Abstract:
A wellhead load ring constructed in the shape of a C-ring is pre-installed in a wellhead in a storage position that maintains full bore of the wellhead. The load ring is secured in this position by shear pins. The shear pins are sheared by a tool that pushes the load ring into an operational position where it rests on a landing shoulder of a support ring. The load ring is further secured in this position by one of several latching methods.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/158,768, filed Oct. 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to well casing hangers in petroleum production wells. More specifically, the present invention relates to a full bore wellhead having a retractable load shoulder for suspending a casing. 
     2. Description of the Related Art 
     In some types of wellhead assemblies casing is suspended by a casing hanger on a load shoulder formed in the bore of the wellhead housing. Generally the load shoulder is formed integrally or permanently attached to the wellhead housing. The fixed load shoulder results in a reduced diameter in the bore below the load shoulder. Any tools or pipe must be smaller than the fixed shoulder. In some wells, more than one load shoulder is utilized for supporting multiple strings of casing. 
     Retrievable load shoulders are also known in the art, employing a running tool to deploy and retrieve the load shoulder selectively. Also, the prior art includes retractable load shoulders that are installed with the wellhead housing, but retracted before running casing. Retrievable and retractable load shoulders provide full bore access. 
     BRIEF SUMMARY OF THE INVENTION 
     A wellhead load ring constructed in the shape of a C-ring is pre-installed in a wellhead in a storage position that maintains full bore of the wellhead. The load ring is preferably secured in this position by shear pins. The shear pins are sheared by a tool that pushes the load ring into an operational position, where it rests on a landing shoulder of a support ring. The load ring is further secured in this position by one of several latching methods. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical cross-sectional view of an upper and lower portion of a wellhead housing showing a load shoulder ring in a storage position in accordance with the principles of the invention described herein. 
     FIG. 2 an enlarged vertical cross section of the wellhead housing shown in FIG. 1, showing the load shoulder ring in a storage position in accordance with the principles of the invention described herein. 
     FIG. 3 is a vertical cross section of the load shoulder ring of FIG. 2, but showing the load shoulder ring in an operational position in accordance with the principles of the invention described herein. 
     FIG. 4 is a vertical cross-sectional view of a second embodiment of the invention, showing a load shoulder ring in a storage position in accordance with the principles of the invention described herein. 
     FIG. 5 is a vertical cross-sectional view of the load shoulder ring of FIG. 4, but showing the load shoulder ring in an operational position in accordance with the principles of the invention described herein. 
     FIG. 6 is a vertical cross-sectional view of a third embodiment of the invention, showing a load shoulder ring in a storage position in accordance with the principles of the invention described herein. 
     FIG. 7 is a vertical cross-sectional view of the load shoulder ring of FIG. 6, but showing the load shoulder ring in an operational position in accordance with the principles of the invention described herein. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, wellhead housing  110  has an axial bore  112 . Axial bore  112  has upper portion  114  and a lower portion  116 , which is an upper portion of a large diameter string of casing. Upper portion  114  has a constant inner diameter and is considered full bore for the purpose of receiving tools and casing during drilling. Lower portion  116  has a diameter larger than upper portion  114 , therefore no portion of bore  112  is less than full bore. Four circumferentially spaced cavities  118  are located at the lower end of the upper portion  114  of axial bore  112 . Cavities  118  are adapted to receive a tool (not shown) as explained later. 
     A split C-ring  120  is located in bore  112  immediately below cavities  118 . C-ring  120  is initially secured to a support ring  122  by a plurality of shear pins  124 . C-ring  120  is in its free state while in this position, and its inner diameter is greater than or equal to the main diameter of bore upper portion  114 . Support ring  122  is statically secured to bore  112  by means of external threads  126  and by resting on lock ring  128 . Support ring  122  has mating shear holes  130  for receiving shear pins  124 . Shear pins  124  are designed to fail at a predetermined load, at which time the resiliency C-ring  1   20  allows it to contract to a smaller inner diameter. FIG.  1  and FIG. 2 show C-ring  120  in a storage position. Support ring  122  has an internal upward facing shoulder  132  and a profile  134  on its inward facing surface that mates with an outward facing lip or protrusion  136  on the upper end of C-ring  120 , when in the operational position. The inner diameter of support ring  122  is not less than the inner diameter of bore upper portion  114 . 
     During operation, wellhead housing  110  is installed within a previously installed tubular wellhead on the subsea surface. Casing  116  extends into the well from wellhead housing  110 . When it is desired to install casing within casing  116 , C-ring  120  is moved to the operational position by a tool (not shown) lowered from above. The tool will preferably be simultaneously running the casing. The tool has fingers that protrude outward and locate in cavities  118  and engages C-ring  120 . The tool is moved downward to shear pins  124  and push C-ring  120  downward. As C-ring  120  moves downward, outward facing wedging surface  138  mates with inward facing wedging surface  140  to force C-ring  120  to a smaller diameter so that it can land on landing shoulder  132 . The smaller inner diameter provides an upward facing load shoulder  142  which is used to hang the additional casing string. As C-ring  120  rests on landing shoulder  132 , protrusion  136  mates with profile  134  to secure C-ring  120  to support ring  122 . 
     FIGS. 4 and 5 show a second embodiment of the present invention. Referring to FIG. 4, wellhead housing  210  has an axial bore  212 . Four circumferentially spaced cavities  218  are located in axial bore  212 . Cavities  218  are adapted to receive a tool (not shown) as explained later. 
     A load shoulder split C-ring  220  and spring split C-ring  222  are located immediately below cavities  218 . C-rings  220 ,  222  respectively, are pre-installed in wellhead  210  as shown in FIG. 4 such that the axial bore  212  remains full bore. Load shoulder split C-ring  220  is located inside spring split C-ring  222  when in a storage position such that the inner diameter of C-rings  220 ,  222  in the storage position are not less than full bore. Spring split C-ring  222  locates in a groove  223  in bore  212 . Shear pins  224  extend through load shoulder split C-ring  220  to secure it to spring split C-ring  222 . Spring split C-ring  222  is located on top of a support ring  226 . Support ring  226  is secured to the wellhead housing by external threads  228 , and further supported by a lock ring (not shown). Support ring  226  has a recess  232  on it upper surface that receives a rib  234  on the lower surface of spring split C-ring  222 . As shown in FIG. 4, spring split C-ring  222  is positioned between upper portion  214  and support ring  226  such that rib  234  and recess  232  retain spring split C-ring  222  to the wellhead housing  210 , but allow radial movement. 
     Load shoulder split C-ring has an outward facing wedging surface  236  on it lower end. Spring split C-ring  222  has a matching inward facing wedging surface  238  below load shoulder split C-rings storage position. Spring split C-ring has a lip  240  below inward facing wedging surface  238 . Load shoulder split C-ring has an upward facing load shoulder  242  on its upper end. 
     During operation, the wellhead housing  210  is installed in a wellhead previously installed on the subsea surface. When it is desired to install casing within wellhead housing  210  , load shoulder C-ring  220  is moved to the operational position by a tool (not shown) lowered from above. The tool, which preferably is simultaneously running the casing, locates in cavities  218  and engages load shoulder C-ring  220 . The tool is moved downward to shear pins  224  and push load shoulder C-ring  220  downward. As load shoulder C-ring  220  moves downward, outward facing wedging surface  236  mates with inward facing wedging surface  238  to force load shoulder C-ring  220  to a smaller diameter and spring split C-ring  222  to a slightly larger diameter, allowing load shoulder split C-ring  220  to pass lip  240  on spring split C-ring  222 . Once pass lip  240 , the smaller inner diameter of load shoulder split C-ring  220  provides an upward facing load shoulder  242  which may be used to hang additional casing string. As C-ring  220  rests on landing shoulder  244 , lip  240  overlaps the top of load shoulder C-ring  220  slightly to secure load shoulder C-ring  220  to support ring  226 . FIG. 5 shows load shoulder C-ring  220  in an operational position, resting on landing shoulder  244  and secured by lip  240 . 
     FIGS. 6 and 7 show yet another embodiment of the present invention. Referring to FIG.6, wellhead housing  310  has an axial bore  312 . Four circumferentially spaced cavities  318  are located in axial bore  312 . Cavities  318  are adapted to receive a tool (not shown) as explained later. 
     A split C-ring  320  is located in bore  312  immediately below cavities  318 . A C-ring  320  is initially secured to a support ring  322  by a plurality of shear pins  324 . C-ring  320  is in its free state while in this position, and its inner diameter is greater than or equal to the main diameter of bore upper portion  314 . A support ring  322  is statically secured to bore lower portion  316  by means of external threads  324  and resting on lock ring  326 . Support ring  322  has mating shear holes  328  for receiving shear pins  324 . Shear pins  324  are designed to fail at a predetermined load, at which time the resiliency C-ring  320  allows it to contract to a smaller inner diameter. FIG. 6 shows C-ring  320  in a storage position. Support ring  322  has an internal upward facing shoulder  330 . Support ring  322 has a recess  332  on its inward facing surface that mates with a retainer ring  334 . Retainer ring  334  is located so that it aligns with a seat or notch  336  on the upper end of C-ring  320  when in the operational position. The inner diameter of support ring  322  is not less than the inner diameter of bore upper portion  314 . 
     During operation, the wellhead housing  310  is installed in a wellhead on the subsea surface. When it is desired to install casing within wellhead housing  310 , C-ring  320  is moved to the operational position by a tool (not shown) lowered from above. The tool locates in cavities  318  and engages C-ring  320 . The tool is moved downward to shear pins  324  and push C-ring  320  downward. As C-ring  320  moves downward, outward facing wedging surface  338  mates with inward facing wedging surface  340  to force C-ring  320  to a smaller diameter so that it can land on landing shoulder  330 . The smaller inner diameter provides as an upward facing load shoulder  342  which is used to hang an additional casing string. As C-ring  320  comes to rest on landing shoulder  330 , retainer ring  334  snaps into notch  336  securing C-ring. 
     The embodiments described above all provide the same advantages. The load shoulders are fully retracted when in the storage position. This allows full bore tools to pass. The design also allows the shoulder operation to be performed simultaneously with running the casing or separately so that the shoulder may be tested prior to running the casing. 
     While the invention has been shown in only some 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 from the scope of the invention.