Downhole measured depth detection from azimuthal borehole imaging

Abstract

Systems, methods, and apparatus, including computer programs encoded on computer-readable media, for detecting downhole measured depth of a borehole are disclosed. A downhole imaging tool of a drilling system may obtain azimuthal borehole images from at least a first sensor and a second sensor of the downhole imaging tool. Image cross-correlation is performed on the azimuthal borehole images. A time delay is determined based on the image cross-correlation on the azimuthal borehole images. A velocity of the downhole imaging tool is determined based on the time delay. A downhole measured depth of the downhole imaging tool within the borehole is determined based on the velocity. The downhole measured depth may be determined dynamically downhole by the downhole imaging tool without communications with surface equipment of the drilling system.

What is claimed is: 
     
         1 . A method for detecting downhole measured depth of a borehole, comprising:
 obtaining, at a downhole imaging tool of a drilling system, azimuthal borehole images from at least a first sensor and a second sensor of the downhole imaging tool;   performing image cross-correlation on the azimuthal borehole images;   determining a time delay based on the image cross-correlation on the azimuthal borehole images; and   determining a velocity of the downhole imaging tool based on the time delay.   
     
     
         2 . The method of  claim 1 , further comprising:
 determining a downhole measured depth of the downhole imaging tool within the borehole based on the velocity.   
     
     
         3 . The method of  claim 1 , wherein the azimuthal borehole images include a first azimuthal borehole image obtained from the first sensor and a second azimuthal borehole image obtained from the second sensor, and determining the time delay based on the image cross-correlation on the azimuthal borehole images comprising:
 extracting a borehole feature in the first azimuthal borehole image using a time window;   performing the image cross-correlation on the second azimuthal borehole image using the extracted borehole feature in the time window as a template for detecting at least a portion of the borehole feature in the second azimuthal borehole image; and   determining the time delay based on a time offset between a first time instant the borehole feature was detected in the first azimuthal borehole image and a second time instant at least the portion of the borehole feature was detected in the second azimuthal borehole image.   
     
     
         4 . The method of  claim 1 , wherein determining the time delay based on the image cross-correlation on the azimuthal borehole images includes determining the time delay by performing a batch loop for the image cross-correlation of a plurality of borehole features in the azimuthal borehole images. 
     
     
         5 . The method of  claim 1 , wherein obtaining the azimuthal borehole images and performing the image cross-correlation on the azimuthal borehole images are performed while the drilling system is performing drilling operations. 
     
     
         6 . The method of  claim 2 , further comprising:
 determining a second downhole measured depth based on accelerometer measurements; and   determining a final downhole measured depth based on the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements.   
     
     
         7 . The method of  claim 6 , wherein the final downhole measured depth is determined dynamically downhole by the downhole imaging tool without communications with surface equipment of the drilling system. 
     
     
         8 . The method of  claim 6 , further comprising:
 determining a weighting ratio for the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements; and   determining the final downhole measured depth by combining the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements based on the weighting ratio.   
     
     
         9 . The method of  claim 8 , wherein the weighting ratio is determined based on at least one of rotation per minute (RPM) measurements, accelerometer measurements, and image resolution. 
     
     
         10 . The method of  claim 1 , wherein the image cross-correlation is a zero-normalized cross-correlation. 
     
     
         11 . A downhole imaging tool for detecting downhole measured depth, comprising:
 at least a first sensor and a second sensor;   one or more processors; and   a computer-readable storage medium having instructions stored thereon that are executable by the one or more processors to cause the downhole imaging tool to:
 obtain azimuthal borehole images from at least the first sensor and the second sensor; 
 perform image cross-correlation on the azimuthal borehole images; 
 determine a time delay based on the image cross-correlation on the azimuthal borehole images; and 
 determine a velocity of the downhole imaging tool based on the time delay. 
   
     
     
         12 . The downhole imaging tool of  claim 11 , further comprising instructions that cause the downhole imaging tool to:
 determine a downhole measured depth of the downhole imaging tool within the borehole based on the velocity.   
     
     
         13 . The downhole imaging tool of  claim 11 , wherein the azimuthal borehole images include a first azimuthal borehole image obtained from the first sensor and a second azimuthal borehole image obtained from the second sensor, and the instructions that cause the downhole imaging tool to determine the time delay based on the image cross-correlation further comprise instructions to cause the downhole imaging tool to:
 extract a borehole feature in the first azimuthal borehole image using a time window;   perform the image cross-correlation on the second azimuthal borehole image using the extracted borehole feature in the time window as a template for detecting at least a portion of the borehole feature in the second azimuthal borehole image; and   determine the time delay based on a time offset between a first time instant the borehole feature was detected in the first azimuthal borehole image and a second time instant at least the portion of the borehole feature was detected in the second azimuthal borehole image.   
     
     
         14 . The downhole imaging tool of  claim 12 , further comprising instructions that cause the downhole imaging tool to:
 determine a second downhole measured depth based on accelerometer measurements; and   determine a final downhole measured depth based on the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements.   
     
     
         15 . The downhole imaging tool of  claim 14 , further comprising instructions that cause the downhole imaging tool to:
 determine a weighting ratio for the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements; and   determine the final downhole measured depth by combining the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements based on the weighting ratio.   
     
     
         16 . The downhole imaging tool of  claim 11 , wherein:
 the first sensor includes a first transmitter and a first receiver, and the second sensor includes a second transmitter and a second receiver, wherein the first receiver and the second receiver are separated by a distance in a depth direction of the borehole; or   the first sensor includes a first transmitter and a first row of a first plurality of receivers, and the second sensor includes a second transmitter and a second row of a second plurality of receivers, wherein the first row of the first plurality of receivers and the second row of the second plurality of receivers are separated by the distance in the depth direction of the borehole; or   the first sensor includes one or more receivers and the second sensor includes one or more receivers, wherein the one or more receivers of the first sensor and the one or more receivers of the second sensor are separated by the distance in the depth direction of the borehole.   
     
     
         17 . A non-transitory computer-readable storage medium having instructions stored thereon that are executable by one or more processors of a downhole imaging tool, the instructions comprising:
 instructions for obtaining, at the downhole imaging tool, azimuthal borehole images from at least a first sensor and a second sensor of the downhole imaging tool;   instructions for performing image cross-correlation on the azimuthal borehole images;   instructions for determining a time delay based on the image cross-correlation on the azimuthal borehole images;   instructions for determining a velocity of the downhole imaging tool based on the time delay; and   instructions for determining a downhole measured depth of the downhole imaging tool within the borehole based on the velocity.   
     
     
         18 . The non-transitory computer-readable storage medium of  claim 17 , wherein the azimuthal borehole images include a first azimuthal borehole image obtained from the first sensor and a second azimuthal borehole image obtained from the second sensor, and the instructions further include:
 instructions for extracting a borehole feature in the first azimuthal borehole image using a time window;   instructions for performing the image cross-correlation on the second azimuthal borehole image using the extracted borehole feature in the time window as a template for detecting at least a portion of the borehole feature in the second azimuthal borehole image; and   instructions for determining the time delay based on a time offset between a first time instant the borehole feature was detected in the first azimuthal borehole image and a second time instant at least the portion of the borehole feature was detected in the second azimuthal borehole image.   
     
     
         19 . The non-transitory computer-readable storage medium of  claim 17 , wherein the instructions further include:
 instructions for determining a second downhole measured depth based on accelerometer measurements; and   instructions for determining a final downhole measured depth based on the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements.   
     
     
         20 . The non-transitory computer-readable storage medium of  claim 19 , wherein the instructions further include:
 instructions for determining a weighting ratio for the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements; and   instructions for determining the final downhole measured depth by combining the downhole measured depth determined from the image cross-correlation and the second downhole measured depth determined from the accelerometer measurements based on the weighting ratio.