Cutting dart and method of using the cutting dart

1. A cutting dart, comprising:

a dart body comprising a first pathway configured to redirect cutting fluid flowing through a coiled tubing so that the cutting fluid flows radially to impinge against an inner surface of the coiled tubing; wherein the dart body is adapted to be pumped through the coil tubing and

a seal positioned around an outer circumference of the dart body, wherein the dart body comprises a nose configured to self-center the cutting dart when landed on a shoulder in the coiled tubing.

2. The dart of claim 1 , wherein the first pathway comprises an inlet at an end of the dart body and an outlet at the outer circumference of the dart body.

3. The dart of claim 1 , wherein a second pathway is configured to allow the cutting fluid to flow past the dart after it impinges against the inner surface.

4. The dart of claim 3 , wherein the nose comprises a plurality of ribs configured to provide the second pathway.

5. The dart of claim 4 , wherein the ribs of the nose protrude from a conical or frustoconical shaped inner surface.

6. The dart of claim 1 , wherein the seal comprises a plurality of flexible ribs extending around the outer circumference of the dart body.

7. The dart of claim 1 , wherein the dart body further comprises a flexible tubular fluidly connecting a portion of the dart body comprising the seal and the portion of the dart body comprising the first pathway.

8. A method of cutting a coiled tubing string in a well bore, the method comprising:

pumping a cutting dart through a coiled tubing until it lands at a location proximate the position at which the coiled tubing is to be cut;

pumping cutting fluid through the coiled tubing and the cutting dart so that the cutting fluid is redirected radially against an inner diameter of the coiled tubing so as to cut the coiled tubing; and

retrieving the coiled tubing from the well bore.

9. The method of claim 8 , wherein the location at which the dart lands is on an internal shaft of an end connector.

10. The method of claim 8 , wherein the cutting fluid is a slurry.

11. The method of claim 8 , wherein the cutting fluid comprises an acid and an acid inhibitor.

12. The method of claim 8 , wherein the location is a shoulder of a coiled tubing string connector.

13. The method of claim 8 , further comprising pumping an anchor dart through the coiled tubing to the location proximate the position at which the coiled tubing is to be cut.

14. The method of claim 13 , further comprising expanding a swellable elastomer to hold the anchor dart at the location proximate the position at which the coiled tubing is to be cut.

15. The method of claim 14 , wherein expanding the swellable elastomer comprises including a fluid capable of accelerating the swelling of the rubber when the dart is loaded at a surface location.

16. The method of claim 14 , further comprising bursting a frangible disk in the anchor dart after expanding the swellable elastomer.

17. The method of claim 16 , wherein the cutting dart lands on the anchor dart so as to position the cutting dart at the location proximate the position at which the coiled tubing is to be cut.

18. The method of claim 8 , further comprising, after the coiled tubing is cut, pumping an anchor dart through the coiled tubing to a location above the position at which the coiled tubing is cut and expanding a swellable elastomer to fix the anchor dart inside the coiled tubing and thereby isolate the coiled tubing prior to retrieving the coiled tubing from the well bore.

19. A coiled tubing assembly, comprising:

a coiled tubing string comprising a proximal end at a surface location and a distal end positioned in a well bore; and

a cutting dart positioned in the coiled tubing string, the cutting dart comprising:

a dart body comprising a first pathway configured to redirect cutting fluid flowing through the coiled tubing so that the cutting fluid flows radially to impinge against an inner surface of the coiled tubing; and

a seal positioned around an outer circumference of the dart body.

20. The coiled tubing assembly of claim 19 , further comprising an end connector attached to the distal end of the coiled tubing string.

21. The coiled tubing assembly of claim 20 , wherein the end connector is an external connector comprising an external housing having a grapple mechanism proximate an outside surface of the distal end of the coiled tubing, and an internal shaft extending into the coiled tubing and configured to provide a shoulder on which the dart can land.

22. The coiled tubing assembly of claim 20 , wherein the end connector is an internal connector comprising an internal shaft extending into the coiled tubing and configured to provide a shoulder on which the dart can land.

23. The coiled tubing assembly of claim 22 , wherein the internal connector comprises an outer sleeve proximate an outside surface of the distal end, the outer sleeve being positioned between an outlet of the cutting dart and the well bore so as to be capable of protecting the well bore from being damaged by the cutting fluid when the coiled tubing is cut.

24. The coiled tubing assembly of claim 19 , wherein the dart body comprises a nose configured to self-center the cutting dart when positioned in the coiled tubing.

25. The coiled tubing assembly of claim 24 , wherein the nose comprises a second pathway configured to allow the cutting fluid to flow past the dart after it impinges against the inner surface.

26. The coiled tubing assembly of claim 25 , wherein the nose comprises a plurality of ribs configured to provide a second pathway.

27. The coiled tubing assembly of claim 26 , wherein the ribs of the nose protrude from a conical or frustoconical shaped inner surface.

28. The coiled tubing assembly of claim of claim 19 , wherein the first pathway comprises an inlet at an end of the dart body and an outlet at the outer circumference of the dart body.

29. The coiled tubing assembly of claim 28 , wherein the seal comprises a plurality of flexible ribs extending around the outer circumference of the dart body.

30. The coiled tubing assembly of claim 19 , wherein the cutting dart is positioned proximate the end connector.

31. The coiled tubing assembly of claim 19 , wherein the coiled tubing string comprises a first tubing string section and a second tubing string section, the first and second tubing string sections coupled together with a coiled tubing string connector.

32. The coiled tubing assembly of claim 31 , wherein the cutting dart is positioned within the coiled tubing string connector, an outlet of the first pathway being positioned below the coiled tubing string connector.

33. The coiled tubing assembly of claim 32 , wherein the dart body further comprises a flexible tubular fluidly connecting a portion of the dart body comprising the seal and the portion of the dart body comprising the first pathway.

34. The coiled tubing assembly of claim 19 , further comprising an anchor dart within the coiled tubing string, the cutting dart being positioned on the anchor dart.

35. The coiled tubing assembly of claim 34 , wherein the anchor dart comprises a swellable elastomer holding the anchor dart in a desired position in the coiled tubing string.

36. The dart of claim 1 , wherein the seal prevents flow of fluid between the outer circumference of the dart and the coiled tubing.

37. The coiled tubing assembly of claim 19 , wherein the seal prevents flow of fluid between the outer circumference of the dart body and the coiled tubing string.

38. A cutting dart, comprising:

a dart body comprising a first pathway configured to redirect cutting fluid flowing through a coiled tubing so that the cutting fluid flows radially to impinge against an inner surface of the coiled tubing; and

a seal positioned around an outer circumference of the dart body, wherein the cutting dart is adapted to be pumped through the coiled tubing and to land on a shoulder positioned in an end connector of the coiled tubing, wherein at least a portion of the coiled tubing is wrapped around a drum.