Abstract:
An outer wellhead member has a bore with a first profile portion and an annular recess. A tubular inner wellhead member with a centralizer/overpull ring is lowered into the outer wellhead member. The centralizer/overpull ring is biased to expand outward to engage the bore of the outer wellhead member to center the inner wellhead member within the bore as the inner wellhead member is lowered through the bore. The recess of the outer wellhead member is adapted to receive the centralizer/overpull ring and oppose axial movement of the centralizer/overpull ring to enable an upward test pull of the inner wellhead member.

Description:
FIELD OF THE INVENTION 
       [0001]    This technique relates in general to running and setting well pipe hangers in wellbores, and, in particular, a well pipe hanger centralizer and overpull indicator. 
       BACKGROUND OF THE INVENTION 
       [0002]    Centralizers have been in use for a long time. As their name suggests they have been used to center a tubular in a borehole. Centralizers are used on well pipe hangers to centralize the hanger, allowing the hanger to land on the corresponding tag shoulder properly, thereby preventing premature actuation of setting resistance devices, such as hanger load rings. The centralizers prevent the casing from side loading the hanger against the wellhead, which could result in premature actuation of setting resistance devices. The centralizers have been made of metal and non-metallic materials such as thermoplastic polyamides, glass, and mineral filled nylons and poly-tetra fluoro ethylene, also known as Teflon and injection molded polyurethane. These centralizers were made in hinged segments that could be clamped onto a tubular and in some applications the centralizers were formed right on to or slipped over the rod or tubular. After the hanger is delivered to the proper position, no positive indication is provided to the operator that the hanger has been delivered to the proper position. 
         [0003]    A need exists for a technique that ensures that a well pipe hanger is properly centralized and set. The following technique may solve one or more of these problems. 
       SUMMARY OF THE INVENTION 
       [0004]    An embodiment of the wellhead assembly as comprised by the present technique has an outer wellhead member with a bore. The bore has a first profile portion and an annular recess. A tubular inner wellhead member is adapted to be lowered into the bore of the outer wellhead member. A centralizer/overpull ring is positioned on the inner wellhead member. The centralizer/overpull ring has a lower band portion and a plurality of resilient finger members extending upwardly therefrom. The plurality of resilient finger members are each separated from one another by a slot and are biased to expand outward to engage the bore of the outer wellhead member to center the inner wellhead member within the bore as the inner wellhead member is lowered through the bore. The recess of the outer wellhead member is adapted to receive the plurality of resilient finger members and oppose axial movement of the centralizer/overpull ring to enable an upward test pull of the inner wellhead member. 
         [0005]    An embodiment of the wellhead assembly as comprised by the present technique has an outer wellhead member that has a bore. The bore has a first profile portion and an annular recess. A tubular inner wellhead member is adapted to be lowered into the bore of the outer wellhead member. A centralizer/overpull ring is positioned on the inner wellhead member. The centralizer/overpull ring has a lower band portion and a plurality of resilient finger members extending upwardly therefrom. The plurality of resilient finger members are each separated from one another by a slot and are biased to expand outward to engage the bore of the outer wellhead member to center the inner wellhead member within the bore as the inner wellhead member is lowered through the bore. The recess of the outer wellhead member is adapted to receive the plurality of resilient finger members and oppose axial movement of the centralizer/overpull ring to enable an upward test pull of the inner wellhead member. A retainer ring is positioned on the inner wellhead member above the centralizer/overpull ring and is adapted to limit the extent to which the plurality of resilient finger members extend radially outward from the inner wellhead member. 
         [0006]    An embodiment of a method for assembling a wellhead assembly as comprised by the present technique includes providing an outer wellhead member that has a bore. The bore has a first profile portion and an annular recess. A tubular inner wellhead member is provided with a resilient retractable and expandable centralizer/overpull ring positioned thereon. The inner wellhead member is lowered into the outer wellhead member with the centralizer/overpull ring in an expanded run-in position. The centralizer/overpull ring is retracted into a recess on the inner wellhead member due to contact of the centralizer/overpull ring with the bore as the inner wellhead member is lowered into the outer wellhead member. When the inner wellhead member has reached a desired position within the outer wellhead member, the centralizer/overpull ring is expanded into the recess of the outer wellhead member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    So that the manner in which the features and benefits of the technique, as well as others which will become apparent, may be understood in more detail, a more particular description of the technique briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is also to be noted, however, that the drawings illustrate only various embodiments of the technique and are therefore not to be considered limiting of the technique&#39;s scope as it may include other effective embodiments as well. 
           [0008]      FIG. 1  is an isolated sectional view of an inner wellhead member, including a load ring and a centralizer/overpull assembly constructed in accordance with the present technique, shown in a set position within an outer wellhead member. 
           [0009]      FIG. 2  is an isolated perspective view of the inner wellhead member of  FIG. 1 , including the load ring and the centralizer/overpull assembly. 
           [0010]      FIG. 3  is an isolated perspective view of the centralizer/overpull ring of  FIG. 1 . 
           [0011]      FIG. 4  is an isolated sectional view of the inner wellhead member, the load ring, and the centralizer/overpull assembly constructed in accordance with this technique. 
           [0012]      FIG. 5  is an isolated sectional view of the inner wellhead member of  FIG. 4 , shown in a landing position within the outer wellhead member. 
           [0013]      FIG. 6  is an isolated sectional view of the inner wellhead member of  FIG. 4 , shown in an overpull position within the outer wellhead member. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present technique now will be described more fully hereinafter with reference to the accompanying drawings in which a preferred embodiment of the technique is shown. This technique may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, this embodiment is provided so that this disclosure will be thorough and complete, and will fully convey the scope of the technique to those skilled in the art. Like numbers refer to like elements throughout. 
         [0015]    Referring to  FIG. 1 , an embodiment of an outer wellhead member  11  is illustrated. In this embodiment, the outer wellhead member  11  is positioned within a landing sub connected to well pipe positioned below a high pressure wellhead housing. However, the outer wellhead member  11  may be a high pressure housing or other housing having an axial bore  13 . 
         [0016]    The axial bore  13  of the outer wellhead member  11  has a tag/load shoulder  15  located within it. In this embodiment, the tag/load shoulder  15  is a circular ledge located at a junction between a larger diameter upper portion of the bore  13  and a slightly smaller diameter lower portion of the bore  13 . In this embodiment, a load ring  17  is carried by the outer wellhead member  11  and is positioned on the tag/load shoulder  15  of the bore  13 . The lower surface of the load ring  17  is substantially geometrically complimentary to tag/load shoulder  15 . The upper surface of the load ring  17  is conical and forms a generally upward facing shoulder  19  that inclines relative to an axis of the bore  13 . A retainer ring  21  is positioned above and engaged with the load ring  17  to maintain the position of the load ring  17  on the tag/load shoulder  15 . The bore  13  also has an annular overpull recess  23  located within it, a select distance below the tag/load shoulder  15 . In this embodiment, the overpull recess  23  is formed by a conical, generally downward facing overpull shoulder  25  that declines relative to the axis of the bore  13  and a surface  27  that is generally cylindrical and concentric to the axis of the bore  13  of the outer wellhead member  11  and extends downward from the overpull shoulder  25 . In this embodiment, the overpull shoulder  25  declines relative to the axis of the bore  13  of the outer wellhead member  11  at an angle of thirty degrees. In alternate embodiments, the overpull shoulder  25  declines relative to the axis of the bore  13  of the outer wellhead member  11  at an angle between thirty degrees and sixty degrees. 
         [0017]    An inner wellhead member  29  lands within the outer wellhead member  11  in the illustrated embodiment and has an axial bore  30 . For example, the inner wellhead member  29  may be a well pipe hanger, such as a casing hanger. As illustrated in  FIGS. 1 and 2 , the inner wellhead member  29  has a profile made up of a load shoulder  31 . In this embodiment, there is one inner wellhead member load shoulder  31  and one outer wellhead member tag/load shoulder  15 . The number of load shoulders  15 ,  31  can vary. An enlarged portion  33  of the inner wellhead member  29  directly above the load shoulder  31  has a diameter that is only slightly less than the inner diameter of the bore  13 . 
         [0018]    In the illustrated embodiment, a load ring  35  is mounted on the inner wellhead member  29  to support the inner wellhead member  29  on the outer wellhead member tag/load shoulder  15 . In this embodiment, the upper surface of the load ring  35  is substantially geometrically complimentary to the load shoulder  31  of the inner wellhead member  29 . An outer portion of the lower surface of the load ring  35  is conical and forms a generally downward facing load shoulder  37  that inclines relative to an axis of the bore  30  of the inner wellhead member  29 . The generally downward facing load shoulder  37  is substantially geometrically complimentary to the upward facing shoulder  19  of the load ring  17 . The load shoulder  37  of the load ring  35  is dimensioned to land on the load shoulder  19  of the load ring  17  in the outer wellhead member bore  13  ( FIG. 1 ). 
         [0019]    A centralizer/overpull assembly  41  is mounted to the inner wellhead member  29 , below the load ring  35 . In this embodiment, the centralizer/overpull assembly  41  comprises a retainer ring  43  and a centralizer/overpull ring  45  positioned within an annular recess  47  on the outer surface of the inner wellhead member  29 . As illustrated in  FIG. 1 , the upper end of the retainer ring  43  is positioned in abutting contact with a portion of the lower surface of the load ring  35  and acts to maintain its position on the inner wellhead member  29 . The lower end  49  of the retainer ring  43  is conical and declines at an angle relative to the axis of the bore  30  of the inner wellhead member  29 . In this embodiment, the lower end  49  of the retainer ring  43  declines at an angle of thirty degrees relative to the axis of the bore  30  of the inner wellhead member  29 . A select distance below the retainer ring  43 , the diameter of the inner wellhead member  29  slightly decreases, thereby forming a generally downward facing shoulder  53 . The diameter of the inner wellhead member  29  increases a select distance below the downward facing shoulder  53 , thereby forming a generally upward facing shoulder  55 . In this embodiment, the generally upward facing shoulder  55  inclines slightly upward at an angle relative to the axis of the bore  30  of the inner wellhead member  29 . 
         [0020]    As illustrated in  FIG. 3 , in this embodiment, the centralizer/overpull ring  45  is a split ring having an annular band  57  with a plurality of resilient finger members  59  extending upward and outwardly from the annular band  57  at an angle θ ( FIG. 1 ) from the axis of the bore  30  of the inner wellhead member  29  to form a collet-like member. In this embodiment, there are six finger members  59  positioned around the diameter of the annular band  57 , each finger  59  being separated from another by a slot  60 . The diameter of the centralizer/overpull ring  45  decreases from the annular band  57  to the finger members  59 , thereby forming a generally upward facing shoulder  61 . The upward facing shoulder  61  is substantially geometrically complimentary to the downward facing shoulder  53  on the inner wellhead  29  ( FIG. 1 ). As illustrated in  FIG. 1 , in this embodiment, the centralizer/overpull ring  45  is connected to the inner wellhead member  29  by a plurality of fasteners  63  that extend through a plurality of apertures  64  in the annular band  57  portion of the ring  45  and into the inner wellhead member  29 . The upper ends  65  of the finger members  59  are conical and decline at angle relative to the axis of the bore  30  of the inner wellhead member. The upper ends  65  of the finger member  59  are substantially geometrically complimentary to the lower end  49  of the retainer ring  43 . In this embodiment, the upper ends  65  of the finger members  59  decline at an angle of thirty degrees relative to the axis of the bore  30  of the inner wellhead member  29 . The engagement between the angled lower end  49  of the retainer ring  43  and the upper ends  65  of the finger members  59  limits the degree to which the finger members  59  extend radially outward from the inner wellhead member  29  beyond the diameter of the enlarged portion  33  of the inner wellhead member  29 . The upper ends  65  of the finger members  59  are also substantially geometrically complimentary to the generally downward facing overpull shoulder  25  in the recess  23  of the outer wellhead member  11 . The lower end  67  of the annular band  57  portion of the centralizer/overpull ring  45  is inclined at an angle relative to the bore of the axis  30  of the inner wellhead member  29  and is substantially geometrically complimentary to the upward facing shoulder  55  in the inner wellhead member  29 . 
         [0021]    As illustrated in  FIG. 4 , in the initial orientation of the inner wellhead member  29  prior to tripping the inner wellhead member  29  into the outer wellhead member  11  ( FIG. 1 ), the centralizer/overpull ring  45  is fully expanded, with the outer diameter of centralizer/overpull ring  45  being greater than or equal to the outer diameter of the enlarged portion  33  of the inner wellhead member  29 . In the expanded position, an outer portion of the lower end  49  of the retainer ring  43  abuttingly contacts an inner portion of the upper ends  65  of the finger members  59 , thereby limiting the extent to which the finger members  59  extend radially outward from the inner wellhead member  29 . 
         [0022]    As illustrated in  FIG. 5 , from the trip-in position ( FIG. 4 ), in operation, as the inner wellhead member  29  is tripped into the well, the centralizer/overpull ring  45  makes contact with the surfaces of the bore  13  of the outer wellhead member  11  and is compressed into the annular recess  47  on the outer surface of the inner wellhead member  29  as the centralizer/overpull ring  45  centralizes the inner wellhead member  29  in the outer wellhead member  11 . When the finger members  59  are in the fully compressed position within the recess  47 , the upper ends  65  of the finger members  59  are not in abutting contact with the lower end  49  of the retainer ring  43 , thereby resulting in a gap between them. 
         [0023]    As the inner wellhead member  29  is further lowered into the bore  13 , the finger members  59  of the centralizer/overpull ring  45  slidingly engage the load ring  17  carried by the outer wellhead member  11  and positioned on the tag/load shoulder  15  of the bore  13 . The finger members  59  of the centralizer/overpull ring  45  contact the load ring  17 , thereby pushing the finger members  59  radially inward into the recess  47 , further compressing the fingers members  59 , allowing the centralizer/overpull ring  45  to move below the load ring  17  and the tag/load shoulder  15 . 
         [0024]    As illustrated by  FIG. 1 , as the inner wellhead member  29  further enters the bore  13 , the load ring  35  of the inner wellhead member  29 , and in particular, the load shoulder  37  lands on the load shoulder  19  of the load ring  17  on the outer wellhead member tag/load shoulder  15 . The inner wellhead member  29  moves downward relative to the outer wellhead member  11  until the load ring  35  of the inner wellhead member  29  is fully engaged with the load ring  17  of the outer wellhead member  11 , and the inner wellhead member  29  is in a set position within the outer wellhead member  11 . In addition, as the inner wellhead member  29  moves downward relative to the outer wellhead member  11 , the centralizer/overpull assembly  41  moves downward with the inner wellhead member  29  until the centralizer/overpull ring  45  reaches the overpull recess  23 . When the inner wellhead member  29  reaches the set position, the centralizer/overpull ring  45  simultaneously reaches the recess  23 , the resilient finger members  59  of the centralizer/overpull ring  45  expand radially outward and into the overpull recess  23 , thereby moving the centralizer/overpull assembly  41  to an expanded position. 
         [0025]    Once fully engaged, the generally downward facing load shoulder  37  of the load ring  35  of the inner wellhead member  29  is in contact with the generally upward facing load shoulder  19  of the load ring  17  of the outer wellhead member  11 . A downward load on the inner wellhead member  29  transfers from the inner wellhead member load shoulder  31  through the load ring  35 , the load ring  17 , and into the outer wellhead member tag/load shoulder  15 . 
         [0026]    A reduction in the weight of the running string is an indication that the inner wellhead member  29  has properly set within the outer wellhead member  11 . As a further assurance, the operator can apply a selected overpull. An overpull is a test where a lifting force is applied by the running string to the inner wellhead member  29 . When in the set position, the upper ends  65  of the finger members  59  of the centralizer/overpull ring  45  rest within the recess  23  on the outer wellhead member  11 . 
         [0027]    As illustrated by  FIG. 6 , and as previously discussed, the upper ends  65  of the finger members  59  of the centralizer/overpull ring  45  are geometrically complimentary to the generally downward facing shoulder  25  of the recess  23 . In order to perform an overpull to determine if the inner wellhead member  29  is properly positioned in the set position within the bore  13  of the outer wellhead member  11 , an upward force is applied to the inner wellhead member  29 . The inner wellhead member  29  initially moves upward relative to the outer wellhead member  11  until the upper ends  65  of the finger members  59  of the centralizer/overpull ring  45  abut against the generally downward facing overpull shoulder  25  of the recess  23 . A defined overpull force, for example, 120,000 pounds, is necessary to move the finger members  59  of the centralizer/overpull ring  45  radially inward into the recess  47  on the inner wellhead member  29 , thereby moving the centralizer/overpull ring  45  to a retracted position. Therefore, the operator will pull upward a fraction of that amount, for example, 60,000 pounds, to determine if the angled upper ends  65  of the finger members  59  of the centralizer/overpull ring  45  are abuttingly contacting the generally downward facing overpull shoulder  25  of the recess  23 . If the pull upward does not result in further upward movement of the inner wellhead member  29 , this indicates that the centralizer/overpull ring  45  is located correctly and, therefore, the inner wellhead member  29  is located correctly within the outer wellhead member  11  and has properly set. The operator can then slack off the weight. 
         [0028]    The centralizer/overpull assembly  41  of the present technique may also be incorporated on an inner wellhead member with a load ring and an activation ring to prevent the load ring from prematurely activating. Non-stationary load rings and activation rings that may be incorporated with the present technique are known in the art. For example, the centralizer/overpull assembly  41  of the present technique could be incorporated with a hanger such as that disclosed in U.S. Pat. No. 7,380,607, herein incorporated by reference in its entirety. In such an embodiment, the centralizer/overpull assembly  41  would extend radially outward from the inner wellhead member to prevent side loading of the load ring or activation ring and premature activation of the load ring. 
         [0029]    The centralizer/overpull assembly  41  of the present technique may also be incorporated on an inner wellhead member that does not include a load ring or a load shoulder. For example, the centralizer/overpull assembly  41  of the present technique may be incorporated on an inner wellhead member that does not have a load ring or a load shoulder, and the centralizer/overpull assembly  41  may be used to perform and overpull test to indicate that the inner wellhead member is properly positioned within an outer wellhead member. 
         [0030]    The technique has significant advantages. The centralizer/overpull assembly acts as an indicator to an operator that the inner wellhead member is properly positioned within the outer wellhead member. Additionally, the centralizer/overpull assembly acts as a centralizer to prevent side loading and premature activation of a load ring to ensure that a load ring is properly set. 
         [0031]    In the drawings and specification, there have been disclosed a typical preferred embodiment of the technique, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The technique has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the technique as described in the foregoing specification and as set forth in the following claims.