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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to packer devices used within a wellbore. 
         [0003]    2. Description of the Related Art 
         [0004]    Packers are used to create a fluid seal within a wellbore between a central work string, such as a production tubing string, and a surrounding tubular, such as a wellbore wall. A common packer design has a central mandrel with an elastomeric packer element surrounding the mandrel. The packer element is set by axially compressing it on the mandrel. As the packer element is compressed axially, the packer element is expanded radially outwardly and into contact with the surrounding surface. 
         [0005]    One problem with packer devices of this type is that of extrusion of the packer element axially along the space between the packer mandrel and the surrounding wellbore. This can occur as a result of high wellbore temperatures, pressures and/or caustic chemicals which act upon the packer element. Severe extrusion of the packer element can cause the seal to fail. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides methods and devices for containing a packer element in a set condition within a wellbore and for preventing or minimizing extrusion of the packer element after setting. An exemplary packer device is described which includes a plurality of deformable packer elements which radially surround a packer mandrel. One or more of the packer elements is contained against axial extrusion using a packer containment system. In a preferred embodiment, the packer containment system includes a flexible metal backup ring, which partially encases the packer element by substantially covering at least one axial side and a portion of the exterior radial surface of the packer element. The packer containment system also includes a plurality of annular support rings, or “petal rings” which have petal-shaped radial protuberances with slots between them. The petal rings are arranged so that the petals of adjacent rings are radially offset. As a result, the slots of each ring are covered by a petal of an adjacent ring. Petal rings are preferred since they may be axially compressed with relatively small amount of force due to the presence of the slots. Because there are multiple support rings used, a strong containment barrier is provided when set which prevents extrusion of a packer element axially along the annular space between the packer device and the inner surface of the surrounding tubular member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
           [0008]      FIG. 1  is a side, partial cross-sectional view of an exemplary packer assembly in accordance with the present invention. 
           [0009]      FIG. 2  is an enlarged cross-sectional view of a packer element containment system in accordance with the present invention. 
           [0010]      FIG. 3  is an enlarged cross-sectional view of the containment system shown in  FIG. 2 , now in a set condition. 
           [0011]      FIG. 4  is an external isometric view of the containment system shown in  FIGS. 2-3 , in an unset condition. 
           [0012]      FIG. 5  is an external isometric view of the containment system shown in  FIGS. 2-3 , in a set condition. 
           [0013]      FIG. 6  is an axial external view of an exemplary petal-type support ring used in the containment system shown in  FIGS. 2-5 . 
           [0014]      FIG. 7  is an external isometric view of the exemplary support ring shown in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]      FIG. 1  illustrates an exemplary packer assembly  10  which includes a central packer mandrel  12 . The packer mandrel  12  can be incorporated into a production tubing string or other work string (not shown), in a manner known in the art. A flowbore  14  is defined within the mandrel  12 . The outer radial surface of the mandrel  12  has an expanded diameter portion  16  which presents a stop shoulder  18 . Radially surrounding the packer mandrel  12  and immediately below the stop shoulder  18  is a packer element portion, generally indicated at  20 , the structure of which will be described in greater detail shortly. A setting sleeve  22  radially surrounds the packer mandrel  12  below the packer element portion  20 . The setting sleeve  22  is axially moveable with respect to the mandrel  12  and presents a compression end  24 . 
         [0016]    The exemplary packer element portion  20  depicted in  FIG. 1  includes an upper end cone  28  which surrounds the mandrel  12  and abuts the stop shoulder  18 . The packer element portion  20  also includes an upper packer element  30  and an upper packer element containment assembly  32 . A first spacer ring  34  separates the upper packer element  30  from a central packer element  36 . A second spacer ring  38  separates the central packer element  36  from a lower packer element  40  and a lower packer element containment assembly  42 . A lower end cone  44  lies adjacent the containment assembly  42  and abuts the compression end  24  of the setting sleeve  22 . 
         [0017]    It is noted that the upper packer element  30 , central packer element  36  and lower packer element  40  are preferably formed of nitrile or another suitable elastomeric material. It is noted that the packer elements  30 ,  36 ,  40  and spacer rings  34 ,  38 , containment assemblies  32 ,  42  and end rings  28 ,  44  are not affixed to the mandrel  12  so that they may slide axially with respect to it. It is noted that, during the initial construction and run in of the packer assembly  10 , the end rings  28 ,  44  are preferably affixed in place using frangible shear screws, as is known in the art 
         [0018]      FIGS. 2 and 3  depict the upper packer element containment assembly  32  in greater detail. It is noted that the lower packer element containment assembly  42  preferably has the same structure and function as upper containment assembly  32 . The upper containment assembly  32  includes a solid backup ring  46  which is substantially formed of a malleable metal of low yield and high ductility. The backup ring  46  includes a close-fitting radially reduced inner annular flange portion  48 . A portion of the inner flange portion  48  is disposed beneath an axially-extending lip  50  of the end cone  28 . An annular web portion  52  of the backup ring  46  extends radially outwardly from the flange portion  48 . The web portion  52  lies axially adjacent the upper packer element  30 . A leg portion  54  extends axially along the outer radial surface  56  of the packer element  30 . The upper packer element  30  is partially encased by the web portion  52  and the leg portion  54 . In particular, the web portion  52  and leg portion  54  of the backup ring  46  help prevent axial extrusion of the element  30  axially toward the end ring  28 . 
         [0019]    Support rings  58 ,  60 ,  62  are located adjacent to the backup ring  46  and are preferably in an abutting relation to the backup ring  46 . The support rings  58 ,  60 ,  62  are preferably each petal-type rings or, “petal rings” with a construction substantially as follows.  FIGS. 6 and 7  illustrate a single exemplary petal ring  58  apart from the other components of the containment assembly  32  and  42 . It is noted, however, that the exemplary construction shown for the petal ring  58  can be representative of the same construction for rings  60 ,  62  as well as each of the rings used in the containment assembly  42 . The ring  58  has a cross-sectional, substantially flat plate-form annular body  64  that is disposed angularly outwardly with respect to the ring&#39;s axis  66  at an angle  68 , which is depicted graphically in  FIG. 7 . Thus, the ring  58  has a generally conical form. The angle  68  may vary depending upon the particular project and design in which the assembly  10  will be used. Preferably, however, the angle  68  is from about 35° to about 45°. Most preferably, the angle  68  is about 40°. The body  64  of the ring  58  includes a plurality of slots  70  which partially divide portions of the body  64  into petal portions  72 . The presence of the slots  70  permits the ring  58  to be deformed or bent more easily during the setting process. The petal rings  58 ,  60 ,  62  are preferably formed of metal and most preferably formed of a malleable metal with low yield and high ductility. 
         [0020]    In the embodiment of the containment assembly  32  depicted in  FIGS. 2-5 , there are three petal rings  58 ,  60 ,  62 . However, there may be fewer than or more than three rings, as desired. A greater number of rings will result in a higher containment force for the packer element  30 . When assembled, the petals  72  of adjacent rings  58 ,  60 ,  62  are offset from one another, as depicted in  FIG. 4  so that a petal  72  of one ring will overlap and cover the slot  70  of an adjacent ring. This will help form a solid barrier against extrusion by blocking the gaps provided by the slots  70 . 
         [0021]    In operation, the packer assembly  10  is set by moving the setting sleeve  22  axially with respect to the mandrel  12  so that the compression end  24  is urged against the end cone  44 . This results in the components  42 ,  40 ,  38 ,  36 ,  34 ,  32 ,  30  and  28  being compressed against the stop shoulder  18 . The setting sleeve  22  may be actuated by one of any number of methods known in the art, including the use of a setting tool (not shown) or hydraulically. As the components are compressed, the packer elements  30 ,  36 , and  40  are expanded radially outwardly as  FIG. 3  shows, so that the packer elements  30 ,  36 ,  40  are set against the external wall  80  of a surrounding tubular. 
         [0022]    When the packer assembly  10  is set in the manner described, the upper and lower packer element containment assemblies  32 , 42  become actuated to prevent axial extrusion of the upper and lower packer elements  30 ,  40 , respectively.  FIGS. 2 and 3  illustrate the operation of the containment assembly  32  moving from unset ( FIG. 2 ) to set ( FIG. 3 ) positions. The web and leg portions  52 ,  54  portions of the backup ring  46  will flex, so that they remain in an encasing relation to the packer element  30  and physically block potential extrusion of the element  30  axially toward the end cone  28 . In addition, the petal rings  58 ,  60 ,  62  are compressed axially to the conditions depicted in  FIGS. 3 and 5 . The slots  70  of the rings  58 ,  60 ,  62  are expanded, allowing the rings to be axially flattened. When axially flattened, the angle  68  of the rings  58 ,  60 ,  62  is increased to approximately 90° (see  FIG. 3 ). The support rings  58 ,  60 ,  62  do not, themselves, necessarily contact the surrounding surface  80  (see  FIG. 3 ) when in the set position. The support rings  58 ,  60 ,  62  form a structural axial barrier to help preserve containment of the packer element  30  by preventing the backup ring  46  from deforming, which might permit extrusion of the packer element  30 . The containment assemblies  32 ,  42  require a relatively small amount of setting force is required, but provide increased resistance to shear forces. 
         [0023]    The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to those skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.

Summary:
Methods and devices for retaining a packer element in a set condition within a wellbore and for preventing or minimizing extrusion of the packer element after setting. A packer device includes a plurality of deformable packer elements which radially surround a packer mandrel. One or more of the packer elements is contained against axial extrusion using a packer containment system. The packer containment system includes a flexible metal backup ring, which partially encases the packer element by substantially covering at least one axial side and a portion of the exterior radial surface of the packer element. The packer containment system also includes a plurality of annular support rings, or “petal rings” which have petal-shaped radial protuberances with slots between them.