Systems and methods for subterranean fluid flow characterization

Abstract

A method of monitoring fluid outflow along a wellbore includes obtaining an acoustic signal from a sensor within the wellbore. The acoustic signal includes acoustic samples across a portion of a depth of the wellbore. In addition, the method includes determining one or more frequency domain features from the acoustic signal. Further, the method includes identifying one or more fluid outflow locations along the portion of the depth of the wellbore using the one or more frequency domain features.

What is claimed is: 
     
         1 . A method of monitoring fluid outflow along a wellbore, the method comprising:
 obtaining an acoustic signal from a sensor within the wellbore, wherein the acoustic signal comprises acoustic samples across a portion of a depth of the wellbore;   determining one or more frequency domain features from the acoustic signal; and   identifying one or more fluid outflow locations along the portion of the depth of the wellbore using the one or more frequency domain features.   
     
     
         2 . The method of  claim 1 , wherein the one or more frequency domain features comprises at least two different frequency domain features. 
     
     
         3 . The method of  claim 1 , wherein the sensor comprises a fiber optic cable disposed within the wellbore. 
     
     
         4 . The method of  claim 3 , wherein the one or more frequency domain features comprises at least one of: a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, a root mean square (RMS) band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, a spectral autocorrelation function, or a normalized variant thereof. 
     
     
         5 . The method of  claim 1 , further comprising:
 denoising the acoustic signal prior to determining the one or more frequency domain features.   
     
     
         6 . The method of  claim 5 , wherein denoising the acoustic signal comprises median filtering the acoustic data. 
     
     
         7 . The method of  claim 6 , further comprising:
 calibrating the acoustic signal.   
     
     
         8 . The method of  claim 7 , further comprising:
 normalizing the one or more frequency domain features prior to identifying the one or more outflow locations using the one or more frequency domain features.   
     
     
         9 . The method of  claim 1 , wherein identifying the one or more fluid outflow locations comprises:
 identifying a background fluid flow signature using the acoustic signal; and   removing the background fluid flow signature from the acoustic signal prior to identifying the one or more fluid outflow locations.   
     
     
         10 . The method of  claim 1 , wherein identifying the one or more fluid outflow locations comprises:
 identifying one or more anomalies in the acoustic signal using the one or more frequency domain features; and   selecting depth intervals of the one or more anomalies as the one or more outflow locations.   
     
     
         11 . The method of  claim 10 , wherein the depth intervals comprise depth intervals between packers within the wellbore, wherein the packers are disposed within an annulus between a tubular member and a wall of the wellbore, and wherein the one or more outflow locations comprise locations where fluid is flowing into the annulus from the tubular member. 
     
     
         12 . The method of  claim 1 , wherein the identifying the one or more fluid outflow locations comprises identifying the one or more fluid outflow locations using a logistic regression model that comprises a multivariate model having the one or more frequency domain features as inputs. 
     
     
         13 . The method of  claim 1 , further comprising:
 determining an allocation of a total fluid flow across the one or more fluid outflow locations using the one or more frequency domain features.   
     
     
         14 . The method of  claim 1 , wherein the sensor comprises a fiber optic-based acoustic sensor. 
     
     
         15 . A system for monitoring fluid outflow along a wellbore, the system comprising:
 a processor;   a memory; and   an analysis program stored in the memory, wherein the analysis program is configured, when executed on the processor, to:
 obtain an acoustic signal, wherein the acoustic signal is received from a sensor within a wellbore, wherein the acoustic signal comprises acoustic samples across a portion of a depth of the wellbore; 
 determine one or more frequency domain features from the acoustic signal; and 
 identify one or more fluid outflow locations along the portion of the depth of the wellbore using the one or more frequency domain features. 
   
     
     
         16 . The system of  claim 15 , wherein the one or more frequency domain features comprises at least two different frequency domain features. 
     
     
         17 . The system of  claim 15 , wherein the sensor comprises a fiber optic cable disposed within the wellbore. 
     
     
         18 . The system of  claim 17 , wherein the one or more frequency domain features comprises at least one of: a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, a root mean square (RMS) band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, a spectral autocorrelation function, or a normalized variant thereof. 
     
     
         19 . The system of  claim 15 , wherein the analysis program is configured, when executed on the processor, to denoise the acoustic signal prior to determining the one or more frequency domain features. 
     
     
         20 . The system of  claim 19 , wherein the analysis program is configured, when executed on the processor, to denoise the acoustic signal by median filtering the acoustic data. 
     
     
         21 . The system of  claim 19 , wherein the analysis program is configured, when executed on the processor, to calibrate the acoustic signal. 
     
     
         22 . The system of  claim 21 , wherein the analysis program is configured, when executed on the processor, to normalize the one or more frequency domain features prior to identifying the one or more outflow locations using the one or more frequency domain features. 
     
     
         23 . The system of  claim 15 , wherein the analysis program is configured, when executed on the processor, to:
 identify a background fluid flow signature using the acoustic signal; and   remove the background fluid flow signature from the acoustic signal prior to identifying the one or more fluid outflow locations.   
     
     
         24 . The system of  claim 15 , wherein the analysis program is configured, when executed on the processor, to:
 identify one or more anomalies in the acoustic signal using the one or more frequency domain features; and   select depth intervals of the one or more anomalies as the one or more outflow locations.   
     
     
         25 . The system of  claim 24 , wherein the depth intervals comprise depth intervals between packers within the wellbore, wherein the packers are disposed within an annulus between a tubular member and a wall of the wellbore, and wherein the one or more outflow locations comprise locations where fluid is flowing into the annulus from the tubular member. 
     
     
         26 . The system of  claim 15 , wherein the analysis program is configured, when executed on the processor, to use a logistic regression model to identify the one or more fluid outflow locations, wherein the logistic regression model uses the one or more frequency domain features as inputs. 
     
     
         27 . The system of  claim 15 , wherein the analysis program is configured, when executed on the processor, to:
 determine an allocation of a total fluid flow across the one or more fluid outflow locations using the one or more frequency domain features.   
     
     
         28 . The system of  claim 15 , wherein the sensor comprises a fiber optic-based acoustic sensor. 
     
     
         29 . A method of monitoring fluid outflow along a wellbore, the method comprising:
 obtaining an acoustic signal from a sensor within the wellbore, wherein the acoustic signal comprises acoustic samples across a portion of a depth of the wellbore;   determining a plurality of frequency domain features from the acoustic signal, wherein the plurality of frequency domain features are obtained across a plurality of depth intervals within the portion of the depth of the wellbore, and wherein the plurality of frequency domain features comprise at least two different frequency domain features;   identifying a plurality of fluid outflows at a plurality of fluid outflow locations within the plurality of depth intervals using the plurality of frequency domain features; and   determining an allocation of a total fluid flow across each of the plurality of fluid outflows using the plurality of frequency domain features.   
     
     
         30 . The method of  claim 29 , wherein identifying the plurality of fluid outflow locations comprises:
 providing the plurality of frequency domain features to a fluid outflow model, wherein the fluid outflow model comprises a logistic regression model; and   determining that the plurality of fluid outflows are present at the plurality of fluid outflow locations based on an output from the fluid outflow model.   
     
     
         31 . The method of  claim 30 , wherein identifying the plurality of fluid outflow locations comprises providing at least a subset of the plurality of frequency domain features as inputs to the fluid outflow model to determine when the fluid outflows are present within the wellbore. 
     
     
         32 . The method of  claim 31 , comprising removing a background signal from the acoustic signal prior to determining the plurality of frequency domain features. 
     
     
         33 . The method of  claim 32 , wherein the sensor comprises a fiber optic-based acoustic sensor.