Patent Application
20060048945
The present invention relates generally to a subsea wellhead assembly interface, and more particularly to a high pressure seal that is formed between the tubing spool and a casing hanger connected to the wellhead.
In conventional subsea wellhead assemblies, a tubing spool connects the wellhead to the blowout preventor stack (“BOP”). As used herein, the terms “connect,” “connects,” and “connected,” are intended to mean either indirect or direction connection. Thus, if a first device “connects” to a second device, that connection may be through a direct connection or through an indirect connection via other devices or connectors. A gasket is in turn seated between the wellhead and the tubing spool to prevent the loss of pressure out of the system. The gaskets used in such systems are typically formed of solid metal rings and are designed to seal at 15,000 psi (15 ksi). For production pressures of 20 ksi, higher rated gaskets need to be used. Furthermore, an 18¾ inch (15 ksi) BOP is required to be used during drilling with wellhead assemblies that will experience production pressures of 20 ksi during production.
It has been desired to construct wellhead assemblies that can withstand 20 ksi production pressures without the need for BOPs as large as 18¾ inches. It is more commercially viable to develop a 13⅝ inch (20 ksi) BOP than a 18¾ inch (20 ksi) BOP. The present invention achieves the desired balance between being able to form a pressure seal that can withstand production pressures of 20 ksi and which can do so within a wellhead assembly that employs a 18¾ inch BOP during 15 ksi drilling and a 13⅝ inch BOP during 20 ksi production.
In one embodiment, the present invention is directed to a wellhead assembly. The wellhead assembly includes a casing hanger landed in and connected to a wellhead and a tubing spool disposed above and adjacent to the casing hanger. The wellhead assembly further includes means for sealing an end of the tubing spool to an opposing end of the casing hanger. In one embodiment, the sealing means includes a gasket disposed between the opposing ends of the tubing spool and casing hanger. In one embodiment, the gasket is formed of a tapered solid metal ring formed with a rib, which can be sized to accommodate variances in the tolerances of the wellhead, casing hanger and tubing spool.
In one embodiment, the wellhead assembly further includes an isolation sleeve coaxially disposed within the casing hanger and tubing spool. The wellhead assembly may further include a pair of isolation sleeve seal assemblies. One of the pair of isolation sleeve assemblies is disposed between the isolation sleeve and the casing hanger and the other of the pair of isolation sleeve seal assemblies is disposed between the isolation sleeve and the tubing spool.
In one embodiment, the wellhead assembly further includes a connector that connects the tubing spool to the casing hanger and applies a preload to the tubing spool and casing hanger. Also, in one embodiment, the wellhead assembly further includes a seal assembly disposed between an outer surface of the casing hanger and an inner surface of the wellhead.
A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings wherein:
The drawings are intended merely to depict representative embodiments and are not intended to be limiting of the present invention the scope of which is defined by the
The details of the present invention will now be described with reference to the accompanying drawings. Turning to
The plurality of nested casing pipes 14 include a conductor pipe 18, which is connected via a plurality of seals to an outside surface of the wellhead 12. The plurality of nested casing pipes 14 also include a surface casing pipe (not shown), which hangs from a casing hanger 20 that is connected via a seal assembly 22 to an inside surface of the wellhead 12. The plurality of nested casing pipes 14 further include a production casing 24, which in turn hangs from a casing hanger 26, which is connected to the inside surface of the wellhead 12, as best shown in
The tubing spool 16 in turn connects the 18¾ inch wellhead assembly 10 to a BOP stack (not shown), which in one certain embodiment is a 13⅝ inch diameter BOP stack. The tubing spool or spool 16 in one certain embodiment is formed of an 13⅝ inch inside diameter 20 ksi tubing.
An isolation sleeve 30 is disposed inside spool 16 and casing hanger 26. The isolation sleeve 30 has a pair of seal assemblies 32 and 34, which seal the lower end of the isolation sleeve to the inside surface of the casing hanger 26 and the upper end of the isolation sleeve to the inside surface of the spool 16, respectively. In one certain embodiment, the lower seal assembly 32 is formed of a metal-to-metal seal with resilient backup and the upper seal 34 is formed of a metal-to-metal seal. The seal assemblies 32 and 34 thus may also be of the type disclosed in U.S. Pat. No. 4,757,860.
The wellhead assembly 10 in accordance with the present invention further includes a seal means, which is disposed between opposing ends of the tubing spool 16 and casing hanger 26. In one embodiment, the sealing means includes a gasket 36. Together the opposing ends of the tubing spool 16 and casing hanger 26 and gasket 36 form a wellhead assembly interface according to the present invention. This interface is best illustrated in
The height of the gasket 36 can be varied depending upon the distance from the top of wellhead 12 to the top of the casing hanger 26. This is done as follows. Before the tubing spool 16 is run, the distance between the top of the wellhead 12 and the top of the casing hanger 26 would be measured. Then the correct height of the gasket 36 can be determined. Then a gasket 36 is made to the correct height. Alternatively, a set of pre-manufactured gaskets 36 of varying height are brought to the well site and the one with the correct height is selected and installed. The gasket 36 is installed so that the tubing spool 16 is preloaded to the casing hanger 26 when the gasket 36 is energized.
In one embodiment, the gasket 36 is attached to the tubing spool 16 using gasket retainer 41 and run in with the tubing spool 16. In an alternate embodiment, just prior to running the tubing spool 16, the gasket 36 can be placed on the casing hanger 26 using a remotely operated vehicle (ROV).
The present invention further includes a connector 42 that connects the tubing spool 16 to the casing hanger 26 and applies a preload to both components. In one exemplary embodiment, the connector 42 includes a latch ring 43, which in one certain embodiment is formed of a plurality of dog segments. The dog segments are arc-shaped members that are assembled end-to-end to form a ring. In one certain embodiment, six (6) such members are employed. In an alternate embodiment, the latch ring is formed of a C-ring.
The latch ring 43 includes a pair of upper and lower teeth 44 and 46. The upper teeth 44 of the latch ring 43 are designed to mate with and engage corresponding teeth formed on an outer surface of the tubing spool 16. The lower teeth 46 of the latch ring 43 are adapted to mate with and engage corresponding teeth formed at an upper end of the wellhead 12. An external force supplied by cam ring 50 (itself activated by pressurized fluid) forces the latch ring 43 to mate with and engage the corresponding teeth on the tubing spool 16 and wellhead 12. As the tapered surfaces of the teeth engage the wellhead 12 and tubing spool 16, the wellhead and tubing spool are forced axially closer to one another. Because the casing hanger 26 is rigidly connected to the wellhead 12, as the wellhead 12 is forced closer to the tubing spool 16, the opposing ends of the tubing spool 16 and casing hanger 26 are forced together. The gasket 36 disposed between the opposing ends of the tubing spool 16 and casing hanger 26 is thereby forced into compression, which in turn forms a fluid tight seal therebetween.
The setting of the isolation sleeve seals 32 and 34 and gasket seal 36 will now be described. First, after the wellhead 12 and casing hanger 26 have been installed but before the tubing spool 16 is run-in, the actual distance between the top of the casing hanger 26 and top of the wellhead 12 is measured. This can be done, e.g., using an ROV (not shown). Next, the height of the gasket 36 is selected based on this height. More specifically, the gasket 36 is sized so that the tubing spool 16 will land on rib 40 at approximately the same time it lands on top of the wellhead 12. In one certain embodiment, the height of the gasket 36 is also sized so that the gasket is preloaded between the tubing spool 16 and the casing hanger 26 to create a seal, which can withstand a pressure of approximately 20 ksi or greater. The gasket 36 can then be attached to the tubing spool 16 via gasket retainer 41 and run-in with the tubing spool 16, as described above. Alternatively, the tubing spool 16 can be run-in without the gasket 36 and the gasket can be installed in situ via the ROV prior to landing the tubing spool 16. Next, the gasket 36 can be set by preloading with the connector. Finally, the isolation sleeve 30 can be landed in the tubing spool 16 and casing hanger 26. The isolation sleeve seal assemblies 32 and 34 can be set using known techniques.
The combination of the upper and lower isolation sleeve assemblies 32 and 34, which serve as the primary 20 ksi seal, and the seal created by the gasket 36, which serves as the secondary 20 ksi seal, form a pressure barrier that prevents high pressure production fluid from leaking out of the wellhead assembly 10 into the subsea environment.
Therefore, the present invention is well-adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.
This application claims the benefit of U.S. Provisional Application No. 60/607,666 filed on Sep. 7, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60607666 | Sep 2004 | US |
