Magnetic Coupling for Downhole Applications

Abstract

The present disclosure relates to a magnetic coupling of a downhole tool that includes a first annular array of magnetic sections, a second annular array of magnetic sections coupled to the first annular array by a magnetic field that transfers rotational motion from the first annular array to the second annular array, and a barrier disposed between the first annular array and the second annular array, the barrier including an erosion-resistant layer. The present disclosure also relates to a method of bootstrapping a magnetic coupling of a downhole tool. The method includes supplying electrical current from a battery to an electromagnetic coil in the magnetic coupling, transferring rotational motion from the magnetic coupling to an alternating current (AC) source and supplying electrical current from the AC source to the electromagnetic coil.

What is claimed is: 
     
         1 . A magnetic coupling of a downhole tool comprising:
 a first annular array of magnetic sections;   a second annular array of magnetic sections coupled to the first annular array by a magnetic field that transfers rotational motion from the first annular array to the second annular array; and   a barrier disposed between the first annular array and the second annular array, the barrier including an erosion-resistant layer.   
     
     
         2 . The magnetic coupling of  claim 1 , wherein:
 the first annular array has a first outer diameter;   the second annular array has a second outer diameter approximately equal to the first outer diameter;   the first annular array and the second annular array are configured to rotate about a common axis of rotation; and   the magnetic field is oriented approximately parallel to the common axis of rotation.   
     
     
         3 . The magnetic coupling of  claim 1 , wherein:
 the first annular array has an inner diameter;   the second annular array has an outer diameter smaller than the inner diameter;   the second annular array is disposed within the inner diameter of the first annular array;   the first annular array and the second annular array are configured to rotate about a common axis of rotation; and   the magnetic field is oriented approximately perpendicular to the common axis of rotation.   
     
     
         4 . The magnetic coupling of  claim 1 , wherein the erosion-resistant layer includes a layer of titanium. 
     
     
         5 . The magnetic coupling of  claim 1 , wherein the second annular array comprises a plurality of permanent magnets. 
     
     
         6 . The magnetic coupling of  claim 5 , wherein a magnet among the plurality of permanent magnets is a samarium cobalt magnet. 
     
     
         7 . The magnetic coupling of  claim 1 , wherein the second annular array comprises a plurality of electromagnetic coils. 
     
     
         8 . The magnetic coupling of  claim 7 , further comprising a bootstrap circuit for energizing the plurality of electromagnetic coils, the bootstrap circuit comprising:
 a battery; and   a first diode coupled to the battery, the first diode permitting the battery to supply electrical current to the plurality of electromagnetic coils.   
     
     
         9 . The magnetic coupling of  claim 8 , the bootstrap circuit further comprising:
 a current source coupled to the second annular array, the current source configured to transform rotation of the second annular array into electrical current; and   a second diode coupled to the current source, the second diode permitting the current source to supply electrical current to the plurality of electromagnetic coils.   
     
     
         10 . A drilling system comprising:
 a drill string;   a magnetic coupling located within the drill string, the magnetic coupling including:
 a first annular array of magnetic sections; 
 a second annular array of magnetic sections coupled to the first annular array by a magnetic field that transfers rotational motion from the first annular array to the second annular array; 
 a barrier disposed between the first annular array and the second annular array, the barrier having an erosion-resistant layer; 
   a motor coupled to the first annular array; and   a load coupled to the second annular array.   
     
     
         11 . The drilling system of  claim 10 , wherein:
 the first annular array has a first outer diameter;   the second annular array has a second outer diameter approximately equal to the first outer diameter;   the first annular array and the second annular array are configured to rotate about a common axis of rotation; and   the magnetic field is oriented approximately parallel to the common axis of rotation.   
     
     
         12 . The drilling system of  claim 10  wherein:
 the first annular array has an inner diameter; 
 the second annular array has an outer diameter smaller than the inner diameter; 
 the second annular array is disposed within the inner diameter of the first annular array; 
 the first annular array and the second annular array are configured to rotate about a common axis of rotation; and 
 the magnetic field is oriented approximately perpendicular to the common axis of rotation. 
 
     
     
         13 . The drilling system of  claim 10 , wherein the erosion-resistant layer includes a layer of titanium. 
     
     
         14 . The drilling system of  claim 10 , wherein the second annular array comprises a plurality of permanent magnets. 
     
     
         15 . The drilling system of  claim 10 , wherein a magnet among the plurality of permanent magnets is a samarium cobalt magnet. 
     
     
         16 . The drilling system of  claim 10 , wherein the second annular array comprises a plurality of electromagnetic coils. 
     
     
         17 . The drilling system of  claim 16 , further comprising a bootstrap circuit for energizing the plurality of electromagnetic coils, the bootstrap circuit comprising:
 a battery; and   a first diode coupled to the battery, the first diode permitting the battery to supply electrical current to the plurality of electromagnetic coils.   
     
     
         18 . The drilling system of  claim 17 , the bootstrap circuit further comprising:
 a current source coupled to the plurality of electromagnetic coils; and   a second diode coupled to the current source, the second diode permitting the current source to supply current to the plurality of electromagnetic coils.   
     
     
         19 . The drilling system of  claim 10 , wherein the load is a generator. 
     
     
         20 . A method of bootstrapping a magnetic coupling of a downhole tool, comprising:
 rotating a first annular array of magnetic sections in a magnetic coupling;   supplying current from a battery to an electromagnetic coil located within a second annular array of magnetic sections in the magnetic coupling;   coupling the first annular array to the second annular array using a magnetic field produced by the electromagnetic coil;   transferring rotational motion from the first annular array to the second annular array using the magnetic field;   transferring rotational motion from the second annular array to an alternating current (AC) source configured to transform rotational motion into electrical current; and   supplying electrical current from the AC source to the electromagnetic coil.   
     
     
         21 . The method of  claim 20 , wherein the magnetic coupling includes a barrier disposed between the first annular array and the second annular array, the barrier including an erosion-resistant layer. 
     
     
         22 . The method of  claim 20 , wherein:
 the first annular array has a first outer diameter;   the second annular array has a second outer diameter approximately equal to the first outer diameter;   the first annular array and the second annular array are configured to rotate about a common axis of rotation; and   the magnetic field is oriented approximately parallel to the axis of rotation.   
     
     
         23 . The method of  claim 20 , wherein:
 the first annular array has an inner diameter;   the second annular array has an outer diameter smaller than the inner diameter;   the second annular array is disposed within the inner diameter of the first annular array;   the first annular array and the second annular array are configured to rotate about a common axis of rotation; and   the magnetic field is oriented approximately perpendicular to the axis of rotation.