Removable Control Line Barrier

Abstract

A hydraulically operated downhole tool located at a depth where control line hydrostatic pressure would normally set the tool is temporarily isolated from hydrostatic pressure and changes thereto from well exposure or downhole operations until properly located. A removable barrier is placed in the control line to the tool at a height from the tool that limits the hydrostatic force exposed to the actuation mechanism for the tool. The preferred barrier is a rupture disc that is selectively broken with applied pressure from a remote location, typically the surface above the well. The mounting depth of the barrier can be varied to control the maximum hydrostatic pressure seen by the tool as it is advanced to the intended position.

We claim: 
     
         1 . An operating assembly for a borehole tool, comprising:
 a hydraulically actuated tool supported on a tubular string for placement at a predetermined depth;   a control line extending to an actuator for said tool, said actuator operating the tool with a predetermined pressure lower than hydrostatic pressure in said control line with said tool at said predetermined depth;   a barrier in said control line that when closed limits hydrostatic pressure on said actuator to below said predetermined pressure as said tool is delivered to said predetermined depth;   said barrier selectively defeated after said tool reaches said predetermined depth.   
     
     
         2 . The assembly of  claim 1 , wherein:
 said barrier comprises at least one rupture disc.   
     
     
         3 . The assembly of  claim 1 , wherein:
 said barrier is located on said control line to take thermal effects on hydrostatic pressure into account to avoid setting said tool with control line hydrostatic pressure before and when the tool reaches said predetermined depth.   
     
     
         4 . The assembly of  claim 1 , wherein:
 said barrier is located on said control line to take into account reduction in tubing reference pressure to said actuator from said tubing when connecting an upper assembly to a lower assembly where said tool is mounted with a wet connect.   
     
     
         5 . The assembly of  claim 1 , wherein:
 said tool comprises at least one of a packer, bridge plug, anchor or valve.   
     
     
         6 . The assembly of  claim 1 , wherein:
 said tool is located at least  4000  meters deep in said borehole.   
     
     
         7 . The assembly of  claim 1 , wherein:
 said barrier is broken with pressure from a surface location for the borehole.   
     
     
         8 . The assembly of  claim 1 , wherein:
 said barrier comprises a remotely operated valve.   
     
     
         9 . The assembly of  claim 8 , wherein:
 said valve is remotely operated from a surface location.   
     
     
         10 . The assembly of  claim 9 , wherein:
 said valve is signaled to open acoustically or with pressure pulses or with an electromagnetic field.   
     
     
         11 . The assembly of  claim 1 , wherein:
 said barrier is broken explosively.   
     
     
         12 . A method of operating a hydraulically actuated borehole tool using a control line, comprising;
 locating the tool at a predetermined depth where hydrostatic pressure in the control line exceeds the pressure in the control line needed for tool actuation;   preventing tool actuation when moving the tool to said predetermined depth by locating a barrier in the control line to keep the hydrostatic pressure between the tool and the barrier below the needed actuation pressure for the tool;   removing the barrier to actuate the tool.   
     
     
         13 . The method of  claim 12 , comprising:
 providing a rupture disc as said barrier.   
     
     
         14 . The method of  claim 12 , comprising:
 locating said barrier to allow a margin of safety with the developed hydrostatic pressure to remain below the pressure that sets the tool from thermal effects in the borehole.   
     
     
         15 . The method of  claim 12 , comprising:
 locating said barrier to compensate for reduction of reference pressure for an actuation system for the tool by a decrease in tubing pressure seen during engagement of a wet connect.   
     
     
         16 . The method of  claim 12 , comprising:
 breaking said barrier with pressure from the surface of the borehole.   
     
     
         17 . The method of  claim 12 , comprising:
 providing a remotely actuated valve as said barrier.   
     
     
         18 . The method of  claim 17 , comprising:
 actuating said valve with pressure pulses or acoustics or an electromagnetic field.