Patent Publication Number: US-8978772-B2

Title: Casing hanger lockdown with conical lockdown ring

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to wellhead casing hangers and, in particular, to a casing hanger lockdown slip ring that converts axial loads into radial loads. 
     2. Brief Description of Related Art 
     Seals are used between inner and outer wellhead tubular members to contain internal well pressure. The inner wellhead member may be a tubing hanger that supports a string of tubing extending into the well for the flow of production fluid. The tubing hanger lands in an outer wellhead member, which may be a wellhead housing, a Christmas tree, or a tubing head. A seal or packoff seals between the tubing hanger and the outer wellhead member. Alternately, the inner wellhead member might be a casing hanger located in a wellhead housing and secured to a string of casing extending into the well. A seal or packoff seals between the casing hanger and the wellhead housing. 
     A variety of seals of this nature have been employed in the prior art. Prior art seals include elastomeric and partially metal and elastomeric rings. Prior art seal rings made entirely of metal for forming metal-to-metal seals are also employed. The seals may be set by a running tool, or they may be set in response to the weight of the string of casing or tubing. One type of prior art metal-to-metal seal has inner and outer walls separated by a conical slot. An energizing ring is pushed into the slot to deform the inner and outer walls apart into sealing engagement with the inner and outer wellhead members. The energizing ring is a solid wedge-shaped member. The deformation of the inner and outer walls exceeds the yield strength of the material of the seal ring, making the deformation permanent. 
     Thermal growth between the casing or tubing and the wellhead may occur, particularly with wellheads located at the surface, rather than subsea. The well fluid flowing upward through the tubing heats the string of tubing, and to a lesser degree the surrounding casing. The temperature increase may cause the tubing hanger and/or casing hanger to move axially a slight amount relative to the outer wellhead member or each other. During the heat up transient, the tubing hanger and/or casing hanger can also move radially due to temperature differences between components and the different rates of thermal expansion from which the component materials are constructed. If the seal has been set as a result of a wedging action where an axial displacement of energizing rings induces a radial movement of the seal against its mating surfaces, then sealing forces may be reduced if there is movement in the axial direction due to pressure or thermal effects. A reduction in axial force on the energizing ring results in a reduction in the radial inward and outward forces on the inner and outer walls of the seal ring, which may cause the seal to leak. A loss of radial loading between the seal and its mating surfaces due to thermal transients may also cause the seal to leak. 
     Prior art apparatuses that attempt to overcome the problems caused by axial movement of the casing hanger or tubing hanger include lockdown seals. Lockdown seals require formation of a groove in the landing sub or wellhead during the manufacturing process. After the wellhead and landing sub are positioned within the wellbore, the lockdown seal is run to the location of the landing sub where a ring of the lockdown seal either expands or contracts into the groove formed into the wellhead or landing sub, respectively. Unfortunately, the groove often fills with debris prior to run-in of the lockdown seal. The debris prevents engagement of the ring and thus, provides no lockdown benefits of the lockdown seal result. 
     Lockdown seals require a significant increase in production costs. This is due in part to increased costs to modify the basic wellhead or landing sub to include the lock ring groove. In addition, the use of these devices necessitate use of specialized tools and other components to properly land and engage the lockdown seal. Furthermore, prior art lockdown seals require some clearance between the landing sub and the lockdown apparatus of the lockdown seal. This clearance allows the lockdown seal to land in the appropriate location relative to the wellhead and landing sub while also providing the necessary space for the lockdown portion of the seal to engage either the wellhead or the landing sub. The clearance also allows the landing sub to shift before the lockdown device properly engages and arrests movement of the landing sub. In such instances, the landing sub may shift axially and cause the seal to fail. Thus, there is a need for a lockdown seal that overcomes the problems in the prior art described above. 
     SUMMARY OF THE INVENTION 
     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 casing hanger lockdown slip ring, and a method for using the same. 
     In accordance with an embodiment of the present invention, a wellhead assembly is disclosed. The wellhead assembly includes a wellhead member defining a bore having a shoulder, the bore having a conical profile that decreases in diameter in an upward direction. The wellhead assembly also includes a hanger landed on the shoulder within the bore of the wellhead member and defining an annulus between the wellhead and the hanger. A hanger seal ring is disposed within the annulus, engaged with an inner surface of the wellhead, and engaged with an outer surface of the casing hanger so that the seal ring prevents flow through the annulus. A nose ring is secured to a lower end of the seal ring and has a conical surface that engages a conical profile in the bore of the wellhead member. The nose ring also engages an outer diameter surface portion of the casing hanger to limit upwards axial movement of the casing hanger. 
     In accordance with another embodiment of the present invention, a seal for sealing an annulus between inner and outer tubular members, wherein the inner tubular member is landed in a bore of the outer tubular member, is disclosed. The seal includes a seal ring adapted to land in the annulus and adapted to expand radially when energized to engage an inner diameter surface of the outer tubular member and an outer diameter surface of the inner tubular member. A lockdown assembly is secured to a lower end of the seal ring and having a conical surface that engages a conical profile the bore of the outer tubular member. The lockdown assembly also engages an outer diameter surface portion of the casing hanger to limit upwards axial movement of the casing hanger. The lockdown assembly has a neck on an upper end of the lockdown assembly, the neck having a groove on an outer diameter of the neck. The seal ring has a lower leg on a lower end of the seal ring, the lower leg having a recess on an inner diameter of the lower leg. A split ring is partially within the groove and partially within the recess, securing the lockdown slip ring to the seal ring. 
     In accordance with yet another embodiment of the present invention, a method for sealing a hanger to a wellhead member is disclosed. The method provides the wellhead member with a bore having a conical profile that decreases in diameter in an upward direction. The method lands the hanger in the wellhead member and defines an annulus between the hanger and the wellhead member, the hanger having an external shoulder at a lower end of the annulus. The method secures a nose ring to a lower end of a hanger seal, the nose ring having a conical surface. The method lands the hanger seal and nose ring in the annulus, and exerts a downward axial force on the hanger seal and pushing the nose ring against the shoulder of the hanger. The method engages the conical surface of the nose ring with the conical profile in the bore of the wellhead member and a surface of the nose ring opposite the conical surface with an outer diameter surface portion of the hanger. The method then energizes the seal to seal the annulus. 
     An advantage of a the disclosed embodiments is that they provide a lockdown seal that seals a casing hanger to a wellhead without requiring an extra trip to run the lockdown portion of the seal. In addition, the disclosed embodiments do not require clearance between the casing hanger and the lockdown portion of the seal in order to engage. Thus, the disclosed embodiments may provide lockdown capability that prevents axial motion of the casing hanger caused by high pressures and thermal expansion. Still further, the disclosed embodiments provide a lockdown seal that can still engage lockdown functions in the event the seal fails to land at the appropriate location or debris otherwise prevents lockdown. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is a vertical cross-sectional view of a casing hanger lockdown seal ring in accordance with an embodiment of the present invention disposed between a wellhead and a casing hanger. 
         FIG. 2  is an enlarged vertical cross-sectional view of the casing hanger lockdown seal ring of  FIG. 1 , shown separate from the wellhead and casing hanger. 
         FIG. 3  is a vertical cross-sectional view of the lockdown seal ring as shown in  FIG. 2 , but energized within an annulus between the wellhead and the casing hanger. 
         FIG. 4  is an enlarged vertical cross-sectional view of a portion of a lockdown slip ring of the seal ring as shown in  FIG. 3 , landed on the casing hanger, but no yet energized. 
         FIG. 5  is an enlarged vertical cross sectional view of the portion of the lockdown slip ring as shown in  FIG. 4 , but energized. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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, and the prime notation, if used, indicates similar elements in alternative embodiments. 
     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 well drilling, running operations, and the like have been omitted in as much 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. 
     Referring to  FIG. 1 , a casing hanger  11  having an axis  14  is shown disposed within a subsea wellhead  13 . Generally, casing hanger  11  will land on a shoulder  12  formed in wellhead  13  to form an annulus  15  between casing hanger  11  and wellhead  13 . In the illustrated embodiment, a portion of an exterior surface of casing hanger  11  contacts a portion of an interior surface of wellhead  13  at a shoulder  12 . A person of ordinary skill in the art will understand that casing hanger  11  and wellhead  13  may be any inner and outer tubular members such that the inner tubular member may fit within a bore of the outer tubular member. 
     A casing hanger seal ring  17  is interposed between casing hanger  11  and wellhead  13 . Casing hanger seal ring  17  substantially fills annulus  15  between casing hanger  11  and wellhead  13 , sealing annulus  15  and setting casing hanger  11  to wellhead  13 . Casing hanger seal ring  17  has an energized and an unenergized position. When in the energized position, as described in more detail with respect to  FIGS. 3 and 5 , casing hanger seal ring  17  will seal the annulus by engaging both the inner diameter surface of wellhead  13  and the outer diameter surface of casing hanger  11 . When in the unenergized position, as shown in  FIGS. 1 ,  2 , and  4 , casing hanger seal ring  17  may be run into the wellbore to land in annulus  15  between casing hanger  11  and wellhead  13 , or pulled from annulus  15  between casing hanger  11  and wellhead  13 . In the illustrated embodiment, casing hanger seal ring  17  includes an energizing ring  19 , a seal ring  21 , a lockdown slip ring  23 , and a locking ring  25 . 
     As shown in  FIG. 2 , lockdown slip ring  23  may comprise two annular rings, a coupling ring  27  and a slip ring  29 . A person skilled in the art will understand that any suitable nose ring may be secured to seal ring  21  as described herein and may or may not include both coupling ring  27  and slip ring  29 . The alternative nose rings will generally engage wellhead  13  as described in more detail below. In the illustrated embodiment, coupling ring  27  has a protrusion  31  at an upper end that defines a retaining groove or slot  33  in an outer diameter surface of protrusion  31 . Groove  33  may be an annular groove or alternatively, groove  33  may extend only partway around the outer circumference of protrusion  31 . Coupling ring  27  also defines an annular upward facing shoulder  35 . Upward facing shoulder  35  extends from an outer diameter of coupling ring  27  to a base of protrusion  31 . In the illustrated embodiment, upward facing shoulder  35  has a width that is approximately half the width of a cross section of coupling ring  27 . 
     A lower end of coupling ring  27  has an approximately triangular shaped cross section having a substantially vertical surface forming the inner diameter of coupling ring  27 . The substantially cylindrical surface extends from the lower end to a top of protrusion  31 . The lower end of coupling ring  27  has a conical slip surface  37  extending from the lower end of coupling ring  27  to a downward facing shoulder  39  axially beneath upward facing shoulder  35 . The diameter of conical slip surface  37  increases in an upward direction. A lower end of the inner diameter surface of coupling ring  27  may include wickers  73  that are adapted to engage a cylindrical outer diameter surface of casing hanger  11  as shown in  FIG. 3  and  FIG. 5 . Wickers  73  may comprise gripping teeth or the like. Downward facing shoulder  39  extends from an outer diameter of coupling ring  27  to a base of or upper end of conical slip surface  37 . A slip ring limiter  41  may protrude from a portion of conical slip surface  37  to define upper and lower coupling ring channels  43 ,  45 , respectively. In the illustrated embodiment, slip ring limiter  41  is a band positioned approximately halfway between a lower end of coupling ring  27  and downward facing shoulder  39 . 
     Slip ring  29  comprises a substantially trapezoidal shaped object in axial cross section having a conical outer surface  46  as shown in  FIG. 4 . Conical surface  46  decreases in diameter in an upward direction. An inner diameter of slip ring  29  comprises a conical slip surface  47  adapted to mate with conical slip surface  37  of coupling ring  27 . A lower end of the conical surface  46  may include wickers  71  adapted to engage a mating conical profile  48  in the bore of wellhead  13 . Wellhead profile  48 , as shown in  FIGS. 4 and 5 , decreases in diameter in an upward direction. Wickers  71  may comprise gripping teeth or the like. A slip ring recess  49  is formed in conical slip surface  47  and extends into slip ring  29  from conical slip surface  47 . Slip ring recess  49  is an annular recess adapted to receive slip ring limiter  41 . As shown, slip ring  29  may slide axially relative to coupling ring  27  through slip ring recess  49 . Slip limiter  41  will limit axial movement of slip ring  29  through contact with upward facing shoulder  51  of slip ring recess  49  and downward facing shoulder  53  of slip ring recess  49 . Slip ring  29  may secure to coupling ring  27  with a shear element, such as shear retaining pin  55 . Shear retaining pin  55  will prevent axial movement of slip ring  29  relative to coupling ring  27  during running of casing hanger  17 . 
     Referring still to  FIG. 2 , seal ring  21  comprises an annular member having an approximately U-shaped cross section  57  with seal ring legs  59 ,  61  and a lower leg  63 . Lower leg  63  extends downward from U-shaped cross section  57 . Lower leg  63  has the same inner and outer diameter as outer leg  61  in this embodiment. Lower leg  63  extends past protrusion  31  of coupling ring  29  proximate to upward facing shoulder  35  of coupling ring  27 . In the illustrated embodiment, the inner diameter of lower leg  63  defines a retainer recess  65  proximate to and facing groove  33 . A retainer ring  67  may be interposed between lower leg  63  of seal ring  21  and protrusion  31  of coupling ring  27  such that retainer ring  67  substantially fills groove  33 . A portion of retainer ring  67  will extend into retainer recess  65 , causing coupling ring  27  to move axially in response to axial movement of seal ring  21 . When thus positioned, the width of the combined protrusion  31  of coupling ring  27  and lower leg  63  of seal ring  21  is approximately equivalent to a width of seal ring  21  across the base of U-shaped cross section  57 . Retainer ring  67  may be any suitable ring such as a split ring or the like. A person skilled in the art will recognize that prior to setting of casing hanger seal  17 , there may be some axial movement of coupling ring  27  relative to seal ring  21 . However, during and after setting of casing hanger seal  17 , coupling ring  27  and seal ring  21  will act as one body. 
     Energizing ring  19  comprises a ring having an axially lower end slightly larger than the slot defined between seal ring legs  59 ,  61  of seal ring  21 . Energizing ring  19  has an upper end adapted to be releasably coupled to a running tool so that the running tool may run casing hanger seal  17  to the location shown in  FIG. 1 , and then operate energizing ring  19  to energize casing hanger seal  17 . 
     As described in more detail below, a running tool will apply an axial force to energizing ring  19 , forcing energizing ring  19  axially into seal ring  21 , providing an interference fit that will press seal ring legs  61 ,  59  of seal ring  21  into adjacent wickers  67  and  69  ( FIG. 1  and  FIG. 3 ). This will seal annulus  15  between casing hanger  11  and wellhead  13  at seal ring  21 . A person skilled in the art will understand that the energizing ring  19  may be energized by a running tool or the like. 
     Referring now to  FIG. 3 , casing hanger seal  17  is run to land and set as shown in  FIG. 3  in a typical running operation. While running into annulus  15 , the elements of casing hanger seal  17  are as illustrated in  FIG. 2 . An axial force is then applied to energizing ring  19 , such as with a running tool. Energizing ring  19  moves downward axially in response such that an end of energizing ring  19  applies a corresponding downward axial force to upper surfaces of seal ring legs  59 ,  61 . Continued application of downward axial force to energizing ring  19  pushes a lower end of slip ring  29  into contact with upward facing shoulder  16  of casing hanger  11 . Lockdown slip ring  23  is then axially compressed between seal ring  21  and upward facing shoulder  16  by energizing ring  19 , causing shear pin  55  to shear. Coupling ring  27  will then move axially downward through slip recess  49 . Eventually, a lower surface of slip retainer  41  may land against upward facing shoulder  51  of slip ring  29 . 
     As shown in  FIG. 5 , downward movement of coupling ring  27  through slip recess  49  causes slip ring  29  to move radially into engagement with wellhead  13  in response. As slip ring  29  moves radially into wellhead  13 , conical surface  46  will fit into a matching conical profile  48  formed in the inner diameter of wellhead  13 . Wickers  71  will grip the surface of wellhead  13 , holding slip ring  29  in engagement with wellhead  13 . Similarly, wickers  73  will engage an outer diameter surface of casing hanger  11 , holding coupling ring  27  in engagement with casing hanger  11 . The outer diameter surface of casing hanger  11  engaged by coupling ring  27  is preferably cylindrical. Conical profile  48  of wellhead  13  may have mating wickers to wickers  71 . The surface of coupling ring  27  engaged to the outer diameter of casing hanger  11  and conical surface  46  of slip ring  29  may have differing friction factors such that the surface of coupling ring  27  is more likely to slip relative to casing hanger  11  than conical surface  46  relative to wellhead profile  48 . This may be achieved in any suitable manner such as by employing different types of wickers  71 ,  73  or teeth on the surfaces, by using a variety of friction gripping coatings, or the like. Also, because wellhead profile  48  and slip ring profile  46  are conical, slippage is less likely over he cylindrical engagement of wickers  73 . A person skilled in the art will understand that both the surface of coupling ring  27  and conical surface  46  may include friction coatings, wickers, or the like. In other embodiments, the outer surface of casing hanger  11  may have mating wickers formed proximate to coupling ring  27  and wickers  73 . 
     A person skilled in the art will recognize that conical surface  46  and conical profile  48  may be formed at matching angles. This allows for mating contact between conical surface  46  and conical profile  48  along any portion of the mating surfaces  46 ,  48 . For example, casing hanger  11  and casing hanger seal  17  may not land appropriately such that, when energized, a lower portion of conical surface  46  of slip ring  29  may only engage an upper portion of conical profile  48  of wellhead  13 . In another example, mating contact between conical surface  46  and conical profile  48  may still occur in the event debris is lodged or partially lodged within conical profile  48 . Slip ring  29  may move axially a sufficient amount to engage conical surface  46  with a portion of conical profile  48 . 
     In embodiments employing an alternative nose ring in place of lockdown slip ring  23 , conical profile  48  and conical surface  46  will still be employed as described herein. The nose ring may be energized in any suitable manner so that conical surface  46  formed on a portion of the nose ring engages conical profile  48  of wellhead  13  as described above. 
     After slip ring  29  and coupling ring  27  are set, further downward axial movement of energizing ring  19  causes an end of energizing ring  19  to insert into the slot formed by seal ring legs  59 ,  61 . As the end of energizing ring  19  inserts into the slot, seal ring legs  59 ,  61  will deform radially into engagement with wickers  67 ,  69 , respectively, as shown in  FIG. 3 . The inner diameter surface of seal ring leg  59  will then be deformed by wickers  67  of casing hanger  11 , and the outer diameter surface of seal ring leg  61  will be deformed by wickers  69  of wellhead  13 , forming a seal of annulus  15 . 
     During subsea operation of wellhead  13 , thermal expansion of casing suspended from casing hanger  11 , or fluid pressure within annulus  15  beneath casing hanger seal  17  may place an upward axial load on casing hanger  11 . As casing hanger  11  attempts to move axially upward relative to wellhead housing  13  in response to such a load, casing hanger seal  17  will counteract this movement in the following manner. As casing hanger seal  11  attempts to move upward, it will transfer the upward axial load to slip ring  29  through upward facing shoulder  16 . This upward axial load will urge slip ring  29  along the mating conical slip surfaces  47 ,  37  relative to coupling ring  27 , transferring the upward axial load radially to press slip ring  29  into tighter radial engagement with conical profile  48  of wellhead  13 . Thus, the upward axial loading will cause slip ring  29  to more tightly radially grip casing hanger  11  to wellhead  13  through casing hanger seal  17 , preventing upward movement of casing hanger  11 . Continued upward movement of slip ring  29  is prevented when upward facing shoulder  51  of slip ring  29  abuts slip limiter  41 , thereby preventing further upward axial movement of casing hanger  11  and increasing the strength of the seal within annulus  15 . In addition, conical surface  46  of slip ring  29  will fit more tightly within matching conical profile  48  of wellhead  13 . This engagement preloads lockdown slip ring  23 . Slip ring  23  is radially expanded and engaged in the wellhead  13 , limiting any upward axial movement of casing hanger  11  when casing hanger seal  17  is energized. Thus, upward axial force applied to slip ring  29  by shoulder  16  of casing hanger  11  will urge slip ring  29  into tighter engagement with wellhead  13  through conical surface  46  and conical profile  48 , providing additional lockdown capability that will prevent upward axial movement of casing hanger  11 . 
     A person skilled in the art will understand that other embodiments casing hanger seal  17  may include a nose ring secured to seal ring  21  in a manner similar to lockdown slip ring  23 . In these embodiments, conical profile  48  will still be formed in a bore of wellhead  13 . The nose ring will include a matching conical portion similar to conical surface  46  that will engage conical profile  48  when casing hanger seal  17  is set or energized within annulus  15  between casing hanger  11  and wellhead  13 . The nose ring may be any suitable nose ring allowing for set of casing hanger seal  17  between casing hanger  11  and wellhead  13  in annulus  15  and engagement of a conical surface of the nose ring with conical profile  48  of wellhead  13 . 
     Accordingly, the disclosed embodiments provide a metal to metal seal that can land and seal an annulus between a casing hanger and a wellhead within a profile that accommodates some misplacement or debris within the profile without needing an additional trip to run a separate lockdown ring. Thus, there is no concern that debris may have landed on the shoulder or filled a dog recess that would prevent lock down of the seal. In addition, the disclosed embodiments provide a metal-to-metal seal with lockdown capability that increases the lockdown strength as pressure loading within the annulus beneath the seal increases. Furthermore, the metal seal disclosed herein eliminates the need for the seal to tolerate some axial shift before sealing; instead the seal preloads against a conical profile of the wellhead and prevents displacement of the casing hanger found in some cyclic loading, allowing the seal to operate for more cycles than in prior art designs. 
     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.