Wells – Processes – Operating valve – closure – or changeable restrictor in a well
Reexamination Certificate
2000-01-10
2001-06-12
Suchfield, George (Department: 3672)
Wells
Processes
Operating valve, closure, or changeable restrictor in a well
C166S088100, C166S088400
Reexamination Certificate
active
06244348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to well production systems, and in particular to a hydraulic seal and check valve between a tubing hanger and a wellhead member for providing hydraulic fluid to a hydraulically operated safety valve.
2. Description of the Prior Art
Downhole safety valves are often used in well production systems. These downhole safety valves are connected into the production tubing string and are designed to shut-off flow through the production tubing string in the case of a malfunction so as to avoid a blowout. Most downhole safety valves are hydraulically operated. Hydraulic pressure maintains the valve in the open position. Removal or interruption of the hydraulic pressure causes the safety valve to shut-off flow through the production tubing string.
A hydraulic line extends to the downhole safety valve from the surface to provide the safety valve with hydraulic fluid pressure. The hydraulic fluid line extends alongside the production tubing string. There are different techniques for connecting the hydraulic fluid line to the exterior of the wellhead or tree. In one type, the wellhead has an annular seal surface in its bore. The tubing hanger has a mating surface which mates with the annular seal surface. A number of hydraulic pas-sages extend through the wellhead and terminate at the seal surface in the bore for supplying hydraulic fluid for various purposes. Similarly, the tubing hanger has a number of hydraulic passages terminating at the mating surface. Seals are located at each of the ports to seal the interface when the tubing hanger lands.
When running the tubing and tubing hanger into the well, it is important to keep the hydraulic passages free of any debris. This can be a problem in the case of a subsea well where the tubing hanger is lowered through a riser in deep water. Also, when running the tubing string, it is necessary to keep the downhole safety valve in an open position, allowing well fluid to flow up the tubing. Otherwise, a pressure differential will exist above the downhole safety valve due to hydrostatic fluid in the well. This differential could cause the tubing to collapse.
In the prior art, the downhole safety valve is held in an open position by a mechanical sleeve that is placed in the valve as the valve is installed in the tubing string. After the tubing hanger has landed in the wellhead, the operator runs a retrieval tool through the tubing string on a wire line to latch into the sleeve and retrieve it, allowing the downhole safety valve to close. While this works well in most occasions, a possibility exists that the sleeve will stick and require the tubing to be pulled for removal of the sleeve.
SUMMARY OF THE INVENTION
In this invention, the tubing hanger has one or more ports at a mating surface for registering with wellhead ports. Seals are located at the tubing hanger ports to interface with the wellhead seal surface. A check valve is carried in each of the insert member ports. The check valve is biased to a closed position which closes the insert member port. This prevents the entry of debris into the hydraulic passage. The check valve has a plunger which engages the seal surface in the bore as the insert member lands in the bore and which moves the check valve to an open position. The check valve is encircled by the seal and protrudes slightly beyond the face of seal prior to landing of the tubing hanger in the wellhead.
Hydraulic fluid pressure is maintained at the downhole safety valve while the tubing is being run to keep the downhole safety valve in an open position. The hydraulic fluid pressure is introduced by securing an adapter to the check valve. Hydraulic fluid pressure passes through the check valve and into the hydraulic fluid pressure line leading to the downhole safety valve. Then, the check valve is moved to the closed position, trapping the hydraulic fluid pressure in the line leading to the downhole safety valve.
The check valve is moved to the closed position by use of a piston located within a chamber in the adapter. The piston divides the chamber into an inner portion and an outer portion. In one method of operation, the operator supplies pressure to the inner portion at a test level sufficient to open the check valve and the safety valve and to test the seals of the hydraulic circuit. The operator then supplies pressure to the outer portion at the same or greater level. Then the operator reduces the pressure in the inner chamber portion to a level less than the bias force of the check valve spring, but sufficient to keep the downhole safety valve open. The pressure differential moves the piston forward into contact with the check valve, keeping it open. The operator then removes the pressure in the outer portion, causing the piston to retract under the force of the bias spring in the check valve. The check valve closes, trapping pressure in the hydraulic line leading to the downhole safety valve.
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Brammer Norman
Gariepy James A.
McConaughy Brett Robert
Bracewell & Patterson LLP
Bradley James E.
Suchfield George
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