Pressure Compensator for Hydrostatically-Actuated Packers

Abstract

Devices and methods for operating a tool within a wellbore. A downhole tool includes a tool operation portion having a moveable tool member and a setting portion having a setting piston and setting chamber. A fluid pressure compensation reservoir is in fluid communication with the setting chamber and containing a pressurized fluid which offsets external hydrostatic pressure.

1 . A tool for operation within a wellbore comprising:
 a tool operation portion having a moveable tool member;   a setting portion comprising:
 a primary setting piston operably associated with the tool member such that movement of the setting piston in response to absolute well pressure moves the tool member; 
 a setting chamber associated with the primary setting piston to release the primary setting piston to move the tool member; 
 a fluid pressure compensation reservoir in fluid communication with the setting chamber and containing a pressurized fluid to offset hydrostatic pressure within the wellbore. 
   
   
   
       2 . The tool of  claim 1  further comprising a fluid communication port disposed between the setting chamber and an annulus of the wellbore, the port being releasably closed to selectively block fluid flow between the annulus and the setting chamber. 
   
   
       3 . The tool of  claim 1  wherein the tool operation portion comprises a packer assembly and the tool member comprises a packer element. 
   
   
       4 . The tool of  claim 1  further comprising a backup setting piston that is actuated by hydraulic pressure from a central flowbore to move the tool member. 
   
   
       5 . The tool of  claim 1  wherein the fluid pressure compensation reservoir is filled with pressurized nitrogen. 
   
   
       6 . The tool of  claim 1  wherein the fluid compensation reservoir is pressurized to a level of pressure above atmospheric pressure. 
   
   
       7 . The tool of  claim 1  further comprising a locking dog disposed within the setting chamber, the locking dog releasably securing the primary setting piston to a central mandrel and releasing the primary setting piston from the central mandrel portion when the setting chamber is filled with fluid from the annulus. 
   
   
       8 . The tool of  claim 7  further comprising a lock sleeve associated with the locking dog, the lock sleeve being moveable within the setting chamber in response to the setting chamber being filled with fluid from the annulus. 
   
   
       9 . The tool of  claim 2  wherein the fluid communication port is releasably blocked by a frangible rupture member. 
   
   
       10 . A packer assembly for use in creating a seal within a wellbore, the packer assembly comprising:
 a central mandrel defining a central flowbore along its length;   a packer assembly surrounding the central mandrel and axially compressible to selectively form a fluid seal with a surrounding wellbore wall;   a primary setting portion for selectively axially compressing the packer assembly, the setting assembly comprising:
 a primary setting piston operably associated with the packer assembly such that movement of the primary setting piston with respect to the central mandrel compresses the packer assembly, the primary setting piston being moveable in response to absolute well pressure; 
 a setting chamber associated with the setting piston such that filling of the setting chamber with fluid will free the primary setting piston to move with respect to the central mandrel; and 
 a fluid pressure compensation reservoir in fluid communication with the setting chamber and containing a fluid that is pressurized at a pressure greater than atmospheric pressure. 
   
   
   
       11 . The packer assembly of  claim 10  further comprising a fluid communication port disposed between the setting chamber and an annulus of the wellbore, the port being releasably closed to selectively block fluid flow between the annulus and the setting chamber. 
   
   
       12 . The packer assembly of  claim 10  further comprising a set of anchoring slips associated with the setting portion to be set by movement of the setting piston. 
   
   
       13 . The packer assembly of  claim 10  wherein the fluid within the compensation reservoir comprises nitrogen. 
   
   
       14 . The packer assembly of  claim 10  further comprising a backup setting piston that actuated by hydraulic pressure from the central flowbore to set the packer assembly. 
   
   
       15 . The packer assembly of  claim 10  wherein the fluid communication port is releasably closed by a frangible rupture member. 
   
   
       16 . A method of operating a tool within a wellbore, comprising the steps of:
 a) providing a tool for operation within a wellbore, the tool comprising:
 a tool operation portion having a settable tool member; 
 a primary setting portion comprising:
 a primary setting piston operably associated with the tool member such that movement of the setting piston sets the tool member, the primary setting piston being moveable in response to absolute well pressure; 
 a setting chamber associated with the primary setting piston such that filling of the setting chamber with fluid will free the primary setting piston to move to set the tool member; 
 a fluid pressure compensation reservoir in fluid communication with the setting chamber; and 
 
   b) filling the fluid pressure compensation reservoir with a fluid that is pressurized at a pressure above atmospheric pressure;   c) disposing the tool within a fluid-filled wellbore;   d) lowering the tool to a desired depth for operation; and   3) moving the primary setting piston under impetus of absolute well pressure to set the tool member.   
   
   
       17 . The method of  claim 16  wherein the tool operation portion comprises a packer assembly and the tool member comprises a packer element. 
   
   
       18 . The method of  claim 16  wherein the fluid pressure compensation chamber is filled with nitrogen. 
   
   
       19 . The method of  claim 16  wherein a fluid communication port to permit fluid access to the setting chamber is releasably closed by a rupture member that is ruptured by absolute well pressure. 
   
   
       20 . The method of  claim 19  wherein the rupture member is ruptured by pressurizing the surrounding wellbore from the surface. 
   
   
       21 . The method of  claim 16  further comprises the step of flowing wellbore fluid into the setting chamber to free the primary setting piston. 
   
   
       22 . The method of  claim 21  wherein the step of flowing wellbore fluid into the setting chamber further comprises the step of moving a lock sleeve with the wellbore fluid to release the primary setting piston to be moved by absolute well pressure. 
   
   
       23 . The method of  claim 16  further comprising the step of actuating a backup setting piston to set the tool member.