Abstract:
A liner hanger uses a spirally shaped slip member that makes at least one revolution about the mandrel being expanded. The slip member is disposed in a groove with tapered end walls that approach each other during radial mandrel expansion due to shrinkage of said mandrel in the longitudinal direction. The shrinkage binds the slip to the mandrel as the slip member approaches the surrounding tubular. The tapered side walls of the groove moving together cam out the slip member into enhanced contact with the surrounding tubular to support the liner or other string below the hanger. The slip member and groove have preferably the same pitch to allow easy mounting with an applied rotational force.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is expandable liner hangers and more particularly a spiral slip design disposed in a groove with tapered side walls to uniformly move the spiral slip member out as expansion reduces the groove width to enhance a grip on a surrounding tubular. 
       BACKGROUND OF THE INVENTION 
       [0002]    Spiral patterns have been used in downhole tools as passages for cement in the context of expansion such as in hangers for liners that are set by expansion. Examples of such spiral paths for flow of displaced fluids during cementing are U.S. Pat. Nos. 6,899,181, see FIG. 9, and 7,055,597, see FIG. 7. 
         [0003]    Another design uses grooves to reduce stress during expansion and as a location for metal displacement under inserts as the inserts engage the surrounding tubular. The stress relieving zones  885  are taught to be spiral in one alternative for the purpose of reducing expansion stress as discussed in paragraph 82 of U.S. Publication 2010/0089591. 
         [0004]    The reality of longitudinal shrinkage during expansion of tubulars has been deployed in liner hangers to drive out slip rings  36  and  38  that are described as a cylindrical shape with a longitudinal split, a cylinder that separates into segments on expansion or a series of segments retained with a band spring in column 3 lines 52-58 of U.S. Pat. No. 7,096,938. The same description is found in the continuation U.S. Pat. No. 7,367,390. 
         [0005]    What has yet to be developed and addressed by the present invention is a slip design that takes advantage of the longitudinal shrinkage during expansion of the hanger and configures the slip design to evenly load the surrounding tubular despite any shape irregularities it may have over an extended length of the hanger. The open nature of the slip design allows for circumferential coverage over a longer length than a longitudinally split cylinder. Beyond that a spiral design can be threaded on during assembly and provides negligible resistance to expansion. The retaining groove not only radially extends a spiral shape but also winds up gripping the slip shape more tightly as the mandrel is radially expanded and the differential longitudinal growth from mandrel expansion cocks the slip member slightly in its retaining groove to prevent shifting until the surrounding tubular wall is engaged. These and other advantages of the present invention will be more apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated figures while recognizing that the full scope of the invention is to be determined by the appended claims. 
       SUMMARY OF THE INVENTION 
       [0006]    A liner hanger uses a spirally shaped slip member that makes at least one revolution about the mandrel being expanded. The slip member is disposed in a groove with tapered end walls that approach each other during radial mandrel expansion due to shrinkage of said mandrel in the longitudinal direction. The shrinkage binds the slip to the mandrel as the slip member approaches the surrounding tubular. The tapered side walls of the groove moving together cam out the slip member into enhanced contact with the surrounding tubular to support the liner or other string below the hanger. The slip member and groove have preferably the same pitch to allow easy mounting with an applied rotational force. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a cylindrically shaped slip ring used in existing expandable liner hangers; 
           [0008]      FIG. 2  shows the spiral slip member on a mandrel; 
           [0009]      FIG. 3  shows the helical slip by itself without the underlying mandrel; 
           [0010]      FIG. 4  is a section view through the mandrel and slip showing the narrowing of the mandrel groove during expansion; 
           [0011]      FIG. 5  shows a segmented slip member in a perspective view; 
           [0012]      FIG. 6  is an alternative embodiment of a slip member that uses wickers to engage the mandrel outer wall making the use of a groove optional; 
           [0013]      FIG. 7  is a section view of the slip member of  FIG. 6  taken through the mandrel wall. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Referring to  FIG. 2  the groove  10  is spirally cut in the mandrel  12  outer surface  14 . While the groove  10  and the slip member  16  that fits at least in part in groove  10  are shown with a constant width, the width can vary as to the groove  10  and the slip member  16  along their respective lengths and preferably but not necessarily in tandem. The pitch represented by arrow  18  can be constant or it can vary. The length of the groove  10  should be sufficient for greater than 360 degree revolution of the slip member  16  and in the preferred embodiment almost three revolutions are illustrated. The slip member  16  can extend for the running length of the groove  10  or it can be shorter such as illustrated where the end of the slip member  16  is not shown near the groove end  20 . 
         [0015]    The groove  10  is defined by a recessed radial surface  22  flanked by outwardly tapering side walls  24 . While all the surfaces are illustrated as flat, other configurations are envisioned. The side walls  24  or bottom  22  can be arcuate. The bottom surface can be undulating and match a similar shape on the face  26  of the slip member  16  shown in  FIG. 3 . The outer surface  27  of the slip member  16  has at least one and preferably a plurality of raised rings  28  that can have equal or unequal height and/or spacing with the intention that as a result of expansion that there is at least a frictional contact with the surrounding tubular (not shown) for support and preferably a penetration of the wall of the surrounding tubular for an enhanced supporting grip into the surrounding tubular so that the liner or other tubular string can be securely supported. While rings with pointed or sharp leading ends for penetration into the surrounding well bore are preferred, other designs that penetrate the surrounding tubular or frictionally engage it are also contemplated. Tungsten carbide inserts or a matrix material such as used in certain drill bits can be placed on the outer surface  30  of the slip member  16 . 
         [0016]      FIG. 4  illustrates what occurs as the mandrel  12  is expanded while either in tension or while the mandrel is placed in compression. As the diameter increases when an expansion cone advances through the bore  32 , the length experiences shrinkage as indicated by arrows  34 . As a result, opposed sidewalls  24  get closer together to cam out the slip member  16  even as the diameter of the slip member  16  grows with the radially expanding mandrel  12 . It should be noted that the sidewalls  24  move toward each other in an initial period before the raised rings  28  make contact with the surrounding tubular. In a subsequent phase the sidewalls  24  continue to come together as the rings  28  encounter and/or penetrate the surrounding tubular wall. It should be noted that the slopes of the sidewalls need not be at the same angle. In some situations it may be preferable to have the slip member  16  to have one end get cammed out before the opposing end of the slip member  16  rather than in a parallel orientation to the outer wall  14 . Since the string being supported is typically below the hanger it may be desirable to have the downhole edge  36  forced out first so that it can get the stronger bite for better support of the hanging load below from the suspended string. Alternatively, within manageable tolerances, the pitch of the slip member  16  can differ from the pitch of the associated groove  10  as long as the slip member can be sufficiently recessed in the groove  10  for run in without being biased outwardly during run in so that it would get pried loose or snag on some internal projection or radial surface in the surrounding tubular for run in. 
         [0017]      FIG. 5  illustrates slip segments  38 ,  40  and  42  separated by thinner spacers  44  and  46  as part of a slip member  16  assembly. The assembly can be longer and a portion is illustrated to make the point that as long as there is 360 degree load distribution that the contact need not occur in a single wrap around the surface  14  but the support can be in different wraps along the groove  10 . The goal is to have in any vertical axis at least one of the slip segments disposed even though above and/or below that segment on that axis there is a connector. The connectors  44  or  46  can be softer than the segments  38 ,  40  and  42  since in the preferred embodiment there is no need for these segments to penetrate a surrounding tubular. The presence of the segments makes the resistance to expansion by the assembly of segments shown in  FIG. 5  practically insignificant. The connectors such as  44  or  46  should be flexible and despite the expansion remain intact to space out the segments  38 ,  40  and  42  and any additional segments that might be used. As another option the connectors  44  or  46  can be stiffer to the point of having a grip enhancing feature on the external face for additional load carrying capability in addition to the segments  38 ,  40  and  42 . The grip enhancing feature can be a continuation from what appears on segments  38 ,  40  and  42  or it can be a different arrangement. 
         [0018]    Optionally the connectors can also be designed to release on one or opposed ends, the segments to which they were initially attached. If this is designed into the assembly it is preferred that the connectors  44  or  46  release at a time when the segments are already in contact with the surrounding tubular so that the release will not facilitate sliding of the released segments in the groove  10 . To prevent such sliding, schematically illustrated travel stops  48  and  50  can be placed in the adjacent groove  10  to prevent such sliding motion. 
         [0019]    The spiral windings can be left hand or right hand oriented. Installation of the spiral slip member can be by a simple threading action. The assembly has enough flexibility to work its way onto the mandrel groove  10  with an applied rotational movement. The entrance at the leading end of the groove  10  can be sloped to aid the slip member  16  in getting started into the groove  10  under the force of a rotational movement applied to the slip member  16  to get it into position for running to a subterranean location. 
         [0020]    Those skilled in the art will appreciate that the spiral orientation of the slip member makes it simple to assembly to the mandrel and allows slip contact with the surrounding tubular over a longer length of the surrounding tubular than a ring structure. The slip material usage is minimized relative to known designs by using a spiraling elongated element instead of a more complex ring structure that employs an array of open areas to minimize resistance to expansion that also has the result of increasing part cost. Simple vertically split cylindrical shapes cannot by definition cover for a full 360 degrees of supporting the tubular string load. Rather, the split by design opens in the expansion mode leaving more load on the balance of the circumference of the now open ring structure thus limiting the capacity of the slip system. 
         [0021]      FIGS. 6 and 7  illustrate an alternative embodiment that makes the use of a groove optional. Comparing  FIGS. 3 and 6  it can be seen that in  FIG. 6  there is a grip enhancement feature  52  on the inside surface of the slip member  16  and a similar grip enhancing treatment  54  on the mandrel  12  on its outer surface  14 . Optionally, a groove such as  10  can be provided to also get the camming action in a radial direction. When used with a groove the grip enhancement feature  52  becomes less significant as the camming feature will move  52  away from the groove bottom such as  22  upon expansion. Without a groove, the inner grip enhancement feature  52  helps to keep the slip member  16  in position during run in and minimize relative rotation as the hanger is advanced to the location of deployment. It should be noted that with the use of a spiral shape and no groove the ultimate orientation of the slip member  16  with respect to the mandrel  12  is not significant as long as more than 360 degrees of support is provided. The feature  52  can be identical to the exterior feature  28  or different. Preferably the outer surface  14  of the mandrel  12  should be textured to enhance grip and prevent relative rotation between the mandrel  12  and the slip member  16  as illustrated at  54  in  FIG. 7 . Optionally, the grip enhancing feature can be on the mandrel outer surface exclusively or on the slip member exclusively or both. When on both the grip enhancing features can be identical or different and include the variations discussed above for item  28  or other configurations. 
         [0022]    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.