Method and apparatus for severing a drill string

1. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string;

pumping the cutting fluid from a surface location down through an internal bore defined by the drill pipe string and through the cutter to remove material from the selected portion of a wall of the drill string;

directing the cutting fluid from the drill pipe string bore into an annulus between the drill pipe string and a surrounding bore wall, and

returning the cutting fluid to the surface.

2. The method of claim 1 , further comprising the step of applying torque or tension to the string.

3. The method of claim 1 , further comprising severing the drill pipe string and then delivering cement through the severed string to form a kick-off plug.

4. The method of claim 1 , wherein the selected portion is the neck of a drill pipe connection and wherein removing material further comprises the step of reducing the loadbearing cross-sectional area of the neck by forming a circumferential cut.

5. The method of claim 4 , wherein the cut is circumferentially continuous.

6. The method of claim 1 , further comprising the step of:

pumping the cutting fluid from a surface location down through an internal bore defined by the drill pipe string and through the cutter to remove material from the selected portion of a wall of the drill pipe string; and

directing the cutting fluid from the drill pipe string bore into an annulus between the drill pipe string and a surrounding bore wall, and returning the cutting fluid to the surface.

7. The method of claim 1 , further comprising the step of providing a fluid bypass device in the string and opening the device to facilitate fluid circulation through the string.

8. The method of claim 7 , further comprising the step of opening the fluid bypass device to bypass fluid pressure loss-inducing drill string elements below the bypass device.

9. The method of claim 7 , further comprising the step of opening the fluid bypass device before activating the cutter.

10. The method of claim 1 , wherein the high velocity outlet stream has a flow speed of at least 100 feet/second.

11. The method of claim 1 , wherein the cutting fluid comprises drilling fluid.

12. The method of claim 1 , further comprising the step of locating the flow passage outlet directly adjacent an inner surface of the drill string.

13. The method of claim 1 , further comprising the step of directing fluid from the cutter at a transverse angle to an axis of the string.

14. The method of claim 1 , further comprising the step of creating at least one of eddies and vortices in the cutting fluid exiting the cutter.

15. The method claim 1 , further comprising the step of directing cutting fluid from the cutter in a continuous circumferential stream.

16. The method of claim 1 , further comprising the step of sealing a body of the cutter to a wall of the string and directing all of the cutting fluid pumped down the string into the cutter.

17. The method of claim 1 , further comprising the step of adding an abrasive material to the cutting fluid.

18. The method of claim 1 , further comprising the step of filtering the cutting fluid to avoid larger particles reaching the cutter.

19. The method of claim 1 , further comprising the step of landing the cutter in a cutter seat.

20. An apparatus for severing a drill pipe string, the apparatus comprising:

a flow-actuated cutter configured to be dropped or pumped into a drill pipe string and to land at a predetermined location in the string, and

wherein circulating cutting fluid down through the drill pipe string actuates the cutter to remove material from a selected portion of the drill pipe string and wherein the cutter is configured such that the cutting fluid exits the cutter in a high velocity stream directed towards an inner surface of the string and the cutter defines at least one of a constriction and a nozzle to provide the high velocity stream at a flow passage outlet, in combination with a seal bore provided in the string and wherein an external seal is provided on a cutter body between a flow passage inlet and the flow passage outlet for cooperating with the seal bore such that all of the cutting fluid pumped down the string is directed into the cutter.

21. The apparatus of claim 20 , further comprising a filter located in a fluid circulation path to prevent particles from reaching and blocking the cutter.

22. The apparatus of claim 20 , in combination with a seat provided in the string and including a cutter locator.

23. The apparatus of claim 22 , wherein the seat is provided by a catcher ring.

24. The apparatus of claim 23 , wherein the ring includes external seals.

25. The apparatus of claim 23 , wherein the ring is adapted for location in an upper part of a locating sub.

26. The apparatus of claim 22 , wherein the seat is configured for location in a cutter locating sub.

27. The apparatus of claim 20 , further comprising the seats being of progressively smaller diameters.

28. The apparatus of claim 20 , further comprising a fluid bypass device for location in the string.

29. The apparatus of claim 28 , wherein the bypass device is adapted for location below the intended severing location.

30. The apparatus of claim 28 , wherein the bypass device is adapted for location above the intended severing location.

31. The apparatus of claim 20 , wherein the flow passage outlet further comprises a flow gap of less than or equal to 0.060 inches.

32. The apparatus of claim 20 , wherein portions of the flow passage are formed of an erosion resistant material.

33. The apparatus of claim 32 , wherein portions of the flow passage are coated with a hard facing material.

34. The apparatus of claim 20 , wherein a fluid outlet is configured to be directly adjacent an inner surface of the drill string.

35. The apparatus of claim 20 , wherein the cutter is configured such that the cutting fluid exits the cutter at a transverse angle to an axis of the string.

36. The apparatus of claim 20 , wherein the cutter is configured such that the fluid exits the cutter in a continuous circumferential stream.

37. The apparatus of claim 20 , in combination with a seal bore provided in the string and wherein an external seal is provided on a cutter body between a flow passage inlet and the flow passage outlet for cooperating with the seal bore such that all of the cutting fluid pumped down the string is directed into the cutter.

38. A method of severing a drill string, the method comprising the steps of:

opening a bypass valve in a stuck string to bypass fluid pressure loss-inducing drill string elements below the bypass valve;

locating a flow-actuated cutter in the drill string; and

circulating fluid through the drill string to actuate the cutter and remove material from a selected portion of the drill string.

39. The method of claim 38 further comprising the steps of:

pumping the fluid from surface down through an internal bore defined by the drill string and through the cutter to actuate the cutter and remove material from the selected portion of a wall of the drill string; directing the fluid from the drill string bore and through the open bypass valve into an annulus between the drill string and a surrounding bore wall, and returning the fluid to surface.

40. The method of claim 38 , further comprising the step of severing the drill string into an upper portion and a lower portion.

41. The method of claim 40 , wherein, once the pipe string has been severed, further comprising the step of delivering cement into the bore through the upper portion of the string to form a kick-off plug above the lower portion of the string that remains in the bore.

42. The method of claim 40 , wherein, once the pipe string has been severed, further comprising the step of removing the lower portion of the string from the bore.

43. The method of claim 40 , further comprising the step of removing at least one device from the lower portion of the string.

44. The method of claim 40 , further comprising the steps of removing the upper portion of the string from the bore and running a further string run into the bore to at least one of engage and mate with the top of the lower section of the string that remains in the hole.

45. The method of claim 40 , further comprising the step of passing wireline equipped with a fishing tool through the further string and into the lower section of the tool.

46. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string; and

wherein the selected portion of the drill pipe string is a neck of a drill pipe connection and wherein removing material further comprises the step of reducing the loadbearing cross-sectional area of the neck by forming a circumferential cut.

47. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string;

providing the cutter with a constriction having a predetermined flow area and, prior to locating the cutter in the drill string, adjusting the size of the flow area with reference to at least one of: drill string hydraulics; fluid circulation equipment, and the size of particulates circulating in the fluid; and

adjusting the size of the flow area by the provision of at least one shim in the cutter.

48. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string;

providing a fluid bypass device in the string and opening the device to facilitate fluid circulation through the string; and

opening the fluid bypass device to bypass fluid pressure loss-inducing drill string elements below the bypass device.

49. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string;

providing a fluid bypass device in the string and opening the device to facilitate fluid circulation through the string; and

opening the fluid bypass device to bypass a packet off section of annulus between the drill string and a surrounding bore wall.

50. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string;

providing a fluid bypass device in the string and opening the device to facilitate fluid circulation through the string; and

opening the fluid bypass device after the drill pipe string has been severed and then pumping cement through the string and through the open bypass device to form a kick-off plug.

51. A method of severing a drill pipe string, the method comprising the steps of:

dropping or pumping a flow-actuated cutter into the drill pipe string;

landing the cutter at a predetermined location in the string;

pumping cutting fluid down through the drill pipe string and through a flow passage in the cutter defining at least one of a constriction and a nozzle to provide a high velocity outlet stream from the cutter and remove material from a selected portion of the drill pipe string; and

severing the string and at least one of: dropping the cutter out of the severed string, and opening a less restricted flow path through the string.

52. An apparatus for severing a drill pipe string, the apparatus comprising:

a flow-actuated cutter configured to be dropped or pumped into a drill pipe string and to land at a predetermined location in the string;

wherein circulating cutting fluid down through the drill pipe string actuates the cutter to remove material from a selected portion of the drill pipe string and wherein the cutter is configured such that the cutting fluid exits the cutter in a high velocity stream directed towards an inner surface of the string and the cutter defines at least one of a constriction and a nozzle to provide the high velocity stream at a flow passage outlet; and

a plurality of seats provided in the string and cooperating with a cutter locator.

53. An apparatus for severing a drill pipe string, the apparatus comprising:

a flow-actuated cutter configured to be dropped or pumped into a drill pipe string and to land at a predetermined location in the string;

wherein circulating cutting fluid down through the drill pipe string actuates the cutter to remove material from a selected portion of the drill pipe string and wherein the cutter is configured such that the cutting fluid exits the cutter in a high velocity stream directed towards an inner surface of the string and the cutter defines at least one of a constriction and a nozzle to provide the high velocity stream at a flow passage outlet;

in combination with a seat provided in the string and including a cutter locator, a profile dimensioned to engage the seat, the cutter locator and the seat being configured to engage and form a seal therebetween.

54. An apparatus for severing a drill pipe string, the apparatus comprising:

a flow-actuated cutter configured to be dropped or pumped into a drill pipe string and to land at a predetermined location in the string;

wherein circulating cutting fluid down through the drill pipe string actuates the cutter to remove material from a selected portion of the drill pipe string and wherein the cutter is configured such that the cutting fluid exits the cutter in a high velocity stream directed towards an inner surface of the string and the cutter defines at least one of a constriction and a nozzle to provide the high velocity stream at a flow passage outlet; and

a plurality of fluid bypass devices being provided for location in the drill sting, each associated with a particular severing location.

55. An apparatus for severing a drill pipe string, the apparatus comprising:

a flow-actuated cutter configured to be dropped or pumped into a drill pipe string and to land at a predetermined location in the string;

wherein circulating cutting fluid down through the drill pipe string actuates the cutter to remove material from a selected portion of the drill pipe string and wherein the cutter is configured such that the cutting fluid exits the cutter in a high velocity stream directed towards an inner surface of the string and the cutter defines at least one of a constriction and a nozzle to provide the high velocity stream at a flow passage outlet; and

the cutter being reconfigurable to allow the cutter to either drop out of the severed string or to open a less restricted flow path through the string.

56. An apparatus for severing a drill pipe string, the apparatus comprising:

a flow-actuated cutter configured to be dropped or pumped into a drill pipe string and to land at a predetermined location in the string;

wherein circulating cutting fluid down through the drill pipe string actuates the cutter to remove material from a selected portion of the drill pipe string and wherein the cutter is configured such that the cutting fluid exits the cutter in a high velocity stream directed towards an inner surface of the string and the cutter defines at least one of a constriction and a nozzle to provide the high velocity stream at a flow passage outlet; and

wherein the cutter further includes at least one shim and the flow passage outlet defines a flow area controlled by the at least one shim.

57. A method of severing a drill string, the method comprising the steps of:

opening a bypass valve in a stuck string to bypass a packed-off section of annulus between the drill string and a surrounding bore wall;

locating a flow-actuated cutter in the drill string; and

circulating fluid through the drill string to actuate the cutter and remove material from a selected portion of the drill string.