초록 ▼

A control system for a downhole tool, such as a subsurface safety valve, features an operating piston that is insensitive to tubing pressure in the valve. The hydrostatic forces from the single control line from the surface are significantly reduced with a branch line to a piston bottom that is slig

A control system for a downhole tool, such as a subsurface safety valve, features an operating piston that is insensitive to tubing pressure in the valve. The hydrostatic forces from the single control line from the surface are significantly reduced with a branch line to a piston bottom that is slightly smaller than the piston top. A variable volume between piston seals is connected to a low pressure compressible fluid reservoir to permit piston movement. The piston can be modular to facilitate assembly or bore offsets in the valve body. Failsafe closure upon seal failures is contemplated.

대표청구항 ▼

We claim: 1. A control system for a downhole valve operated from the surface, comprising: a housing having a though bore to contain tubing pressure and a valve member therein movable between an open and a closed position; a piston assembly, in a wall that forms said housing, having an upper and a l

We claim: 1. A control system for a downhole valve operated from the surface, comprising: a housing having a though bore to contain tubing pressure and a valve member therein movable between an open and a closed position; a piston assembly, in a wall that forms said housing, having an upper and a lower end and operably connected to said valve member; a first connection in said housing in fluid communication with said upper end of said piston assembly and a second connection in said housing in fluid communication with said lower end of said piston assembly, an always open passage between said first and second connections to provide offsetting forces on said piston assembly from pressure in said passage. 2. The system of claim 1, further comprising: a single control line from the surface connected to said passage. 3. The system of claim 1, wherein: said passage is at least in part exposed to pressure in said through bore. 4. The system of claim 1, wherein: said passage extends substantially in said wall of said housing. 5. A control system for a downhole valve operated from the surface, comprising: a housing having a though bore to contain tubing pressure and a valve member therein; a piston assembly, in a wall that forms said housing, having an upper and a lower end and operably connected to said valve member; a first connection in said housing in fluid communication with said upper end of said piston assembly and a second connection in said housing in fluid communication with said lower end of said piston assembly, a passage between said first and second connections to provide offsetting forces on said piston assembly from pressure in said passage; said upper and lower ends of said piston assembly have different diameters. 6. The system of claim 5, wherein: said piston assembly is disposed in upper and lower opposed and spaced bores and further comprises an upper bore seal and a lower bore seal exposed to tubing pressure. 7. The system of claim 6, wherein: said upper and lower bore seals exposed to tubing pressure are substantially the same dimension, making said piston assembly insensitive to tubing pressure. 8. The system of claim 7, wherein: said piston assembly comprises a control line pressure seal in said upper bore having a larger dimension than said upper bore seal. 9. The system of claim 8, wherein: said control line pressure seal and said upper bore seal define a first variable volume chamber in said upper bore, said first variable volume chamber containing a compressible fluid. 10. The system of claim 9, wherein: said first variable volume chamber in fluid communication with a larger reservoir. 11. The system of claim 10, wherein: said reservoir operates at least at atmospheric pressure. 12. The system of claim 10, wherein: said control line pressure seal defines a second variable volume chamber in said upper bore accessed through said first connection; said lower bore seal defines a third variable volume chamber in said lower bore accessed by said second connection. 13. The system of claim 12, wherein: said reservoir is in selective flow communication with said passage. 14. The system of claim 13, wherein: said selective flow communication between said reservoir and said passage comprises a pressure sensitive normally closed valve. 15. The system of claim 14, wherein: said normally closed valve comprises a rupture disc. 16. The system of claim 15, wherein: said piston assembly comprises two parts joined by a connector that can accommodate misalignment of said bores. 17. The system of claim 16, wherein: said piston assembly is operatively engaged, between said spaced bores, to a biased flow tube that is operably connected to said valve member that comprises a flapper. 18. The system of claim 10, wherein: said reservoir is at least as large as the volume of said first variable volume chamber. 19. The system of claim 12, wherein: failure of said lower bore seal puts said piston assembly in a position where said valve member is closed. 20. The system of claim 14, wherein: failure of said lower bore seal or said first or second connection pressurizes said passage and opens said pressure sensitive normally closed valve.