Methods and systems for robust and accurate determination of wireline depth in a borehole

Abstract

This invention relates in general to measuring depth of well-tools, such as logging tools or the like, in a borehole. Embodiments of the present invention may provide for disposing conducting areas along a wireline that may be used to suspend and move the well-tool in the borehole, where the conducting areas may be disposed along the wireline at predetermined locations. A reader may be located at a reference location and may read when a conducting area passes through the reference location and this information may be used to determine the depth of the well-tool in the borehole. Additionally, this invention provides for combining depth measurements from the conducting areas with measurements from odometer wheels in frictional contact with the wireline and/or time of flight measurements of optical pulses passed along a fiber optic cable coupled with the wireline to accurately and robustly measure the depth of the wireline in the borehole.

1 . A system for determining depth of a well-tool in a borehole penetrating an earth formation comprising:
 a wireline configured to couple with said well-tool and to suspend said well-tool in the borehole;   a plurality of conducting areas disposed along the wireline at predetermined locations, wherein each of said predetermined locations define a measured length of the wireline, and wherein each of the plurality of conducting areas have a higher electrical conductivity than the wireline;   a reader coil comprising a series of loops of conducting material, wherein the reader coil and the wireline are configured to provide that the wireline passes proximally to the reader coil when the wireline is moved in and out of the borehole;   an alternating current source coupled with the reader coil; and   a detector coupled with the reader coil configured to detect changes in the electrical properties of the reader coil.   
   
   
       2 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the plurality of conducting areas are disposed below an armor layer and said armor layer is configured as an outer layer of the wireline. 
   
   
       3 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the detector detects changes in impedance of the reader coil. 
   
   
       4 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the plurality of conducting areas are configured in groupings of one or more of the conducting areas arranged in a logical pattern and wherein each of the groupings are disposed at the predetermined locations. 
   
   
       5 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 4 , wherein the logical pattern of the groupings of the conducting areas are arranged so as to encode binary data. 
   
   
       6 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the plurality of conducting areas comprise a plurality of conducting bands, and wherein each of the conducting bands is configured to encircle the wireline. 
   
   
       7 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the plurality of conducting areas are disposed along a tape that is wound around the wireline. 
   
   
       8 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the tape is disposed below an armoring surface layer of the wireline. 
   
   
       9 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the wireline is configured to pass through the reader coil as the wireline moves in and out of the borehole. 
   
   
       10 . The system for determining depth of the well-tool in the borehole penetrating the earth formation as recited in  claim 1 , wherein the reader coil comprises a first coil and a second coil connected in a bridge circuit with the detector disposed at the center of the bridge circuit, and wherein the wireline is configured to pass through the first coil and the second coil as the wireline moves in and out of the borehole. 
   
   
       11 . A method for determining depth of a well-tool in a borehole penetrating an earth formation where the well-tool is suspended in the borehole from a wireline and the wireline is configured with a plurality of conductive bands with higher conductivity than material comprising the wireline disposed at predetermined distances along the wireline, the method comprising the steps of:
 passing the wireline through a reader coil;   using the wireline to position the well-tool in the borehole;   passing an alternating electrical current through the reader coil; and   detecting changes in electrical properties of the reader coil.   
   
   
       12 . The method for determining the depth of the well-tool in the borehole penetrating the earth formation where the well-tool is suspended in the borehole from the wireline and the wireline is configured with the plurality of conductive bands with higher conductivity than the material comprising the wireline disposed at predetermined distances along the wireline as recited in  claim 11 , the method further comprising:
 arranging the conductive bands along the wireline in a logical arrangement.   
   
   
       13 . The method for determining the depth of the well-tool in the borehole penetrating the earth formation where the well-tool is suspended in the borehole from the wireline and the wireline is configured with the plurality of conductive bands with higher conductivity than the material comprising the wireline disposed at predetermined distances along the wireline as recited in  claim 11 , the method further comprising:
 passing the wireline over an odometer wheel, wherein the wireline and odometer wheel are configured to provide that the odometer wheel rotates as the wireline passes over the odometer wheel;   determining a rotation amount of the odometer wheel as the wireline passes over the odometer wheel as the well-tool is positioned in the borehole; and   communicating the rotation amount and the detected changes in the electrical properties of the reader coil to a processor; and   processing the depth of the well-tool in the borehole from the rotation amount and the detected changes in the electrical properties of the reader coil to a processor.