Magnetic tool for retrieving metal objects from a well bore

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.