Magnetic retrieval apparatus

1. A downhole retrieval tool, comprising:

a mandrel having a longitudinal axis extending from a first end of the mandrel to a second end of the mandrel;

an inner sleeve disposed around the mandrel;

a plurality of magnets coupled to the inner sleeve; and

an outer sleeve disposed around the plurality of magnets, wherein the inner sleeve and the plurality of magnets are rotatable relative to the mandrel, and wherein the outer sleeve includes a plurality of outer sleeve valleys that extend into a corresponding plurality of valleys between two adjacent magnets, wherein two adjacent outer sleeve valleys are circumferentially spaced relative to one another about the outer sleeve, the plurality of outer sleeve valleys extending along the longitudinal axis from the first end of the mandrel to the second end of the mandrel.

2. The tool of claim 1 , wherein the inner sleeve includes one or more channels for receiving the plurality of magnets.

3. The tool of claim 2 , wherein each magnet is attached to the inner sleeve by a fastener extending through the magnet and a fastener aperture in the corresponding channel.

4. The tool of claim 3 , further comprising a plurality of apertures extending between two adjacent channels.

5. The tool of claim 1 , wherein each magnet includes a “north” pole and a “south” pole,” wherein the north pole is disposed on a left side or a right side of the magnet and the south pole is disposed on the other side of the magnet.

6. The tool of claim 1 , further comprising two stabilizers, wherein one stabilizer is coupled to each end of the inner sleeve.

7. The tool of claim 6 , further comprising a bearing disposed between each stabilizer and the mandrel.

8. The tool of claim 6 , further comprising a key and groove connection for coupling the inner sleeve to the stabilizers.

9. The tool of claim 8 , wherein the key has a groove configured to receive the outer sleeve.

10. The tool of claim 1 , wherein each stabilizer includes a plurality of stabilizer valleys, wherein each stabilizer valley is aligned with a corresponding outer sleeve valley.

11. The tool of claim 1 , further comprising a spacer disposed between two adjacent magnets, wherein the spacer contacts both adjacent magnets.

12. The tool of claim 1 , wherein at least one magnet includes at least two retainer bores to facilitate handling of the at least one magnet.

13. A downhole retrieval tool, comprising:

a mandrel having a longitudinal axis extending from a first end of the mandrel to a second end of the mandrel;

an inner sleeve disposed around the mandrel;

a plurality of magnetic columns coupled to the inner sleeve; the plurality of magnetic columns having a plurality of magnets, wherein the plurality of magnetic columns are circumferentially spaced around the inner sleeve; and

an outer sleeve disposed around the plurality of magnetic columns, wherein the inner sleeve and the plurality of magnetic columns are rotatable relative to the mandrel, and wherein the outer sleeve includes a plurality of outer sleeve valleys that extend into and aligned with a corresponding plurality of valleys between two adjacent magnetic columns, the plurality of outer sleeve valleys extending along the longitudinal axis from the first end of the mandrel to the second end of the mandrel.

14. The tool of claim 13 , wherein the inner sleeve includes a plurality of channels for receiving the plurality of magnetic columns, wherein each magnetic column is partially disposed in a corresponding channel.

15. The tool of claim 14 , wherein each magnet in each magnetic column is attached to the inner sleeve by a fastener extending through the magnet and a fastener aperture in each channel.

16. The tool of claim 15 , wherein each magnet in each magnetic column includes at least one retainer bore to facilitate handling of each magnet.

17. The tool of claim 15 , further comprising a column of apertures between two adjacent channels.

18. The tool of claim 13 , further comprising a spacer disposed between two adjacent magnets in each magnetic column, wherein each spacer contacts both adjacent magnets.

19. A downhole retrieval tool, comprising:

a mandrel having a longitudinal axis extending from a first end of the mandrel to a second end of the mandrel;

an inner sleeve disposed around the mandrel;

a plurality of magnetic columns having a first end and a second end coupled to the inner sleeve, each magnetic column extending in a direction of the longitudinal axis from the first end to the second end, each of the plurality of magnetic columns having a plurality of magnets; and

an outer sleeve disposed around the plurality of magnetic columns, wherein the inner sleeve and the plurality of magnetic columns are rotatable relative to the mandrel, and wherein the outer sleeve includes a plurality of outer sleeve valleys that extend into a corresponding plurality of valleys between two adjacent magnetic columns, wherein the plurality of outer sleeve valleys and the corresponding plurality of valleys between two adjacent magnetic columns both extend in the direction of the longitudinal axis.

20. The tool of claim 19 , wherein the inner sleeve includes a plurality of channels for receiving the plurality of magnetic columns, wherein each magnetic column is partially disposed in a corresponding individual channel of the plurality of channels.

21. The tool of claim 20 , wherein each magnet is attached to the inner sleeve by a fastener extending through the magnet and a fastener aperture in the corresponding individual channel of the plurality of channels.

22. The tool of claim 21 , further comprising a column of apertures extending in the direction of the longitudinal axis between two adjacent channels of the plurality of channels.

23. The tool of claim 21 , wherein each magnet includes at least one retainer bore to facilitate handling of each magnet.