U.S. patent application number 13/428898 was filed with the patent office on 2013-09-26 for wellhead assembly having a sinusoidal sealing profile and a method to assemble the same.
This patent application is currently assigned to VETCO GRAY INC.. The applicant listed for this patent is Daniel Ralph Barnhart, Nicholas Peter Gette. Invention is credited to Daniel Ralph Barnhart, Nicholas Peter Gette.
Application Number | 20130248199 13/428898 |
Document ID | / |
Family ID | 48226625 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130248199 |
Kind Code |
A1 |
Gette; Nicholas Peter ; et
al. |
September 26, 2013 |
WELLHEAD ASSEMBLY HAVING A SINUSOIDAL SEALING PROFILE AND A METHOD
TO ASSEMBLE THE SAME
Abstract
An outer tubular wellhead member having wickers formed in a bore
of the outer tubular wellhead member that vary in axial position
and methods to assemble a subsea wellhead including the same is
disclosed. The plurality of circumferentially extending wickers are
formed in sealing profiles of the wellhead member. Each wicker
varies axially in position around the circumference of the bore so
that when a seal member engages each wicker, the wicker deforms the
surface of the annular seal to form circumferential sealing bands
at each wicker from an upper end of the sealing profile to a lower
end of the sealing profile, upper portions of each wicker deforming
the surface of the annular seal before lower portions of the same
wicker so that fluid between adjacent wickers flows from the higher
axial location of the wicker to the lower axial location of the
wicker to limit hydraulic lock.
Inventors: |
Gette; Nicholas Peter;
(Houston, TX) ; Barnhart; Daniel Ralph; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gette; Nicholas Peter
Barnhart; Daniel Ralph |
Houston
Houston |
TX
TX |
US
US |
|
|
Assignee: |
VETCO GRAY INC.
Houston
TX
|
Family ID: |
48226625 |
Appl. No.: |
13/428898 |
Filed: |
March 23, 2012 |
Current U.S.
Class: |
166/368 ;
166/88.3 |
Current CPC
Class: |
E21B 2200/01 20200501;
E21B 33/043 20130101; E21B 33/035 20130101 |
Class at
Publication: |
166/368 ;
166/88.3 |
International
Class: |
E21B 33/035 20060101
E21B033/035; E21B 19/00 20060101 E21B019/00 |
Claims
1. A wellhead assembly comprising: an outer tubular wellhead member
with a bore having an axis and a sealing surface extending an axial
distance along an inner diameter surface of the bore; wickers in
the sealing surface circumscribing the bore along an axially
undulating path; an inner tubular member in the outer tubular
wellhead member; and a seal element between the inner tubular
wellhead member and the outer tubular wellhead member and urged
against the wickers to form a sealing interface.
2. The wellhead assembly of claim 1, wherein the axial position of
each wicker varies sinusoidally.
3. The wellhead assembly of claim 2, wherein each wicker of the
plurality of wickers is substantially parallel to adjacent
wickers.
4. The wellhead assembly of claim 1, wherein the wickers are
equidistantly spaced from each adjacent wicker.
5. The wellhead assembly of claim 1, further comprising wickers in
a sealing surface on an outer diameter surface of the inner tubular
member, the wickers circumscribing the inner tubular member along
an axially undulating path.
6. The wellhead assembly of claim 1, further comprising partial
wickers in the sealing surface, wherein each partial wicker extends
along a portion of the circumference of the bore and follows an
axially undulating path.
7. The wellhead assembly of claim 6, wherein partial wickers are
proximate axial ends of the sealing surface.
8. The wellhead assembly of claim 6, wherein each of the partial
wickers are substantially similar.
9. The wellhead assembly of claim 6, wherein adjacent partial
wickers are equidistantly spaced from each other.
10. A wellhead assembly comprising: an outer tubular wellhead
member with a bore having an axis and a sealing surface extending
an axial distance along an inner diameter surface of the bore;
wickers in the sealing surface circumscribing the bore along an
axially undulating path; partial wickers in the sealing surface,
wherein each partial wicker extends along a portion of the
circumference of the bore and follows an axially undulating path;
an inner tubular member in the outer tubular wellhead member; and a
seal element between the inner tubular wellhead member and the
outer tubular wellhead member and urged against the wickers to form
a sealing interface.
11. The wellhead assembly of claim 10, further comprising wickers
in a sealing surface on an outer diameter surface of the inner
tubular member, the wickers circumscribing the inner tubular member
along an axially undulating path.
12. The wellhead assembly of claim 11, further comprising partial
wickers in the sealing surface on the outer diameter surface of the
inner tubular member, wherein each partial wicker extends along a
portion of the outer diameter surface and follows an axially
undulating path
13. The wellhead assembly of claim 10, wherein the axial position
of each wicker varies sinusoidally.
14. The wellhead assembly of claim 10, wherein each wicker of the
plurality of wickers is substantially parallel to adjacent
wickers.
15. A method of forming a wellhead assembly comprising: (a)
providing an outer tubular wellhead member having a bore, an axis,
and an inner surface of the outer tubular wellhead member having
wickers that circumscribe the bore and vary axially in position
around the circumference of the bore; (b) inserting an inner
tubular wellhead member in the outer tubular wellhead member; (c)
inserting an annular seal in an annulus between the outer tubular
wellhead member and the inner tubular wellhead member; and (d)
urging the seal against the wickers so that the wickers deform the
seal and create a barrier in the annulus.
16. The method of claim 15, wherein step (a) further comprises
providing each wicker with a sinusoidally varying axial
position.
17. The method of claim 15, wherein step (a) further comprises
providing wickers on an outer circumference of the inner tubular
wellhead member.
18. The method of claim 15, wherein step (a) further comprises
providing partial wickers on the outer tubular wellhead member,
wherein the partial wickers extend along a portion of the
circumference of the bore.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates in general to subsea wellheads and,
in particular, to a metal sealing system for subsea wellheads and
related subsea equipment disposed in the subsea wellhead and a
method to assemble the same.
[0003] 2. Brief Description of Related Art
[0004] In hydrocarbon production wells, a wellhead housing is
located at the upper end of the well. The wellhead housing is a
large tubular member having an axial bore extending through it.
Casing will extend into the well and will be cemented in place. A
casing hanger, which is on the upper end of the casing, will land
within the wellhead housing. The exterior of the casing hanger is
spaced from the bore of the wellhead housing by an annular
clearance which provides a pocket for receiving an annulus seal.
Annular spaces within concentric members, such as the wellhead
housing and the casing hanger, may be exposed to high pressures
downhole that require isolation from within the wellhead housing
and/or production tree. One manner of isolation involves setting
seals within the annular spaces to form a pressure barrier between
the downhole pressure and the ambient pressure to the wellhead
housing.
[0005] There are many types of annulus seals, including rubber,
rubber combined with metal, and metal-to-metal. One metal-to-metal
seal in use has a U-shape, having inner and outer walls or legs
separated from each other by an annular clearance. An energizing
ring, which has smooth inner and outer diameters, is pressed into
this clearance to force the legs apart to seal in engagement with
the inner surface of the outer wellhead member and with the
exterior of the inner wellhead member.
[0006] Some annular seals utilize wickers. Wickers may be located
on the exterior of the inner wellhead member, in the bore of the
outer wellhead member, or both. The outer leg of the seal embeds
into the wickers of the outer wellhead member while the inner leg
of the seal embeds into the wickers of the inner wellhead member.
This provides the function of both locking the annulus seal in
place and axial restraint to the inner wellhead member, as well as
forming a seal between the outer wellhead member and the inner
wellhead member. Lockdown is the term used for the capacity and
capability of the inner wellhead member and seal assembly to stay
in place vertically in the wellhead when a pressure or other force
is applied from below. This force may be, for example, the result
of annulus pressure build-up or from thermal growth of the casing
attached to a bottom of the hanger or a combination of both. A
sufficient lockdown capacity is needed to ensure that the seal
integrity is maintained and the inner wellhead member and seal
remain static.
[0007] The sealing wickers are machined directly into the bore of
the outer wellhead member or landing subs and the neck of the inner
wellhead member. The annulus seal is made of a sufficiently
deformable metal to allow it to deform against the wickers. The
deformation occurs as the wickers "bite" into the annulus seal. In
order to cause the seal to deform without damaging the wickers, the
annulus seal is made of a metal that is softer than the steel used
for the inner and outer wellhead members. The wicker bite resists
the lockdown force from the inner wellhead member as a shear
resistance. The higher the wicker bite, the higher the lockdown
capacity. The lower the wicker bite, the lower the lockdown
capacity.
[0008] An energizing ring is pressed into the seal between the
inner and outer legs to deform the seal against the wickers. This
causes the seal to form in a top down manner, forming sequential
sealing bands at progressively lower axial locations as each wicker
is engaged by the annulus seal. As these wellhead assemblies are
disposed in subsea locations, fluid will fill the annulus into
which the annulus seals are disposed prior to setting of the seal.
As the sealing bands are formed, fluid may be trapped between each
wicker. The trapped fluid builds up pressure quickly due to its
high bulk modulus. This pressure buildup causes hydraulic lock that
limits total engagement or "bite" between the wickers and the
annular seal. The limited engagement of the wickers reduces the
total lockdown and damage tolerance capabilities of the annulus
seals. Therefore, there is a need for an improved sealing assembly
that decreases instances of hydraulic lock, thereby increasing
lockdown capacity and damage tolerance of the annulus seals.
SUMMARY OF THE INVENTION
[0009] These and other problems are generally solved or
circumvented, and technical advantages are generally achieved, by
preferred embodiments of the present invention that provide a
wellhead assembly having a sinusoidal sealing profile and a method
to assemble the same.
[0010] In accordance with an embodiment of the present invention, a
wellhead assembly is disclosed. The wellhead assembly includes an
outer tubular wellhead member with a bore having an axis and a
sealing surface extending an axial distance along an inner diameter
surface of the bore. Wickers are formed in the sealing surface, the
wickers circumscribing the bore along an axially undulating path.
The wellhead assembly also includes an inner tubular member in the
outer tubular wellhead member, and a seal element between the inner
tubular wellhead member and the outer tubular wellhead member. The
seal element may be urged against the wickers to form a sealing
interface.
[0011] In accordance with another embodiment of the present
invention, a wellhead assembly is disclosed. The wellhead assembly
includes an outer tubular wellhead member with a bore having an
axis and a sealing surface extending an axial distance along an
inner diameter surface of the bore. Wickers are formed in the
sealing surface and circumscribe the bore along an axially
undulating path. Partial wickers are also formed in the sealing
surface. Each partial wicker extends along a portion of the
circumference of the bore and follows an axially undulating path.
The wellhead assembly also includes an inner tubular member in the
outer tubular wellhead member, and a seal element between the inner
tubular wellhead member and the outer tubular wellhead member. The
seal element may be urged against the wickers to form a sealing
interface.
[0012] In accordance with yet another embodiment of the present
invention, a method of forming a wellhead assembly is disclosed.
The method provides an outer tubular wellhead member having a bore,
an axis, and an inner surface of the outer tubular wellhead member
having wickers that circumscribe the bore and vary axially in
position around the circumference of the bore. The method inserts
an inner tubular wellhead member in the outer tubular wellhead
member and an annular seal in an annulus between the outer tubular
wellhead member and the inner tubular wellhead member. The method
urges the seal against the wickers so that the wickers deform the
seal and create a barrier in the annulus.
[0013] An advantage of a preferred embodiment is that it provides a
wellhead assembly that may seal with multiple independent sealing
surfaces with reduced risk of hydraulic lock. This is accomplished
by providing a flowpath for fluid residing between wickers to move
out of the wicker area during setting of the wellhead assembly. In
addition, the disclosed embodiments provide increased lockdown
capacity by the seal, thereby limiting instances of upward movement
of a casing hanger sealed to a high pressure housing or wellhead.
Still further, the disclosed embodiments provide a wellhead
assembly with increased tolerance for wellbore damage when
installing the wellhead assembly in subsea locations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the features, advantages and
objects of the invention, as well as others which will become
apparent, are attained, and can be understood in more detail, more
particular description of the invention briefly summarized above
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings that form a part of this
specification. It is to be noted, however, that the drawings
illustrate only a preferred embodiment of the invention and are
therefore not to be considered limiting of its scope as the
invention may admit to other equally effective embodiments.
[0015] FIG. 1 is a sectional view of a high pressure housing of a
subsea wellhead in accordance with an embodiment of the present
invention.
[0016] FIG. 2 is an enlarged sectional view of a plurality of
wickers of the high pressure housing of FIG. 1 in accordance with
an embodiment of the present invention.
[0017] FIG. 2A is an enlarged view of a portion of the plurality of
wickers of the high pressure housing of FIG. 2, in accordance with
an embodiment of the present invention.
[0018] FIG. 3 is a sectional view of the high pressure housing of
FIG. 1 having additional components of a subsea wellhead assembly
disposed therein in accordance with an embodiment of the present
invention.
[0019] FIG. 4 is a schematic sectional view of a portion of the
wellhead assembly of FIG. 3, illustrating a seal assembly in an
unenergized or unset position between the high pressure housing and
a casing hanger in accordance with an embodiment of the present
invention.
[0020] FIG. 5 is a schematic sectional view of the portion of the
wellhead assembly of FIG. 4, illustrating the seal assembly in an
energized or set position between the high pressure housing and the
casing hanger in accordance with an embodiment of the present
invention.
[0021] FIG. 6 is a schematic view of a portion of the plurality of
wickers of FIG. 2, illustrating fluid movement during energization
of the seal assembly of FIGS. 4 and 5 in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings which
illustrate embodiments of the invention. This invention may,
however, be embodied 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 the
scope of the invention to those skilled in the art. Like numbers
refer to like elements throughout.
[0023] In the following discussion, numerous specific details are
set forth to provide a thorough understanding of the present
invention. However, it will be obvious to those skilled in the art
that the present invention may be practiced without such specific
details. Additionally, for the most part, details concerning
wellhead placement, construction, operation, and the like have been
omitted inasmuch as such details are not considered necessary to
obtain a complete understanding of the present invention, and are
considered to be within the skills of persons skilled in the
relevant art. As used herein, terms such as above and below are
used to describe relative position of components of the invention
as illustrated and are not intended to limit the disclosed
embodiments to a vertical or horizontal orientation.
[0024] FIG. 1 illustrates a partial sectional view of a high
pressure housing 13 of a subsea wellhead assembly 11. Subsea
wellhead assembly 11 may be any suitable wellhead assembly
disposable in a subsea environment to drill and produce fluid from
a subsea location. In the illustrated embodiment, high pressure
housing 13 provides a pressure vessel interface between a blowout
preventer (not shown) and well casing (not shown) disposed in high
pressure housing 13. High pressure housing 13 may include one or
more of the following: a dual seal profile at the wellhead
connector interface, a blowout preventer isolation test tool seal
area, a running tool cam profile, and one or more hanger seal
profiles 15. Seal profiles 15 may be formed in a bore 17 of high
pressure housing 13. Bore 17 and high pressure housing have a
common axis 19. A person skilled in the art will recognize that one
or more casing hangers and associated casing strings as well as one
or more tubing hangers and associated tubing strings may be
disposed within high pressure housing 13. In some embodiments, a
lockdown bushing or lockdown hanger may be disposed within high
pressure housing 13 to provide additional pressure capacity for the
system. A person skilled in the art will also recognize that a
separate seal profile 15 may be formed in bore 17 for every hanger
or bushing expected to be disposed within high pressure housing 13.
A person skilled in the art will understand that other equipment,
such as subsea trees and the like, may include sealing profiles 15
as described herein.
[0025] FIG. 2 illustrates a detailed view of seal profile 15 of
high pressure housing 13. Seal profile 15 may be formed of a
plurality of wickers 21. As shown in FIG. 2, wickers 21 are grooves
formed in bore 17 of high pressure housing 13. Referring to FIG.
2A, each wicker 21 may have a triangular cross sectional profile
having a crest 23, an upper flank 25, and a lower flank 27. In an
embodiment, crests 23 of adjacent wickers 21 are separated by a
distance 29. In an embodiment, distance 29 may be approximately
one-eighth of an inch. A person skilled in the art will understand
that distance 29 may vary as needed for the particular application
to which high pressure housing 13 is put to use. For example,
distance 29 may be increased or decreased as needed to increase or
decrease lockdown capacities and damage tolerance capabilities of
wellhead assembly 11. Upper flank 25 and lower flank 27 of adjacent
wickers 21 join at a valley 31. A person skilled in the art will
recognize that valleys 31 may be spaced by a distance equivalent to
distance 29 and may vary as needed for the particular application
of high pressure housing 13. Each wicker 21 may have a depth 33
from crest 23 to valley 31. In the illustrated embodiments, depth
33 is uniform for any given axial cross section of high pressure
housing 13. Similarly, distance 29 may be uniform for any given
axial cross section of high pressure housing 13. In an embodiment
wickers 21 are machined into bore 17 of high pressure housing 13
with a computer numerical controlled lathe or a cam driven manual
machine. In other embodiments, high pressure housing 13 may be cast
with wickers 21. A person skilled in the art will understand that
any suitable method may be used to form wickers 21.
[0026] Each crest 23 circumscribes bore 17 so that a crest 23 may
be traced from a circumferential location, around bore 17 to return
to the circumferential location where the trace began. For example,
each crest 23 may form a continuous line around the circumference
of bore 17 so that the trace starts and finishes at the same axial
height and radial position as it started. Similarly, upper flank
25, lower flank 27, and valley 31 of each wicker 21 may be traced
from a circumferential location, around bore 17 to return to the
circumferential location where the trace began. Crests 23 of each
wicker 21 may vary axially around the circumference of bore 17 as
shown in FIG. 2. For example, if location 22 is designated as a
baseline height for the upper most wicker 21 of the plurality of
wickers 21, locations 24, 28, and 30 may all have different axial
positions relative to location 22. In this example, a trace of the
upper most wicker 21 beginning at location 22 would be continuous
around bore 17 and return to location 22. As shown, some locations
of uppermost wicker 21 may be positioned axially higher relative to
location 22. For example locations 28 and 30 have higher axial
positions in bore 17 relative to location 22. Similarly, some
locations of upper most wicker 21 may be positioned axially lower
than location 22. For example location 24 has a lower axial
position in bore 17 than location 22. Still further, some locations
may be positioned at the same axial height as location 22. For
example, location 26 is has an equivalent axial height as location
22. In the illustrated embodiment, crests 23 have multiple
locations both axially higher and axially lower than location 22
while maintaining a continuous line circumscribing bore 17. In the
illustrated embodiment, the axial variation of crests 23 of wickers
21 oscillates in a sinusoidal manner. Thus, the axial position of
crest 23 varies with an equivalent amplitude both axially above and
axially below initial location 22. Similarly, upper flanks 25,
lower flanks 27, and valleys 31 vary axially around the
circumference of bore 17 with crest 23 as described above. In this
manner, each wicker 21 may have locations of higher, lower, and
equivalent axial position relative to an initial position selected
at an arbitrary circumferential location of wickers 21. Optionally,
wickers 21 may follow a path of approximately any waveform, whether
or not the waveform is sequential, symmetric, or curved. A person
skilled in the art will understand that axial location of a
particular wicker or plurality of wickers 21 may vary with a
variety of different shapes and patterns to vary the height of a
seal band formed by seal profile 15 as described in more detail
below.
[0027] As shown in FIG. 2, sealing profile 15 may include partial
wickers 32. Partial wickers 32 are formed in bore 17 so that
wickers 21, 32 substantially populate a total height 34 of sealing
profile 15. Partial wickers 32 have a similar depth 33, pitch or
height 29, and component parts, upper flanks 25, lower flanks 27,
crests 23, and valleys 31 as each wicker 21. Partial wickers 32 may
only be partially formed so that a trace of a partial wicker 32 is
not continuous around the circumference of bore 17. Partial wickers
32 may vary in height axially in a manner similar to wickers 21
creating partial fluid channels for the flow of fluid described in
more detail below. In the example of FIG. 2, partial wickers 32
each extend a distance less than the circumference of bore 17 and
are spaced apart from each adjacent partial wicker 32. Although
shown as being substantially equidistant, partial wickers 32 can
have varying lengths and be space apart at regular or irregular
distances.
[0028] Illustrated in a side sectional view in FIG. 3 is one
example of a wellhead assembly 35 and a running tool 37 inserted in
wellhead assembly 35. Running tool 37 includes an inner mandrel 39,
having a threaded upper end for connection to a raising and/or
lowering device, such as a drill pipe (not shown). The drill pipe,
which in an example depends downward from a drilling platform (not
shown), can be used for raising, lowering, and operating running
tool 37. Wellhead assembly 35 of FIG. 3 includes high pressure
housing 13, also referred to as an outer annular wellhead housing.
Running tool 37 is shown landing a casing hanger 41 within high
pressure housing 13. After landing casing hanger 41 in high
pressure housing 13, an annular space is formed between respective
portions of casing hanger 41 and high pressure housing 13.
Additional hangers of similar configurations are illustrated
coaxially within high pressure housing 13 and below casing hanger
41. The additional hangers include, a bridging hanger 43 and
another casing hanger 45 beneath the bridging hanger 43. Seal
assemblies 47 are illustrated set in the annular spaces between
each of the hangers 41, 43, 45 and high pressure housing 13 as
described in more detail below. At each seal assembly 47 location,
a sealing profile 15 may be formed in high pressure housing 13.
[0029] Referring to FIG. 4, high pressure housing 13 is a large
tubular member located at the upper end of a well, such as a subsea
well. Casing hanger 41 is a tubular conduit secured to the upper
end of a string of casing (not shown). Casing hanger 41 has an
upward facing shoulder 51 on its exterior. An exterior wall 53 of
casing hanger 41 is parallel to the wall of bore 17 but spaced
inwardly. This results in an annular pocket, clearance, or annulus
52 between casing hanger exterior wall 53 and bore 17. Wickers 55
are located on exterior wall 53 of casing hanger 41. Wickers 55 are
similar to wickers 21 of FIGS. 2-2A adapted to circumscribe
exterior wall 53 of casing hanger 41. Wickers 55 may have a similar
sinusoidal axial positional variation. When disposed in high
pressure housing 13, wickers 55 of casing hanger 41 may be radially
adjacent to wickers 21 of high pressure housing 13.
[0030] Seal assembly 47 lands in annulus 52 between casing hanger
exterior wall 53 and bore 17. Seal assembly 47 may be made up
entirely of metal components. These components may include a
generally U-shaped seal member 57. Seal member 57 has an outer wall
or leg 59 and a parallel inner wall or leg 61, the legs 59, 61
being connected together at the bottom by a base and open at the
top. The inner diameter of outer leg 59 is radially spaced outward
from the outer diameter of inner leg 61. This results in an annular
clearance 63 between legs 59, 61. The inner diameter and the outer
diameter are smooth cylindrical surfaces parallel with each other.
Similarly, the inner diameter of inner leg 61 and the outer
diameter of outer leg 59 are smooth, cylindrical, parallel
surfaces.
[0031] An energizing ring 65 is employed to force legs 59, 61
radially apart from each other and into sealing engagement with
wickers 21, 55 as shown in FIG. 5. Wickers 55, 21 bite into inner
leg 61 and outer leg 59, respectively, of seal assembly 47 as
energizing ring 65 forces outer and inner legs 59, 61 against
wickers 21, 55. Energizing ring 65 has an outer diameter that will
frictionally engage the inner diameter of outer leg 59. Energizing
ring 65 has an inner diameter that will frictionally engage the
outer diameter of inner leg 61. The radial thickness of energizing
ring 65 is greater than the initial radial dimension of the
clearance 63.
[0032] In the illustrated embodiments, bore 17 may be filled with
fluid during running, landing, and setting of casing hanger 41 and
seal assembly 47. As energizing ring 65 moves axially downward into
clearance 63, so that the seal is formed by engaging wickers 21
from top to bottom of sealing profile 15. Upper wickers 21 such as
wicker 21A of FIG. 6 bite into and deform the sealing surface of
seal member 57 to create a sealing band at wicker 21A. As U-shaped
seal member 57 engages successive wickers 21.sub.1-n, 55.sub.1-n,
circumferential seal bands may be formed at each wicker 21, 55
sequentially from an upper end of seal member 57 to a lower end of
seal member 57. U-shaped member 57 engages each wicker 21, 55
proximate to an inflection point 67 where the wickers change
direction, illustrated in FIG. 6. Continued axial downward movement
of energizing ring 65 causes U-shaped seal member 57 to engage
successively more of each wicker 21, 55, deforming seal member 57
into valleys 31. As this occurs, fluid residing between adjacent
crests 23 of each wicker 21, 55, for example between crest 23.sub.1
and crest 23.sub.2 of wickers 21.sub.2 and 21.sub.2, respectively,
flows from inflection points 67 toward inflection points 69 where
wickers 21, 55 change direction opposite inflection point 67 as
shown by arrows 71. For example, as shown in FIG. 6, fluid may flow
from higher relative locations 26, 28, and 30 toward location 24.
In some embodiments, a portion of the fluid residing between
adjacent crests 23 flows out of wickers 21, 55. In this manner, the
volume of #fluid that may be trapped by U-shaped seal member 57
between adjacent wickers 21, 55 may be reduced. Reduction of fluid
volume between U-shaped seal member 57 and wickers 21, 55 increases
engagement between U-shaped seal member 57 and wickers 21, 55,
deforming more of U-shaped seal member 57 into wickers 21, 55 to
create higher lockdown capacities and reduce instances of hydraulic
lock during seal setting. Curving the wickers increases their
effective length and thus their total volume.
[0033] Accordingly, the disclosed embodiments provide numerous
advantages. For example, the disclosed embodiments provide a
wellhead assembly that may seal with multiple independent sealing
surfaces with reduced risk of hydraulic lock. This is accomplished
by providing a flowpath for fluid residing between wickers to move
out of the wicker area during setting of the wellhead assembly. In
addition, the disclosed embodiments provide increased lockdown
capability by the seal, thereby limiting instances of upward
movement of a casing hanger sealed to a high pressure housing or
wellhead. Still further, the disclosed embodiments provide a
wellhead assembly with increased tolerance for wellbore damage when
installing the wellhead assembly in subsea locations.
[0034] It is understood that the present invention may take many
forms and embodiments. Accordingly, several variations may be made
in the foregoing without departing from the spirit or scope of the
invention. Having thus described the present invention by reference
to certain of its preferred embodiments, it is noted that the
embodiments disclosed are illustrative rather than limiting in
nature and that a wide range of variations, modifications, changes,
and substitutions are contemplated in the foregoing disclosure and,
in some instances, some features of the present invention may be
employed without a corresponding use of the other features. Many
such variations and modifications may be considered obvious and
desirable by those skilled in the art based upon a review of the
foregoing description of preferred embodiments. Accordingly, it is
appropriate that the appended claims be construed broadly and in a
manner consistent with the scope of the invention.
* * * * *