US20130068450A1

US20130068450A1 - Wicker profile for enhancing lockdown capacity of a wellhead annulus seal assembly

Info

Publication number: US20130068450A1
Application number: US13/237,687
Authority: US
Inventors: Ashutosh Chandrashekhar Phadke; Vikram Tutpet Keshavamurthy; Vikranth Harthikote Nagaraja; Fasalu Rahman B
Original assignee: Vetco Gray LLC
Current assignee: Vetco Gray LLC
Priority date: 2011-09-20
Filing date: 2011-09-20
Publication date: 2013-03-21

Abstract

A wellhead assembly comprises an outer tubular wellhead member with a bore having an axis and a concentric inner seal surface, an inner tubular wellhead member for receiving an annular seal landed within the outer tubular wellhead member defining a seal pocket between them, the inner tubular member having a concentric outer seal surface, and a plurality of circumferentially extending, parallel wickers formed in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular. A profile of at least one of the wickers differs from a profile of at least some of the other wicker.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates in general to a method and apparatus to form a high pressure seal between two wellbore members, and in particular to wickers having an increased lockdown capability.
2. Description of the Related Art
Seals are used between inner and outer wellhead tubular members to contain internal well pressure. The inner wellhead member may be a casing hanger that supports a string of casing extending into the well for the flow of production fluid. The casing hanger lands in an outer wellhead member, which may be a wellhead housing, a Christmas tree, or a casing head. A packoff (or other seal assembly) seals the annulus between the casing hanger and the outer wellhead member. Alternately, the inner wellhead member can be a tubing hanger located in a wellhead housing and secured to a string of tubing extending into the well. A pack off (or other seal assembly) seals the annulus between the tubing hanger and the wellhead housing. In another alternative design, the inner wellhead member may be an isolation sleeve, such as might be used to isolate high pressure, abrasive fracturing fluids from certain portions of the wellhead. A packoff (or other seal assembly) seals the annulus between the isolation sleeve and the outer wellhead member.
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.
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, providing axial restraint to the inner wellhead member, as well as forming a seal. 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 on 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 remains static.
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.
The future of oil and gas exploration lies in deep waters and greater depth (for pay-zone) under the seabed, which renders the subsea equipment to harsh conditions like high pressure and high temperatures (HPHT), sour fluid etc. This calls for designing the subsea equipment and tools for this widened HPHT envelope. The all-metal seal, in discussion, is a very critical component of the wellhead system that performs annulus sealing as well as acts as a lockdown device. This HPHT condition causes a greater hanger movement due to higher thermal growth and annulus pressure build-up. Usually, this movement of the hanger is constrained by the seal. The invention caters to the above problem of greater hanger movement at the same time maintaining the field-proven design. The proposed all-metal seal rated to a higher lockdown capacity would allow higher reliability.
An improved system that provides a more robust and reliable lockdown capacity is sought.

SUMMARY OF THE INVENTION

In view of the foregoing, various embodiments of the present invention advantageously provide seal assemblies to address shortfalls of the prior art. Embodiments of the present application provide enhanced lockdown capacity which widens the application in which the seal can be used, thus aiding hydrocarbon producers in being able to pursue wells in more extreme environments. Embodiment of the current application provide increased sealing capability and reliability, can use existing tools for installation.
In one embodiment of the current application, a wellhead assembly comprises an outer tubular wellhead member with a bore having an axis and a concentric inner seal surface, an inner tubular wellhead member for receiving an annular seal landed within the outer tubular wellhead member defining a seal pocket between them, the inner tubular member having a concentric outer seal surface, and a plurality of circumferentially extending, parallel wickers formed in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular. A profile of at least one of the wickers differs from a profile of at least some of the other wicker.
In an alternative embodiment, the assembly further comprises an annular seal that is adapted to be disposed within the seal pocket and to be urged against the wickers on the outer tubular and the inner tubular to create a seal and to resist upward motion of the inner tubular relative to the outer tubular and wherein the plurality of wickers are adapted to deform a surface of the annular sealing ring.
In yet another embodiment, the wickers on at least one of the seal surfaces are located in a bottom region of the seal pocket, a middle region of the seal pocket which is above the bottom region, and a top region of the seal pocket which is above the middle region, and wherein the profiles of the wickers in each of the regions differs from the profiles in each of the other regions. The profile of the wickers in the bottom region may be substantially similar to each other, the profile of the wickers in the middle region may be substantially similar to each other, and the profile of the wickers in the top region may be substantially similar to each other.
In an alternative embodiment, the profile of the wickers in the bottom region are different than the profile of the wickers in the middle region and the top region, and the profile of the wickers in the middle region are different than the profile of the wickers in the top region.
In another alternative embodiment, the wickers in the bottom region have more material on the top flank of each wicker than on the bottom flank of each wicker, the profile of the wickers in the middle region are symmetrical about a mid plane of each wicker, the wickers in the top region have more material on the bottom flank of each wicker than on the top flank of each wicker.
In yet another alternative embodiment, the wickers in the bottom region have a tilted mid plane symmetrically dividing each wicker in half, the tilted mid plane being inclined relative to a normal plane perpendicular to the axis, resulting in more material below the normal plane in each wicker, and the wickers in the top region have a tilted mid plane symmetrically dividing each wicker in half, the tilted mid plane being inclined relative to a normal plane perpendicular to the axis, resulting in more material above the normal plane in each wicker.
In other alternative embodiments, the wickers may have a mid-plane passing through a crest of each wicker that is normal to the axis, and the wickers in the top region and in the bottom region may be asymmetrical about their respective mid-plane. Alternatively, the wickers may have a mid-plane passing through a crest of each wicker that is normal to the axis, and some of the wickers may be asymmetrical about their respective mid-plane. In some embodiments, the wickers may have an aspect ratio of less than 1.0.
In other embodiments of the current application, a wellhead assembly comprises an outer tubular wellhead member with a bore having an axis and a concentric inner seal surface, an inner tubular wellhead member for receiving an annular seal landed within the outer tubular wellhead member defining a seal pocket between them, the inner tubular member having a concentric outer seal surface, and a plurality of circumferentially extending, parallel wickers formed of a material in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular. The wickers may have a mid plane passing through a crest of each wicker dividing each wicker substantially in half, and a normal plane passing through the crest and perpendicular to the axis. The material above the normal plane of at least one of the wickers may not equal the material below the normal plane of such at least one wicker.
In other embodiments, at least one wicker may have a mid plane inclined relative to the normal plane, resulting in more material below the normal plane in each wicker than above. Alternatively, at least one wicker may have a mid plane inclined relative to the normal plane, resulting in more material above the normal plane in each wicker than below. The mid plane and normal plane of each wicker are parallel to each other and a profile of at least one wicker is asymmetrical about its mid plane.
In alternative embodiments, an upper flank and a lower flank of at least one wicker are at the same angle relative to the axis, the mid plane bisects a base of such wicker equidistant from a top and a bottom of the base of such wicker, and there is more material above the mid plane than below. Alternatively, an upper flank and a lower flank of at least one wicker may be at the same angle relative to the axis, the mid plane may bisect a base of such wicker equidistant from a top and a bottom of the base of such wicker, and there may be more material below the mid plane than above.
In yet other embodiments, at least one wicker has a mid plane inclined relative to the normal plane, resulting in more material below the normal plane in each wicker than above, and at least one wicker has a mid plane inclined relative to the normal plane, resulting in more material above the normal plane in each wicker than below. The wickers may be symmetrical about the mid plane and asymmetrical about normal plane.
In other embodiments of the current application, a wellhead assembly comprises an outer tubular wellhead member with a bore having an axis and a concentric inner seal surface, an inner tubular wellhead member for receiving an annular seal landed within the outer tubular wellhead member defining a seal pocket between them, the inner tubular member having a concentric outer seal surface, and a plurality of circumferentially extending, parallel wickers formed in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular. Each adjacent wicker being separated by a valley and having a wicker radial width measured from the base of the valley to a crest, and an axial length dimension measured as the distance between the base of the valley on either side of such wicker. The wicker radial width of at least one wicker is equal to no more than the axial length dimension. In some embodiments, the valley between the wickers comprises a curved surface having a radius of at least 0.04 inches.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of the invention, as well as others which will become apparent, may be understood in more detail, a 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, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.

FIG. 1 is a sectional view of portions of a wellhead assembly providing a annulus seal

FIG. 2 a is a sectional view of a prior art wicker profile.

FIG. 2 b is a sectional view of a wicker profile of an embodiment of the current application.

FIG. 2 c is a sectional view of a wicker profile of another embodiment of the current application.

FIG. 2 d is a sectional view of a wicker profile of another embodiment of the current application.

FIG. 3 a is a sectional view of a wicker profile of another embodiment of the current application.

FIG. 3 b is a sectional view of a wicker profile of another embodiment of the current application.

FIG. 4 a is a sectional view of a prior art sectional view of wickers.

FIG. 4 b is a sectional view of a section of wickers of another embodiment of the current application.

DETAILED DESCRIPTION

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. Prime notation, if used, indicates similar elements in alternative embodiments.
Referring to FIG. 1, an outer wellhead member 10 is presented. In the illustrated embodiment, the wellhead member 10 is a conventional high pressure housing for a subsea well. It is a large tubular member located at the upper end of a well, such as a subsea well. Wellhead housing 10 has an axial bore 12 extending through it. An inner wellhead member 14 is located within axial bore 12. In the illustrated embodiment, the inner wellhead member is a casing hanger 14, which lands in the wellhead housing 10. Casing hanger 14 is a tubular conduit secured to the upper end of a string of casing (not shown). Casing hanger 14 has an upward facing shoulder 16 on its exterior. The exterior wall 18 of casing hanger 14 is parallel to the wall of bore 12 but spaced inwardly. This results in an annular pocket or clearance between casing hanger exterior wall 18 and bore 12. A set of wickers 20 is located on the exterior surface 18 of casing hanger 14. A similar set of wickers 22 may also be located radially across on an inner surface bore 12. Wickers 20, 22 are circumferential grooves defined by parallel circumferential ridges and valleys. They are not threads. Wickers 20, 22 may be configured as one of the embodiments of FIG. 2 b, 2 c, 2 d, 3 a, 3 b or 4 b.
A seal assembly 26 lands in the pocket between casing hanger exterior wall 18 and bore wall 12. Seal assembly 26 may be made up entirely of metal components. These components may include a generally U-shaped seal member 28. Seal member 28 has an outer wall or leg 30 and a parallel inner wall or leg 32, the legs 30, 32 being connected together at the bottom by a base and open at the top. The inner diameter of outer leg 30 is radially spaced outward from the outer diameter of inner leg 32. This results in an annular clearance 36 between legs 30, 32. The inner diameter and the outer diameter are smooth cylindrical surfaces parallel with each other. Similarly, the inner diameter of inner leg 32 and the outer diameter of outer leg 30 are smooth, cylindrical, parallel surfaces.
An energizing ring 40 is employed to force legs 30, 32 radially apart from each other and into sealing engagement with wickers 20, 22. The wickets 20, 22 bite into the inner leg 30 and outer leg 32, respectively, of the seal assembly 26 as the energizing ring 40 forces the legs 30, 32 against the wickers 20, 22. Energizing ring 40 has an outer diameter that will frictionally engage the inner diameter of outer leg 30. Energizing ring 40 has an inner diameter that will frictionally engage the outer diameter of inner leg 32. The radial thickness of energizing ring 40 is greater than the initial radial dimension of the clearance 36.
During the seal setting process, wickets 20 at the bottom region 42 of the housing bore are deformed at a top flank 44 (FIG. 2 a) of the wicker. The magnitude of this top flank 44 deformation keeps reducing with every subsequent wicker along the length towards a middle region 46, such that the farther away a wicker 20 is located below wickers 20 in the middle region 46, the greater the deformation of top flank 44. The profile of the wickets in the middle region 46 during the sealing process remain unchanged. Wickers at the top region 48 of the housing bore are deformed at a bottom flank 50. The magnitude of this bottom flank 50 (FIG. 2 a) deformation keeps reducing with every subsequent wicker along the length towards middle region 46, such that the farther above a wicker 20 is located from middle region 46, the greater the deformation of bottom flank 50. These local plastic deformations follow this consistent pattern and reduce the effectiveness of the wickers. Embodiments of the current invention modify the prior art wicker flank such that local modifications are made in a pattern to counter the deformation and keep the “v” shaped wicker profile intact after seal setting. This provides for increased lockdown capabilities.
The prior art wicker 52 of FIG. 2 a, has a uniform profile in all regions horizontally, of the outer wellhead member, with a symmetrical profile about wicker mid plane 54. Wicker mid-mid plane 54 bisects the profile of each wicker and crest 60 such that an equal volume of the wicker is above and below mid plane 54 from the base 55 of the wicker to at least the midpoint of its radial width 57. Mid plane 54 bisects crest 60 equidistant along an axial length of crest 60. Flanks 44, 50 intersect each other at a fairly sharp crest 60.
Embodiments of the current application are illustrated in FIGS. 2 b-2 d. In the bottom region 42 (FIG. 1), wickers 56 of FIG. 2 b are used. The profile of wicker 56 is such that top flank 44 comprises more material 58 near crest 60 than does bottom flank 50. Before the seal setting process, the profile of wicker 56 is not symmetrical about wicker mid plane 54. The excess material 58 is sacrificial in nature in that it is expected to undergo deformation during the seal setting process. Because of this expected deformation of excess material 58, at the end of the seal setting process, wicker 56 is expected to have a substantially symmetrical “v” shaped profile about wicker mid plane 54. In this embodiment, flank 44 may be the same angle relative to axis 23 as the prior art wicket 52, which may be 55 degrees as an example. Excess material 58 has a flat upper surface intersected by flank 44. Crest 60 has a greater axial length than prior art wicker 52.
The wickers in the middle region 46 will comprise wickers 62 of FIG. 2 c. Wicker 62 has a profile that is symmetrical about wicker mid plane 54. Because there is no deformation of the wickers 20 in middle region 46 during the seal setting process, wickers 62 will substantially maintain their symmetrical “v” shaped profile about wicker mid plane 54. Wickers 62 may be the same as prior art wickers 52.
In the top region 48, wickers 64 of FIG. 2 d are used. The profile of wicker 64 is such that bottom flank 50 comprises more material 66 near crest 60 than does top flank 44. Before the seal setting process, the profile of wicker 64 is not symmetrical about wicker mid plane 54. The excess material 66 is sacrificial in nature in that it is expected to undergo deformation during the seal setting process. Because of this expected deformation of excess material 66, at the end of the seal setting process, wicker 64 is expected to have a substantially symmetrical “v” shaped profile about wicker mid plane 54. In this embodiment, flank 50 may be the same angle relative to axis 23 as the prior art wicket 52, which may be 55 degrees as an example. Excess material 66 has a flat lower surface intersected by flank 50. Crest 60 has a greater axial length than prior art wicker 52.
The use of varying wicker profiles in top region 48, middle region 46 and bottom region 42 will provide for stronger wickers after the seal setting process. This in turn allows the seal assembly 26 to resist a higher upward force of hanger 14 and gives the wickers 20 a greater lockdown capacity.
In addition to providing local modifications to wicker profiles, the ability of the wickers 22 to resist an upward force from hanger 14 alternatively may be improved by designing the profile such that wicker axes 54 is not perpendicular to the central axis 23 of the wellbore. The prior art wicker 52 of FIG. 2 a has a wicker mid plane 54 that is normal or perpendicular to a central axis 23 of the bores 12, 18. In FIGS. 3 a and 3 b, wicker 72 has a wicker mid plane 54 that is not perpendicular to axis 23 as seen by comparing mid plane 54 to normal plane 70 that is perpendicular to axis 23. Instead crest 60 of wicker 72 is tilted downward, while maintaining the “v” shaped profile of wicker 72. This results in wicker mid plane 54 being at an acute angle 74 with normal plane 70. Angle 74 may be for example, in the range of 2 to 5 degrees. Upper flank 44 has a lesser angle relative to axis 23 than lower flank 50. For example, upper flank 44 may be 50 degrees relative to axis 23 and lower flank 50 may be 65 degrees relative to axis 23. The lengths of flanks 44, 50 may be the same. Crest 60 has a same height as in FIG. 2 a. The lower flanks 50 of wicker 72 are inclined more than the lower flanks 50 of prior art wickers 52. Them material in wicker 72 above normal plane 70 exceeds the material below normal plane 70. Wickers 72 may be employed in upper region 48.
A higher upward force is required to deform the wickers 72, which are tilted downward, as compared to the amount of force required to deform horizontally aligned wickers 52 of the prior art. Therefore use of wickers 72 results in the ability of the seal assembly 26 to resist a higher upward force of hanger 14 and hence provides a higher lockdown capacity than using prior art wickers 52.
Similarly, in lower region 42, wickers upward tilting wickers 68 of FIG. 3 b may be employed. Wicker 68 has a wicker mid plane 54 that is not perpendicular to axis 23 as seen by comparing mid plane 54 to normal plane 70 that is perpendicular to axis 23. Instead crest 60 of wicker 68 is tilted upward, while maintaining the “v” shaped profile of wicker 68. This results in wicker mid plane 54 being at an acute angle 75 with normal plane 70. Angle 75 may be for example, in the range of 2 to 5 degrees. Upper flank 44 has a greater angle relative to axis 23 than lower flank 50. For example, upper flank 44 may be 65 degrees relative to axis 23 and lower flank 50 may be 50 degrees relative to axis 23. The lengths of flanks 44, 50 may be the same. Crest 60 has a same height as in FIG. 2 a. The lower flanks 50 of wicker 68 are inclined more than the lower flanks 50 of prior art wickers 52. The material in wicker 68 below normal plane 70 exceeds the material above normal plane 70.
A higher upward force is required to deform the wickers 68, which are tilted upward, as compared to the amount of force required to deform horizontally aligned wickers 52 of the prior art. Therefore use of wickers 68 results in the ability of the seal assembly 26 to resist a higher upward force of hanger 14 and hence provides a higher lockdown capacity than using prior art wickers 52.
In alternative embodiments of the present application, the aspect ratio of wicker 20,22 profiles is also optimized. FIG. 4 a illustrates prior art wicker section 76 which comprises individual wickers 78. Each individual wicker 78 is generally “v” shaped in profile. Generally “v” shaped fillets or valleys 80 separate each wicker 78. The radial width 82 of each wicker divided by the axial length 84 of each wicker defines the aspect ratio of a wicker 78. The radial width 82 of each wicker is generally measured from the bottom of the valley 80 to the crest 60 of such ridge. The axial length 84 is generally measured as the distance between the bottom of the valleys 80 on either side of such crest 60.
FIG. 4 b illustrates an improved wicker aspect ratio of the present application. Wicker section 86 comprises a plurality of individual wickers 88. Wickers 88 are generally “v” shaped in profile. Generally “u” shaped valleys 90 separate each wicker 88. The radial width 92 of each wicker divided by the axial length 94 of the base of each wicker defines the aspect ratio of a wicker 88. Wickers 88 have a lower aspect ratio than prior art wickers 78 (FIG. 4 a). In the prior art of FIG. 4 a, the aspect ration is instead in the range of 2.5 to 3.0. In the embodiment of FIG. 4 b, the aspect ratio is less than 1.0. That is, the radial width 92 of the wicker is not greater than the axial length 94 of the base of such wicker. In one embodiment, the aspect ration be for example, approximately 0.7 or in another embodiment, 0.68. Flanks 44 and 52 of an embodiment of the current application, as show in FIG. 4 b may incline at the same angle relative to axis 23 as in the prior art of FIG. 4 a.
With a lower aspect ratio, the valleys 90 may comprise a larger radius curve. In the prior art, the radius of each valley 80 was 0.01 to 0.02 inches. In an embodiment of the current application, the radius of each valley 90 is in the range of 0.04 to 0.05 inches, and may be, for example, 0.045 inches. The radius of the valley is, however, limited by the maximum penetration depth of the wicker for obtaining the desired seal penetration while still maintaining enough clearance to avoid hydro locking.
A lower aspect ratio is achieved by decreasing the depth of valleys 90, creating a shorter radial width 82 of each wicker 88. Alternatively, a lower aspect ratio can be achieved by increasing the axial length 94 of each wicker. A combination of decreasing the depth of valleys 90 and increasing the axial length 94 may also be used to decrease the aspect ratio. Both the increased axial length 94 and shorter radial width 92 allow an individual wicker 88 to better resist deformation during upward hanger 14 movement. This results in a stronger wicker with greater lockdown capacity.
In the drawings and specification, there has been disclosed a typical preferred embodiment of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification. For example, although primarily illustrated in the context of a casing hanger landed within a modified high-pressure wellhead housing, one of ordinary skill in the art will recognize that the featured seal assembly and methods can be readily employed with respect to tubing within modified casing or other tubing.

Claims

1. A wellhead assembly comprising:

an outer tubular wellhead member with a bore having an axis and a concentric inner seal surface;

an inner tubular wellhead member for receiving an annular seal landed within the outer tubular wellhead member defining a seal pocket between them, the inner tubular member having a concentric outer seal surface;

a plurality of circumferentially extending, parallel wickers formed in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular; wherein

a profile of at least one of the wickers differs from a profile of at least some of the other wickers.

2. The assembly of claim 1, further comprising an annular seal that is adapted to be disposed within the seal pocket and to be urged against the wickers on the outer tubular and the inner tubular to create a seal and to resist upward motion of the inner tubular relative to the outer tubular and wherein the plurality of wickers are adapted to deform a surface of the annular seal.

3. The assembly of claim 1, wherein the wickers on said at least one of the seal surfaces are located in a bottom region of the seal pocket, a middle region of the seal pocket which is above the bottom region, and a top region of the seal pocket which is above the middle region, and wherein the profiles of the wickers in each of the regions differs from the profiles in each of the other regions.

4. The assembly of claim 3, wherein:

the profile of the wickers in the bottom region are substantially similar to each other;

the profile of the wickers in the middle region are substantially similar to each other; and

the profile of the wickers in the top region are substantially similar to each other.

5. The assembly of claim 3, wherein:

the wickers are formed of a material;

the profile of the wickers in the bottom region are different than the profile of the wickers in the middle region and the top region; and

the profile of the wickers in the middle region are different than the profile of the wickers in the top region.

6. The assembly of claim 3, wherein:

the wickers in the bottom region have more material on a top flank of each wicker than on a bottom flank of each wicker;

the profile of the wickers in the middle region are symmetrical about a mid plane of each wicker; and

the wickers in the top region have more material on the bottom flank of each wicker than on the top flank of each wicker.

7. The assembly of claim 3, wherein:

the wickers in the bottom region have a tilted mid plane symmetrically dividing each wicker in half, the tilted mid plane being inclined relative to a normal plane perpendicular to the axis, resulting in more material below the normal plane in each wicker; and

the wickers in the top region have a tilted mid plane symmetrically dividing each wicker in half, the tilted mid plane being inclined relative to a normal plane perpendicular to the axis, resulting in more material above the normal plane in each wicker.

8. The assembly of claim 3, wherein:

the wickers have a mid-plane passing through a crest of each wicker that is normal to the axis; and

the wickers in the top region and in the bottom region are asymmetrical about their respective mid-plane.

9. The assembly of claim 1, wherein the wickers have a mid-plane passing through a crest of each wicker that is normal to the axis, and some of the wickers are asymmetrical about their respective mid-plane.

10. The assembly of claim 1, wherein the wickers have an aspect ratio of less than 1.0.

11. A wellhead assembly comprising:

a plurality of circumferentially extending, parallel wickers formed of a material in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular; wherein

the wickers have a mid plane passing through a crest of each wicker dividing each wicker substantially in half, and a normal plane passing through the crest and perpendicular to the axis; and

the material above the normal plane of at least one of the wickers does not equal the material below the normal plane of such at least one wicker.

12. The assembly of claim 11, wherein at least one wicker has a mid plane inclined relative to the normal plane, resulting in more material below the normal plane in each such wicker than above.

13. The assembly of claim 11, wherein at least one wicker has a mid plane inclined relative to the normal plane, resulting in more material above the normal plane in each such wicker than below.

14. The assembly of claim 11, wherein the mid plane and normal plane of each wicker are parallel to each other and a profile of at least one wicker is asymmetrical about its mid plane.

15. The assembly of claim 14, wherein:

an upper flank and a lower flank of at least one wicker are at the same an_gle relative to the axis;

the mid plane bisects a base of such wicker equidistant from a top and a bottom of the base of such wicker; and

there is more material above the mid plane than below.

16. The assembly of claim 14, wherein:

an upper flank and a lower flank of at least one wicker are at the same angle relative to the axis;

there is more material below the mid plane than above.

17. The assembly of claim 11, wherein:

at least one wicker has a mid plane inclined relative to the normal plane, resulting in more material below the normal plane in each such wicker than above; and

at least one wicker has a mid plane inclined relative to the normal plane, resulting in more material above the normal plane in each such wicker than below.

18. The assembly of claim 17, wherein the wickers are symmetrical about the mid plane and asymmetrical about the normal plane.

19. A wellhead assembly comprising:

a plurality of circumferentially extending, parallel wickers formed in at least one of the seal surfaces of the outer tubular and on the outer surface of the inner tubular, each adjacent wicker being separated by a valley and having:

a wicker radial width measured from the base of the valley to a crest;

an axial length dimension measured as the distance between the base of the valley on either side of such wicker; and wherein

the wicker radial width of at least one wicker is equal to no more than the axial length dimension.

20. The assembly of claim 19, wherein the valley between the wickers comprises a curved surface having a radius of at least 0.04 inches.