Pressure actuable downhole tool and a method for actuating the same

1. A pressure actuable downhole tool comprising:

an actuator piston sealed in a chamber and axially movable in the chamber to actuate the pressure actuable downhole tool on exposure of the actuator piston to a predetermined pressure;

a communication line extending from a throughbore to an opening in the chamber to transmit a downhole fluid pressure to the actuator piston;

a trigger piston moveable between a first configuration in which the communication line is substantially fluidly isolated from the chamber and the actuator piston and a second configuration which permits fluid communication along the communication line to activate the actuator piston; and

a control line radially spaced form the throughbore, the control line having an opening to the chamber to selectively deliver pressurized driving fluid into the chamber to drive the actuator piston.

2. The pressure actuable downhole tool of claim 1 , wherein the trigger piston is selectively actuable to selectively move the actuator piston in order to actuate the pressure actuable downhole tool.

3. The pressure actuable downhole tool of claim 1 , wherein at least part of the pressure actuable downhole tool comprises seals to substantially fluidly isolate the communication line in the first configuration.

4. The pressure actuable downhole tool of claim 1 , wherein the actuator piston has at least two seal assemblies, axially spaced from one another along the actuator piston to seal the actuator piston within the chamber, and wherein the seal assemblies are located on either side of the communication line within the chamber to substantially fluidly isolate the communication line.

5. The pressure actuable downhole tool of claim 4 , wherein the trigger piston is selectively actuable to move the actuator piston from the first to the second configuration by moving the actuator piston by a predetermined length such that both of the seal assemblies locate on one side of the communication line.

6. The pressure actuable downhole tool of claim 1 , wherein the opening of the control line within the chamber is axially spaced from the opening of the communication line in the chamber.

7. The pressure actuable downhole tool of claim 1 , wherein the trigger piston and the actuator piston are both sealed in the same chamber, and wherein the trigger piston is located in the chamber between the opening of the control line in the chamber and the opening of the communication line in the chamber.

8. The pressure actuable downhole tool of claim 7 , comprising a trigger piston stop to restrain movement of the trigger piston within an area of the chamber defined between the opening of the communication line in the chamber and the opening of the control line in the chamber.

9. The pressure actuable downhole tool of claim 7 , wherein the trigger piston is movable in response to the supply of hydraulic fluid through the opening of the control line in the chamber.

10. The pressure actuable downhole tool of claim 1 , wherein the trigger piston is spaced axially from the actuator piston.

11. The pressure actuable downhole tool of claim 1 , wherein respective positions of the actuator piston in the first and second configurations are spaced apart from one another, and the actuator piston is moved axially for a distance between the retrospective positions before actuating the pressure actuable downhole tool in the second configuration.

12. The pressure actuable downhole tool of claim 1 , wherein the pressure actuable downhole tool is selected from the group consisting of:

packers;

inflatable elements;

gripping tools;

slips;

valves;

sliding sleeves; and

other flow control devices.

13. The pressure actuable downhole tool of claim 1 , wherein the actuator piston has a locking mechanism to restrict movement of the actuator piston in the second configuration.

14. The pressure actuable downhole tool of claim 1 comprising, wherein the pressure actuable downhole tool has a locking mechanism to restrict movement from the second configuration to the first configuration.

15. A method of actuating a pressure actuable downhole tool having a throughbore, the method comprises:

(a) providing a pressure responsive actuator piston sealed in a chamber, wherein the pressure responsive actuator piston is arranged to move axially in the chamber, providing a communication line communicating downhole pressure to the pressure responsive actuator piston, wherein the communication line extends from the throughbore to the chamber transmitting fluid pressure from the throughbore to the chamber, and providing a trigger piston moveable between a first configuration in which the communication line is substantially fluidly isolated and a second configuration which permits fluid communication along the communication line to activate the pressure responsive actuator piston;

(b) substantially fluidly isolating the communication line in the first configuration;

(c) running the downhole tool;

(d) actuating the trigger piston to selectively deliver a supply of pressurized driving fluid into the chamber through a control line to move the pressure responsive actuator piston within the chamber, and thereby move the trigger piston, and thereby allowing downhole fluid pressure to activate the pressure responsive actuator piston via the communication line, wherein the control line is spaced from the throughbore; and

(e) actuating the downhole tool.

16. The method of claim 15 , wherein the method includes:

increasing fluid pressure within the throughbore; and using the increased the downhole fluid pressure from the throughbore to actuate the downhole tool via the communication line.

17. The method of claim 15 , wherein the method includes:

supplying pressure through the control line to move the trigger piston against the pressure responsive actuator piston.