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PRIORITY INFORMATION 
   This application is a continuation of U.S. patent application Ser. No. 10/441,521, filed on May 20, 2003 now U.S. Pat. No. 7,096,938. 

   FIELD OF THE INVENTION 
   The field of this invention is expanding tubulars and more particularly a gripping system for hangers or patches that is energized by longitudinal dimension change of the tubular induced by the expansion process. 
   BACKGROUND OF THE INVENTION 
   When downhole tubulars crack or otherwise need repair, patches or cladding are inserted to the proper depth and expanded into contact over the damaged area. As a result of expansion, the cladding assumes a sealed relation with the surrounding tubular. In other applications a hanger attached to a tubular string is inserted into a larger tubular. Expansion is used to anchor and seal the newly inserted string to the existing string. 
   Expansion is accomplished by driving a swage through the hanger or cladding. Applied hydraulic pressure from the surface is used to stroke a piston, which, in turn, drives the swage. An anchor assembly initially is energized to hold the hanger in response to applied pressure. Initially, the running tool that delivered the hanger is released when the anchor grabs the hanger to provide support for the hanger as the piston strokes the swage to obtain initial support. Once initial support is accomplished the anchor is released and the stroker for the swage is re-cocked for a repetition of the process until the swage passes through the hanger. 
   The specification for the tubular being repaired or the tubular in which the hanger is to be attached can vary widely. The condition of that tubular can also affect its internal diameter. 
   When using a swage that has a fixed dimension care must be taken to properly size it for the anticipated inside diameter where the patch or hanger is to be attached. The problem is that there is uncertainty as to the actual inside diameter after years of service. Additionally, a given swage size may be used for a variety of casing weights of a given size. If the actual diameter is smaller than anticipated, there may not be enough available force in the stroking mechanism for the swage to drive it through. In this case the swage will stall and the expansion cannot be properly completed without time-consuming trips out of the hole and replacement swages. Even worse, the swage could hang up in the hanger if it can&#39;t be driven all the way through. 
   One expensive way around this is to use a variable diameter swage that has the ability to change dimension in response to unexpected inside diameter dimension in the tubular in which the patch or hanger is to be attached. Fixed diameter swages are more economical and, in the past, some efforts have been made when using a fixed swage to compensate for unexpected variation from the planned inside diameter.  FIGS. 1 and 2  show a prior technique for compensating for dimensional variations in the casing 
   Referring to  FIG. 1 , a fixed diameter swage  10  is disposed inside the hanger or cladding  12  and the entire assembly is in position for expansion inside casing  14 . When hanger is mentioned it will be considered to also encompass other downhole structures such as patches or cladding. Hanger  12  has an exterior serrated surface  16  built into it for eventual engagement with the casing  14 , as shown in  FIG. 2 . An inner sleeve  18  made of soft material underlays the serrations  16 . The intent is for the swage  10  to go inside sleeve  18 . If the inside diameter turns out to be smaller than anticipated, then the swage  10  will deform sleeve  18  by design. This can happen because sleeve  18  is made deliberately soft. The objective is to prevent the swage from stalling when the inside diameter of the casing turns out to be smaller than expected. Using sleeve  18  also helps to give the swage  10  an opportunity to provide sufficient contact force against casing  14  by the serrations  16  when the actual inside diameter turns out to be somewhat larger than expected. Yet the ability to provide flexibility and latitude for the actual inside diameter being smaller or larger than anticipated is limited in this design. The apparatus of the present invention seeks to provide greater latitude for diameter variations in both directions that may be incurred in the field. Additionally, the present invention seeks to improve the grip and provide resistance against release from net forces in opposed directions. One way this is accomplished is to take advantage of the phenomenon of longitudinal dimension change of the hanger under compressive or tensile stress that occurs as force is applied to drive the swage. The slip is articulated for radial extension from longitudinal shrinkage to allow a greater variation of inside diameters in which a proper grip can be maintained and the swage driven through without stalling. These and other advantages of the present invention will be more readily appreciated by those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below. 
   SUMMARY OF THE INVENTION 
   A slip for an expanding hanger or patch is disclosed. The slip is mounted over the hanger body and has an internal profile that nests within a mating profile on the exterior of the hanger. When the swage is forced through the hanger, the hanger shrinks longitudinally and as a result the slip is cammed radially to the extent the inside diameter of the surrounding tubing permits. As the swage is further advanced, the diameter of the hanger increases in the region where longitudinal dimension change has already taken place forcing the slip into preferably penetrating contact with the inside wall of the surrounding tubular. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a run in view of a prior art hanger; 
       FIG. 2  is the view of  FIG. 1  in the set position; 
       FIG. 3  is a run in view of a part of a hanger showing the distinct slip and the camming mechanism; 
       FIG. 4  is the view of  FIG. 3  with the slip set in the surrounding tubular without an opportunity to be cammed away from the hanger; 
       FIG. 5  is the view of  FIG. 3  after the slip has had room inside the tubular inside diameter to be cammed out before being forced against the wall of the surrounding tubular; 
       FIGS. 6   a - 6   b  shows the upper end of a hanger in the set position with slips disposed in mirror image orientation. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The overall layout can best be understood from  FIG. 6 . The casing  20  has a split or an area of perforation  22  that needs to be covered with the hanger  24 . Alternatively, hanger  24  may be mounted at the uphole end of a tubing string (not shown) such that when it is expanded by the swage  26  the final result is support for the string from the casing  20 . Swage  26  has a fixed diameter and is mounted for sliding movement with respect to running tool  28 . Hanger  24  has a groove  30  into which a latch  32  on the running tool  28  is initially held. In this manner, a running string (not shown) can support the hanger  24  for proper placement in the casing  20 . Generally, the swage  26  is driven by a hydraulic stroker device (not shown). Initially, application of hydraulic pressure through the running string actuates the schematically illustrated anchor  34  for an initial grip of the hanger  24 . After some advancement of the swage  26  a grip is established between the hanger  24  and the casing  20 , as will be described below. Such expansion of the hanger  24  also results in a release of latch  32  from groove  30 . Thereafter, by cycles of applying and removing the hydraulic pressure, the swage  26  is advanced until it clears the opposite end of the hanger  24 . Those skilled in the art will appreciate that the anchor  34  can be mounted downhole of the swage  26  (as shown) or uphole of the swage  26  and still obtain sequential grips to allow repeated stroking to advance the swage  26  to its desired end of travel. The above-described technique for stepwise advancement of a fixed diameter swage  26  is a known procedure and sets the stage for the detailed description of the operation of the invention. 
   It should be noted that in  FIG. 6 , the swage  26  is bearing down and initiating expansion by fixating the uphole end of hanger  24 . The lower end of hanger  24  is not restrained but merely held by the anchor  34 . The swage actually puts the hanger  24  in tension. For a diameter expansion of about 20% the length will decrease by about 5%. Alternatively, the swage can be forced in an uphole direction with the upper end of the hanger  24  being retained. In this situation, the hanger  24  will be in compression and the wall thickness will try to remain constant. Since the volume will remain constant after expansion, the length will shrink even more than expansion under tension. It is this change in length, as the expansion is underway that is employed in the present invention to push out the slips such as  36  and  38  to the wall of the casing across clearance  66 , if present. This use of longitudinal dimension change to drive the slip allows for greater flexibility to have the hanger  24  get a bite in a wider range of casing inside diameters than was possible in the prior designs. 
   Broadly stated, one aspect of the invention is the ability to take advantage of the longitudinal shrinkage of the hanger  24 , when placed under compressive or tensile stress from swaging. 
     FIG. 6   a  illustrates slips  36  and  38 . Slip  36  has serrations or other surface treatment  40  so that upon expansion it can preferably penetrate into the wall of the casing  20 . The surface treatment  40  can also incorporate hard materials such as carbide inserts or it can be a regular pattern of protrusions or a series of rings or a thread or any other grip enhancing treatment or coating of the exterior of the slip  36 . Slip  36  is preferably a split ring with a single split longitudinally. Alternatively, the slip  36  can be a plurality of segments held to hanger  24  with a band spring or other retainer that can allow the segments to be cammed outwardly as will be described below. In another form, slip  36  can be a solid thin walled ring that can be cammed out if space permits by simply yielding or by fracturing. In the preferred embodiment slip  38  is identical to slip  36  and is installed in a mirror image manner. As seen in  FIG. 6   a , slip  36  has a shoulder  42  adjacent to a mating shoulder  44  near the uphole end  46  of hanger  24 . Slip  38  is identical but is oppositely oriented so that it has a shoulder  48  near shoulder  50  on hanger  24 . Shoulder  48  is oriented closer to the downhole end of hanger  24 . While two mirror image slips  36  and  38  have been shown near one end of hanger  24 , those skilled in the art will appreciate that slips  36  and  38  can be in the same as opposed to mirror image orientation. Only one slip such as  36  or  38  can be used or even more than the two slips shown can be placed near a given end of the hanger  24 . The design of each slip can vary and some variations are suggested above. These variations can be mixed or matched. 
     FIG. 3  illustrates a portion of slip  36  with the casing  20  represented by a dashed line. Shoulder  42  is disposed close to shoulder  44  on hanger  24 . Hanger  24  has a recessed surface  52  that begins at shoulder  42  and a plurality of projections  54 . Typically, a projection  54  is trapezoidal in section and has opposed surfaces  56  and  58  that have intersecting slopes. In between is a preferably flat surface  60 . Slip  36  has an interior surface  62  with voids  64  that preferably conform in shape to projections  54 . Shape conformity is merely the preferred mode and is not essential. The indicated shape using inclined surfaces separated by a flat surface for the projections  54  or for conforming voids  64  is simply the preferred embodiment. Those skilled in the art will appreciate that the invention encompasses shapes that can nest during run in, as shown in  FIG. 3  to allow a clearance  66  to exist. Then, when swage  26  begins moving into hanger  24  its length will decrease and to the extent a clearance  66  still exists, the nesting relation turns into a camming relationship as the slip  36 , or for that matter any other similarly mounted slip, is moved outwardly due to longitudinal shrinkage of the hanger  24  under stress loading. For example, if the planned expansion is about 20% the longitudinal shrinkage is approximately 5%. As shown in  FIG. 5 , the further a given projection is from a point on the hanger  24  that is restrained the greater the offset between previously nested pairs of projection and corresponding depression. For example, projection  68  is fully misaligned from depression  70  so as to fully cam out the lower end  72  of slip  36 . Further uphole, projection  74  is somewhat less misaligned from depression  76  while still further uphole projection  78  is separated from but virtually still in alignment with depression  80 .  FIG. 5  illustrates that where the inside diameter of the casing  20  permits, driving the swage  26  through hanger  24  will shorten it drawing the various projections about 5% of their original distance from the restrained point of the hanger  24 . Initially, until shoulder  42  on slip  36  engages shoulder  44  on hanger  24  any slack between the projections and depressions will be taken out. Thereafter, as the projections keep moving, shortening their original distance from the restrained point by about 5% or more depending on the amount of diametric expansion, due to longitudinal shrinkage the camming action commences to the extent a clearance to the inside casing wall is present. The maximum radial displacement due to shrinkage of the hanger  24  is shown in  FIG. 5 . It happens when flat surface  60  is on interior surface  62  of the slip  36 . While the preferred embodiment has been shown with projections on the hanger  24  and nesting depressions on the slip  36 , those skilled in the art will appreciate that the desired camming action can occur by presenting the projections on the slip  36  and the nested depressions on the hanger  24 . It is only after the camming action described above, which occurs due to shrinkage of the hanger  24  from the swage  26  moving through it, that the swage  26  can force the slip  36  into a preferably biting relation with the casing  20  through expansion of the diameter in the area of the slip  36 . The camming of slip  36  begins before the diameter under it is actually expanded. 
   One extreme is illustrated in  FIG. 4  where the inside wall of the casing  20  is so close to slip  36  that camming action cannot occur. In this case, the applied stress that would otherwise result in longitudinal shrinking of the hanger  24  instead merely reduces the wall thickness of the hanger  24  since the slip  36  acts to fixate its end as the expansion begins. 
   While the preferred method described above is to longitudinally shrink the hanger  24  those skilled in the art will appreciate that it is the camming action caused by relative movement that results in the ability of the hanger  24  to compensate for inside diameters of the casing  20 . Thus any technique that results in a camming action to move a slip such as  36  outwardly, up to the point of closing an available clearance, where the camming takes place before the diameter under the slip is actually expanded, is within the scope of the invention, whether the camming is caused by shrinkage or growth of one member with respect to another or induced by other techniques. 
   Those skilled in the art will appreciate that the lower end (not shown) of the hanger  24  can be similar to what has been illustrated for a slip layout in  FIG. 6 . Alternatively, the slip arrangements can be different at opposing ends or slips can be used on only one end and still be within the scope of the invention. 
   After expansion, a net uphole directed dislodging force pushes shoulder  42  of slip  36  against shoulder  44  of hanger  24  to help the slip  36  dig in better to resist such force. In the opposite direction, the engagement between shoulders  48  and  50  also helps slip  38  retain its grip. In general, during the camming action, shoulder engagement between a slip and the hanger  24  converts what may have previously been longitudinal displacement into radially cammed movement. 
   Those skilled in the art will now appreciate that the present invention with slips that can be cammed out, or not, depending on the inside diameter of the casing  20 , allows the apparatus a greater flexibility to obtain the proper grip in a broader range of casing inside diameters than the prior designs such as shown in  FIGS. 1 and 2 . The radial range of camming is flexible from none to a maximum value where the slip is fully cammed out as a result of complete misalignment between a previously nested projection and depression or whatever the outer limit of the camming mechanism that is used due to the available relative movement. Optionally, resilient seals can be employed with the slips to enhance the sealing against the casing  20 . 
   The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:

Summary:
A slip for an expanding hanger or patch is disclosed. The slip is mounted over the hanger body and has an internal profile that nests within a mating profile on the exterior of the hanger. When a compressive force is applied to the hanger, it shrinks longitudinally and as a result the slip is cammed radially to the extent the inside diameter of the surrounding tubing permits. When the swage is advanced, the diameter of the hanger increases forcing the slip into preferably penetrating contact with the inside wall of the surrounding tubular.