Patent Application
20140238699
1. Field of Invention
The present disclosure relates in general to a wellhead assembly having a seal between coaxial members, where wickers are formed on a surface of the seal.
2. Description of Prior Art
Seals are typically inserted between inner and outer wellhead tubular members to contain internal well pressure. The inner wellhead member is generally a hanger for supporting either casing or tubing that extends into the well. Outer wellhead members are usually one of a wellhead housing, or can be a casing hanger when the inner member is a tubing hanger. A variety of seals located between the inner and outer wellhead members are known. Examples of known seals are elastomeric, metal, and combinations thereof and elastomeric rings. The seals may be set by a running tool, or they may be set in response to the weight of the string of casing or tubing. One type of metal-to-metal seal has seal body with inner and outer walls separated by a cylindrical slot, forming a “U” shape. An energizing ring is pushed into the slot in the seal to deform the inner and outer walls apart into sealing engagement with the inner and outer wellhead members, which may have wickers formed thereon. The energizing ring is typically a solid member with a lower end having a wedge-shaped cross section. The deformation of the seal's inner and outer walls exceeds the yield strength of the material of the seal ring, making the deformation permanent.
Thermal growth between the casing or tubing and the wellhead may occur. The well fluid flowing upward through the tubing, and annulus fluids, heats the string of tubing, and to a lesser degree the surrounding casing. The temperature increase may cause the tubing hanger and/or casing hanger to move axially a slight amount relative to the outer wellhead member. During the heat up transient, annulus pressure may build up as the fluids comprising the volume below the seal try to expand. This annulus pressure build-up and thermal expansion of the casing and/or tubing string combine to exert a large upward axial force, often referred to as a “lockdown force”, against the annulus seal. If this force exceeds the retention capacity of the seal, the pressure controlling barrier between the inner and outer wellhead tubular members can be compromised. Seal leakage can also occur due to a collection of debris on the wickers that interferes with energizing the seal and introduces a leak path across the wickers.
A large axial load between the seal and its mating surfaces due to thermal transients may also cause the seal to leak. One approach to preventing this type of movement is through the use of lockdown C-rings on the seal. The C-rings engage the outer tubular member and/or the hanger when the seal is set, locking the seal to the hanger, as well as the hanger to the wellhead. Another approach has been to use the sealing element itself as a locking mechanism. In these approaches, lockdown as well as sealing is thus provided by the seal. Further, a lockdown style hanger may be utilized to lock the casing hanger in place. This requires an extra trip to install the lockdown style hanger.
Disclosed herein is an example of a seal assembly for use in a wellhead assembly which includes an annular seal body which is made up of an elongate inner leg, an elongate outer leg set radially outward from the inner leg, and an elongate slot defined between the inner and outer legs. Wickers are provided on a curved surface of the seal body and selectively engage a tubular surface within the wellhead assembly. The wickers can be on the inner leg, the outer leg, or on both legs. Optionally, the tubular can be a casing hanger, tubing hanger, or wellhead housing. The seal assembly can further include a protective foam layer adhered to the wickers.
Also disclosed herein is a wellhead assembly which includes inner and outer wellhead tubulars, an annulus between the inner and outer tubulars, and an annular seal in the annulus. In this example the annular seal is made up of an inner leg that is in selective sealing contact with the inner tubular, an outer leg that is in selective sealing contact with the outer tubular, a space between the inner and outer legs, and wickers on a circumference of a curved surface of the seal. In an example, the wickers are on an inner surface of the inner leg and project into an outer surface of the inner tubular. Optionally, the wickers can be on an outer surface of the outer leg and project into an inner surface of the outer tubular. In another example, wickers are on an inner surface of the inner leg and are on an outer surface of the outer leg. An inlay may be set in one of the inner and outer tubulars and strategically located for engagement with the wickers when the legs are in sealing contact with the tubulars. In one example the seal includes nickel alloy.
A method of sealing an annulus between an inner and outer tubular in a wellhead assembly is disclosed herein. In one example the method includes providing a seal assembly with an annular seal body with inner and outer legs, and with wickers that circumscribe a curved surface on the body, inserting the seal assembly into the annulus, and urging the inner and outer legs radially apart and into respective sealing engagement with an outer surface of the inner tubular and an inner surface of the outer tubular. The wickers can be on an outer surface of the outer leg and embed into the inner surface of the outer tubular during the step of urging the legs apart. In an alternative, the wickers can be on an inner surface of the inner leg and embed into the outer surface of the inner tubular when the legs are urged apart. The method can further involve removing the seal assembly from the wellhead assembly, applying a protective layer onto the wickers, and repeating the steps of inserting and urging apart.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.
It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.
Shown in
Inserted within annulus 20 is a seal assembly 22 shown urged into sealing contact with the respective outer and inner surfaces of intermediate casing hanger 14 and wellhead housing 18. An annular retaining ring 24 threadingly engages an upper end of the seal assembly 22 and annular energizing ring 26 is shown inserted within the seal assembly 22. Energizing Ring 26 urges inner leg 28 of the seal assembly 22 radially inward and against the intermediate casing hanger 14. Energizing ring 26 also urges outer leg 30 of seal assembly 22 radially outward against casing hanger 18. The seal assembly 22 is an annular member having a curved surface along its outer radius and inner radius. The legs 28, 30 are elongate members whose elongate sides extend in a direction substantially parallel with an axis AX of the seal assembly 22. Outer leg 30, which is shown into sealing contact with an inner surface of wellhead housing 18, further includes wickers 34 on its outer radial surface, and which extend an axial length on the outer radial surface.
When the seal assembly 22 is energized and outer leg 30 is urged radially outward, wickers 34 project radially outward and into the wellhead housing 18; a sealing surface is formed along the interface between the outer leg 30 and wellhead housing 18. The material of the seal assembly 22 is harder than material of the wellhead housing 18 so that the wickers 34 can penetrate and plastically deform the wellhead housing 18. An optional inlay 36 may be strategically located on the inner circumference of the wellhead housing, so the wickers 34 engage the inlay 36 when seal assembly 22 is energized. In this example, inlay 36 can be formed from a metal softer than wellhead housing 18 and the metal making p seal assembly 22. Example materials for the seal assembly include nickel-based alloys, such as Inconel® 718. In addition to providing a sealing interface between the seal assembly 22 and wellhead housing 18, engaging wickers 34 with wellhead housing 18 can also create a coupling which opposes axial respective movement between seal assembly 22 and wellhead housing that may be introduced by thermal expansion and other similar occurrences.
Referring now to
Referring back to
The wellhead assembly 10 is shown in
The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.
