Tool for measuring wellbore geometry

Abstract

A downhole tool is disclosed for measuring wellbore geometry. The downhole tool may include a body with a bore extending at least partially therethrough. The body may include a radial recess. An arm may be movably coupled to the body at a first end portion of the arm. The arm may be within the radial recess in a retracted position and be pivotable in a radially-outward direction relative to the body to an expanded position. A measurement device coupled to the body may measure the pivoting motion of the arm. A piston coupled to the body may be movably coupled to a second end portion of the arm, and the piston may respond to changes in hydraulic pressure to pivot the arm between the retracted position and the expanded position.

What is claimed is: 
     
         1 . A downhole tool for measuring wellbore geometry, comprising:
 a body having a bore extending at least partially therethrough, the body also having an aperture formed radially therein;   an arm having a first end portion movably coupled to the body, the arm being pivotable between a retracted position in which the arm is within the aperture and an expanded position in which the arm is at least partially radially-outward relative to the body;   a measurement device coupled to the body and configured to measure a pivoting motion of the arm; and   a piston disposed in the bore of the body and movably coupled to a second end portion of the arm, the piston responsive to hydraulic pressure to cause the arm to pivot between the retracted position and the expanded position.   
     
     
         2 . The downhole tool of  claim 1 , the arm being configured to pivot through an angle between 1° and 20°. 
     
     
         3 . The downhole tool of  claim 1 , the arm being configured to contact a wall of a wellbore when in the expanded position. 
     
     
         4 . The downhole tool of  claim 3 , further comprising:
 a roller coupled to the arm, the roller being configured to contact the wall of the wellbore when the arm is in the expanded position.   
     
     
         5 . The downhole tool of  claim 1 , the measurement device including a magnet configured to move axially within the measurement device. 
     
     
         6 . The downhole tool of  claim 5 , further comprising:
 an electronic device coupled to the body, the electronic device including a magnetometer.   
     
     
         7 . The downhole tool of  claim 6 , the magnetometer being configured to measure a distance that the magnet moves. 
     
     
         8 . The downhole tool of  claim 5 , the magnet being configured to move axially a distance proportional to a pivoting rotation of the arm. 
     
     
         9 . The downhole tool of  claim 8 , the measurement device being configured to use the pivoting rotation of the arm to determine the diameter of a wellbore. 
     
     
         10 . The downhole tool of  claim 1 , the arm being biased toward the configured to be positioned radially-inward from an outer surface of the body when in the retracted position in the aperture and at least partially radially-outward relative to the outer surface of the body when in the expanded position. 
     
     
         11 . A tool for measuring geometry, comprising:
 a body having an axial bore extending at least partially therethrough;   a piston coupled to the body and configured to move axially within the body from a first position to a second position when hydraulic pressure of a fluid in the bore is increased;   a spring gear assembly coupled to the piston and configured to rotate when the piston moves between the first position and the second position;   an arm coupled to the body and the spring gear assembly and configured to move radially relative to the body when the spring gear assembly rotates; and   a measuring device coupled to the arm and configured to measure the movement of the arm.   
     
     
         12 . The tool of  claim 11 , the piston including a shaft having plurality of teeth coupled thereto and axially spaced along the shaft, the spring gear assembly including a gear having a plurality of teeth coupled thereto and circumferentially spaced around at least a portion of the gear, the plurality of teeth of the gear being configured to engage the plurality of teeth of the shaft. 
     
     
         13 . The tool of  claim 12 , the piston being configured to use engagement of the plurality of teeth of the shaft with the plurality of teeth of the gear to convert the axial movement of the piston to rotational movement of the gear when the piston moves between the first position and the second position. 
     
     
         14 . The tool of  claim 13 , further comprising:
 a connector coupled to and disposed between the arm and the spring gear assembly, the connector configured to pivot the arm radially when the piston moves between the first position and the second position.   
     
     
         15 . The tool of  claim 11 , the measuring device being configured to use the measured movement of the arm to determine a diameter of a wellbore. 
     
     
         16 . A method for measuring a diameter of a wellbore while performing a downhole drilling or remedial operation, comprising:
 increasing a pressure of a fluid in a bore that extends through a body of a downhole tool within a wellbore;   moving a piston axially within the body from a first position to a second position in response to the increased pressure in the bore;   pivoting an arm movably coupled to the body radially-outward in response to the piston moving from the first position to the second position;   sensing the pivoting of the arm with a measuring device coupled to the arm while drilling or performing a remedial operation; and   determining a diameter of the wellbore based upon the pivoting of the arm.   
     
     
         17 . The method of  claim 16 , wherein pivoting the arm comprises:
 rotating a gear to the body in response to the piston moving from the first position to the second position; and   pivoting the arm radially-outward in response to the rotation of the gear.   
     
     
         18 . The method of  claim 16 , wherein determining the diameter of the wellbore comprises:
 moving a magnet axially a distance proportional to an amount by which the arm pivots; and   determining the diameter of the wellbore based upon the axial distance the magnet moves.   
     
     
         19 . The method of  claim 16 , further comprising:
 contacting a wall of the wellbore with a roller coupled to the arm when the arm is positioned radially-outward from the body.   
     
     
         20 . The method of  claim 19 , further comprising:
 rotating the downhole tool while the arm is positioned radially-outward from the body such that the roller rolls along the wall of the wellbore.