Magnetic tool for retrieving metal objects from a well bore

Abstract

A magnetic tool for retrieving metal objects from a wellbore has a plurality of magnet assemblies spaced longitudinally along a tool body. Each magnet assembly has a plurality of magnet members covering a majority surface area of the tool body. Each magnet member has a magnet body and a shield encasing the magnet body and protecting the individual magnet body from striking force created by the attracted metal particles. The shield is preferably made from a non-ferrous material and allows concentration of the magnetic force away from the tool body and into the casing annulus.

1 . An apparatus for retrieving metal objects from a wellbore, comprising: 
 a cylindrical tool body with a central opening therethrough;    a plurality of magnet assemblies spaced longitudinally along the length of the tool body and covering a majority of surface area of said tool body, each of said magnet assemblies comprising a plurality of elongated magnet members spaced equidistantly from each other about the circumference of said tool body, each of said magnet members comprising a separate shield protecting at least an outer front wall of a corresponding magnet member.    
   
   
       2 . The apparatus of  claim 1 , wherein each of said magnet members comprises a magnet body and a shield mounted about said magnet body.  
   
   
       3 . The apparatus of  claim 2 , wherein said is configured to encase the magnet body.  
   
   
       4 . The apparatus of  claim 2 , wherein said shield is provided with means for concentrating magnetic force and directing said magnetic force outwardly from the tool body.  
   
   
       5 . The apparatus of  claim 2 , wherein said shield comprises an inner wall engaging the tool body and an outer wall, and wherein said inner wall has greater thickness than the outer wall.  
   
   
       6 . The apparatus of  claim 2 , wherein said shield comprises an inner wall contacting the tool body, an outer wall, and a side wall, and wherein said side wall and said outer wall form settling surfaces for the metal objects being attracted by the magnet body.  
   
   
       7 . The apparatus of  claim 2 , wherein said shield has a configuration complementary to a configuration of a corresponding magnet body.  
   
   
       8 . The apparatus of  claim 7 , wherein said magnet body and said shield each have a generally trapezoidal cross-section.  
   
   
       9 . The apparatus of  claim 1 , wherein said tool body is provided with an upper sub located above said magnet assemblies and a lower sub located below said magnet assemblies, said upper sub and said lower sub allowing connection of said body to a drill string lowered into the well bore.  
   
   
       10 . The apparatus of  claim 1 , wherein said tool body is provided with a plurality of recesses for receiving an inner wall of a corresponding magnet member therein.  
   
   
       11 . An apparatus for retrieving metal objects from a wellbore, comprising: 
 a cylindrical tool body with a central opening therethrough;    a plurality of magnet assemblies spaced longitudinally along the length of the tool body and covering a majority of surface area of said tool body, each of said magnet assemblies comprising a plurality of elongated magnet members, each of the magnet members comprising a magnet body encased in a non-magnetic shield.    
   
   
       12 . The apparatus of  claim 11 , wherein said shield has a configuration facilitating concentration of magnetic force outwardly away from the tool body.  
   
   
       13 . The apparatus of  claim 12 , wherein said shield has an inner wall fitted into a recess formed in the tool body, a side wall and an outer wall, and wherein said inner wall has thickness greater than said side wall and said outer wall.  
   
   
       14 . The apparatus of  claim 13 , wherein said side wall and said outer wall form a settling surface for the metal objects being attracted by the magnet body.  
   
   
       15 . The apparatus of  claim 11 , wherein each of said magnet members has a cross section of a generally trapezoidal configuration, and wherein said magnet members are secured longitudinally on the tool body.  
   
   
       16 . An apparatus for retrieving metal objects from a wellbore, comprising: 
 a cylindrical tool body with a central opening therethrough;    a plurality of magnet assemblies spaced longitudinally along the length of the tool body and covering a majority of surface area of said tool body, each of said magnet assemblies comprising a plurality of magnet members detachably secured on said tool body, each of said magnet members comprising a magnet body encased in a shield, said shield having configuration complementary to a configuration of a corresponding magnet body.    
   
   
       17 . The apparatus of  claim 16 , wherein each of said magnet members is fitted into a corresponding recess formed in the tool body.  
   
   
       18 . The apparatus of  claim 16 , wherein said shield comprises an inner wall, an outer wall and a side wall, and wherein said inner wall has a thickness smaller than the thickness of the outer wall and the side wall to facilitate concentration of magnetic force created by the magnet body away from the tool body.  
   
   
       19 . The apparatus of  claim 16 , wherein said tool body is provided with an upper sub located above said magnet assemblies and a lower sub located below said magnet assemblies, said upper sub and said lower sub allowing connection of said body to a drill string lowered into the wellbore.  
   
   
       20 . A method of retrieving metal particles from a well bore, comprising the following steps: 
 providing a tool body having a central opening therein;    providing a plurality of magnet assemblies longitudinally spaced along said tool body, each magnet assembly comprising a plurality of magnet members, said magnet members covering a majority surface area of said tool body, each of said magnet members comprising a shield separately encasing individual magnet bodies;    detachably non-rotatably securing each of said magnet members on said tool body; and    lowering said body into the well bore and imparting rotation to said tool body, thereby creating a magnetic field and causing metal particles to settle on said magnet assemblies.    
   
   
       21 . The method of  claim 18 , wherein exterior surfaces of said magnet members define metal particles settling area.  
   
   
       22 . The method of  claim 18 , further comprising a step of forming each of said shields from a non-ferrous material.  
   
   
       23 . The method of  claim 18 , further comprising a step of forming each of said shields having an inner wall, an outer wall and a side wall, and positioning the inner wall of each of said shields in a corresponding recess formed in the tool body.  
   
   
       24 . The method of  claim 21 , further comprising a step of forming each of said shields with the inner wall having a thickness greater than thickness of said outer wall and said side wall, thereby concentrating magnetic force away from the tool body and into the well bore.  
   
   
       25 . The method of  claim 20 , further comprising the step of providing said shield and said magnet body with complementary configurations.  
   
   
       26 . The method of  claim 20 , further comprising a step of providing said tool body with with an upper sub located above said magnet assemblies and a lower sub located below said magnet assemblies, said upper sub and said lower sub allowing connection of said body to a drill string lowered into the wellbore.  
   
   
       27 . A method of retrieving metal particles from a well bore, comprising the following steps: 
 providing a tool body having a central opening therein;    providing a plurality of magnet assemblies longitudinally spaced along said tool body, each magnet assembly comprising a plurality of magnet members, each of said magnet members comprising a shield separately encasing individual magnet bodies for creating individual protecting barrier about entire exterior surface of the magnet body against striking force created by attracted metal particles;    detachably securing each of said magnet members on said tool body;    lowering said body into the well bore; and    imparting rotation to said tool body, thereby creating a magnetic field and causing metal particles to settle on said magnet assemblies.    
   
   
       28 . The method of  claim 27 , further comprising a step of forming each of said shields with the inner wall having a thickness greater than thickness of said outer wall and said side wall, thereby concentrating magnetic force away from the tool body and into the well bore.