Downhole trigger apparatus

1. A downhole triggering tool, comprising:

a tool-engaging portion movable from a first position to a second position under the action of an external force; and

a release mechanism for selectively permitting movement of the tool-engaging portion from the first position to the second position, the tool engaging portion being restrained against the external force by the release mechanism through a force reducing mechanism.

2. The downhole triggering tool of claim 1 , wherein the force reducing mechanism reduces a magnitude of the external force by a sufficient amount to permit operation of the release mechanism.

3. The downhole triggering tool of claim 2 , wherein the force reducing mechanism comprises a series of levers.

4. The downhole triggering tool of claim 3 , wherein the series of levers is in the form of a rolling lever.

5. The downhole triggering tool of claim 1 , wherein the force reducing mechanism comprises a gear train.

6. The downhole triggering tool of claim 1 , wherein the tool-engaging portion includes a male portion receivable within a tool female portion.

7. The downhole triggering tool of claim 6 , wherein the male portion is in the form of a plug.

8. The downhole triggering tool of claim 1 , wherein the tool-engaging portion is a female portion receivable of a tool male portion.

9. The downhole triggering tool of claim 1 , wherein the tool-engaging portion defines a valve body engagable with a valve seat defined on a downhole tool to be actuated.

10. The downhole triggering tool of claim 1 , wherein the external force is well pressure.

11. The downhole triggering tool of claim 1 , wherein the external force is a biasing member.

12. The downhole triggering tool of claim 11 , wherein the biasing member is a spring.

13. The downhole triggering tool of claim 1 , wherein the release mechanism is activated from a remote location.

14. The downhole triggering tool of claim 1 , wherein the release mechanism is self-activated.

15. The downhole triggering tool of claim 14 , wherein the self-activated release mechanism responds to a change in an environmental condition.

16. The downhole triggering tool of claim 15 , wherein the self-activated release mechanism responds to an increase in well pressure.

17. The downhole triggering tool of claim 14 , wherein the release mechanism includes a timer mechanism that activates the release mechanism after a fixed period of time.

18. The downhole triggering tool of claim 17 , wherein the timer mechanism is a wind-up clock.

19. The downhole triggering tool of claim 18 , wherein the wind up clock is a 12-hour clock.

20. The downhole triggering tool of claim 17 , wherein the timer mechanism is an electronic timer.

21. The downhole triggering tool of claim 17 , wherein the output from the force reducing mechanism is a reduced force applied to a first lever, the first lever being part of the release mechanism.

22. The downhole triggering tool of claim 21 , wherein the timer mechanism moves to a position that permits the first lever to move to a release position, which in turn permits the tool-engaging portion to move to the second position.

23. A downhole tool, comprising:

a setting tool comprising a fluid actuated piston arrangement in selective fluid communication with a fluid source, and a downhole tool-engaging portion; and

a triggering tool comprising a setting tool-engaging portion movable from a first position to prevent fluid communication between the fluid source and piston arrangement of the setting tool, and a second position to permit fluid communication between the fluid source and piston arrangement, wherein the setting tool-engaging portion is moved under the action of an external force, the triggering tool further comprising a release mechanism for selectively permitting movement of the setting tool-engaging portion from the first position to the second position, the external force being transmitted to the release mechanism via a force reducing mechanism.