Actuating mechanism
An actuating mechanism for use in a tool such as a plug used in oil and gas wells. The mechanism being operable under pressure in the well bore to set the plug in a first natural closed state for a pressure under a predetermined pressure range; a second closed state wherein the plug is locked closed regardless of the pressure; and a third open state by increasing the pressure to the predetermined pressure range and holding the pressure in the range for a predetermined time. Electronic and mechanical, dual piston, actuating mechanisms are described as is a method of controlling fluid flow in a well bore using the plug and performing a pressure test against the plug.
1. An actuating mechanism for operating a tool used in a well bore, the mechanism comprising first and second pistons; the first piston including a damping element for delaying movement of the first piston relative to the second piston under an applied pressure; the second piston acting on a retaining element; the retaining element adapted to hold the second piston in an intermediate position when the applied pressure is within a predetermined range and allow movement of the first piston to a final position; the retaining element allowing the second piston to move to a secondary position when the applied pressure is above the predetermined range; a locking element which prevents movement of the first piston when the second piston is in the secondary position; an actuating member whose movement operates the tool; and a securing element for retaining the actuating member in a first position until released by virtue of the first piston reaching the final position, whereby the actuating member moves to a second position and operates the tool.
2. An actuating mechanism as claimed in claim 1 wherein the first and second pistons include substantially conical drive faces with apexes directed towards the applied pressure.
3. An actuating mechanism as claimed in claim 1 wherein the damping element is a fluid metering device.
4. An actuating mechanism as claimed in claim 3 wherein the fluid metering device comprises a fluid filled chamber through which the first piston passes and a portion of the first piston includes a restrictor to regulate fluid flow between upper and lower compartments of the chamber.
5. An actuating mechanism as claimed in claim 4 wherein a pressure balance piston is located in the chamber, around the first piston so as to control the size of the chamber in order to compensate for thermal effects and pressure differences between inside and outside the chamber.
6. An actuating mechanism as claimed in claim 1 wherein the retaining element is a spring.
7. An actuating mechanism as claimed in claim 6 wherein the retaining element is a collet.
8. An actuating mechanism as claimed in claim 1 wherein the locking element is a sleeve such that the retaining element and the locking element engage to control movement of the pistons.
9. An actuating mechanism as claimed in claim 1 wherein the actuating member is a sleeve and the securing element is one or more locking keys which engage with the sleeve.