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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 61/074,741, filed Jun. 23, 2008, the full disclosure of which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to production of oil and gas wells, and in particular to a device for coupling together high and low pressure wellhead housings. 
     DESCRIPTION OF RELATED ART 
     Systems for producing oil and gas from subsea wellbores typically include a subsea wellhead assembly that includes a wellhead housing attached at a wellbore opening, where the wellbore extends through one or more hydrocarbon producing formations. A typical subsea well assembly undergoes several installation procedures, including drilling, completion, and production installation procedures. Subsea well assemblies generally include an outer or low pressure wellhead housing from which a string of conductor pipe descends downward into the well. An inner or high pressure wellhead housing is coaxially landed and set within the outer wellhead housing. The inner wellhead housing can support one or more casing hangers and attached strings of casing inserted into the well. A latch and groove arrangement can be employed to support the inner housing in the outer housing. Setting the inner wellhead housing within the outer wellhead housing often requires axially forcing the inner wellhead housing in the outer wellhead housing until the latch and groove are in alignment. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a device for assembling a portion of a subsea wellhead housing that is used to set inner wellhead housing within outer wellhead housing; which is typically referred to as bootstrapping. The device disclosed herein amplifies the forces applied to a bootstrapping tool to produce a desired bootstrapping output force. The device employs a system of wedges to gain a mechanical advantage for force amplification. In one optional embodiment the bootstrap mechanism comprises a tapered activating tool that drives a set of wedges laterally between the shell of a bootstrap assembly and the top of inner wellhead housing. In this embodiment the system of wedges includes the tapered shape of the activating tool and the wedges that extend laterally over the top of the inner wellhead housing. An elongated stinger made of drill pipe is attached to the lower end of the tool to provide a downward force for driving the bootstrapping tool within the lateral wedges. Laterally urging these wedges results in a downward force applied to the top surface of the high pressure housing. The shell lower end couples with the outer wellhead housing and prevents the outer wellhead housing from moving downward with respect to the shell. The downward force applied to the inner wellhead housing urges it downward away from the shell into locking engagement with the outer wellhead housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of an embodiment of a wellhead assembly engaged with a bootstrap device. 
         FIG. 1A  depicts in a sectional view an enlarged portion of the wellhead assembly of  FIG. 1 . 
         FIG. 2  is a cross sectional view of an embodiment of a wellhead assembly being formed by a bootstrap device. 
         FIG. 3  illustrates the bootstrap device of  FIG. 2  being withdrawn from the wellhead assembly. 
         FIGS. 4 and 4A  show in side partial sectional views, operational steps of an alternative bootstrap mechanism. 
         FIG. 5  illustrates a perspective view the bootstrap mechanism of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus and method of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. This subject of the present disclosure 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. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
     It is to be understood that the subject of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the subject disclosure and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the subject disclosure is therefore to be limited only by the scope of the appended claims. 
     Provided in a side cross sectional view in  FIG. 1  is one embodiment of a bootstrapping tool/assembly  20  in accordance with the present disclosure. The assembly  20  can be used to couple inner and outer wellhead housings, such as for a subsea well. The bootstrap assembly  20  of  FIG. 1  includes a housing running tool  22 , a bootstrap shell or frame  24 , and a wedge assembly  26 . The housing running tool  22  is a generally elongated member shown latched within the inner circumference of a high pressure housing  28 . The housing running tool  22  includes a dog latch assembly  30  for selectively attaching to the high pressure housing  28 . The dog latch assembly  30  comprises dogs  32  disposed therein that can selectively project radially outward for coupling with corresponding profiles  34 . The outer circumference of each dog  32  is shown contoured to mate with the profile  34  formed in the high pressure housing  28 . An elongated tubular  36  is shown attached to the lower end of the housing running tool  22 . The tubular  36 , which can be drill pipe, provides a passive weight that, as will be described in more detail below, generates an activating force for bootstrapping the high pressure housing  28  within a low pressure housing  38 . Conductor pipe  40  extending downward from the low pressure housing  38  circumscribes casing  41  shown attached to the high pressure housing  28  to form an annulus  42  therebetween. 
     An actuating tool  44  is formed on the upper portion of the housing running tool  22  above the dog latch assembly  30 . The actuating tool  44  is attached on its upper end to drill pipe  46 . The drill pipe  46  provides a raising and lowering means for the housing running tool  22 . A profile  48  is formed on the outer periphery of the actuating tool  44 . The profile  48  is a wedge shaped configuration, preferably conical, whose diameter increases upwards along the length of the actuating tool  44 . 
     As shown in  FIG. 1 , the wedge assembly  26  is generally annular and disposed between upper terminal surface of the high pressure housing  28  and the shell  24 . The wedge assembly  26  includes wedges  50  and a ring  52 , where the wedges  50  are disposed on top of the ring  52  and oriented transverse to the ring  52  circumference. Ridges (not shown) may optionally be provided on the ring  52  upper surface for aligning and retaining the wedges  50 . Bolts  54  are illustrated extending through elongated slots (not shown) in the wedges  50  and into the ring  52 . The elongated slot and bolt  54  arrangement limits wedge  50  travel and further aids in wedge  50  orientation. The ring  52  has a contour that largely matches the upper terminal end of the high pressure housing  28  and may make up a single piece over all or a substantial portion of the high pressure housing  28  upper end. Optionally, the ring  52  may be multiple segments strategically located on the high pressure housing  28  upper surface. A number of wedges  50  may be included that are laterally oriented within the assembly  26 . The wedge  50  cross section thickness increases as it approaches the assembly  26  inner diameter. In one embodiment, the wedges  50  are arranged equidistant apart around the wedge assembly  26 . 
     In one embodiment the shell  24  is made up of an annular disk like base or upper section  56  and cylindrical walls  58  extending downward from the upper section  56  outer diameter. Optionally, elongated members, such as arms or beams may form a structural connection between the low pressure housing  38  and high pressure housing  28  to bootstrap the two together. The upper section  56  lies in a plane largely perpendicular to the housing running tool  22  axis, and includes a passage along its axis through which the housing running tool  22  is inserted. The shell  24  upper section  56  includes a lower surface  60  shown resting on the wedge assembly  26  upper surface. The lower surface  60  is angled to correspond to the increasing wedge  50  thickness and may also include ridges or slots for aligning the wedges  50 . More specifically, in the embodiment of  FIG. 1 , the lower surface  60  tapers downward toward the high pressure housing  28  with increasing radius, thereby increasing the upper section  56  thickness. As shown, a latch assembly  62  is provided on walls&#39;  58  lower terminal end; the latch assembly  62  is formed to engage a raised shoulder  64  on the low pressure housing  38  outer circumference. Latch assembly  62  may be a split ring that snaps inward as it engages recess  64 . Other latching means exist for selectively coupling the shell  24  to the low pressure housing  38 ; examples include a C-ring, collet fingers, and an interference press fit, to name but a few. 
     In one embodiment of use of the bootstrap assembly  20  disclosed herein, the assembly  20  is latched to the high pressure housing  28  on a floating platform above the sea. In this example, the low pressure housing  38  has been landed on the seafloor over a wellbore bored through the seafloor. The assembly  20  with its downwardly depending drill pipe  36  and attached high pressure housing  28  is lowered subsea toward the wellbore for mating with the low pressure housing  38 . In one embodiment, the upper drill pipe  46  provides the lowering means. Accordingly, in this configuration the dogs  32  of the dog latch assembly  30  are engaged with the profile  34  on the high pressure housing  28 . The wedge assembly  26  is retained between the upper end of the high pressure housing  28  and the lower surface  60 . The shell  24  shown seated on the wedge assembly  26 , may be temporarily secured in place when lowering the assembly onto the housing. 
     Continued lowering of the assembly ultimately stabs the high pressure housing  28  coaxially within the low pressure housing  38 . Adding corresponding conical shapes to the high pressure housing  28  lower end and low pressure housing  38  upper end eases high pressure housing  28  insertion within the low pressure housing  38 .  FIG. 1A  illustrates in a sectional view, an enlarged portion of the interface between the high and low pressure housings  28 ,  38 . As shown in  FIG. 1 , when initially landed onto the low pressure housing  38 , a gap  66  remains between a shoulder  68  formed on the outer circumference of the high pressure housing  28  and a shoulder  70  on the inner circumference of the low pressure housing  38 . The latch assembly  62  latches with the raised shoulder  64  thereby preventing downward movement of the low pressure housing  38  with respect to the shell  24 . The raised shoulder  64  may alternatively be a permanently formed protrusion on the outer circumference of the low pressure housing  38 , or may be made up of multiple protrusions, similar to a collet assembly. Once latched an upward force applied to the shell  24  transfers to low pressure housing  38 . 
     After the initial landing, and for fully engaging the high pressure housing  28  with the low pressure housing  38 , the dogs  32  of the dog latch assembly  30  are released from the profile  34 . Hydraulics or a mechanical linkage (not shown) can be provided within the tool assembly  20  for actuating the latch assembly  30 . Optionally, the dog latch assembly  30  can be provided so that rotating or stroking the drill pipe  46  retracts or extends the dogs  32 . The mass of the drill pipe  36 , combined with the mass of the housing running tool  22  and drill pipe  46 , causes the running tool  22  to drop downward to a lower position within the high pressure housing  28 . An example of the downward movement with the running tool  22  in the lowered position is provided in a side cross sectional view in  FIG. 2 . A load shoulder  72  shown formed on the high pressure housing  28  inner circumference, is engagable by the running tool  22  in the lower portion to limit downward travel of the running tool  22  within the high pressure housing  28 . 
       FIG. 2  also depicts the outer profile  48  radially outwardly urging the wedges  50  by its downward movement through a bore in the base  56 . This moves each wedge  50  so a thicker section is between the lower surface  60  and high pressure housing  28 . As explained above, the latch assembly  62  is engaged with the recess  64  on outer wellhead housing  38 , thus an upward force on the base tensions the frame  24  walls that in turn exerts oppositely directed forces on each of the high pressure housing  28  and low pressure housing  38 . As the wedges  50  move radially outward, they exert an upward force on shell  24  and a downward force on wellhead housing  28 . The forces urge together the opposing shoulders  68 ,  70 , thereby reducing or eliminating the gap  66 . Another latch  74  is included for coupling the low pressure housing  38  and high pressure housing  28  once shoulders  68 ,  70  engage one another. In the embodiment shown, the latch  74  includes a C-ring disposed on the outer circumference of a portion of the high pressure housing  28 . The downward force applied to the high pressure housing  28  moves the high pressure housing  28  and the C ring into alignment with a corresponding channel of the low pressure housing  38 . The alignment allows the C ring to expand into a locking engagement between these two housings  28 ,  38  for an additional securing means between the two housings  28 ,  38 . 
     Shown in  FIGS. 1 and 2  is a bar puller  76  transversely mounted on the actuating tool  44  above the outer profile  48 . The bar puller end  78  includes a rabbet like contour formed to couple with a groove  80  on an upper end of a latch release bar  82 . As seen in  FIG. 2 , when the actuating tool  44  is at its full downstroke, the puller end  78  has engaged the groove  80  thereby coupling the bar puller  76  and latch release bar  82 .  FIG. 3  provides a side partial sectional view of the actuating tool  44  on its subsequent upstroke. The coupling between the end  78  and the groove  80  pulls the latch release bar  82  upward from within the shell  24 . The latch release bar  82  is connected to a latch release assembly (not shown) within the shell  24 . Drawing the latch release bar  82  upward actuates the latch release assembly separating the latch assembly  62  from the recess  64  so the shell  24  can be decoupled from the low pressure housing  38 . The release assembly may include a lower portion of bar  82  that extends through a hole in the sidewall of the frame  24  and pushes latch ring  64  radially outward from its engagement with recess  62 . Continued upward movement of the tool  44  contacts the upper surface of the dog latch assembly  30  with the lower end of the ring  52  to retrieve the shell  24  from the wellhead assembly. 
     Optionally, removing the boot strap assembly  20  may begin by releasing the engagement between the groove  64  and the latch assembly  62  with a remotely operated vehicle (ROV). For example, in the embodiment where the latch  62  is a C ring, the split portion may be engaged and pushed outward thereby urging the ring totally out of the channel  64  on the low pressure housing  38  and into the shell  24 . This disengagement allows shell  24  to move upward. The shell  24  can alternatively be pulled upward by contact of an extended profile (not shown) extending from the outer surface of the housing running tool  22  and into contact with the upper end  56  of the shell  24 . 
     Advantages of the present device include the use of two separate wedge portions, one being the profiles  48  on the activating tool  44  and the other being the wedges  50  of the wedge assembly  26 . Mechanical advantage is provided by the tool  44  length combined with the relatively short outward radial movement of the wedges  50  to provide a downward force and movement of the high pressure housing  28 . In one example, approximately 50,000 lbs of drill pipe weight provided as the tubular  36  could deliver a boot strapping force of about 1,000,000 lbs for coupling the high pressure housing  28  onto the low pressure housing  38 . 
     An alternative system for releasing the bootstrap mechanism is shown in a side partial sectional view in  FIG. 4  In the embodiment, the bootstrap assembly  20 A includes a latch release ring  84  is shown coaxially disposed atop the frame  24 . A split C-ring  85  is shown in a groove  86  formed along the latch release ring  84  outer circumference. The C-ring  85  outer radial surface is profiled shown depending radially inward along a path from its middle to its upper end. A release bar  87 , similar to the release bar  82 , is shown projecting axially through the latch release ring  84  having its upper end bolted atop the latch release ring  84 . Below the latch release ring  84 , the release bar  87  extends through the shell  24  into coupling engagement with the latch assembly  62 . In the configuration shown the latch release ring  84  is spaced apart from the shell upper section  56  that tensions the release bar  87  to retain the latch assembly  62  in an open configuration. A retention bar  88  is shown that also projects axially through the latch release ring  84 . A spring  89  provided around the bar  88  is preloaded against the bar  88  upper end to apply a downward force against the latch release ring  84 . In one embodiment, up to eight release bars  87  and/or eight retention bars  88  are included with the assembly  20 A; in another embodiment, the release bars  87  are spaced equidistance apart and the retention bars  88  are spaced equidistance apart. An outer shell  90  is shown circumscribing the actuating tool  44  that is dimensioned for selective coaxial placement around the shell  24 . The outer shell  90  is depicted as a tubular member depending downward from attachment with the actuating tool  44 . In its natural uncompressed configuration, the split C-ring  85  outer circumference exceeds the latch release ring  84  outer circumference. However, as shown in  FIG. 4 , the outer shell  90  contacts and compresses the split C-ring  85  so that at least a portion of it remains within the groove  86 . 
     A groove  92  shown in the shell  90 . On its lower end the groove  92  forms a ledge in the shell  90  inner surface substantially perpendicular to the shell  90  wall. On its upper end, the groove  92  transitions along a line that is oblique to the shell  90  inner surface. The groove  92  shape and split C-ring  85  are correspondingly profiled on their respective upper portions thereby preventing coupling between the split C-ring  85  and the groove  92  as the outer shell  90  slides downward. As shown in  FIG. 4A , the actuating tool  44  is being urged through the central opening of the array of wedges  50  in the wedge assembly  26  to slide the groove  92  past the split C-ring  85  and land the latch release ring  84  on top of the shell upper surface  56 . This pushes the release bar  87  downward allowing coupling between the latch assembly  62  and raised shoulder  64  so that the upward force from the outwardly extending array of wedges  50  upwardly pulls the shell  24  and low pressure housing  38  with respect to the high pressure housing  28 . While the assembly  20 A is at or near the bottom of its downward travel, the latch assembly  62  remains activated by the spring  89  through its downward force onto the release ring  84  that is transferred to the release bar  87 . 
     Referring now to  FIG. 5 , as the tool  44  is drawn upwards along with the attached outer shell  90 , the split C-ring  85  radially expands outward as it becomes aligned with the groove  92 . The perpendicularly oriented groove  92  lower surface engages the lower side of the split C-ring  85  thereby coupling the shell  90  with the latch release ring  84 . As the shell  90  is further drawn upward, this upwardly pulls the latch release ring  84  and release bar to decouple the latch assembly  62  and raised shoulder  64  so the shell  24  can be raised upward. In some instances it may not be possible to push the actuating tool  44  to full downstroke position. Thus strategically positioning the groove  92  enables engaging the latch release ring  84  even if the actuating tool  44  does not reach full downstroke. 
     The present system and method described herein, therefore, is well adapted to carry out and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Summary:
A running tool for coaxially setting together subsea wellhead housings, such as a high pressure wellhead housing within a low pressure wellhead housing. The tool includes a conically shaped body that is insertable within the inner most housing, a frame with a base, an axial bore and latches. The base perpendicularly rests on top of an inner housing and the latches extend from the base to connect with an outer housing. The bore is formed to accommodate the tool freely therethrough. Wedge shaped members are provided between the base and inner housing top having their wide ends contactable by the tool. Urging the tool through the bore pushes the wedges radially outward that imparts a force between the base and inner housing top in one direction. The attached latches apply an oppositely directed force onto the outer housing.