The method of  claim 1 , wherein identifying the first fluid flow location comprises comparing the first plurality of frequency domain features with a fluid flow event signature, and/or wherein identifying the second fluid flow location comprises comparing the second plurality of frequency domain features with a fluid flow event signature. 
     
     
         10 . The method of  claim 1 , further comprising:
 correlating the first fluid flow location with one or more structural features within the wellbore; and   determining a source of the fluid flow at the first fluid flow location based on the correlating of the first fluid flow location with the one or more structural features.   
     
     
         11 . The method of  claim 1 , wherein the wellbore comprises one or more tubular strings and one or more annuli disposed between at least one of: i) two adjacent tubular strings of the one or more tubular strings, ii) a tubular string of the one or more tubular strings and a formation, or iii) both i and ii, and wherein identifying the first fluid flow location or the second fluid flow location comprises determining an annulus of the one or more annuli and a depth at which the first fluid flow location or the second fluid flow location is present. 
     
     
         12 . A system for abandoning a wellbore, the system comprising:
 a receiver unit comprising a processor and a memory, wherein the receiver unit is configured to receive an acoustic signal from a sensor disposed in a wellbore, wherein a processing application is stored in the memory, and wherein the processing application, when executed on the processor, configures the processor to:   receive a first baseline acoustic signal data set from the sensor, wherein the first baseline acoustic signal data set comprises an indication of the acoustic signal received over a first depth interval while the wellbore is shut in;   receive a first flowing acoustic signal data set, wherein the first flowing acoustic signal data set comprises an indication of the acoustic signal received over the first depth interval while a first pressure differential is induced within the wellbore;   determine a baseline fluid flow log using the first baseline acoustic signal data set;   determine a flowing fluid flow log using the first flowing acoustic signal data set;   subtract the baseline fluid flow log from the flowing fluid flow log to provide a first sample data set;   determine a first plurality of frequency domain features of the first sample data set;   identify a first fluid flow location within the wellbore using the first plurality of frequency domain features;   determine a change in a flow rate or flow mechanism at the first fluid flow location using the first sample data set; and   generate an output indicative of the first fluid flow location and a change in the flow rate or flow mechanism at the first fluid flow location.   
     
     
         13 . The system of  claim 12 , wherein the processing application, when executed on the processor, further configures the processor to:
 receive a second baseline acoustic signal data set from within the wellbore, wherein the second baseline acoustic signal data set comprises an indication of the acoustic signal received over a second depth interval of the wellbore while the wellbore is shut in, subsequent the setting of a barrier at or above the identified first fluid flow location, wherein the second depth interval overlaps the first depth interval;   receive a second flowing acoustic signal data set, wherein the second flowing acoustic signal data set comprises an indication of the acoustic signal received over the second depth interval while a second pressure differential is induced within the wellbore, subsequent the setting of the barrier at or above the identified first fluid flow location;   determining a second baseline fluid flow log using the second baseline acoustic signal data set;   determining a second flowing fluid flow log using the second flowing acoustic signal data set;   subtract the second baseline fluid flow log from the second flowing fluid flow log to provide a second sample data set;   determine a second plurality of frequency domain features of the second sample data set;   determine that a fluid flow rate or a fluid flow mechanism at the first fluid flow location within the wellbore has been reduced or eliminated and/or identify a second fluid flow location using the second plurality of frequency domain features; and   generate an output indicative of the identified reduction or elimination of the fluid flow at the first fluid flow location and/or indicative of the second fluid flow location.   
     
     
         14 . The system of  claim 12 , further comprising:
 validating the barrier based on the identified reduction or elimination of fluid flow rate or the fluid flow mechanism at the first fluid flow location.   
     
     
         15 . The system of  claim 12 , further comprising:
 the sensor, wherein the sensor comprises a fibre optic cable disposed within the wellbore; and   an optical generator coupled to the fibre optic cable, wherein the optical generator is configured to generate a light beam and pass the light beam into the fibre optic cable.   
     
     
         16 . The system of  claim 12 , wherein the wellbore comprises one or more tubular strings and one or more annuli disposed between at least one of: i) two adjacent tubular strings of the one or more tubular strings, ii) a tubular string of the one or more tubular strings and a formation, or iii) both i and ii, and wherein where the first fluid flow location, the second fluid flow location, or both comprise: a location of flow from a formation into the wellbore, a location of flow between the formation and an annulus between a tubular string and the wellbore wall, or a location of flow between annuli formed between a plurality of tubular strings in the wellbore. 
     
     
         17 . The method of  claim 16 , wherein inducing the first pressure differential and/or inducing the second pressure differential comprises:
 opening a flow valve within an annulus of the one or more annuli; and   inducing a fluid flow based on opening of the flow valve.   
     
     
         18 . The system of  claim 16 , wherein the first pressure differential and/or the second pressure differential is indicative of a difference in pressure between an annulus of the one or more annuli and an adjacent flow path in the wellbore. 
     
     
         19 . The system of  claim 12 , wherein the processing application, when executed on the processor, further configures the processor to:
 integrate or time average an acoustic intensity within specified frequency bands for fluid flow in the wellbore, and   determine a relative fluid flowrate for fluid flow based on the integrated acoustic intensity.   
     
     
         20 . The system of  claim 12 , wherein the output comprises a fluid flow log. 
     
     
         21 . A method of comparing acoustic signals obtained between different acoustic sensor operations in a wellbore, the method comprising:
 obtaining a first baseline sample data set over a first depth interval within a wellbore, wherein the first baseline data set is a sample of an acoustic signal originating within the wellbore;   determining at least one frequency domain feature of the first baseline sample data set;   inducing a first pressure differential within the wellbore;   obtaining a first acoustic data set over the first depth interval within the wellbore while inducing the first pressure differential;   determining at least one frequency domain feature of the first acoustic data set;   subtracting the at least one frequency domain feature of the first baseline sample data set from the at least one frequency domain feature of the first acoustic data set to obtain a first sample data set over the first depth interval;   obtaining a second baseline sample data set over a second depth interval within the wellbore, wherein the second baseline sample data set is a sample of an acoustic signal originating within the wellbore, wherein the second depth interval overlaps with the first depth interval;   determining at least one frequency domain feature of the second baseline sample data set;   inducing a second pressure differential within the wellbore;   obtaining a second acoustic data set over the second depth interval within the wellbore while inducing the second pressure differential;   determining at least one frequency domain feature of the second acoustic data set;   subtracting the at least one frequency domain feature of the second baseline sample data set from the at least one frequency domain feature of the second acoustic data set to obtain a second sample data set over the second depth interval; and   comparing the second sample data set to the first sample data set over the second depth interval.   
     
     
         22 . The method of  claim 21 , further comprising:
 determining a fluid flow reduction at a fluid flow location based on comparing the second sample data set to the first sample data set.   
     
     
         23 . The method of  claim 21 , wherein the first baseline sample data set and the first acoustic data set are obtained with an acoustic sensor disposed in the wellbore within the first depth interval, wherein the second baseline sample data set and the second acoustic data set are obtained with the acoustic sensor disposed in the wellbore within the second depth interval, and wherein the method further comprises:
 removing the acoustic sensor from the wellbore between obtaining the first baseline sample data set and obtaining the second baseline sample data set.   
     
     
         24 . A system for of comparing acoustic signals obtained between different acoustic sensor operations in a wellbore, the system comprising:
 a receiver unit comprising a processor and a memory, wherein the receiver unit is configured to receive an acoustic signal from a sensor disposed in a wellbore, wherein a processing application is stored in the memory, and wherein the processing application, when executed on the processor, configures the processor to:   receive a first baseline sample data set over a first depth interval within the wellbore, wherein the first baseline data set is a sample of an acoustic signal originating within the wellbore;   determine at least one frequency domain feature of the first baseline sample data set;   receive a first acoustic data set over the first depth interval within the wellbore, wherein the first acoustic data sat is an acoustic signal obtained while a first pressure differential is induced within the wellbore;   determine at least one frequency domain feature of the first acoustic data set;   subtract the at least one frequency domain feature of the first baseline sample data set from the at least one frequency domain feature of the first acoustic data set to obtain a first sample data set over the first depth interval;   receive a second baseline sample data set over a second depth interval within the wellbore, wherein the second baseline sample data set is a sample of an acoustic signal originating within the wellbore, wherein the second depth interval overlaps with the first depth interval;   determine at least one frequency domain feature of the second baseline sample data set;   receive a second acoustic data set over the second depth interval within the wellbore, wherein the second acoustic data sat is an acoustic signal obtained while a second pressure differential is induced within the wellbore;   determine at least one frequency domain feature of the second acoustic data set;   subtract the at least one frequency domain feature of the second baseline sample data set from the at least one frequency domain feature of the second acoustic data set to obtain a second sample data set over the second depth interval;   compare the second sample data set to the first sample data set over the second depth interval; and   generate an output indicative of the comparison between the second sample data set and the first sample data set.   
     
     
         25 . A method of abandoning a wellbore, the method comprising:
 obtaining a first sample data set over a first depth interval within a wellbore, wherein the first sample data set comprises a first acoustic data set having a first baseline acoustic sample data set subtracted therefrom, wherein the first acoustic data set is obtained over the first depth interval while a first pressure differential is induced in the wellbore, and wherein the first baseline acoustic sample data set is obtained over the first depth interval while the wellbore is shut in;   identifying a fluid flow location within the first depth interval using the first sample data set;   obtaining a second sample data set over a second depth interval within a wellbore, wherein the second sample data set is obtained after a barrier is set at or above the fluid flow location, wherein the second sample data set comprises a second acoustic data set having a second baseline acoustic sample data set subtracted therefrom, wherein the second acoustic data set is obtained over the second depth interval while a second pressure differential is induced in the wellbore, wherein the second baseline acoustic sample data set is obtained over the second depth interval while the wellbore is shut in, and wherein the second depth interval overlaps the first depth interval;   comparing the first sample data set to the second sample data set; and   determining whether or not fluid flow at the fluid flow location is substantially blocked by the barrier.   
     
     
         26 . The method of  claim 25 , wherein identifying the fluid flow location within the first depth interval using the first sample data set comprises determining a plurality of frequency domain features of the first sample data set. 
     
     
         27 . The method of  claim 26 , wherein the plurality of frequency domain features of the first sample data set comprise at least two frequency domain features selected from the group consisting of a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, an RMS band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, spectral entropy, a spectral autocorrelation function, and combinations thereof. 
     
     
         28 . A system for abandoning a wellbore, the system comprising:
 a receiver unit comprising a processor and a memory, wherein the receiver unit is configured to receive an acoustic signal from a sensor disposed in a wellbore, wherein a processing application is stored in the memory, and wherein the processing application, when executed on the processor, configures the processor to:   receive a first baseline acoustic sample data set and a first acoustic data set from the sensor, wherein the first acoustic data set is an acoustic signal obtained over a first depth interval while a first pressure differential is induced in the wellbore, and wherein the first baseline acoustic sample data set is an acoustic signal obtained over the first depth interval while the wellbore is shut in,   determine a first sample data set over a first depth interval within the wellbore, wherein the first sample data set comprises the first acoustic data set having the first baseline acoustic sample data set subtracted therefrom;   identify a fluid flow location within the first depth interval using the first sample data set;   receive a second baseline acoustic sample data set and a second acoustic data set from the sensor, wherein the second acoustic data set is an acoustic signal obtained over a second depth interval while a second pressure differential is induced in the wellbore and after a barrier is set at or above the fluid flow location, and wherein the second baseline acoustic sample data set is an acoustic signal obtained over the second depth interval while the wellbore is shut in and after the barrier is set at or above the fluid flow location;   determine a second sample data set over the second depth interval within the wellbore, wherein the second sample data set comprises the second acoustic data set having the second baseline acoustic sample data set subtracted therefrom;   compare the first sample data set to the second sample data set; and   determine whether or not fluid flow at the fluid flow location is substantially blocked by the barrier; and   generate an output indicative the determination of whether or not the fluid flow at the fluid flow location is substantially blocked by the barrier.