An open hole packer uses mandrel expansion and a surrounding sealing element that can optionally have a swelling feature and further a seal enhancing feature of a ring with an internal taper to match an undercut on the mandrel exterior. As a swage progresses to the taper at the transition between the ring and the extending flat fingers, the fingers get plastically deformed in an outward radial direction to push out the sealing element. Shrinkage of the mandrel axially due to radial expansion brings a ring on the mandrel outer surface under the fingers to act as a support for the fingers against the seal which is pushed against the open hole. Mirror image orientations are envisioned to aid in retaining pressure differentials in opposed directions. Another external mandrel ring extends into the seal to keep its position during differential pressure loading.

FIELD OF THE INVENTION 
       [0001]    The field of the invention is expandable open hole packers and more particularly those that use the expansion process for increasing sealing contact pressure and using applied pressure differential to enhance the sealing force. 
       BACKGROUND OF THE INVENTION 
       [0002]    Packers are mounted on tubular strings and have to pass through close clearances in existing tubulars to get to the location where the packer is to be deployed. In some cases the dimensional difference between the drift diameter of the existing tubular that the packer needs to pass and the set dimension is so great as to create problems in getting a reliable seal. The limits of the tubular in expansion can be reached in situations where the mandrel is expanded. Some examples of packers set by expansion can be seen in U.S. Pat. Nos. 6,959,759; 6,986,390; 7,051,805 and 7,493,945. 
         [0003]    Some designs rely on the element to swell in the presence of well fluids such as water or hydrocarbons, such as: U.S. Pat. Nos. 7,387,158; 7,478,679; 7,730,940; 7,681,653; 7,552,768; 7,441,596; 7,562,704; 7,661,471. In some of these designs the reduction in stiffness and resulting contact pressure is offset with applied axial compressive forces triggered with the swelling as shown in U.S. Pat. No. 7,552,768 or thereafter as a result of pressure differentials such as U.S. Pat. No. 7,392,841. Swelling to make a seal is a time consuming process which can mean significant additional operator cost if the swelling has to conclude to a sealing condition before other steps can be undertaken in a well completion. 
         [0004]    Some designs rely on axial mandrel shrinkage to apply an axial boost force to ends of a sealing element that is being radially expanded as illustrated in U.S. Pat. No. 7,431,078. 
         [0005]    Other designs involved the use of packer cups that could be run through another tubular and then spring outwardly in the larger wellbore to obtain a seal. These designs suffered from potential damage during run in that could destroy their ability to seal. Their inherent design limited the speed that they could be run into or removed from a wellbore without swabbing the well coming out or pressurizing the formation on the trip into the well. 
         [0006]    Some designs used tubular expansion combined with exterior rings that moved relatively to each other to extend the reach of a packer in the wellbore as illustrated in U.S. Pat. No. 7,661,473. This design also had an option for using a swelling material  44  as the sealing element. The expansion enhancing mechanism went the length of the seal element and due to the ramp structure it employed to enlarge wound up adding to the initial dimension while providing only a limited amount of enhancement in the radial direction to the underlying mechanical expansion of the mandrel. 
         [0007]    US Publication 20050000697 illustrates a technique of corrugating pipe downhole to make it more flexible for subsequent expansion. US Publication 2010 0314130 illustrates using internal spacers and driving a swage through them to expand a seal into a wellbore wall. 
         [0008]    What is needed and provided by the present invention, among other features, is the ability to parlay the expansion force of the mandrel into a rotational movement of fingers attached to a ring. The fingers bend outwardly to move the sealing element toward a wellbore wall to enhance the sealing contact. The fingers can bend independently so as to make the pushing out of the seal conform to a surrounding borehole wall that is not necessarily round and can be oval or irregular. The mandrel features an external ring that due to shrinkage of the mandrel as it is expanded winds up under the bent fingers to further hold out the fingers against the sealing element to maintain the seal. The ring and finger structure permits fluid to get under an end of the sealing element and to further aid in pushing the element against the borehole wall which can be open hole. Another ring from the mandrel exterior extends into the element to retain it against sliding force from pressure differentials. Various options are possible such as orienting the rings with fingers in mirror image orientations to enhance seal against differential pressures from above or below the set seal. The ring itself can be an extrusion barrier and as another option the seal can extend the length of the fingers and their base ring. Those skilled in the art will better appreciate the various aspects of the present invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims. 
       SUMMARY OF THE INVENTION 
       [0009]    An open hole packer uses mandrel expansion and a surrounding sealing element that can optionally have a swelling feature and further a seal enhancing feature of a ring with an internal taper to match an undercut on the mandrel exterior. As a swage progresses to the taper at the transition between the ring and the extending flat fingers, the fingers get plastically deformed in an outward radial direction to push out the sealing element. Shrinkage of the mandrel axially due to radial expansion brings a ring on the mandrel outer surface under the fingers to act as a support for the fingers against the seal which is pushed against the open hole. Mirror image orientations are envisioned to aid in retaining pressure differentials in opposed directions. Another external mandrel ring extends into the seal to keep its position during differential pressure loading. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of the finger ring in the supporting position after expansion of the mandrel; 
           [0011]      FIG. 2  is a section view of the run in position of the packer; 
           [0012]      FIG. 3  is the view of  FIG. 2  after expansion has started; 
           [0013]      FIG. 4  is the view of  FIG. 3  at the conclusion of expansion and before differential pressure loading; 
           [0014]      FIG. 5  is the view of  FIG. 4  with a pressure differential applied from above; 
           [0015]      FIG. 6  shows a mirror image arrangement to boost the sealing force against differentials from opposed directions; 
           [0016]      FIG. 7  is a perspective view of the exterior of the finger ring in the run in position; 
           [0017]      FIG. 8  is an alternative embodiment to  FIG. 2  shown in the run in position; 
           [0018]      FIG. 9  is the view of  FIG. 8  in the set position with differential pressure from below; 
           [0019]      FIG. 10  is an alternate view of  FIG. 6  showing the fixation keyway. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]      FIG. 2  shows the elements of the packer assembly  10  in one embodiment. A mandrel  12  has a taper  14  that forms an undercut  15  on the outer surface of the mandrel  12 . The support ring  16  is an assembly that has an initially split ring  18  that allows the assembly  16  to be slipped over the mandrel  12  and positioned as shown whereupon the ring  18  can be welded back into a cohesive circular shape and secured to the mandrel  12 . Alternatively, the support ring can be slipped over the mandrel and then mechanically deformed at the taper  14  so that the fingers are flush on the undercut  15 . The assembly  16  has alternating fingers  20  and  22  that are best seen in  FIG. 1 . Fingers  22  have end components  24  that span over gaps  26  that have rounded lower ends  28  to dissipate stress that accumulates at the transition between the ring  18  and the fingers  20  and  22 . There is a tapered transition  28  between the ring  18  and the fingers  20  and  22 . The sealing element  30  in this embodiment overlays the fingers  20  and  22  at end  32 . Location  34  represents the end of the bonding between the sealing element  30  and the mandrel  12 . A circumferential ring  36  extends from the outer surface  38  of the mandrel  12  and inside the undercut  15 . In the run in position the ring  36  is spaced from lower end  40  of the fingers  20  an  22 . Radial expansion of the mandrel  12  will cause mandrel  12  to shrink longitudinally and bring the ring  36  under the ends  40  of fingers  20  and  22 . The fingers  22  at their respective ends  24  will initially be contacted by ring  36  as the mandrel  12  shrinks axially from radial expansion from within. Another ring  42  extends from outer surface  38  in the undercut  15  and into the seal  30 . This ring  42  is more for fixation of the seal  30  in the set position with applied pressure differentials and also has some benefit in stopping fluid leak paths between the seal  30  and the outer surface  38  of the mandrel  12 . While a single illustrative ring  36  or  42  are illustrated additional rings or even other shapes or segmented rings can be used. 
         [0021]    The drift dimension of ring  18  is at least as large as the sealing element  30  for run in to provide protection to the sealing element  30   
         [0022]      FIG. 3  compared with  FIG. 2  illustrates what happens as the swage advances and the taper  14  that defines the undercut  15  is progressively removed. What happens is that the fingers  20  and  22  are plastically deformed at the transition  28  so that the cantilevered fingers  20  and  22  have their free ends  40  come away from the mandrel  12  to define a temporary gap  44  between the mandrel  12  and the ends  40  that has the effect of creating a hump in the sealing element  30  as the ends  40  that have been plastically deformed now push a hump  46  created in the sealing element  30  against the borehole wall  48 . Some fingers  20  or  22  move further than others depending on the shape of the open hole where the packer assembly  10  is being expanded. It should also be noted in  FIG. 3  that the ring  36  has moved axially due to mandrel shrinkage from expansion so that it is now under the fingers  20  and  22 . Location  34  illustrates where the bonding of the seal  30  to the mandrel  12  stops in a more dramatic form. It should be noted that when expanding the mandrel  12  that the ring  18  can either be expanded or not to get the effect described above. 
         [0023]      FIG. 4  shows the expansion completed and no applied differential pressure. The undercut  15  is eliminated. The underside  50  of the ring  18  no longer has a taper as in the  FIG. 2  position. The mandrel  12  has shrunk placing ring  36  under the fingers  20  and  22  to the left of the ends  40 . Ends  40  are cantilevered into the sealing element  30  pinching it against the open hole wellbore wall  48 . The gaps  26  between fingers  20  and  22  have enlarged due to the expansion as can be seen by comparing  FIG. 7  for the run in and  FIG. 1  for the expanded state. Ring  42  is pushed further into the sealing element  30  to retain it against axial movement in response to applied differential pressure and also to enhance the ability to resist leak paths that can start between the sealing element  30  and the outer surface  38  of the mandrel  12 . By this time in the expansion the fingers  20  and  22  have been initially plastically deformed urging ends  40  against the seal element  30  until the seal element  30  is against the borehole wall, followed by the mandrel  12  then raising the ring  36  back into contact with the now plastically bent fingers  20  and  22  have bent about the axis at the taper  28 . The expansion has increased the diameter of the mandrel  12  and added to that increase is the height of the ring  36  and the thickness of the finger  20  or  22  all of which now support the sealing element  30  into the borehole wall  48 . 
         [0024]    As can be seen in  FIG. 5  arrows  52  pressure differential from above goes through the slots  26  that are seen in  FIG. 1  and goes all the way back to location  34  where the bonding to the mandrel  12  stops. In essence a long pocket  54  is formed at an end of the sealing element  30  so that in resisting pressure differential from uphole the end of the sealing element  30  takes on the characteristics of an upwardly facing packer cup against differential from uphole represented by arrow  52 . It should be noted that issues of damage on delivery that packer cups typically have are avoided because for the run in position of  FIG. 2  the sealing element  30  is retracted into the undercut  15  and further protected by ring  18  that sticks out radially at least as far as the sealing element  30 . Ring  42  keeps the sealing element  30  from shifting under the load represented by arrow  52 . Also shown in  FIG. 5  is an end  40 ′ portion of a finger such as  20 ′ or  22 ′ of a mirror image assembly  10 ′ that is best seen in  FIG. 6 . 
         [0025]    The support ring  18  can be initially split so that it can be fit over the mandrel  12  and axially fixated by having a groove  19  that fits over a key  21 . The location of the key and the groove can be reversed. When there is differential pressure as indicated by arrow  52  is will more likely communicate past ring  18  in any clearance gap after expansion around ring  18  and within tubular wall  48 . 
         [0026]      FIG. 6  shows two assemblies  10  and  10 ′ in mirror image orientations. In this view they are shown in the run in position but in the set position with a differential in the direction of arrow  52  in  FIG. 5  or in the opposite direction to arrow  52  one of the illustrated ends exhibits the shape of the sealing element  30  that is shown in  FIG. 5  but the orientation is opposite hand depending on the direction of the pressure differential. In essence the behavior is akin to opposed packer cups with the upper one pointing uphole and the lower one pointing downhole. Although the sealing element  30  is shown to be continuous over the fingers  20  and  22  and  20 ′ and  22 ′ of the opposed assemblies and any gaps in between, those skilled in the art will appreciate that the sealing element  30  can also be in segments and optionally the segments can extend to ends  40  or  40 ′ of the illustrated assemblies  10  or  10 ′, as more clearly illustrated in  FIGS. 8 and 9 . 
         [0027]      FIG. 8  is the run in position of assembly  10 ″ that has fingers  20 ″ and  22 ″ as described previously except that the sealing element  30 ″ stops near or at end  40 ″. In this version, the ring  18 ″ is covered by the sealing element  30 ″ and the ring  18 ″ is covered over with the sealing element  30 ″ such that the ring  18 ″ can function as a type of extrusion barrier or at minimum as a stabilizer ring to prevent axial shifting of the sealing element  30 ″. The response during expansion of the mandrel  12 ″ is as described before. The undercut  15 ″ is removed and the fingers  20 ″ and  22 ″ are plastically bent near transition  28 ″ so that the sealing element  30 ″ engages the borehole wall  48 ″. In the illustrated embodiment differential pressure loading in the direction of arrow  56  makes the assembly behave similarly to an extended packer cup. Additional assemblies can be aligned in the same direction as backup or in mirror image orientation to be able to energize with differentials in opposed directions. Those skilled in the art will also realize that in the  FIG. 6  embodiment can have a single assembly in a given orientation or multiples in the same orientation. 
         [0028]    What is shown is an assembly that has a low protected profile for run in due to the sealing element being retracted and in an undercut and protected by a ring structure with extending fingers that define gaps between them. The gaps are closed at the cantilevered ends as alternating fingers overlap ends of adjacent fingers. The tapered transition in the ring and finger structure makes the fingers turn out in plastic deformation against a surrounding sealing element to hold the sealing element out against the borehole wall. Such support can be enhanced with a ring that positions itself under the fingers to hold their ends out against the sealing element. The seal enhancing assemblies when mounted on the ends of a sealing element also allow well fluids to reach the underside at the ends of the sealing element. In situations where such element is a swelling element, the end swelling is enhanced as the actuating fluid such as water or hydrocarbons fully surrounds the end of the sealing element for enhanced swelling and thus sealing. The gaps between the fingers that enlarge during expansion also promote such fluid exposure not only to enhance swelling but also to enhance the sealing force from pressure delivered between the mandrel and the sealing element to give the sealing element the operating characteristics of a packer cup without the downsides of such seals such as low pressure differential tolerance, damage on run in and swabbing the well on the way out. The illustrated designs allow for a seal to form rapidly without having to delay other procedures waiting for swelling only to make the seal as in previous designs. The boost sealing force occurs from under the sealing element as opposed to axially oriented spring systems as used in the past. The expansion process and configuration of the finger ring creates packer cup like behavior in an annularly shaped element. The use of an undercut allows the sealing element to be protected for run in by the ring of the finger ring assembly. The undercut dovetails with a taper on the transition between the ring and the fingers to create the pivoting plastic deformation of the fingers that presses out the sealing element. The plastic pivoting movement can be further bolstered by a support ring that moves into position due to axial shrinkage that results from expansion especially with the mandrel in compression. Mirror image assemblies are contemplates as well as sealing elements that end at the end of the fingers that can have the support that moves into position due to axial shrinkage during expansion or that support can be optionally omitted. Retention devices can also extend from the mandrel into the sealing element to assist in axial fixation and minimizing of leak paths between the sealing element and the mandrel. The sealing element ends that overlap the fingers are not bonded to the fingers or the mandrel so as to facilitate fluid entry under the sealing element for a boost force. The sealing element can optionally swell to enhance the seal. Multiple assemblies in the same orientation are also envisioned for backup purposes. The entire string that delivers the mandrel does not need to be expanded but rather just the mandrel itself is sufficient for expansion to get the desired sealing benefit of the present invention. Alternatively portions of the delivering string or the entire string can be expanded into the borehole wall with the expandable packer segments. Any tubular joints that are under the sealing element need not still seal after the expansion as the sealing element against the borehole wall will cover such joints. 
         [0029]    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.