Patent Application
20170284165
This disclosure relates in general to metal-to-metal wellhead seals, and in particular to an energizing ring for deforming a seal ring into a set position, the energizing ring having inner and outer diameter surfaces containing reliefs to prevent fluid from being trapped in wickers in the wellhead and hanger.
One type of subsea well has a wellhead housing at the sea floor. One or more casing hangers land in the bore of the wellhead housing, each secured to an upper end of a string of casing. After cementing the casing, a running tool sets a packoff or seal between the casing hanger and the wellhead housing.
One type of packoff has a metal ring with inner and outer legs separated by an annular slot. The running tool pushes an energizing ring into the slot, which radially deforms the inner and outer legs into sealing engagement with the wellhead housing and the casing hanger. One or both of the seal surfaces in the wellhead housing and on the casing hanger may have a set of wickers. The wickers are parallel grooves, each having a sharp crest. The sharp crests of the wickers embed into the seal ring surface when set with the energizing ring.
The wellhead housing will be filled with a liquid, which may be drilling fluid, before the seal ring sets. When the seal ring wall moves radially into engagement with the wickers, some of the liquid may be trapped in the wickers, forming a hydraulic lock. The trapped liquid can result in high pressure build up in the wickers, which restricts the depth that the wickers embed into the seal ring. The lesser depth or engagement can reduce the effectiveness of the seal ring.
A wellhead seal assembly comprises a metal seal ring having annular inner and outer legs separated by an annular slot. An energizing ring inserts into the slot, the energizing ring having inner and outer diameter surfaces that extend upward from a lower end of the energizing ring. The inner and outer diameter surfaces engage the inner and outer legs of the seal ring to radially deform the inner and outer legs when the energizing ring is moved downward in the slot to a set position. At least one partially circumferential relief is on at least one of the inner and outer diameter surfaces of the energizing ring. The relief extends upward from the lower end a selected distance less than an axial dimension of the inner and outer diameter surface.
Because of the relief, the energizing ring does not deform part of the seal ring as much as other parts, preventing sealing engagement of a lower section of the seal ring with the wickers. The relieved area allows trapped liquid to flow out of the wickers during the setting process.
The relief may be located on the outer diameter surface, the inner diameter surface, or both. In the embodiment shown, at least one relief comprises an outer diameter relief on the outer diameter surface and an inner diameter relief on the inner diameter surface. The inner and outer diameter reliefs are located adjacent each other at a same angular position on the energizing ring. In the embodiment shown, there are two inner diameter reliefs and two outer diameter reliefs circumferentially spaced apart from each other.
The relief is a machined groove having a base surface that tapers upward from the lower end of the energizing ring, relative to the axis. In the embodiment shown, the relief has a curved upper edge. A circumferential length of the relief is greater than an axial dimension of the relief from the lower end of the energizing ring to a midpoint of the curved upper edge.
So that the manner in which the features, advantages and objects of the disclosure, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the disclosure briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the disclosure and is therefore not to be considered limiting of its scope as the disclosure may admit to other equally effective embodiments.
The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems 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.
Referring to
A casing hanger 17 secured to an upper end of a string of casing (not shown) lands on a shoulder in the bore of wellhead housing 11. Casing hanger 17 has a cylindrical outer seal surface 18 spaced radially inward from wellhead housing seal surface 13. In this example, outer seal surface 18 also has a set of wickers 19. Wickers 19 may have the same configuration as wickers 15, but the axial length of wickers 19 may differ from the axial length of wickers 15. In this embodiment, the axial length of wickers 15 is greater than the axial length of wickers 19. Optionally, wickers could be located on only one of the seal surfaces 13, 18.
After the casing (not shown) attached to casing hanger 17 has been cemented, the running tool positions a seal ring 21 in the pocket between wickers 15, 19. Seal ring 21 is an annular steel member with an annular inner wall or leg 23 and an annular outer wall or leg 25. An annular slot 27 extends between inner leg 23 and outer leg 25.
The seal assembly includes a metal energizing ring 29 that has an outer diameter surface 31 and an inner diameter surface 33. When a running tool (not shown) moves energizing ring 29 downward in slot 27, inner diameter surface 33 slides against inner leg 23 and outer diameter surface 31 slides against outer leg 25. The radial thickness of the portion of energizing ring 29 between outer diameter surface 31 and inner diameter surface 33 is greater than the radial width of slot 27. The downward movement of energizing ring 29 radially and permanently deforms inner and outer legs 23, 25. Outer leg 25 moves radially outward and embeds into wickers 15, foliating a sealing engagement. Inner leg 23 moves radially inward and embeds into wickers 19, forming a sealing engagement.
Referring to
Each set of adjacent reliefs 41, 43 creates a bridge section 45 on lower rim 35 that is smaller in radial thickness than a remaining portion of lower rim 35. The radial thickness of bridge section 45 could be less than one-half a radial thickness of the remaining portion of lower rim 35, for example. In this example, each relief 41, 43 has a base surface 47 that appears curved when viewed from the bottom, as shown in
The circumferential dimension cd of each base surface 47 measured along the circumference of outer diameter surface 31 or inner diameter surface 33 at lower rim 35 is much less than 360 degrees. As an example, the circumferential dimension cd of each relief 41, 43 is illustrated as being about 20 degrees, but that could differ. The circumferential dimension cd of base surface 47 of each outer diameter relief 41 may be about the same as the circumferential dimension cd of base surface 47 of each inner diameter relief 43. The circumferential distance between one outer diameter relief 41 and the other outer diameter relief 41 is much greater than the circumferential dimension cd of outer diameter relief 41.
The radial depth rd of each relief 41, 43, measured at lower rim 35 and a midpoint of each base surface 47 is at least equal to the radial depth of wickers 15 or 19. The radial depths rd of outer diameter reliefs 41 may be the same as the radial depths rd of inner diameter reliefs 43.
Referring to
Referring to
Referring to
During the running operation, the bore of wellhead housing 11 will be filled with a liquid, which may be drilling fluid or mud. The liquid will immerse wickers 15, 19 before setting seal ring 21. The lower section of seal inner leg 23 has two circumferentially spaced apart portions, each radially inward from one pair of reliefs 41, 43. Each portion will not deform radially inward as far as the remaining circumferential part of the lower section of seal inner leg 23. These portions of seal ring inner leg 23 may contact wickers 19 but will not sealingly embed in wickers 19. This lower section, which only extends for two or three wickers, will not seal with two or three of the wickers of wickers 19. The lower section of seal outer leg 25 similarly does not embed and seal in the lowermost two or three wickers 15 because of reliefs 41.
Reliefs 43 do not affect the sealing engagement of the upper portion of seal ring inner leg 23 with wickers 19. Reliefs 41 do not affect the sealing engagement of the upper portion of seal ring outer leg 25 with wickers 15. For example, the upper portion of seal ring inner leg 23 will typically embed into and seal with six or seven of the wickers of wickers 19 The upper portion of seal ring outer leg 25 will typically embed into and seal with six or seven of the wickers of wickers 15.
The downward movement of energizing ring 29 causes seal ring inner leg 23 to seal gradually from the upper end downward. The gradual sealing forces any trapped liquid in the upper portion of wickers 19 downward into the lower portion of wickers 19. The prevention of sealing engagement of the lower section of seal ring inner leg 23 with the lowermost two or three wickers 19 allows in any trapped liquid in these lowermost wickers 19 to flow downward from wickers 19. The downward movement of energizing ring 29 causes sealing engagement of outer leg 25 with wickers 15 to occur simultaneously and in the same manner as inner leg 23.
It is to be 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.
