Abstract:
An extrusion gap reduction device includes an outer housing; an inner housing movably disposed relative to the outer housing. A plurality of petals movably connected to the inner housing. One or more of the plurality of petals including a follower responsive to a cam surface of the outer housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of an earlier filing date from U.S. Provisional Application Ser. No. 61/985,104 filed Apr. 28, 2014, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    In the downhole industry ubiquitous use is made of packers of all sorts. Advancements over the years have made them nearly impervious to chemical or thermal attack and they work extremely well for their various intended purposes. One condition inherent in packer use that continues to be a noticeable detriment is the extrusion gap or the annular space between a tubular against which the packer is to seal and the mandrel or other structure having a gage diameter less than that of the inside diameter of the tubular against which the packer is intended to seal. It is of course axiomatic that such a gap must exist as if it did not, the difficulty with which components run into the tubular against which the packer is intended to seal would be overwhelming and hence contraindicated. Many different back up configurations have been tried with varying success to reduce the extrusion gap but the art always welcomes other apparatus that will allow for reduction in the extrusion gap either more effectively or in additional scenarios. 
       SUMMARY 
       [0003]    An extrusion gap reduction device includes an outer housing; an inner housing movably disposed relative to the outer housing; and a plurality of petals movably connected to the inner housing, one or more of the plurality of petals including a follower responsive to a cam surface of the outer housing. 
         [0004]    A packer system includes an element; and at least one extrusion gap reduction device including an outer housing; an inner housing movably disposed relative to the outer housing; and a plurality of petals movably connected to the inner housing, one or more of the plurality of petals including a follower responsive to a cam surface of the outer housing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
         [0005]      FIG. 1  is a perspective view of an extrusion gap reduction device in a closed position; 
           [0006]      FIG. 2  is a perspective view of the device illustrated in  FIG. 1  with the outer housing removed to allow visualization of the more radially inwardly located components of the device; 
           [0007]      FIG. 3  is the device illustrated in  FIG. 1  in a set position still in perspective view; 
           [0008]      FIG. 4  is the device illustrated in  FIG. 1  in a set position from one end; 
           [0009]      FIG. 5  is a perspective view of another embodiment of the device illustrated in  FIG. 1  with the outer housing removed to allow visualization of an alternate petal configuration; 
           [0010]      FIG. 6  is a perspective view of a packer system having an element and an extrusion gap reduction device of  FIG. 1  at each axial end of the element; 
           [0011]      FIGS. 7-9  illustrate alternate edge shapes. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIGS. 1 through 4  simultaneously, the device  10  comprises an outer housing  12  and an inner housing  14  that are rotatable relative to one another. The degree of relative rotation between the outer housing  12  and the inner housing  14  is limited by a groove  16  (see  FIG. 2 ) located in inner housing  14  and a lug  18  configured to move with the outer housing  12 . In the illustrated embodiment, the lug  18  is affixed to outer housing  12 . It is to be understood that any means of attachment to the outer housing would be acceptable and is contemplated in order to prevent motion between the lug and the outer housing that would affect outer housing to inner housing relative position. For example the lug could be press fit, welded, adhesively affixed, integrally machined, etc. It is not required that the lug  18  not, for example, spin relative to outer housing  12 . 
         [0013]    Further illustrated in each Figure is a plurality of petals  20 . Each petal is independently rotatable about a connection such as, for example, a pivot pin  22  and positionally affected by a displacement follower  24  such as a pin. The relative rotation between the outer housing  12  and the inner housing  14  causes the displacement followers to each ride a cam surface  26  from a recess  28  to an outside surface  30  of the outer housing  12 . It is to be noted however that while the followers  24  riding onto outside surface  30  is illustrated, it is of course contemplated that the followers  24  need not actually exit the recesses  28  but rather only that the petals collectively actually achieve a larger diametric dimension in the set position than in the closed position. This can occur with the cam surface urging the displacement followers  24  radially outwardly even though the followers are not displaced enough to reach the outer housing surface  30  and such might occur in a tubular that is somewhat smaller diametrically than one for which the device  10  is specifically designed. It is also contemplated that a particular device is not intended to use the outer surface of outer housing  12  in order to, for example, maintain the displacement followers  24  in a more protected condition within the outer housing  12  when in the set position, for example, in an embodiment where the recesses are closed grooves instead of open as illustrated. 
         [0014]    The number of petals may be as illustrated or may be another number as desired for a particular application. The more petals that are used, the closer the resultant outside dimensions of the flower will be to the inside surface of the tubular against which the packer is intended to be set, assuming the tubular is circular in cross section. 
         [0015]    In one embodiment, as shown, each petal is configured as a simple arcuate section and produces the shape of petals illustrated in  FIG. 4 . One will notice that the outermost surface in  FIG. 4  is more flowerlike than a circle. This leaves much smaller extrusion gaps than would exist without the device described herein and the remaining gaps are not annularly complete so the device will in this configuration significantly reduce extrusion. In this embodiment, the arc length of each petal is sufficient to span a distance between a next adjacent petal of the plurality of petals on both sides of the subject petal. In another embodiment, referring to  FIG. 5 , the extrusion gap can be reduced even further by modifying the shape of the of the petals to have a first region  32  that is roughly curved to exhibit an arcuate edge  34  to roughly match the outer surface  30  of the outer housing while a second region  36  is roughly curved to approximate the inside diameter of the tubular. In this way, the coverage will be complete when deployed but still allow collapse to the gage diameter of the outer housing. In other embodiments, the edge  32  or  36  need not be arcuate but may be linear or even reverse arcuate or other shapes (see  FIGS. 7 ,  8  and  9 ). The second region  36  may also be linear or reverse arcuate or other shapes. Where the edge is arcuate, it will have an arc length sufficient to span a distance between where the first and second regions meet and a next adjacent petal&#39;s second region to provide for the complete coverage against extrusion noted above. 
         [0016]    Referring to  FIG. 6 , a packer system is illustrated having the extrusion gap reduction devices  10  disposed at either axial end of a packing element  40 . It will be understood that a product could be configured this way or could be configured with one of the devices  10  and not the one on the opposite side of the packing element. It is also to be understood that any kind of packing element  40  can be substituted for that shown. 
         [0017]    A borehole with the packer system illustrated is beneficial to the industry as the element is better contained and will be more resistant to extrusion than an equivalent element used without the device(s) described herein. 
         [0018]    It will be understood that the operable parts can be reversed such that the petals are pinned to the outer housing and cammed with the inner housing rather than described above without departing from the scope of the invention. 
         [0019]    While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.