Downhole tool utilizing opposed pistons

Abstract

A subsurface safety valve has a tubular valve housing, a valve closure member movable between an open and a closed position, an axially movable opening flow tube for opening the valve closure member. Hydraulic pressure from a control line is used to move a first piston, which in turn moves the axially movable opening prong through the closure member. A balance line can be used to provide a hydrostatic pressure against a second piston. The first and second pistons are coupled to a sliding member within the valve housing. Thus, the opposed piston arrangement substantially offsets any downward force on the first piston.

We claim:  
     
         1 . A downhole tool having an element movable by a piston force between a first and second position comprising: 
 (a) a valve housing;    (b) a first piston movable within the housing;    (c) a second piston movable within the housing,    wherein the first and second pistons are coupled to each other.    
     
     
         2 . The downhole tool of  claim 1  further comprising: 
 (d) a valve closure member captured in the housing and movable between an open and closed position;  
 (e) an axially shiftable flow tube captured in the housing for opening the valve closure member.  
 
     
     
         3 . The downhole of  claim 1  wherein the first piston is coupled to a control line.  
     
     
         4 . The downhole tool of  claim 3  wherein the second piston is coupled to a balance line.  
     
     
         5 . The downhole tool of  claim 2  further comprising: 
 (f) a spring within the housing and opposing the motion of the axially shiftable flow tube.  
 
     
     
         6 . The downhole tool of  claim 1  wherein the first and second pistons are coupled to a movable member.  
     
     
         7 . The downhole tool of  claim 1  further comprises first and second control lines coupled to a surface pressure source.  
     
     
         8 . The downhole tool of  claim 4  wherein the valve housing comprises a first and second piston chamber for capturing the first and second pistons, and wherein the control line and balance line are coupled to the valve housing to move the pistons in opposite directions.  
     
     
         9 . The downhole tool of  claim 4  wherein the valve housing comprises a first and second piston chamber for capturing the first and second pistons, and wherein a hydrostatic pressure is applied by the balance line to the second piston which is substantially equal and offsetting to a hydrostatic pressure applied by the control line to the first piston.  
     
     
         10 . A method of operating a downhole tool placed in the flow path of a well tubing string within a well, comprising the steps of: 
 (a) coupling a control line to a first piston chamber having a first piston;    (b) coupling a balance line to a second piston chamber having a second piston; and    (c) coupling both the first and second pistons to a movable member.    
     
     
         11 . The method of  claim 10  further comprising: 
 (d) supplying a substantially equal hydrostatic pressure through both the control line and the balance line.  
 
     
     
         12 . The method of  claim 10  further comprising: 
 (d) supplying a sufficient pressure through the control line to move the first piston downward.  
 
     
     
         13 . The method of  claim 12  further comprising: 
 (e) overcoming an opposing spring force; and  
 (f) forcing an opening prong through a closure member.  
 
     
     
         14 . A safety valve for use in a well comprising: 
 (a) a valve housing;    (b) a first piston movable within the housing;    (c) a second piston movable within the housing; wherein the first and second pistons are coupled to each other;    (d) a valve closure member captured in the housing and movable between an open and closed position;    (e) an axially shiftable flow tube captured in the housing for opening the valve closure member.    
     
     
         15 . The safety valve of  claim 14  wherein the first piston is coupled to a control line.  
     
     
         16 . The safety valve of  claim 14  wherein the second piston is coupled to a balance line.  
     
     
         17 . The safety valve of  claim 14  wherein the valve housing comprises a first and second piston chamber for capturing the first and second pistons, and wherein the control line and balance line are coupled to the valve housing to move the pistons in opposite directions.  
     
     
         18 . The safety valve of  claim 14  wherein the valve housing comprises a first and second piston chamber for capturing the first and second pistons, and wherein a hydrostatic pressure is applied by the balance line to the second piston which is substantially equal and offsetting to a hydrostatic pressure applied by the control line to the first piston.