Downhole tool for sidetracking

Abstract

A downhole tool for drilling a sidetracked borehole. The downhole tool includes a body having an axial bore formed at least partially therethrough. At least one magnetometer is within the body. The magnetometer is configured to measure a magnetic field. A processor may be in communication with the at least one magnetometer. The processor may be configured to receive measurements from the at least one magnetometer, determine an orientation of the downhole tool based upon the received measurements, and selectively maintain the orientation of the downhole tool or change the orientation of the downhole tool based upon the determined orientation.

What is claimed is: 
     
         1 . A downhole tool for drilling a sidetracked borehole, comprising:
 a body having an axial bore formed at least partially therethrough;   at least one magnetometer coupled to the body, the magnetometer configured to measure a magnetic field; and   a processor in communication with the at least one magnetometer, the processor configured to:
 receive measurements from the at least one magnetometer; 
 determine an orientation of the downhole tool based upon the received measurements; and 
 maintain the orientation of the downhole tool or change the orientation of the downhole tool based upon the determined orientation of the downhole tool. 
   
     
     
         2 . The downhole tool of  claim 1 , further comprising:
 a drill bit coupled to the body.   
     
     
         3 . The downhole tool of  claim 2 , the at least one magnetometer being configured to rotate with the body or drill bit. 
     
     
         4 . The downhole tool of  claim 2 , the at least one magnetometer being configured to be substantially geostationary as the body or dill bit rotates. 
     
     
         5 . The downhole tool of  claim 1 , the magnetometer being configured to measure a magnetic field generated by at least one magnet within a wellbore. 
     
     
         6 . The downhole tool of  claim 5 , the at least one magnet coupled to a deflection member within a metal casing within the wellbore. 
     
     
         7 . The downhole tool of  claim 1 , the at least one magnetometer including two or more magnetometers that are axially offset from one another by a distance from 0.05 m to 2 m. 
     
     
         8 . The downhole tool of  claim 1 , further comprising:
 at least one accelerometer coupled to the body.   
     
     
         9 . The downhole tool of  claim 8 , further comprising:
 at least one gyroscope coupled to the body, the gyroscope configured to measure rotation of the body.   
     
     
         10 . The downhole tool of  claim 1 , wherein the body comprises a rotary steerable tool. 
     
     
         11 . A method of drilling, comprising:
 running a downhole tool into a wellbore having casing therein, the downhole tool including:
 a body having an axial bore formed at least partially therethrough; 
 a plurality of sensors within the axial bore of the body, the plurality of sensors including a first sensor having limited accuracy within the wellbore, and a second sensor being susceptible to interference from the casing; and 
 a processor coupled to the body and in communication with the plurality of sensors; 
   drilling a borehole that diverts from the wellbore;   obtaining location or orientation data using the plurality of sensors;   determining an orientation of the downhole tool with the processor based upon location or orientation data obtained by the second sensor while within the wellbore; and   steering the downhole tool based upon the determined orientation of the downhole tool.   
     
     
         12 . The method of  claim 11 , wherein the second sensor includes a magnetometer and obtaining location or orientation data includes obtaining magnetic field data generated by at least one magnet in the wellbore, which at least one magnet overcomes interference from the casing. 
     
     
         13 . The method of  claim 13 , the at least one magnet being coupled to a deflection member within the wellbore. 
     
     
         14 . The method of  claim 13 , the first sensor having limited accuracy while oriented in a substantially vertical direction. 
     
     
         15 . A method of drilling, comprising:
 forming an opening in a metal casing within a wellbore;   drilling a sidetracked borehole diverting from the wellbore at the opening in the metal casing using a downhole tool including:
 a body; 
 at least one magnetometer coupled to the body; 
 a processor coupled to the body and in communication with the at least one magnetometer; and 
 a drill bit coupled to the body; 
   measuring a magnetic field generated by at least one magnet within the metal casing with the at least one magnetometer, the at least one magnet being coupled to a whipstock within the wellbore;   determining an orientation of the downhole tool with the processor based upon measurements from the at least one magnetometer; and   steering the downhole tool based upon the determined orientation of the downhole tool.   
     
     
         16 . The method of  claim 15 , further comprising rotating the body as the drill bit drills the sidetracked borehole. 
     
     
         17 . The method of  claim 16 , the at least one magnetometer being configured to rotate with the body. 
     
     
         18 . The method of  claim 16 , the at least one magnetometer being substantially geostationary. 
     
     
         19 . The method of  claim 15 , the at least one magnetometer including at least two magnetometers, and the at least one magnet including at least two magnets, a spacing between the at least two magnetometers being about equal to a spacing between the at least two magnets. 
     
     
         20 . The method of  claim 15 , wherein steering the downhole tool further includes:
 maintaining the orientation of the downhole tool when the orientation is substantially aligned with a predetermined drill path for the sidetracked borehole; and   turning the downhole tool when the orientation is not substantially aligned with the predetermined drill path.