Pressure operated apparatus and method

1. A downhole pressure operated apparatus, comprising:

a piston member mounted within a piston bore and being reconfigurable from a lock configuration to an unlock configuration in response to a pressure sequence applied within the piston bore, wherein the piston member comprises a lock profile; and

a lock member arranged in a cavity which opens into the piston bore, wherein when the piston member is in the lock configuration the lock member is supported by the piston member such that the lock member partially extends into the piston bore and engages the lock profile of the piston member to restrict movement of the piston member in a first direction towards the unlock configuration,

wherein in response to a first pressure event of the pressure sequence the piston member is moveable in a second direction to desupport the lock member and permit said lock member to be wholly received into the piston bore and allow the piston member to move in the first direction towards the unlock configuration in response to a subsequent second pressure event of the pressure sequence.

2. The downhole pressure operated apparatus according to claim 1 , wherein the first and second pressure events collectively define a pressure cycle of the pressure sequence.

3. The downhole pressure operated apparatus according to claim 1 , wherein at least one of the first pressure event and the second pressure event comprises pressure modified within the piston bore on at least one side of the piston member and being configured to cause a variation in a pressure differential across the piston member.

4. The downhole pressure operated apparatus according to claim 1 , wherein the first pressure event comprises one of increasing or decreasing pressure within the piston bore, and the second pressure event comprises the other of increasing or decreasing the pressure within the piston bore.

5. The downhole pressure operated apparatus according to claim 1 , comprising a plurality of the lock members located within the cavity, wherein, in use, the lock members sequentially engage and release the piston member in response to multiple sequential ones of the pressure events applied within the piston bore until a final lock member of the plurality of lock members is wholly received into the piston bore, allowing the piston member to move in the first direction towards the unlock configuration.

6. The downhole pressure operated apparatus according to claim 5 , wherein, in use, a first lock member of the plurality of lock members is initially supported by the piston member such that the first lock partially extends into the piston bore and engages the lock profile of the piston member to restrict movement of the piston member in the first direction towards the unlock configuration, and in response to the first pressure event applied within the piston bore the piston member is moveable in the second direction to desupport the first lock member and permit said first lock member to be wholly received into the piston bore, and in response to the second pressure event applied within the piston bore the piston member is moveable in the second direction until a second lock member of the plurality of lock members becomes supported by the piston member such that the second lock member partially extends into the piston bore and engages the lock profile of the piston member to restrict movement of the piston member in the first direction towards its the unlock configuration.

7. The downhole pressure operated apparatus according to claim 5 , comprising a restrictor being configured to prevent multiple ones of the lock members from being received into the piston bore during a single movement of the piston member in response to a single one of the pressure events in the piston bore.

8. The downhole pressure operated apparatus according to claim 1 , wherein the lock profile of the piston member comprises:

an axial lock surface which axially engages the lock member to restrict axial movement of the piston member in the first direction; and

a radial support surface which supports the lock member in a position which is partially extended into the piston bore, wherein movement of the piston member in the second direction misaligns the lock member from the radial support surface, allowing the lock member to be desupported and wholly received within the piston bore.

9. The downhole pressure operated apparatus according to claim 1 , wherein the piston bore is connectable to at least one of i) an internal volume of a tubing string, such that pressure within the tubing string is applied within the piston bore, and ii) a wellbore annulus region, such that pressure within the wellbore annulus region is applied within the piston bore.

10. The downhole pressure operated apparatus according to claim 1 , wherein the piston member is biased by a biasing force in one of the first and second directions, such that a pressure applied within the piston bore acts together with the biasing force to facilitate movement of the piston member in the first and second directions, and wherein in a first operation a first of the pressure applied within the piston bore establishes a force on the piston member to overcome the biasing force and thus cause movement of the piston member in the desired direction.

11. The downhole pressure operated apparatus according to claim 1 , comprising a control which facilitates controlled communication of a medium between opposing first and second sides of the piston member, such that the same medium is used as both a medium to apply the pressure event within the piston bore on the first side of the piston member while at the same time providing a biasing force on the opposite second side of the piston member.

12. The downhole pressure operated apparatus according to claim 11 , wherein the control comprises a first flow path comprising a fluid restriction which permits at least one of:

the opposing first and second sides of the piston member to become pressure balanced in a static mode of operation; and

a back pressure to be generated on one of the first and second sides of the piston member during a dynamic mode of operation in which the medium flows through the fluid restriction in a first flow direction from the first side to the second side of the piston member, such that the back pressure permits the pressure on the first side of the piston member to be elevated above the pressure on the second side of the piston member to establish a pressure differential to move the piston member.

13. The downhole pressure operated apparatus according to claim 12 , wherein the medium is compressible to permit movement of the piston member when the pressure differential is present.

14. The downhole pressure operated apparatus according to claim 12 , wherein the control comprises a second flow path comprising a one way valve which permits flow therethrough in a second flow direction from the second side of the piston member to the first side to provide relief of fluid from the second side of the piston member.

15. The downhole pressure operated apparatus according to claim 1 , wherein the piston member is mounted within the piston bore to define first and second chambers, and wherein the lock member is received within one of the first and second chambers during reconfiguring of the piston member in response to the pressure sequence.

16. The downhole pressure operated apparatus according to claim 1 , wherein the piston member defines at least one of a mechanical lock and a valve member.

17. The downhole pressure operated apparatus according to claim 1 , wherein a fluid isolation provided when the piston member is in the lock configuration maintains a hydraulic lock in one of a first and second fluid zones, with the hydraulic lock released when the piston member is configured in the unlock configuration.

18. A downhole method, comprising:

providing a piston member of a pressure operated apparatus in an initial lock configuration within a piston bore, wherein said piston member is retained in said lock configuration by a lock member which is supported by the piston member such that the lock member partially extends into the piston bore and engages a lock profile of the piston member to restrict movement of the piston member in a first direction towards an unlock configuration;

establishing a first pressure event within the piston bore to move the piston member in a second direction to desupport the lock member and permit said lock member to be wholly received into the piston bore; and

establishing a second pressure event within the piston bore to move the piston member in the first direction towards the unlock configuration and facilitate an associated operation.

19. The method according to claim 18 , comprising providing multiple of the lock members which sequentially engage and retain the piston member in the lock configuration upon applying multiple pressure cycles comprising the first and second pressure events within the piston bore, until a final lock member of the lock members is wholly received into the piston bore, allowing the piston member to move in the second direction towards the unlock configuration.

20. A pressure operated apparatus, comprising:

a piston member mounted within a piston bore and being reconfigurable from a lock configuration to an unlock configuration to facilitate an associated operation; and

a plurality of lock members, arranged to sequentially restrict movement of the piston member towards the unlock configuration,

wherein the piston member is reciprocally moveable within the piston bore in response to sequential pressure events applied within the piston bore to sequentially move the lock members from a first retaining position to a second release position, until all of the lock members are moved to the second release position to permit the piston member to be reconfigured to the unlock position,

wherein a first of the sequential pressure events moves the piston member in a second direction, and a second of the sequential pressure events moves the piston member in a first direction; and

wherein the first and second sequential pressure events collectively define a pressure cycle of the pressure sequence.