Drill string check valve

1. A drilling method comprising:

running a drill string into a bore with a flapper valve located towards a distal end of the string and above a drill bit mounted on the distal end of the string, with the flapper valve held in an open configuration by an axially extending valve retainer extending at least partially through the valve;

translating the valve retainer to a position beyond the valve into a catcher below the valve and above the drill bit, wherein the catcher receives and retains the valve retainer to permit the valve to assume a closed configuration and prevent flow up through the body; and then

drilling the bore while pumping fluid down through the string from surface to the drill bit.

2. The drilling method of claim 1 , comprising providing a tool in the string between the flapper valve and the drill bit, pumping fluid from the surface through the flapper valve and permitting communication via pressure pulses between the tool and the surface.

3. The drilling method of claim 2 , comprising communicating via pressure pulses between the tool and the surface while the flapper valve is held in the open configuration.

4. The drilling method of claim 2 , comprising communicating via pressure pulses between the tool and the surface while the flapper valve is permitted to assume the closed configuration.

5. The drilling method of claim 2 , wherein the tool comprises one or more of a mud motor, MWD tool and LWD tool.

6. The method of claim 1 , comprising pumping fluid through the open flapper valve.

7. The method of claim 1 , comprising translating an activating device down through the drill string to engage with the valve retainer and substantially occlude the string, creating a fluid pressure differential across the valve retainer, and utilising the fluid pressure differential to translate the valve retainer beyond the valve.

8. The method of claim 7 , comprising subsequently dissolving, degrading or eroding at least a portion of the activating device.

9. The method of claim 1 , comprising pumping fluid through the string and through or around the caught retainer to the drill bit.

10. The method of claim 1 , comprising providing two flapper valves and holding both valves open with the valve retainer.

11. The method of claim 1 , comprising locating a first valve in a body through a first end of the body and locating a second valve in the body through a second end of the body.

12. The method of claim 1 , comprising locating the valve in a body and axially translating the valve retainer into the valve and the body from one end of the body such that a leading end of the retainer moves the flapper to the open position as the retainer is advanced into the body.

13. The method of claim 1 , comprising incorporating the valve in a drilling bottom hole assembly (BHA) above an MWD tool.

14. Drill string check valve apparatus comprising:

a tubular body:

a flapper valve mounted in the body and having a flapper movable between an open position and a closed position;

an axially extending valve retainer mounted in the body and being translatable from a running position to a drilling position, in the running position the valve retainer extending at least partially through the valve to maintain the flapper in the open position, and in the drilling position the valve retainer permitting the flapper to move to the closed position to prevent flow up through the body, in the closed position the valve operating as a check valve, allowing fluid to be pumped down through the drill string from surface to a drill bit, but preventing flow in the opposite direction, wherein the valve retainer is configured to be translated beyond the valve to permit the valve to assume the closed configuration; and

a catcher located below the valve, for receiving and retaining the valve retainer.

15. The apparatus of claim 14 , wherein the valve retainer comprises a valve retainer member.

16. The apparatus of claim 15 , wherein the valve retainer member comprises a tubular member.

17. The apparatus of claim 16 , wherein the tubular member defines a substantially cylindrical outer surface.

18. The apparatus of claim 16 , wherein the tubular member defines a substantially cylindrical inner surface.

19. The apparatus of claim 14 , wherein the flapper is biased towards the closed position.

20. The apparatus of claim 14 , wherein the valve retainer maintains the valve in a fully open position, such that the open valve defines a substantially unobstructed bore.

21. The apparatus of claim 14 , in combination with an activating device configured to cooperate with the valve retainer and allow the retainer to be translated to the drilling position.

22. The apparatus of claim 21 , wherein the activating device is configured to be dropped or pumped from surface.

23. The apparatus of claim 21 , wherein the activating device is configured to facilitate application of a fluid pressure force to the valve retainer.

24. The apparatus of claim 23 , wherein the activating device is configured to engage with a seat on the valve retainer and substantially occlude the body.

25. The apparatus of claim 21 , wherein the activating device is configured to at least partially dissolve, degrade or erode.

26. The apparatus of claim 21 , wherein the activating device is configured to positively engage with the valve retainer.

27. The apparatus of claim 14 , wherein the valve retainer is releasably retained in the running position.

28. The apparatus of claim 27 , wherein the valve retainer is releasably retained in the running position by one or more releasable retainers.

29. The apparatus of claim 14 , wherein the catcher is configured to also receive and retain an activating device.

30. The apparatus of claim 14 , wherein the catcher is configured to provide a flow path around the caught retainer to permit fluid to be pumped down through the string from surface to a drill bit located below the apparatus on the drill string.

31. The apparatus of claim 14 , comprising more than one valve.

32. The apparatus of claim 14 , comprising two flapper valves.

33. The apparatus of claim 32 , wherein a single valve retainer maintains both valves open.

34. The apparatus of claim 14 , wherein the body includes a box-box tubular member.

35. The apparatus of claim 14 , wherein the body includes an internal shoulder and the apparatus is configured such that upwards pressure forces applied to a closed valve are transferred to the body via the shoulder.

36. The apparatus of claim 14 , wherein the apparatus is configured such that upwards pressure forces applied to a closed valve are held by an adjacent string element.

37. The apparatus of claim 14 , wherein the valve retainer comprises an assembly of a retaining member for extending through the valve and a mounting member for locating the retaining member in the body.

38. The apparatus of claim 37 , wherein the retaining member is releasably secured to the mounting member.

39. The apparatus of claim 37 , wherein the mounting member is configured to be retained in the body by an adjacent string element.

40. The apparatus claim 14 , wherein the valve retainer is configured to be axially translated into the valve and body from one end of the body, a leading end of the retainer moving the flapper to the open position as the retainer is advanced into the body.

41. A drilling bottom hole assembly (BHA) incorporating apparatus according to claim 14 , the apparatus being located above a drill bit.

42. The drilling BHA of claim 41 , wherein one or more of a mud motor, MWD tool and LWD tool is located between the apparatus and the drill bit.

43. Drill string check valve apparatus comprising:

a tubular body configured for location in a drill string above a drill bit:

tandem flapper valves mounted in the body, each valve having a flapper movable between an open position and a closed position;

a valve retainer mounted in the body and being translatable from a running position to a drilling position, in the running position the valve retainer extending at least partially through the valves to maintain the flappers in the open position, and in the drilling position the valve retainer permitting the flappers to move to the closed position, in the closed position the flappers operating as check valves, allowing fluid to be pumped down through the drill string from surface to the drill bit, but preventing flow in the opposite direction, wherein the valve retainer is configured to be translated beyond the valve to permit the valve to assume the closed configuration; and

a catcher located below the valve, for receiving and retaining the valve retainer.

44. A drilling method comprising:

running a drill string into a bore with tandem flapper valves located at a distal end of the string and above a drill bit mounted on the distal end of the string, with the flapper valves held in an open configuration by a valve retainer extending at least partially through the valves;

translating the valve retainer to a position beyond the valves into a catcher located below the valves and above the drill bit, wherein the catcher receives and retains the valve retainer to permit the valves to assume a closed configuration and prevent flow up through the body; and then

drilling the bore while pumping fluid down through the drill string from surface and through the flapper valves to the drill bit.