Abstract:
A subsea wellhead assembly includes a housing with a bore containing at least one conical generally upward facing load shoulder that inclines relative to an axis of the bore. A hanger is lowered into the housing, the hanger having at least one conical downward facing load shoulder that inclines at a lesser inclination relative to an axis of the bore than the upward facing load shoulder. A split load ring has an inner profile that slidingly engages the downward facing load shoulder and an outer profile that slidingly engages the upward facing load shoulder. The load ring is carried by the hanger for movement between a retracted position, wherein the outer profile is spaced radially inward from the upward facing load shoulder, and an expanded position wherein the outer profile is in engagement with the upward facing load shoulder.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to provisional application 60/579,629, filed Jun. 15, 2004. 

   FIELD OF THE INVENTION 
   This invention relates in general to wellhead equipment for oil and gas wells, and in particular to a casing hanger full bore load ring mechanism. 
   BACKGROUND OF THE INVENTION 
   A typical subsea wellhead assembly includes a wellhead housing that supports one or more casing hangers. One type of wellhead housing has a conical load shoulder machined within its bore. The casing hanger lands on and is supported by the load shoulder. In this type, the diameter of the housing bore below the bore is less than the diameter of the housing above the bore by a dimension equal to a radial width of the load shoulder. 
   In another type, referred to as “full bore”, the wellhead housing has a groove with substantially the same diameter above and below the groove. The load shoulder is a split ring that is installed subsequently in the groove. The casing hanger is supported by the load shoulder. This procedure allows a larger diameter bore to be employed during drilling operations. The load shoulder may be installed on a special running tool or it may be run with the casing hanger. 
   SUMMARY OF THE INVENTION 
   In this invention, the wellhead housing has a bore containing at least one conical generally upward facing load shoulder that inclines relative to an axis of the bore. A casing hanger is landed in the housing. The hanger has at least one conical downward facing load shoulder that inclines at a lesser inclination relative to an axis of the bore than the upward facing load shoulder. A split load ring is carried by the hanger for supporting the hanger on the upward facing load shoulder. The load ring has an inner profile that slidingly engages the downward facing load shoulder of the hanger and an outer profile that slidingly engages the upward facing load shoulder of the housing. The load ring is carried by the hanger for movement between a retracted position, wherein the outer profile is spaced radially inward from the upward facing load shoulder, and an expanded position wherein the outer profile is in engagement with the upward facing load shoulder. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a vertical sectional view of a casing hanger and load ring shown in the set position within a wellhead housing and constructed in accordance with this invention. 
       FIG. 2  is an enlarged quarter sectional view of the casing hanger of  FIG. 1 , shown prior to setting. 
       FIG. 3  is an enlarged quarter sectional view of the casing hanger of  FIG. 1 , shown after setting. 
       FIG. 4  is a view similar to  FIG. 2 , but taken along a different section plane to illustrate the flowby slots. 
       FIG. 5  is an enlarged sectional view of the right half of the casing hanger of  FIG. 1 , but shown prior to setting and along a different sectional plane to illustrate the anti-rotation key. 
       FIG. 6  is a vertical sectional view of the casing hanger and wellhead of  FIG. 1 , showing an additional casing hanger landed on the casing hanger of  FIG. 1 . 
       FIG. 7  is a quarter sectional view of an alternate embodiment of a casing hanger and load ring constructed in accordance with this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , wellhead housing  11  is normally located at the upper end of a well at the sea floor and has an axial bore  13 . Bore  13  has a tag shoulder  15  located within it. Tag shoulder  15  is a circular ledge located at a junction between a larger diameter upper portion in bore  13  and a slightly smaller diameter lower portion of bore  13 . 
   An internal grooved profile, formed in bore  13  above tag shoulder  15 , comprises a plurality of load shoulders  17 , each facing generally upward and inward, resulting in a generally saw-tooth configuration. A cylindrical stop space  19  is located between each load shoulder  17 . Each stop spaces  19  is approximately the same axial length as one of the grooves that define one of the load shoulders  17 . 
   A casing hanger  21  lands within wellhead housing  11 . Casing hanger  21  has a lower threaded end  23  for securing to a string of casing (not shown) that extends into and is cemented in the well. Casing hanger  21  has a profile made up of a plurality of load shoulders  25 , which preferably are fewer than wellhead housing shoulders  17 . In this embodiment, there are two casing hanger load shoulders  25  and four wellhead housing load shoulders  17 . The number of load shoulders  17 ,  25  can vary. In the preferred embodiment, each casing hanger load shoulder  25  has a greater radial depth and axial dimension than each wellhead housing load shoulder  17 . Hanger load shoulders  25  preferably face downward and outward at a different angle than the upward and inward facing wellhead housing load shoulders  17 . Preferably, the angle a relative to a vertical axis of hanger load shoulders  25  is less than an angle b of wellhead housing load shoulders  17  to a vertical axis, thus hanger load shoulders  25  are steeper. This results in a difference in angles indicated by the numeral  27  on the right side of  FIG. 1 . In one embodiment, angle a is approximately 55 degrees and angle b is approximately 60 degrees, resulting an angle difference  27  being 5 degrees. 
   Referring briefly to  FIG. 4 , hanger  21  also has a plurality of vertical flowby slots  29  to allow the upward flow of cement returns during the cementing of the casing. Flowby slots  29  extend through hanger load shoulders  25 . An enlarged portion  30  of hanger  21  directly above load shoulders  25  has a diameter only slightly less than the inner diameter of bore  13 , and flowby slots  29  extend through this portion as well. 
   Referring again to  FIG. 1 , a split load ring  31  is movably mounted on hanger  21  to support hanger  21  on wellhead housing load shoulder  17 . Load ring  31  is resiliently biased inwardly, so that prior to landing, as shown in  FIGS. 2 ,  4  and  5 , its natural resiliency will cause it to remain retracted. Load ring  31  has a plurality of external load shoulders  33  for mating with wellhead housing load shoulders  17 . Load ring  31  has internal shoulders  34  for mating with hanger load shoulders  25 . Internal load shoulders  34  face upward and inward at the same angle as hanger load shoulders  25 . Load ring external shoulders  33  face downward and outward at the same angle as wellhead housing load shoulders  17 . 
   The angles of external load ring shoulders  33  differ from internal load ring shoulders  34 . Differential angle  27  is selected to just overcome the resistance created by frictional effects occurring when load ring  31  moves from the retracted position of  FIGS. 2 ,  4  and  5  to the set position of  FIGS. 1 and 3 . The cylindrical stop spaces  19  between wellhead housing load shoulders  17  are contacted by mating portions of load ring  31  during setting to prevent load ring  31  from traveling radially outward farther than the desired amount. Mating cylindrical surfaces on load ring  31  between external shoulders  33  will contact stop spaces  19  to create a positive radial outward stop. 
   Referring briefly again to  FIG. 4 , load ring  33  has a plurality of flowby slots  35  in its interior that align with flowby slots  29  in hanger  21 . Flowby slots  35  are located radially inward from external load shoulders  33 . Slots  29  and  35  combine to create flow channels for cement returns. Preferably, the lower end  37  of load ring  31  is perpendicular to the axis of wellhead housing  11 . 
   Referring to  FIGS. 2 and 3 , an activation ring  39  serves to cause load ring  31  to move from the retracted position of  FIG. 2  to the set position of  FIG. 3 . Activation ring  39  is a non-expandable ring that is axially movable relative to hanger  21 . Activation ring  39  has a tag shoulder  41  that is dimensioned to land on tag shoulder  15  in wellhead housing bore  13 . Hanger  21  has an annular recess  43  on its outer diameter that is radially inward of activation ring  39 . A split latch ring  45  with an outward bias is carried in hanger annular recess  43 . Activation ring  39  has a mating annular recess  47  on its inner diameter that aligns with annular recess  43  during the running position. Latch ring  45  is dimensioned to be partly in activation ring recess  47  and partly in hanger recess  43  in the running position as shown in  FIG. 2 . This position prevents activation ring  39  from any axial movement relative to hanger  21 . 
   In this embodiment, a plurality of trigger pins  49  extend radially from activation ring recess  47  to the outer diameter of activation ring  39 . The outer ends of each pin  49  protrudes slightly past the outer diameter of activation ring  39  just below tag shoulder  41 . A head or inner end of each trigger pin  49  contacts the outer diameter of latch ring  45 . Trigger pins  41  keep latch ring  45  within the mating recesses  43  until activation ring tag shoulder  41  lands on tag shoulder  15 , then cause latch ring  45  to move out of engagement with annular recess  47 . 
   Referring to  FIGS. 2 and 3 , a thin-walled ring  46  extends downward from activation ring  39 . Ring  46  has a rib on its inside diameter that fits tightly to the outer diameter of hanger  21 . A small annular detent rib  48  is formed on the outer diameter of hanger  21  for engagement by the rib on ring  46 . In the running position of  FIG. 2 , rib  48  is located above the rib of ring  46 . In the set position of  FIG. 3 , rib  48  is located below the rib of ring  46 . 
   Referring to  FIG. 4 , a plurality of flowby slots  50  extend axially through activation ring  39 . Each flowby slot  50  is vertically aligned with flowby slots  35  and  29 . As shown in  FIG. 4 , an anti-rotation key  52  is employed to make sure that flowby slots  35 ,  29  and  50  remain in vertical alignment with each other. Key  52  locates within mating recesses formed on hanger  21 , in activation ring  39 , and in load ring  31 . Fasteners  54  secure key  52  in this position to prevent any rotation of activation ring  39  or load ring  31  relative to hanger  21 . 
   In the running operation of hanger  21 , load ring  31  will be in the retracted position shown in  FIG. 2 . The outer diameter of load ring  31  in this position is no greater than the outer diameter of hanger  21  at enlarged diameter portion  30 . The resiliency of load ring  31  biases it to the retracted position and keeps load ring  31  from moving radially outward from the position shown in  FIG. 2  while running in. The rib on thin-walled ring  46  will be located below rib  48 . As hanger  21  enters bore  13 , tag shoulder  41  ( FIG. 2 ) will land on wellhead housing tag shoulder  15 . The outer ends of trigger pins  49  will contact bore  13  below tag shoulder  15  and move radially inward, pushing latch ring  45  to a retracted position. In the retracted position, latch ring  45  locates wholly within hanger recess  43 , releasing hanger  21  for downward movement relative to activation ring  39 . As hanger  21  continues to move downward, activation ring  39  contacts the lower end of load ring  31 , effectively pushing load ring  31  up hanger  21 , which moves load ring  31  radially outward into housing load shoulders  17 , as shown in  FIG. 3 . Also, at the same time the weight on hanger  31  causes rib  48  to snap past the rib on ring  46  and move below to the position of  FIG. 3 . 
   As hanger  21  moves downward relative to load ring  31 , hanger load shoulders  25  exert a downward and outward force normal to load shoulders  25 . At the same time, wellhead housing load shoulders  17  provide an upward and inward reactive force normal to load shoulder  17 . These forces are not directly opposed because of the different angles of load shoulders  17 ,  25 . The reactive force from shoulders  17  is not directed as much radially inward as the downward force from shoulders  25  is directed radially outward, thus resulting in a net outward directed force being applied to load ring  31 . The frictional effects between load ring  31  and load shoulders  17 ,  25  tend to retard the radial outward movement of load ring  31 , thus the net outward force due to the difference  27  in angles is calculated to be somewhat more than the opposed frictional force. Steeper angles for load shoulders  17  and  25  would provide more outward net force to load ring  31  during setting, but would reduce the axial load capacity. 
   Once fully engaged, a small axial clearance  51  ( FIG. 3 ) will exist between the upper end of activation ring  39  and lower end  37  of load ring  31 . Downward load on hanger  21  transfers from hanger load shoulders  25  through load ring  31  to wellhead housing load shoulders  17 . Clearance  51  avoids any downward load being transferred to wellhead housing tag shoulder  15 . 
   Slacking off the weight in running string will indicate that load ring  31  has set. As a further assurance, the operator can apply a selected overpull. The casing and hanger  21  will move upward slightly relative to activation ring  39  and load ring  31 until rib  48  contacts the rib on ring  46 . A selected overpull, say 200,00 pounds, will be necessary to cause rib  48  to snap past the rib of ring  46 , thus the operator will pull upward a fraction of that amount, such as 100,000 pounds, to determine if rib  48  is pushing against the rib on ring  46 . If so, this indicates that load ring  31  has properly set. The operator can then slack off the weight. 
   The angular difference  27  ( FIG. 1 ) between load shoulders  17  and  25  assures that load ring  31  reaches the full radially engaged position wherein it engages stop spaces  19  between load shoulders  17  of wellhead housing  11 . During cementing, fluid flowing up the annulus surrounding the casing flows up flowby slots  50 ,  35  and  29  ( FIG. 4 ). 
   Referring to  FIG. 6 , an additional upper casing hanger  53  may land on casing hanger  21  to support a smaller diameter string of casing (not shown). Upper hanger  53  has a threaded end  55  for securing to the smaller diameter casing. Upper hanger  53  also has a movable load ring  57  that may be constructed the same as load ring  31 . Wellhead housing  11  has an upper profile of load shoulders  59  that may be configured the same as load shoulders  17 . In this embodiment, a tag shoulder similar to tag shoulder  15  is not needed because the assembly of upper hanger  53  lands on lower hanger  21 . 
   An activation ring  61  is mounted to the lower end of upper hanger  53 . Activation ring  61  may be secured to upper hanger  53  by shear pins (not shown) that initially pin activation ring  61  to upper hanger  53  in a running position. When activation ring  61  lands on the upper end of lower hanger  21 , the weight of the running string applied to upper hanger  53  shears the pins and causes upper hanger  53  to move downward relative to activation ring  61  and load ring  57 . 
   A mudline hanger assembly is shown in the embodiment of  FIG. 7 . A housing  63  at the sea floor extends upward from the well. Housing  63  has a plurality of load shoulders  65  configured generally as in the first embodiment. Flowby passages  67 ,  69  are formed in the wall of housing  63 . A hanger  71 , located at the upper end of a string of casing (not shown), lands in housing  63 . Hanger  71  has a load ring  73  constructed generally as in the first embodiment, except that it does not have flowby slots because all of the cement returns are handled by flowby passages  67 ,  69 . In this embodiment, hanger  71  has two load shoulders  75 , and housing  63  has three load shoulders  65 , but the number could vary. The angles of load shoulders  75  and  65  preferably differ as in the first embodiment. 
   An activation ring  77  may be secured to hanger  71  by trigger pins as in the first embodiment. This embodiment could also use the detent rib and collet finger arrangement of the first embodiment, if desired. Activation ring  77  lands on a tag shoulder in the bore of housing  63  and causes load ring  73  to set in the same manner as upper casing hanger  53  ( FIG. 6 ). A packoff assembly  79  secures to the upper end of hanger  71 . Assembly  79  remains with hanger  71  and has a seal assembly  81  that seals to wickers  83  formed in housing  63 . Other types of adapters and sealing mechanisms are feasible. 
   The invention has significant advantages. The difference between the load shoulders in the housing and on the casing hanger reduces friction while setting. The reduction in friction allows the load shoulders to be oriented at larger angles relative to the axis to support larger axial loads. The load shoulder arrangement increases the load bearing capacity of the hanger and wellhead housing. 
   While the invention has been shown in only two 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.