SG187325A1

SG187325A1 - Annulus seal utilizing energized discrete soft interfacial sealing elements

Info

Publication number: SG187325A1
Application number: SG2012048815A
Authority: SG
Inventors: Michael Shaw
Original assignee: Vetco Gray Inc
Priority date: 2011-07-05
Filing date: 2012-07-02
Publication date: 2013-02-28
Also published as: GB2492654A; SG10201408439SA; AU2012203917A1; BR102012016522A2; US20130008672A1; GB201211908D0; NO20120769A1; CN102865048A

Abstract

A seal assembly (21) for sealing an annulus (20) between inner (14) and outer (12) wellhead members comprises an energizer ring (38) having inner and outer legs (41, 43) separated by a slot (39), formed of a high strength elastic material and having a central axis and an inner diameter seal ring (50) formed of an inelastic material located on an inner side of the inner leg (43) for creating a seal between the inner wellhead member (14) the energizer (38). An outer diameter seal ring (48) formed of an inelastic material is located on an outer side of the outer leg (41) for creating a seal between the energizer (38) and the outer wellhead member (12). The seal assembly (21) may have an initial radial dimension from inner surface (55) of the inner diameter seal ring (50) to an outer surface (57) of the outer diameter seal ring (48) that is adapted to be greater than a radial width of the annulus (20), causing the legs (41, 43) to deflect towards each other when inserted in the annulus (20).Figure 1

Description

ANNULUS SEAL UTILIZING ENERGIZED DISCRETE SOFT

INTERFACIAL SEALING ELEMENTS

BACKGROUND OF THE INVENTION

1 Field of the Invention

[0001] This invention relates in general to wellhead assemblies and in particular to seal assemblies for sealing between inner and outer wellhead members. 2. Description of the Related Art

[0002] 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.

[0003] A variety of annulus seals of this nature have been employed. Conventional annulus seals include, for example, elastomeric and partially metal and elastomeric rings. Prior art subsea stab type seals may utilize elastomeric materials which are compressed into an interference fit annulus. These are simple designs, easy to install, retain a reasonable constant load when unpressurised over time due to their inherent elasticity and are soft enough to flow and seal on minor defects. However such materials have a limited range of use in terms of temperature and fluid compatibility. They may swell and degrade mechanically in certain fluid environments, such as those found in many wellheads, and can suffer from explosive failure if subjected to rapidly decreasing pressure in a gas environment.

[0004] Prior art seal rings made entirely of metal for forming metal-to-metal seals are also employed. In order to cope with internal stressing remote from the interfaces, metal seals of the prior art are made from hard high strength materials which make sealing at the interface difficult and require generating of huge loads to provide any degree of damage tolerance. This in turn will itself cause damage to the same surfaces. To overcome this, coatings in the form of spray coatings or plating or melted inlays, such as brazing have been used to bond a secondary softer material to the metal seal. These coatings are often difficult to apply, costly, inefficient in material usage, tend to increase the hardness of the sprayed material and are typically difficult to apply thick enough to provide the volume of material required to seal on serious defects.

[0005] A third option for the prior art has been to use inelastic thermoplastic materials such as polytetrafluoroethylene, or moulded graphite for the sealing apparatus. These do not have any inherent elasticity and so require some secondary parts, such as internal springs, to provide an elastic response to the changing environment that ensures the seal retains a reasonable constant load when unpressurised over time and so ensuring a seal is maintained at all times. Due to the low strength of thermoplastic materials they generally cannot sustain the loads required to cause significant plastic flow at the interface and so do not tend to seal well on damaged surfaces.

[0006] Therefore while metal or inelastic materials allow a much wider temperature range, do not swell or degrade mechanically in most fluid environments and do not suffer from explosive gas decompression, they do represent many other technical problems, most notably an inability to seal on damaged surfaces. Damage to subsea parts cannot be fully monitored or controlled and therefore seal failure due to damaged surfaces represents a significant cost risk when running equipment subsea.

[0007] Therefore, there is a need for an annulus seal that would maintain a seal that can seal on serious surface defects, operate over a much wider temperature range, does not swell or degrade mechanically in most fluid environments, does not suffer from explosive gas decompression and can be easily and cheaply manufactured.

SUMMARY OF THE INVENTION

[0008] In view of the foregoing, various embodiments of the present invention advantageously provide seal assemblies to address shortfalls of the prior art. Various embodiments of the present application use soft inelastic materials in a situation where the seal is highly loaded, by removing the inelastic material from the highly stressed unsupported areas and replacing it with a high strength energizer. Alternative embodiments use thick soft metallic materials, in fully annealed condition if required, with no need for a metallurgical or other type of bond to the base component.

[0009] More specifically, the current application provides a seal assembly for sealing an annulus between inner and outer wellhead members comprising an energizer ring having inner and outer legs separated by a slot which is formed of a high strength elastic material and has a central axis, an inner diameter seal ring formed of an inelastic material located on an inner side of the inner leg for creating a seal between the inner wellhead member and the energizer, and an outer diameter seal ring formed of an inelastic material located on an outer side of the outer leg for creating a seal between the energizer and the outer wellhead member.

[00010] In certain embodiments, the seal assembly has an initial radial dimension from inner surface of the inner diameter seal ring to an outer surface of the outer diameter seal ring that is adapted to be greater than a radial width of the annulus, causing the legs to deflect towards each other when inserted in the annulus. This deflection generates radial loads in the energizer which in turn creates contact loads in both seal rings.

[00011] The seal assembly may further comprise a plurality of anti-extrusion devices for restricting an axial dimension of each of the seal rings when the seal assembly is set. The anti- extrusion devices may comprise an annular band on the inner side of the inner leg and protruding inward from the inner leg, an annular band on the outer side of the outer leg and protruding outward from the outer leg, and an annular recess in each of the bands. Each of the seal rings is located in one of the recesses and radially protrudes therefrom prior to setting of the seal assembly. Prior to setting of the seal assembly, an axial dimension of each annular recess is greater than an axial dimension of each seal ring. The annular bands are adapted to contact the inner and outer wellhead members when the seal ring assembly is set.

[00012] In an alternative embodiment, the anti-extrusion devices comprise a pair of wedge rings, the wedge rings having a mating wedge surface that causes one of the wedge rings to slide radially inward and the other to slide radially outward. In another alternative embodiment, the anti-extrusion device comprises an inner wedge ring having an inner wedge ring surface, an outer wedge ring having an outer wedge ring surface, and inner and outer wedge surfaces on a base of the energizer that slidingly engage the inner wedge ring surface and the outer wedge ring surface during setting of the seal assembly to convey the wedge rings apart from each other.

[00013] In certain other embodiments, the seal assembly further comprises a second energizer ring having inner and outer legs facing in an opposite direction to said first mentioned energizer ring. The inner diameter seal ring and the outer diameter seal ring may be formed of an inelastic material selected from a group consisting of lead, tin, silver, gold, tantalum, virgin polytetrafluoroethylene, filled polytetrafluoroethylene or polyetheretherketone, or compression molded graphite.

[00014] In other embodiments, the current application also provides a wellhead assembly comprising an outer wellhead member having a bore and an axis, an inner wellhead member located in the bore and defining an annulus between the inner and outer wellhead members, an energizer ring having inner and outer legs separated by a slot, formed of a high strength elastic (nominally metallic) material and having a central axis, an inner diameter seal ring formed of an inelastic material located on an inner side of the inner leg for creating a seal between the inner wellhead member and the energizer, and an outer diameter seal ring formed of an inelastic material located on an outer side of the outer leg for creating a seal between the energizer and the outer wellhead member, wherein the legs deflect towards each other when inserted in the annulus, causing the seal rings to radially deform.

[00015] The wellhead assembly may further comprise a plurality of anti-extrusion devices for restricting an axial dimension of each of the seal rings when set in the annulus. The anti- extrusion devices may comprise an annular band on the inner side of the inner leg and protruding inward from the inner leg, an annular band on the outer side of the outer leg and protruding outward from the outer leg, and an annular recess in each of the bands, wherein prior to setting of the seal assembly each of the seal rings is located in one of the recesses and radially protrudes therefrom and an axial dimension of each annular recess is greater than an axial dimension of each seal ring.

[00016] Other embodiments of the current application provide an apparatus for sealing an annulus between inner and outer wellhead members, the seal assembly comprising a first energizer ring having inner and outer legs separated by a slot, formed of a high strength elastic (nominally metallic) material and having a central axis, a second energizer ring having inner and outer legs facing in an opposite direction to the first energizer ring, an inner diameter seal ring formed of an inelastic material located on an inner side of each of the inner legs for creating a seal between the inner wellhead member the energizers, an outer diameter seal ring formed of an inelastic material located on an outer side of each of the outer legs for creating a seal between the energizers and the outer wellhead member, and a plurality of anti-extrusion devices for restricting an axial dimension of each of the seal rings when the seal assembly is set.

[00017] In one embodiment of such apparatus, when a force is applied in an axial direction to set the apparatus in the annulus, the inner seal rings move inward to abut the inner wellhead member and the outer seal rings move outward to abut the outer wellhead member. The anti extrusion devices may comprise an inner wedge ring having an inner wedge ring surface, an outer wedge ring having an outer wedge ring surface, and inner and outer wedge surfaces on a base of each energizer that slidingly engage the inner wedge ring surface and the outer wedge ring surface during setting of the apparatus to convey the wedge rings apart from each other.

[00018] Yet another embodiment of the present application provides a method for sealing an annulus between inner and outer wellhead members, the method comprising the steps of: (a) positioning an energizer within the annulus, the energizer ring having inner and outer legs separated by a slot, formed of a high strength elastic (nominally metallic) material and having a central axis; (b) creating a seal between the inner wellhead member and the energizer with an inner diameter seal ring formed of an inelastic material located on an inner side of the inner leg; and (c) creating a seal between the energizer and the outer wellhead member with an outer diameter seal ring formed of an inelastic material located on an outer side of the outer leg.

[00019] Steps (b) and (c) may further comprise applying sufficient force to the energizer to deflect the legs of the energizer towards each other by elastic deformation and cause plastic deformation of the inner diameter seal ring and outer diameter seal ring. Steps (b) and (c) may be further aided by the application of fluid pressure which expands the energizer, causing the legs of the energizer to deflect away from each other, thereby causing further plastic deformation of the inner diameter seal ring and outer diameter seal ring.

The method may also further comprise the step of limiting the axial expansion of the inner diameter seal ring and the outer diameter seal ring with an anti-extrusion device.

The step of limiting the axial expansion of the inner diameter seal ring and the outer diameter seal ring may be performed by an annular band on the inner side of the inner leg and protruding inward from the inner leg and an annular band on the outer side of the outer leg and protruding outward from the outer leg, wherein an annular recess is formed in each of the bands and wherein prior to setting of the seal assembly, each of the seal rings is located in one of the recesses and radially protrudes therefrom, and an axial dimension of each annular recess is greater than an axial dimension of each seal ring.

BRIEF DESCRIPTION OF THE DRAWINGS

[00020] 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.

[00021] FIG. 1 is a sectional view of portions of a wellhead assembly providing a annulus seal;

[00022] FIG. 2 is a sectional view of a portion of a seal assembly according to an embodiment of the present invention;

[00023] FIG. 3 is a sectional view of the seal assembly of FIG 2;

[00024] FIG. 4 is a sectional view of a portion of a seal assembly according to an alternative embodiment of the present invention ; and

[00025] FIG. 5 is a sectional view of the seal assembly of FIG 4.

[00026] FIG. 6 is an additional sectional view of the seal assembly of FIG 4.

DETAILED DESCRIPTION

[00027] 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.

[00028] FIG. 1 illustrates, for example, portions of a wellhead assembly 10 including a seal assembly 21, which may be a seal assembly according to any of the embodiment of the present application. The wellhead assembly 10 can include an outer tubular 12 affixed at an upper end of a wellbore (not shown) and coaxially circumscribing an inner tubular 14. The outer tubular 12 may be, for example, a high-pressure wellhead housing or a casing hanger. The inner tubular 14 may be, for example, a casing hanger, casing, tubing hanger, production tubing, or an isolation sleeve.

[00029] Inner tubular 14 transitions from an upper region with a larger outer diameter 26 higher within the wellhead assembly 10, to a lower region with a smaller outer diameter 28 lower within the wellhead assembly 10 through a downward facing shoulder 30. Outer tubular transitions from an upper region with a larger inner diameter 32 higher within the wellhead assembly to a lower region with a smaller inner diameter 34 lower within the wellhead assembly through an upward facing shoulder 36.

[00030] The spaced apart distance between the respective inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14, respectively form an annulus 20. Within annulus 20 is seal assembly 21. Seal assembly 21 is ring shaped. The diameter of the opening in the center of the ring shaped assembly 21 is sized so that inner diameter sealing surface 22 of seal assembly 21 makes contact with the outer diameter surface 18 of the inner tubular 14. The outer diameter of the ring shaped assembly 21 is sized so that outer diameter sealing surface 24 of seal assembly 21 makes contact with inner surface 16 of outer tubular 12. Embodiments of seal assembly 21 are shown in FIGS 2-6.

[00031] Turning now to FIG 2, in one embodiment, the seal assembly may comprise an energizer 38. Energizer 38 is shown as a single "U" section shaped ring creating an upward facing internal slot or groove 39. Internal groove 39 results in energizer 38 having an outer leg 41 and an inner leg 43, defined by the shape of internal groove 39. Energizer 38 comprises an outer circumferential recess 40 on the outer surface 42 of energizer 38 and an inner circumferential recess 44 on the inner surface 46 of energizer 38. Outer circumferential recess 40 contains an outer diameter sealing ring 48 and inner circumferential recess 44 contains an inner diameter sealing ring 50. Sealing rings 48, 50 are shown with a solid square cross section but they may have other alternative cross sections, such as rectangular, semi-circular, circular, oval, or other workable shape. Sealing rings 48, 50 may be extruded, machined complete, compression formed from wire and joined at the ends or fabricated by other known methods.

[00032] As is shown in FIG 2, when energizer 38 is not positioned within annulus 20 (FIG 3), the axial height of outer circumferential recess 40 is bigger than the axial height of outer diameter sealing ring 48 and the axial height of inner circumferential recess 44 is bigger than the axial height of inner diameter sealing ring 50. This allows room for sealing rings 48, 50 to expand in height when the width of the sealing rings 48, 50 is compressed, as shown in FIG 3, when seal assembly 21 is located within annulus 20. Sealing rings 48, 50 are not fixed or bonded to energizer 38. This avoids a complicated or costly bonding process, allows for easy replacement of the sealing rings 48,50, and allows the sealing rings 48, 50 to more readily flow into defects.

[00033] Energizer 38 has circumferential bands or protrusions 52 that project outward from outer surface 42 of energizer 38 above and below outer circumferential recess 40.

Circumferential bands or protrusions 54 project inward from inner surface 46 of energizer 38 above and below inner circumferential recess 44. Protrusions 52, 54 have circumferential end surfaces 56, 58, respectively. Annular recesses 40, 44 are located with in each of the bands 52, 54 respectively.

[00034] As show in FIG 3, when energizer 38, is located within annulus 20, outer sealing ring 48 is in sealing engagement with inner surface 16 of outer tubular 12 and the energizer 38. Inner sealing ring 50 is in sealing engagement with outer diameter surface 18 of the inner tubular 14 and energizer 38. Energizer 38 is positioned above downward facing shoulder 30 of inner tubular 14 and below upward facing shoulder 36 of outer tubular 12. In alternative embodiments, shoulder 30 may be upward facing and shoulder 36 may be downward facing. In yet other alternative embodiments, shoulders 30, 36 may both face upwards or both face downwards. Internal groove 39 of energizer 38 is open to the pressure of the well fluid contained within annulus 20. In the embodiment of FIG 3, the pressure side is at the higher end of annulus 20 and therefore internal groove 39 opens upward. In alternative embodiment, the pressure side may be at the lower end of annulus 20, in which case, the groove 39 would open downward. A retainer ring 60 is located below energizer 38 to limit downward movement of energizer 38 within annulus 20.

[00035] Seal assembly 21 may be installed within annulus 20 with a interference between the inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14. In this case, the initial radial dimension of the energizer 38, measured from end surface 56 to end surface 58 is larger than the distance between inner surface 16 of outer tubular 12 and the energizer 38, outer diameter surface 18 of the inner tubular 14. Similarly, the initial radial dimension from inner surface 55 of the inner diameter seal ring 50 to an outer surface 57 of the outer diameter seal ring 48 greater than a radial width of the annulus between inner surface 16 of outer tubular 12 and the energizer 38, outer diameter surface 18 of the inner tubular 14.

Therefore legs 41, 43 of energizer 38 will have to deflect inward towards each other when inserted within annulus 20. This inward deflection of legs 41, 43 of energizer 38 generate an outward radial elastic load. This will cause sealing rings 48, 50 to be compressed between inner surface 16 of outer tubular 12 and the energizer 38, outer diameter surface 18 of the inner tubular 14 and energizer 38, respectively.

[00036] The compressive forces causes plastic or permanent deformation of sealing rings 48, 50, causing them to fill the recesses 40 and 44 and to seal with and fill any defects in outer tubular 12 and inner tubular 14. The deformation of sealing rings 48, 50 is contained to the interior of recesses 40, 44, which act as anti-extrusion means. End surfaces 56, 58 of protrusions 52 and 54 will contact the inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14, respectively, to limit the outward radial forces on sealing rings 48, 50. The combination of the elastic deformation of energizer 38 and plastic deformation of sealing rings

48, 50 creates a constant elastic contact pressure at each of the sealing interfaces which does not diminish with time or load history or temperature, and creates a seal at low pressure and also possibly at high pressure.

[00037] Alternatively, the radial outward elastic load of energizer 38 may be created by the fluid pressure within annulus 20. In this embodiment, the fluid pressure within annulus 20 and groove 39 will act on the inside surfaces of groove 39, which is open to the pressure of the fluid contained within annulus 20, applying a radial force on legs 41, 43. In the same manner as discussed above, this will cause sealing rings 48, 50 to be compressed between inner surface 16 of outer tubular 12 and the energizer 38, and the outer diameter surface 18 of the inner tubular 14 and energizer 38, respectively.

[00038] The compression causes plastic or permanent deformation of sealing rings 48, 50, causing them to fill the recesses 40 and 44. The deformation of sealing rings 48, 50 is contained to the interior of recesses 40, 44, which act as anti-extrusion means. End surfaces 56, 58 of protrusions 52 and 54 will contact the inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14, respectively, to limit the outward radial forces on sealing rings 48, 50. The combination of the elastic deformation of energizer 38 and plastic deformation of sealing rings 48, 50 creates a constant elastic contact pressure at each of the sealing interfaces.

In this case, a drop in pressure may cause a drop in elastic loading of the energizer 38. Another alternative embodiment is to combine both an interference fit and fluid pressure loading on energizer 38. In this embodiment, the energizer 38 and seal rings 48, 50 will still maintain a seal in the event of a complete loss of fluid pressure, but the elastic forces of energizer 38 may be augmented by fluid pressure within annulus 20 and groove 39.

[00039] Sealing rings 48, 50 are formed of soft inelastic materials and may be for example, a soft metal such as lead, tin, silver, gold or tantalum, an inelastic thermoplastic, such as virgin polytetrafluoroethylene, filled polytetrafluoroethylene or polyetheretherketone, or other inert inelastic materials such as compression molded graphite. Sealing rings 48, 50 may alternatively be formed of other soft inelastic materials. An appropriate soft inelastic material will be selected so that sealing rings 48, 50 will flow readily into defects on the inner surface 16 of outer tubular 12 and the outer diameter surface 18 of the inner tubular 14 and create sufficient contact pressure on the surface of any such defect to create a seal when subjected to radial loading. Where there is no defect present the sealing rings 48, 50 will simply deform and flow upwards and downwards in the recesses 40, 44 to fill the available space, while creating a seal on the defect free inner surface 16 of outer tubular 12 and the outer diameter surface 18 of the inner tubular 14.

[00040] Energizer 38 is formed from material that is strong enough to withstand the internal fluid pressure within the annulus 20 as well as any internal loads generated by the interference fit between the energizer 38, the inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14, without undergoing significant plastic deformation, which could limit the load that could be applied to energizer 38 or cause failure of energizer 38 and thus cause the seal assembly 21 to fail. Energizer 38 must therefore be made from material with higher strength or that is harder than the material used to make the sealing rings 48, 50. Preferably, energizer 38 is made from steel, or where corrosion is of concern from steel or nickel based alloy.

[00041] In an alternative embodiment, as shown in FIG 4, the seal assembly may comprise two energizers, including a primary energizer 62 and a backside energizer 64. Energizers 62, 64 are shown as single "U" section shaped rings. Primary energizer 62 has an upward facing internal slot or groove 66, which results in energizer 62 having an outer leg 68 and an inner leg 70, defined by the shape of internal groove 66. Backside energizer 64 has a downward facing internal slot or groove 72, which results in energizer 64 having an outer leg 74 and an inner leg 76, defined by the shape of internal groove 72. Energizers 62, 64 may have alternative shaped cross sections.

[00042] Primary inner diameter seal ring 78 is located external to leg 70 of primary energizer 62 and primary outer diameter seal ring 80 is located external to leg 68 of primary energizer 62.

Backside inner diameter seal ring 82 is located external to leg 76 of backside energizer 64 and backside outer diameter seal ring 84 is located external to leg 74 of backside energizer 64.

Sealing rings 78, 80, 82, 84 are shown with a solid rectangular cross section but they may have other alternative cross sections, such as square, semi-circular, circular, oval, or other workable shape. Sealing rings 78, 80, 82, 84 may be extruded, machined complete, compression formed from wire and joined at the ends or fabricated by other known methods.

[00043] An inner intermediate anti-extrusion ring 86 is located below primary inner diameter seal ring 78 and above backside inner diameter seal ring 82. A lateral portion 102 of inner intermediate anti-extrusion ring 86 extends between primary energizer 62 and backside energizer 64. An outer intermediate anti-extrusion ring 88 is located below primary outer diameter seal ring 80 and above backside outer diameter seal ring 84. A lateral portion 104 of outer intermediate anti-extrusion ring 88 extends between primary energizer 62 and backside energizer 64.

[00044] In the embodiment of FIG 4, intermediate anti-extrusion rings 86, 88 are generally wedge shaped with upward facing shoulders 83 which engage downward facing wedge surfaces or shoulders 85 of primary energizer 62. Downward facing wedge surface or shoulder 87 of anti-extrusion rings 86, 88 engage upward facing shoulders 89 of backside energizer 64.

[00045] Primary anti-extrusion rings 90, 91 are located above primary seal rings 78, 80 and backside anti-extrusion rings 92, 93 are located below backside seal rings 82, 84. In the embodiment of FIG 4, the primary anti-extrusion rings 90, 91 consist of a pair of rings with a wedge shaped cross section. Outer primary anti-extrusion ring 90 has an upper surface which is essentially horizontal and an angled downward facing surface 94. Inner primary anti-extrusion ring 91 has a lower surface which is essentially horizontal and an angled upward facing surface 96. Downward facing surface 94 of outer primary anti-extrusion ring 90 engages upward facing surface 96 of Inner primary anti-extrusion ring 91. Inner backside anti-extrusion ring 92 has an upper surface which is essentially horizontal and an angled downward facing surface 98. Outer primary anti-extrusion ring 93 has a lower surface which is essentially horizontal and an angled upward facing surface 100. Downward facing surface 98 of inner backside anti-extrusion ring 92 engages upward facing surface 100 of outer backside anti-extrusion ring 93.

[00046] Before being inserted in an annulus, the inner diameter of the inner diameter seal rings 78, 82 is smaller than the inner diameter of the primary anti-extrusion rings 90, 91 intermediate inner anti-extrusion ring 86, and backside anti-extrusion rings 92, 93. Similarly, the outer diameter of the outer diameter seal rings 80, 84 is larger than the outer diameter of primary anti-extrusion rings 90, 91 intermediate outer anti-extrusion ring 88, and backside anti-extrusion rings 92, 93. In addition, the height of the seal rings 78, 80 is shorter than the distance between the primary anti-extrusion rings 90, 91 and the intermediate anti-extrusion rings 86, 88. The height of the seal rings 82,84 is shorter than the distance between the intermediate anti-extrusion rings 86, 88, and the backside anti-extrusion rings 92, 93. This allows room for sealing rings 78,

80, 82, 84 to expand in height when the width of the sealing rings 78, 80, 82, 84 is compressed, as shown in FIG 5, when seal assembly 21 is located within annulus 20. Sealing rings 78, 80, 82, 84 are not fixed or bonded to energizers 62, 64. This avoids a complicated or costly bonding process, allows for easy replacement of the sealing rings 78, 80, 82, 84, and allows the sealing rings 78, 80, 82, 84 to more readily flow into defects.

[00047] When seal assembly 21 of FIG 5 is positioned within an annulus 20, primary outer diameter seal ring 80, is in sealing engagement with inner surface 16 of outer tubular 12 and with the primary energizer 62. Primary inner diameter seal ring 78 is in sealing engagement with outer diameter surface 18 of the inner tubular 14 and with primary energizer 62. Backside outer diameter seal ring 84, is in sealing engagement with inner surface 16 of outer tubular 12 and with the backside energizer 64. Backside inner diameter seal ring 82 is in sealing engagement with outer diameter surface 18 of the inner tubular 14 and with backside energizer 64. Seal assembly 21 is positioned above downward facing shoulder 30 of inner tubular 14 and below upward facing shoulder 36 of outer tubular 12.

[00048] As shown in FIG 6, when seal assembly 21 is fully set within annulus 20, backside anti-extrusion rings 92, 93 will be restrained from further downward movement. For example, backside anti-extrusion rings 92, 93 may land on shoulders 106 on the inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14. In alternative embodiments, a retainer ring or similar devise may be used instead.

[00049] By continuing to apply a downwards force to primary anti-extrusion rings 90, 91, downward facing surface 98 of inner backside anti-extrusion ring 92 engages and slides along upward facing surface 100 of outer backside anti-extrusion ring 93. This causes the inner backside anti-extrusion ring 92 to move towards and come into contact with inner surface 16 of outer tubular 12 and outer backside anti-extrusion ring 93 to move towards and come into contact with outer diameter surface 18 of the inner tubular 14. Backside anti-extrusion rings 92, 93 will together then cover the full diameter of annulus 20, limiting the downward expansion of backside seal rings 82, 84.

[00050] This downward force on primary anti-extrusion rings 90, 91 will cause primary energizer 62 to move towards backside energizer 64. This causes upward facing shoulders 83 of intermediate anti-extrusion ring to engage downward facing shoulders 85 of primary energizer

62, and downward facing shoulder 87 of anti-extrusion rings 86, 88 engage upward facing shoulders 89 of backside energizer 64, forcing the intermediate outer anti-extrusion ring 88 to move towards inner surface 16 of outer tubular 12 and intermediate inner anti-extrusion ring 86 to move towards outer diameter surface 18 of the inner tubular 14. Movement of the anti- extrusion rings 86, 88 may be limited either by inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14 respectively, or by the closed ends of energizers 62, 64 contacting upper and lower surfaces of lateral portions 102, 104 of anti-extrusion rings 86, 88.

[00051] The downward force on primary anti-extrusion rings 90, 91 will additionally cause downward facing surface 94 of outside primary anti-extrusion ring 90 engages and slide along upward facing surface 96 of inner primary anti-extrusion ring 91. This will result in inner primary anti-extrusion ring 90 to moving towards and coming into contact with outer diameter surface 18 of the inner tubular 14 and outer primary anti-extrusion ring 91 moving towards and coming into contact with inner surface 16 of outer tubular 12. Primary anti-extrusion rings 90, 91 will together then cover the full diameter of annulus 20, limiting the upward expansion of primary seal rings 78, 80. A retaining mechanism, such as retaining ring 108 will be used to maintain the downward force on primary anti-extrusion rings.

[00052] Seal assembly 21 may be installed within annulus 20 with a interference between the inner surface 16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14. The compression on the energizers 62, 64 causes legs 68, 70 of primary energizer 62 and legs 74, 76 of backside energizer 64 to deflect inwardly, generating an outward radial elastic load. This will cause sealing rings 80, 84 to be compressed between inner surface 16 of outer tubular 12 and the energizers 62, 64 respectively, and sealing rings 78, 82 to be compressed between outer diameter surface 18 of the inner tubular 14 and energizers 62, 64, respectively. The compressive forces causes plastic deformation of sealing rings 78, 80, 82, 84, causing them to deform and become thinner and taller. The increase in height of sealing rings 78, 80 is contained to the space between the primary anti-extrusion rings 90, 91 and the intermediate anti-extrusion rings 86, 88.

The increase in height of sealing rings 82, 84 is contained to the space between the intermediate anti-extrusion rings 86,88 and the backside anti-extrusion rings 92, 93. The combination of the elastic deformation of energizers 62, 64 and plastic deformation of sealing rings 78, 80, 82, 84 creates a constant elastic contact pressure at each of the sealing interfaces which does not diminish with time or load history or temperature, and creates a seal at low pressure and also possibly at high pressure.

[00053] Alternatively, the radial outward elastic load of energizers 62, 64 may be created by the fluid pressure within grooves 66, 72, which applies an outward force on legs 68, 70, 74, 76, casing outward radial deflections of legs 68, 70, 74, 76. In the same manner as discussed above, this will cause sealing rings 78, 80, 82, 84 to be compressed between inner surface 16 of outer tubular 12 and the energizers 62, 64, and the outer diameter surface 18 of the inner tubular 14 and energizers 62, 64, respectively. The compressive forces causes plastic deformation of sealing rings 78, 80, 82, 84, causing them to deform and become thinner and taller. The increase in height of sealing rings 78, 80 is contained to the space between the primary anti-extrusion rings 90, 91 and the intermediate anti-extrusion rings 86, 88. The increase in height of sealing rings 82, 84 is contained to the space between the intermediate anti-extrusion rings 86,88 and the backside anti-extrusion rings 92, 93. The combination of the elastic deformation of energizers 62, 64 and plastic deformation of sealing rings 78, 80, 82, 84 creates a constant elastic contact pressure at each of the sealing interfaces.

[00054] Sealing rings 78, 80, 82, 84 are formed of soft inelastic materials and may be for example, a soft metal such as lead, tin, silver, gold or tantalum, an inelastic thermoplastic, such as virgin polytetrafluoroethylene, filled polytetrafluoroethylene or polyetheretherketone, or other inert inelastic materials such as compression molded graphite. Sealing rings 78, 80, 82, 84 may alternatively be formed of other soft inelastic materials. An appropriate soft inelastic material will be selected so that sealing rings 78,80, 82, 84 will flow readily into defects on the inner surface 16 of outer tubular 12 and the outer diameter surface 18 of the inner tubular 14 and create sufficient contact pressure on the surface of any such defect to create a seal when subjected to radial loading. Where there is no defect present the sealing rings 78, 80, 82, 84 will simply deform and flow upwards and downwards to fill the available space, while creating a seal on the defect free inner surface 16 of outer tubular 12 and the outer diameter surface 18 of the inner tubular 14.

[00055] Energizers 62, 64 are formed from material, such as steel or nickel or alloy thereof, that is strong enough to withstand the internal fluid pressure within the annulus 20 as well as any internal loads generated by the interference fit between the energizers 62, 64, the inner surface

16 of outer tubular 12 and outer diameter surface 18 of the inner tubular 14, without undergoing significant plastic deformation, which could limit the load that could be applied to energizers 62, 64 or cause failure of energizer 62, 64 and thus cause the seal assembly 21 to fail. Energizers 62, 64 must therefore be made from material with higher strength or that is harder than the material used to make the sealing rings 78, 80, 82, 84.

[00056] In the drawings and specification, there have 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

THAT CLAIMED IS:

1. A seal assembly (21) for sealing an annulus (20) between inner (14) and outer (12) wellhead members, the seal assembly comprising: an energizer ring (38) having inner (43) and outer (41) legs separated by a slot (39), formed of a high strength elastic material and having a central axis; an inner diameter seal ring (50) formed of an inelastic material located on an inner side of the inner leg (43) for creating a seal between the inner wellhead member the energizer (38); and an outer diameter seal ring (48) formed of an inelastic material located on an outer side of the outer leg (41) for creating a seal between the energizer (38) and the outer wellhead member (12).

2. The seal assembly (21) of claim 1, wherein the seal assembly (21) has an initial radial dimension from inner surface (55) of the inner diameter seal ring (50) to an outer surface (57) of the outer diameter seal ring (48) that is adapted to be greater than a radial width of the annulus (20), causing the legs (41, 43) of the energizer ( 38) to deflect towards each other when inserted in the annulus (20).

3. The seal assembly (21) of claim 1 further comprising a plurality of anti-extrusion devices for restricting an axial dimension of each of the seal rings (48, 50) when the seal assembly is set.

4. The seal assembly (21) of claim 3, wherein the anti-extrusion devices comprise: an annular band (54) on the inner side of the inner leg (43) and protruding inward from the inner leg (43); an annular band (52) on the outer side of the outer leg (41) and protruding outward from the outer leg (41);

an annular recess (40, 44) in each of the bands (52, 54); and wherein each of the seal rings (48, 50) is located in one of the recesses (40, 44) and radially protrudes therefrom prior to setting of the seal assembly (21).

5. The seal assembly (21) of claim 4, wherein prior to setting of the seal assembly (21), an axial dimension of each annular recess (40, 44) is greater than an axial dimension of each seal ring (48, 50).

6. The seal assembly (21) of claim 4, wherein the annular bands (52, 54) are adapted to contact the inner (14) and outer (12) wellhead members when the seal assembly (21) is set.

1. The seal assembly (21) of claim 3, wherein the anti-extrusion devices comprise a pair of wedge rings (90, 91), the wedge rings having a mating wedge surface (96, 94) that causes one of the wedge rings to slide radially inward and the other to slide radially outward.

8. The seal assembly (21) of claim 3, wherein the anti-extrusion devices comprise: an inner wedge ring (88) having an inner wedge ring surface (83); an outer wedge ring (86) having an outer wedge ring surface; and inner and outer wedge surfaces (85) on a base of the energizer (62) that slidingly engage the inner wedge ring surface and the outer wedge ring surface (83) during setting of the seal assembly (21) to convey the wedge rings apart from each other.

9. The seal assembly (21) of claim 1, wherein the inner diameter seal ring (50) and the outer diameter seal ring (48) are formed of an inelastic material selected from a group consisting of lead, tin, silver, gold, tantalum, virgin polytetrafluoroethylene, filled polytetrafluoroethylene, polyetheretherketone, or compression molded graphite.

10. The seal assembly of claim 1 further comprising: a second energizer ring (64) having inner (76) and outer (74) legs facing in an opposite direction to the first mentioned energizer ring; inner diameter seal rings (78, 82) located on an inner side of each of the inner legs for creating a seal between the inner wellhead member (14) and the energizers; outer diameter seal rings (80, 84) located on an outer side of each of the outer legs for creating a seal between the energizers and the outer wellhead member (12); and a plurality of anti-extrusion devices (90, 91, 86, 88, 92, 93) for restricting an axial dimension of each of the seal rings (78, 82, 80, 84) when the seal assembly (21) is set.

11. A method for sealing an annulus (20) between inner (14) and outer (12) wellhead members, the method comprising the steps of: (a) positioning an energizer ring (38) within the annulus (20), the energizer ring (38) having inner (43) and outer (41) legs separated by a slot (39), formed of an elastic material and having a central axis; (b) creating a seal between the inner wellhead member (14) and the energizer (38) with an inner diameter seal ring (50) formed of an inelastic material located on an inner side of the inner leg (43); and (c) creating a seal between the energizer (38) and the outer wellhead member (12) with an outer diameter seal ring (48) formed of an inelastic material located on an outer side of the outer leg (41).

12. The method of claim 11, wherein steps (b) and (c¢) further comprise applying sufficient force to the energizer (38) to deflect the legs (41, 43) of the energizer towards each other by elastic deformation and cause plastic deformation of the inner diameter seal ring (50) and outer diameter seal ring (48).

13. The method of claim 11, wherein steps (b) and (c¢) further comprise providing a fluid under pressure within the slot (39) to apply a radial force on the legs (41, 43) and cause plastic deformation of the inner diameter seal ring (50) and outer diameter seal ring (48).

14. The method of claim 11 further comprising the step of limiting the axial expansion of the inner diameter seal ring (50) and the outer diameter seal ring (48) with an anti-extrusion device.

15. The method of claim 14, wherein the step of limiting the axial expansion of the inner diameter seal ring (50) and the outer diameter seal ring (48) is performed by an annular band (54) on the inner side of the inner leg (43) and protruding inward from the inner leg (43) and an annular band (52) on the outer side of the outer leg (41) and protruding outward from the outer leg (41), wherein an annular recess (40, 44) is formed in each of the bands (52, 54) and wherein prior to setting of the energizer ring (38): each of the seal rings (48, 50) is located in one of the recesses (40, 44) and radially protrudes therefrom; and an axial dimension of each annular recess (40, 44) is greater than an axial dimension of each seal ring (48, 50).