Abstract:
A wellhead housing has a casing hanger with an actuator mechanism to provide for direct transfer of casing and pressure loads to the housing even in conditions where the casing hanger may be set in a high position in the wellhead housing on a load shoulder, or in a casing hanger in the wellhead housing for an earlier installed, larger diameter casing string.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates in general to subsea wellhead assemblies, and in particular to a wellhead housing, wherein an actuator mechanism causes the load on a casing hanger in the wellhead housing to be transferred to the housing even in the event the casing hanger may be set in a high position in the wellhead housing. 
         [0003]    2. Description of the Prior Art 
         [0004]    In a typical subsea well, wellhead housing is positioned on the floor of a body of water at the upper end of the well. The wellhead housing is a tubular member having a bore aligned with the well bore. A string of large diameter casing attaches to the lower end of the wellhead housing and extends into the well bore. After further drilling into the earth through the wellhead housing, a smaller diameter string of casing is installed. A casing hanger at the upper end of the smaller diameter string of casing is landed in the bore on a load shoulder in the wellhead housing. 
         [0005]    Debris and cuttings from the well are a continuing concern in subsea wellhead equipment design and operation. The debris and cuttings can become lodged or located between the casing hanger and other load bearing structure in the wellhead, such as another casing hanger in a stack in the wellhead housing or the wellhead housing itself. Thus, there were concerns with proper seating of casing hangers for load transfer or sharing purposes. The problem became worse when several hangers were stacked on top of each other, as was typical in subsea wellheads. 
         [0006]    For the uppermost, stacked hangers, the use of shim sets with adjustable shims was contemplated. Adjustments were to be made after appropriate measurements were made in the wellhead housing at the wellhead to determine the required amount of adjustment. However, a separate trip of equipment from the surface to the wellhead was required which was time consuming and thus expensive. There was also concern expressed about the ability to make accurate measurements to determine the required adjustment. 
       SUMMARY OF THE INVENTION 
       [0007]    Briefly, the present invention provides a new and improved wellhead assembly, having wellhead housing with a bore and an installed casing hanger in the bore. The wellhead housing has a support shoulder adjacent the bore and a telescoping casing hanger for securing to a string of casing and lowering into the wellhead housing. A split, resilient load ring is carried in a retracted initial position on the casing hanger. The load ring is movable outwardly to a set position in engagement with the wellhead housing. An actuator is mounted with the casing hanger below the load ring for moving the load ring from the initial position to the set position. The actuator includes a resilient mechanism for adjusting for height variations between the position of the load ring and the support shoulder during movement of the load ring to the set position to land the telescoping casing hanger in the wellhead housing. 
         [0008]    The present invention further provides a new and improved method for installing a telescoping casing hanger atop an installed casing hanger in a bore of wellhead housing at the upper end of a well in a body of water. A support shoulder is provided in the bore of the wellhead housing. A split, resilient load ring is mounted in a recessed initial position in the telescoping casing hanger. An actuator is mounted on the telescoping hanger below the load ring, and then a string of casing is secured to the telescoping casing hanger and the telescoping casing hanger lowered into the wellhead housing. The telescoping hanger is landed on the installed casing hanger. The load ring is activated with the actuator and moved to expand and land on the support shoulder of the wellhead housing, and the casing hanger lands on the load ring. The position of the load ring on the support shoulder is adjusted to compensate for differences in the landed height of the telescoping hanger and the installed casing hanger. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a vertical sectional view of a portion of a wellhead housing having a telescoping casing hanger according to the present invention located in a landed position. 
           [0010]      FIG. 2  is an enlarged view of a portion of the structure circled and identified by reference numeral  2  in  FIG. 1 . 
           [0011]      FIG. 3  is an enlarged view taken partly in vertical section of the portion of the telescoping casing hanger of  FIG. 1 . 
           [0012]      FIG. 4  is an enlarged view of a portion of the structure circled and identified by reference numeral  4  in  FIG. 3 . 
           [0013]      FIGS. 5A ,  5 B,  5 C and  5 D are vertical sectional views of the structure of  FIG. 4  during an activation sequence of landing the telescoping casing hanger of the present invention in normal landed position. 
           [0014]      FIGS. 6A ,  6 B,  6 C and  6 D are vertical sectional views of the structure of  FIG. 4  during an activation sequence of landing the telescoping casing hanger of the present invention in a higher than normal landed position. 
           [0015]      FIGS. 7A and 7B  are vertical sectional views of the structure of  FIG. 4  during a sequence of confirming proper landing of the telescoping casing hanger of the present invention. 
           [0016]      FIGS. 7C and 7D  are vertical sectional views of the structure of  FIG. 4  during a deactivation sequence of retrieving or pulling the telescoping casing hanger of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    In the drawings, a telescoping casing hanger H according to the present invention is shown ( FIG. 1 ) landed on a previously installed hanger such as a bridging hanger B in a wellhead housing  10 . The wellhead housing  10  is of the conventional type installed as a component of a subsea wellhead assembly located at the sea floor. The telescoping casing hanger H includes an activation ring  12  which is mounted extending circumferentially below a collar or shoulder  14  of the body  16  of the telescoping casing hanger H. The activation ring  12  takes the form of an upper activation ring sleeve member  18  ( FIG. 4 ), a lower activation ring sleeve member  20  and a compressible spring  22 . A wave spring is suitable form of spring for the spring  22 , although others might be used. 
         [0018]    A load ring  24  is mounted on an upper surface  26  of the upper activation ring member  18  extending circumferentially about the casing hanger body  16  between the shoulder  14  and the activation ring  12 . The load ring  24  is a split, resilient ring and adapted to transfer load from the casing hanger H to the wellhead housing. The load ring  24  has a tapered upper inner surface  28  adapted for engagement with and relative sliding movement with respect to a corresponding tapered circumferentially extending lower surface  30  of the casing hanger body  16 . 
         [0019]    As will be set forth, the load ring  24  is moved inwardly and outwardly with respect to a load transfer landing shoulder  32  formed in an annular groove or bore  34  extending about the interior of the wellhead housing  10  to land the casing hanger H in the wellhead housing  10 . Such movement takes place during the landing and extraction or pulling of the casing hanger H in the wellhead housing  10 . 
         [0020]    The activation ring  12  also includes an outer collar  36  mounted on an outer surface  38  of the lower activation ring member  20 . A set of circumferentially disposed pins  40  are mounted with the collar  36  extending downwardly for engagement an upper portion  42  of a previously installed casing hanger, such as bridging hanger B, in the wellhead housing  10 . 
         [0021]    The telescoping casing hanger H includes a lock ring  44  with circumferentially extending outwardly inclined surfaces. The lock ring  44  is mounted for movement within a circumferential slot  46  formed between correspondingly inclined surfaces formed extending circumferentially about the casing hanger body  16  adjacent the upper activation ring member  18 . 
         [0022]    When the casing hanger H is being lowered or tripped into the well bore, the lock ring  44  prevents the activation ring  12  from moving if prematurely contacted. This in turn prevents the load ring  24  from early movement. In this way, the casing hanger H is not damaged during movement in the well bore as a result of premature operation of activation ring  12  caused by contact with obstructions which might be encountered in the well bore. 
         [0023]    A snap ring  50  is mounted in a corresponding slot  52  extending circumferentially about a lower outer portion of the activation ring member  18 . The snap ring  50  is fitted into the slot  52  and extends outwardly to engage a lip formed in an inner side of the lower activation ring member  20 . The snap ring  50  in the preloaded position shown in  FIG. 4  captures the spring  22  and maintains the spring  22  in a preloaded state so that a large axial force is required to telescopically collapse the activation ring  12 . 
         [0024]    The activation ring  12  also includes one or more circumferentially extending ratchet lip or rim members  54  on its upper inner surface adjacent the casing housing body  16 . The ratchet member structure  54  extends downwardly and is adapted to engage an overpull check ring  56 . The overpull check ring  56  includes an outwardly extending lip  58  extending about the casing hanger body  16  above the upper activation ring member  18 . Overpull check ring  56  is mounted in a circumferentially extending recess or groove formed in the casing housing body member  16 . 
         [0025]    The overpull check ring  56  due to this location engages and locks the activation ring  12  only when the load ring  24  has fully expanded ( FIGS. 5C and 5D ). This allows an operator to make an overpull once the casing hanger has landed. As will be set forth, the overpull check ring  56  thus permits verification or confirmation that the telescoping casing hanger  16  is properly landed in the wellhead housing  10  and the load transferring mechanisms have properly functioned. 
         [0026]    In the operation of the present invention, an activation sequence in situations when the casing H is landed at its intended normal height position on the previously installed hanger B in the wellhead housing is illustrated in  FIGS. 5A through 5D . The casing hanger H and associated casing suspended beneath it is lowered through a riser downwardly into the wellhead housing  10 . The pins  40  come into contact with the structure of the previously installed hanger. The pins  40  are pressed upwardly into the body of the casing hanger H ( FIG. 5A ) forcing the lock ring  44  to retract ( FIG. 5A ) and unlock the activation ring  12 . Further displacement of the casing hanger H downwardly ( FIG. 5B ) occurs as a result of slacking off casing weight. This brings the now unlocked and movable activation ring  12  into contact ( FIG. 5C ) with the top surface of the hanger B already installed below the casing hanger H. 
         [0027]    Further weight downwardly on the casing hanger H collapses the wave spring  22  of the casing hanger H and causes outward expansion of the load ring  24  until contact is made with the bore  34  of the wellhead housing  10 , thus limiting further outward expansion. The load ring  24  is now fully set ( FIG. 5D ) and the casing hanger H is in position for load transfer purposes. The preload on the spring  22  captured by the activation ring  12  is at a force level greater than the maximum expansion load on the load ring  24  to permit this to occur. 
         [0028]      FIGS. 6A through 6D  illustrate an activation sequence in the event that the hanger B below the casing hanger H is sitting at a higher than normal position due the presence of cuttings or other debris. By comparison of  FIGS. 6A through 6D  with  FIGS. 5A through 5D  it can be seen that the load ring  24  in  FIGS. 6A and 6B  is at a higher position with respect to the bore  34  of the wellhead housing  10  than in  FIGS. 5A and 5B . The pins  40  come into contact and are pressed upwardly into the body of the casing hanger H ( FIG. 6A ). Activation of pins collapses internal lock ring ( 7 B) 
         [0029]    Activation ring expands load ring until it contacts housing wall ( 7 C). The activation ring  12  expands the load ring  24  until it contacts the inner wall of the wellhead housing  10  ( FIG. 6C ), at a higher position than illustrated in  FIG. 5C . 
         [0030]    Further weight applied downwardly by slacking casing weight on the casing hanger in the position illustrated in  FIG. 6C  collapses the wave spring  22  and load ring  24  is now fully set ( FIG. 6D ). It can be seen that the casing hanger H in  FIG. 6D  is also now at the fully landed normal height position shown in  FIG. 5D . 
         [0031]    The sequence of events described above occurs sequentially and seamlessly and requires only the slacking off of casing weight in order to take place. As has been set forth the presence of the overpull check ring  56  which is engaged with the activation ring  12  ( FIG. 7A ) allows the operator to confirm ( FIG. 7B ) that proper landing has occurred by making an overpull on the installed assembly. 
         [0032]    In order to deactivate and remove the casing hanger H when it is landed either position, with the load ring  24  fully set ( FIG. 7A ), the casing hanger H is lifted until top of load ring  24  contacts wellhead housing in the position shown in  FIG. 7B . Further lifting tension or force shears the engagement ( FIG. 7C ) between the overpull check ring  56  and the ratchet structure  54  on the activation ring  12 , allowing the load ring  24  to collapse to a position where the load ring  24  is fully collapsed ( FIG. 7D ) and it is now possible to pull the casing hanger H out of wellhead housing  10 . 
         [0033]    The present invention has significant advantages. It provides an improved rate of success due to the capability to accommodate variations in installed height of casing hangers due to cuttings, debris or otherwise. The present invention provides an assembly that is much less sensitive to the presence of cuttings or debris. This permits the well operator more time for drilling operations rather than circulation and hole conditioning operations. 
         [0034]    While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing form the scope of the invention.