Apparatus for preventing separation of downhole motor from drillstring

1. A downhole motor for a drillstring, the motor comprising:

a housing having upper and lower portions coupled to one another;

a rotor disposed in the lower portion;

a seat disposed in the upper portion, the seat having a lower side toward the lower portion and having an upper side toward the upper portion;

an extension having a first end coupled to the rotor in the lower portion and having a second end disposed in the upper portion beyond the upper side of the seat; and

an expandable shoulder disposed on the second end of the extension and being expandable on the second end at least from an unexpanded state to an expanded state, the expandable shoulder in the unexpanded state on the extension being passable through the seat at least from the lower side to the upper side, the expandable shoulder in the expanded state on the extension being engageable with at least the upper side of the seat in response to separation of the upper and lower portions of the housing from one another,

wherein the expandable shoulder comprises a washer disposed on the second end of the extension, and

wherein the second end of the extension comprises a conical surface on which the washer is disposed, the washer expanded on the conical surface after insertion of the second end of the extension past the seat and into the upper portion of the housing.

2. The motor of claim 1 , wherein the second end of the extension comprises a nut threaded thereon and tightened to expand the washer on the conical surface.

3. The motor of claim 2 , wherein the nut threaded on the second end of the extension comprises the conical surface on which the washer is expanded.

4. The motor of claim 1 , wherein the first end of the extension threads onto the rotor.

5. The motor of claim 1 , wherein the seat comprises a shoulder disposed around an inside of the upper portion of the housing.

6. The motor of claim 5 , wherein the shoulder defines a plurality of slots therein.

7. The motor of claim 1 , wherein the washer of the expandable shoulder comprises a plurality of segments disposed on the second end of the extension.

8. The motor of claim 7 , wherein the conical surface on which the washer of the expandable shoulder is disposed comprises a conical ring disposed on the second end of the extension and having the segments arranged thereabout.

9. The motor of claim 8 , wherein the segments and the conical ring comprises an arrangement of tongues and grooves holding the segments on the conical ring.

10. An assembly for a downhole apparatus having a rotatable mandrel disposed in an outer housing, the assembly comprising:

an upper housing coupled to the outer housing;

a seat disposed in the upper housing, the seat having a lower side toward the outer housing and having an upper side toward the upper housing;

an extension having a first end coupled to the rotatable mandrel in the outer housing and having a second end disposed in the upper housing beyond the upper side of the seat; and

an expandable shoulder disposed on the second end of the extension and being expandable on the second end at least from an unexpanded state to an expanded state, the expandable shoulder in the unexpanded state on the extension being passable through the seat at least from the lower side to the upper side, the expandable shoulder in the expanded state on the extension being engageable with at least the upper side of the seat in response to displacement of the extension,

wherein the expandable shoulder comprises a washer disposed on the second end of the extension, and

wherein the second end of the extension comprises a conical surface on which the washer is disposed, the washer expanded on the conical surface after insertion of the second end of the extension past the seat and into the upper housing.

11. The assembly of claim 10 , wherein the second end of the extension comprises a nut threaded thereon and tightened to expand the washer on the conical surface.

12. The apparatus of claim 11 , wherein the nut threaded on the second end of the extension comprises the conical surface on which the washer is expanded.

13. The assembly of claim 10 , wherein the upper housing threads to the outer housing.

14. The assembly of claim 10 , wherein the first end of the extension threads onto the mandrel.

15. The assembly of claim 10 , wherein the seat comprises a shoulder disposed around an inside of the upper housing.

16. The assembly of claim 15 , wherein the shoulder defines a plurality of slots therein.

17. The assembly of claim 10 , wherein the washer of the expandable shoulder comprises a plurality of segments disposed on the second end of the extension.

18. The assembly of claim 17 , wherein the conical surface on which the washer of the expandable shoulder is disposed comprises a conical ring disposed on the second end of the extension and having the segments arranged thereabout.

19. The assembly of claim 18 , wherein the segments and the conical ring comprise an arrangement of tongues and grooves holding the segments on the conical ring.

20. A method of assembling a drilling motor, comprising:

positioning an expandable shoulder on an upper end of an extension for a rotor of the drilling motor, the expandable shoulder being expandable on the upper end at least from an unexpanded state to an expanded state;

holding the expandable shoulder in the unexpanded state on the upper end with a nut;

inserting the upper end of the extension, the unexpanded expandable shoulder, and the nut past a seat in an upper housing portion of the motor; and

expanding the expandable shoulder to the expanded state on the upper end of the extension to be engageable with at least an upper side of the seat in response to displacement of the extension by plastically deforming a ring on a conical surface by tightening the nut on the upper end of the extension.

21. The method of claim 20 , further comprising attaching a lower end of the extension to the rotor.

22. The method of claim 20 , further comprising attaching the upper housing portion of the motor to a lower housing portion of the motor having the rotor disposed therein.

23. A method of assembling a drilling motor, comprising:

positioning an expandable shoulder on an upper end of an extension for a rotor of the drilling motor, the expandable shoulder being expandable on the upper end at least from an unexpanded state to an expanded state;

holding the expandable shoulder in the unexpanded state on the upper end with a nut;

inserting the upper end of the extension, the unexpanded expandable shoulder, and the nut past a seat in an upper housing portion of the motor; and

expanding the expandable shoulder to the expanded state on the upper end of the extension to be engageable with at least an upper side of the seat in response to displacement of the extension by elastically deforming a collet by tightening the nut on the upper end of the extension.

24. The method of claim 23 , further comprising attaching a lower end of the extension to the rotor.

25. The method of claim 23 , further comprising attaching the upper housing portion of the motor to a lower housing portion of the motor having the rotor disposed therein.

26. A method of assembling a drilling motor, comprising:

positioning an expandable shoulder on an upper end of an extension for a rotor of the drilling motor, the expandable shoulder being expandable on the upper end at least from an unexpanded state to an expanded state;

holding the expandable shoulder in the unexpanded state on the upper end with a nut;

inserting the upper end of the extension, the unexpanded expandable shoulder, and the nut past a seat in an upper housing portion of the motor; and

expanding the expandable shoulder to the expanded state on the upper end of the extension to be engageable with at least an upper side of the seat in response to displacement of the extension by expanding a plurality of segments outward by tightening the nut on the upper end of the extension.

27. The method of claim 26 , further comprising attaching a lower end of the extension to the rotor.

28. The method of claim 26 , further comprising attaching the upper housing portion of the motor to a lower housing portion of the motor having the rotor disposed therein.