You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
RELATED APPLICATION 
     This application is a divisional application of, and claims priority to, U.S. patent application Ser. No. 12/156,408 filed May 30, 2008, now U.S. Pat. No. 7,703,542, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/933,183, filed Jun. 5, 2007. 
    
    
     BACKGROUND 
     The invention is directed to expandable casing packing element systems for use in oil and gas wells and, in particular, expandable casing packing element systems having extrudable sealing elements for sealing open-hole wells. 
     Expandable casing having a sealing element such as a packer have been used to seal the annulus of open-hole wells. In operation, after the well is drilled into the earth formation, the expandable casing is run into the well. The expandable casing has disposed on it, or as part of the expandable casing string, a sealing device such as a packer. The packer is designed to divide the well by sealing against the well formation, thereby isolating a lower portion of the well from an upper portion of the well. 
     After the expandable casing is run into the desired location in the well, a cone or other device can be transported through the bore of the expandable casing. As the cone, such as a swage, travels downward, the expandable casing is expanded by the cone. The expansion of the expandable casing causes the sealing device to contact the formation and separate the open-hole well into at least two isolated regions, one above the sealing device and one below the sealing device. 
     The expandable casing and sealing devices disclosed herein include components that, to the inventors&#39; knowledge, are novel and non-obvious from previous expandable casing and sealing devices. 
     SUMMARY OF INVENTION 
     Broadly, the expandable casing packing element systems disclosed herein include an expandable casing member having a sealing device comprising a sealing element disposed between at least two retainer rings. In one embodiment, both retainer rings have flat cross-sections and the sealing element is forced radially outward by the expansion of the expandable casing against the two retainer rings such that the sealing element protrudes outwardly beyond the retainer rings and engages the wall of the a wellbore in three locations. The wellbore may be an opened-hole wellbore or a cased wellbore. In another embodiment, both of the two retainer rings include flares that extend outwardly from the body of the expandable casing to which they are attached. As the expandable casing is expanded, the flares are forced inward to compress the sealing element which is then extruded radially outward through a gap between the two retainer rings to engage and seal off the wellbore. 
     Also disclosed is a method comprising the steps of: (a) running an expandable casing string having a packing element system attached thereto into a wellbore defined by an inner wall surface, the packing element system having a sealing element and at least two retainer rings, at one of the at least two retainer rings overlapping the sealing element; (b) applying a radial load to expand the expandable casing, causing the sealing element to be extruded outwardly by at least one of the at least two retainer rings applying an inward force to the sealing element; and (c) continuing to apply the radial load causing the sealing element to move radially outward into sealing engagement with the inner wall surface of the wellbore. In one particular embodiment, the wellbore is cased. In another specific embodiment, the wellbore is an opened-hole wellbore. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of one embodiment of an expandable casing having a sealing device,  FIG. 1  showing the expandable casing as it is being expanded from its run-in position to its expanded or set position. 
         FIG. 2  is a cross-sectional view of another specific embodiment of an expandable casing having a sealing device,  FIG. 2  showing the expandable casing in its run-in position. 
         FIG. 3  is a cross-sectional view of the expandable casing shown in  FIG. 2  shown in its expanded or set position. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     Referring now to  FIG. 1 , in one specific embodiment, expandable casing  30  is disposed within well  20  that has been drilled into formation  26 . Well  20  is defined by well inner wall surface  22 . Expandable casing  30  has upper end  32 , lower end  34 , bore  36  defined by inner wall surface  38 , outer wall surface  39 , and axis  40 . Expandable casing  30  includes run-in diameter  42 , set diameter  44 , and transitional diameter  46 . Run-in diameter  42  is less than set diameter  44  and transitional diameter  46  illustrates the location of a cone (not shown) or other device used to expand expandable casing  30  from the run-in diameter  42  to the set diameter  44 . Although a cone is described as being used to expand expandable casing  30  from the run-in diameter  42  to the set diameter  44 , it is to be understood that any device or method known to persons of ordinary skill in the art may be used to expand expandable casing  30 . 
     As illustrated in  FIG. 1 , disposed on outer wall surface  39  of expandable casing  30  are upper sealing device  50  and lower sealing device  60 . In this embodiment, upper sealing device  50  is identical to lower sealing device  60  except that upper sealing device  50  is shown in the set position and lower sealing device  60  is shown in the run-in position. It is to be understood, however, that expandable casing  30  may have only one sealing device  50 ,  60 , or more than two sealing devices  50 ,  60 . For convenience, both upper and lower sealing devices  50 ,  60  will be discussed in greater detail with reference to like numerals. 
     Sealing devices  50 ,  60  include annular deformable sealing elements  51  having upper ends  52  and lower ends  54 , upper retainer ring  56 , and lower retainer ring  58 . Sealing element  51  is a deformable element formed from an deformable material so that radial outward movement of sealing element  51  away from axis  40  and into upper and lower retainer rings  56 ,  58  causes sealing element  51  to extrude into sealing contact with inner wall surface  22  of well  20 . Suitable materials for forming sealing element  51  include, but are not limited to, elastomers, rubbers, polymers, or thermoplastics. 
     Additionally, sealing element  51  may have any shape desired or necessary to provide the requisite compression, deformation, or “extrusion” to form the seal with inner wall surface  22  of well  20 . As shown in  FIG. 1 , in this specific embodiment, sealing element  51  is formed in the shape of a sleeve having a thicker center portion as compared to upper and lower ends  52 ,  54 . This thicker portion is disposed between upper and lower retainer rings  56 ,  58  and, as shown with reference to sealing device  60 , has an outer diameter that is equal to the outer diameter of both upper and lower retainer rings  56 ,  58  when in the run-in position. It is to be understood, however, that sealing element  51  may have an outer diameter that is less than the outer diameter of one or both of upper or lower retainer rings  56 ,  58  when in its run-in position or it may have an outer diameter that is greater than the outer diameter of one or both upper or lower retainer rings  56 ,  58  when in its run-in position. 
     Further, in the embodiment shown in  FIG. 1 , upper and lower ends  52 ,  54  are shown protruding above and below upper and lower retainer rings  56 ,  58 ; however, upper and lower ends  52 ,  54  are not required to protrude above and below upper and lower retainer rings in this manner. 
     Sealing element  51  is maintained against outer wall surface  39  of expandable casing  30  using any device or method known to persons of ordinary skill in the art. For example, sealing element  51  may be chemically bonded to outer wall surface  39 . Alternatively, sealing element  51  can be maintained solely by upper and lower retainer rings  56 ,  58 . 
     Upper retainer rings  56  and lower retainer rings  58  are expandable members disposed around the outer diameter of sealing element  51  and, thus, can maintain or assist in maintaining sealing element  51  along outer wall surface  39 . In this embodiment both upper retainer ring  56  and lower retainer ring  58  have a relatively flat vertical cross-section parallel or substantially parallel to the axial length of the expandable casing  30 . As additionally shown in  FIG. 1 , both upper and lower retainer rings  56 ,  58  have an axial length greater than their width so that the inner diameter surface area of both upper and lower retainer rings  56 ,  58  are in contact with sealing element  51  to facilitate extrusion of sealing element  51  during expansion of expandable casing  30 . 
     Although the shape of upper and lower retainer rings  56 ,  58  are discussed with reference to  FIG. 1 , it is to be understood that upper and lower retainer rings  56 ,  58  may have any shape desired or necessary to provide the necessary force against sealing element  51  during expansion of expandable casing  30  so that sealing element  51  is extruded to seal against inner wall surface  22  of well  20 . 
     Further, upper and lower retainer rings  56 ,  58  may be formed from any material known to persons of ordinary skill in the art. For example, one or both of upper and lower retainer rings  56 ,  58  may be formed from stiffer elastomers, polymers, or metals such as steel. 
     After expandable casing  30  is properly located within well  20 , a cone (not shown) or other expanding device is run through bore  36  of expandable casing  30 . As the cone travels downward, i.e., downhole, expandable casing  30  is forced radially outward from axis  40 . In so doing, run-in diameter  42  is radially expanded to transition diameter  46  and ultimately to set diameter  44 . As a result of the radial expansion of expandable casing  30 , sealing element  51  is forced into upper and lower retainer rings  56 ,  58 . Although upper and lower retainer rings  56 ,  58  are radially expandable, they are formed from a material that is stronger, i.e., more resistance to expansion, compared to the material used to form sealing element  51 . As a result, as expandable casing  30  is expanded, sealing material  51  is compressed, deformed, or extruded in between outer wall surface  39  of expandable casing and the inner wall surfaces of upper and lower retainer rings  56 ,  58  defined by the inner diameters of upper and lower retainer rings  56 ,  58 . Due to the compression of sealing element  51  between outer wall surface  39  of expandable casing  30  and the inner wall surfaces of upper and lower retainer rings  56 ,  58 , the center portion of sealing element  51  is extruded outwardly in between upper and lower retainer rings  56 ,  58 ; upper end  52  of sealing element  51  is extruded outwardly above upper retainer ring  56 ; and lower end  54  of sealing element  51  is extruded outwardly below lower retainer ring  58  until all three portions of sealing element  51  form a seal against inner wall surface  22  of well  20 . The distance between the outer diameter of upper and lower retainer rings  56 ,  58  and inner wall surface  22  of well  20  is referred to as the extrusion gap. 
     Referring now to  FIGS. 2-3 , in another embodiment, expandable casing  130  has upper end  132 , lower end  134 , bore  136  defined by inner wall surface  138 , outer wall surface  139 , and axis  140 . Expandable casing  30  includes run-in diameter defined by run-in radius  142  ( FIG. 2 ) and set diameter defined by set radius  144  ( FIG. 3 ). Run-in radius  142  and, thus, the run-in diameter, is less than set radius  144  and, thus, the set diameter. Expandable casing  130  is radially expanded using a cone (not shown) or other device used to expand expandable casing  130  from the run-in diameter defined by run-in radius  142  to the set diameter defined by set radius  144  in the same manner as the embodiment discussed above with respect to  FIG. 1 . 
     As illustrated in  FIG. 2 , expandable casing  130  is in the run-in position. Disposed on outer wall surface  139  of expandable casing  130  is sealing device  150 . Although only a single sealing device  150  is shown, it is to be understood that more than one sealing device may be disposed on outer wall surface  139  of expandable casing  130 . 
     Sealing device  150  includes annular sealing element  151 , upper retainer ring  156  and lower retainer ring  158 . Annular sealing element  151  is a deformable element formed from a deformable material such as those discussed above with respect to sealing element  51 . In this embodiment, sealing element  151  has a trapezoid section such that the inner surface of sealing element  151  has a longer axial length along outer wall surface  139  than the axial length of the outer surface defined by the outer diameter of sealing element  151 . 
     Upper retainer ring  156  has upper flare portion  157  and lower retainer ring  158  has lower flare portion  159  thereby forming a cavity between upper retainer ring  156  and lower retainer ring  158  with a gap between the lowermost end of upper retainer ring  156  and the uppermost end of lower retainer ring  158 . Sealing element  151  is disposed within the cavity. In one specific embodiment, sealing element  151  is maintained along outer wall surface  139  through any device or method known to persons of ordinary skill in the art, such as through chemical bonding or by upper and lower retainer rings  156 ,  158 . 
     As with the embodiment shown in  FIG. 1 , upper and lower retainer rings  156 ,  158  may be formed from any material known to persons of ordinary skill in the art. For example, one or both of upper and lower retainer rings  156 ,  158  may be formed from stiffer elastomers, polymers, or metals such as steel. 
     Upper flare portion  157  and lower flare portion  159  may have any shape or angle relative to the remaining vertical portions of upper and lower flare portions. For example, upper and lower flare portions  157 ,  159  may be at an angle in a range greater than 0 degrees and less than 90 degrees relative to the vertical portions of upper and lower flare portions  157 ,  159 . Additionally, the angle at which upper flare portion  157  intersects the remaining portion of upper retainer ring may be different from the angle at which lower flare portion  159  intersects the remaining portion of lower retainer ring  158 . In one specific embodiment, both of these angles are within the range from 30 degrees to 60 degrees so that sufficient inward force can be applied to sealing element  151  during expansion of expandable casing  130  to extrude sealing element  151  through the gap between the lowermost and uppermost ends of upper retainer ring  156  and lower retainer ring  158 , respectively. In the embodiment shown in  FIGS. 2-3 , upper and lower flare portions  157 ,  159  are reciprocally shaped to receive sealing element  151  so that a portion of both upper and lower flare portions  157 ,  159  contact sealing element  151  during run-in. 
     Upper and lower retainer rings  156 ,  158  can be secured to outer wall surface  139  through any device or method known to persons of ordinary skill in the art. For example, upper and lower retainer rings  156 ,  158  may be welded or epoxied to outer wall surface  139 . Alternatively, upper and lower retainer rings  156 ,  158  may be secured or formed integral with an expandable mandrel (not shown) that is then secured such as through threads to an expandable casing string. 
     As shown in  FIG. 2 , sealing element  151  of sealing device  150  is in its run-in position such that it does not protrude outwardly from outer wall surface  139  past upper or lower retainer rings  156 ,  158 . It is to be understood that although sealing element  151  is shown as having an outer diameter equal to the outer diameters of upper and lower retainer rings  156 ,  158 , sealing element  151  may have either an outer diameter that is less than the outer diameter of one or both of upper or lower retainer rings  156 ,  158  when in its run-in position, or an outer diameter that is greater than the outer diameter of one or both of upper or lower retainer rings  156 ,  158  when in its run-in position. 
     After expandable casing  130  is properly located within well (not shown), a cone (not shown) or other expanding device is run through bore  136  of expandable casing  130 . As the cone travels downward, i.e., downhole, expandable casing  130  is forced radially outward from axis  140 . In so doing, the run-in diameter illustrated by run-in radius  142  is radially expanded to a transition diameter (not shown) and ultimately to set diameter illustrated by set radius  144  ( FIG. 3 ). As a result of the radial expansion of expandable casing  130 , sealing element  151  is forced into upper and lower flare portions  157 ,  159  of upper and lower retainer rings  156 ,  158 . As with upper and lower retainer rings  56 ,  58 , upper and lower retainer rings  156 ,  158  are radially expandable; however, they are formed from a material that is stronger, i.e., has more resistance to expansion, compared to the material used to form sealing element  151 . As a result, as expandable casing  130  is expanded, upper and lower flare portions  157 ,  159  bend inward toward axis  140  as expandable casing  130  expands and, thus, compress, deform, or extrude sealing element  151  within the cavity in between outer wall surface  139  of expandable casing  130  and upper and lower flare portions  157 ,  159 . In other words, upper flare portion  157  and lower flare portion  159  become more straightened in line with the remaining portions of upper retainer ring  156  and lower retainer ring  158 , respectively, so that sealing element  151  is forced radially outward. 
     Due to the compression of sealing element  151  between outer wall surface  139  of expandable casing  130  and the upper and lower flare portions  157 ,  159 , sealing element  151  is extruded outwardly from the cavity through the gap located between the lowermost end of upper retainer ring  156  and the upper most end of lower retainer ring  158  until sealing element  151  forms a seal against the inner wall surface of the well. This distance between the outermost diameters of upper and lower retainer rings  156 ,  158  and the inner wall surface of the well is referred to as the extrusion gap. 
     It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. For example, the sealing devices may be disposed on an expandable mandrel that is placed within an expandable casing string. Additionally, the expandable casing may have one or more sealing devices  50  or  60  together with one or more sealing devices  150 . Moreover, a spacer may be disposed in between outer wall surface  39  of expandable casing  30  and the inner diameter of sealing element  151  to assist in extrusion of sealing element  151  during expansion of expandable casing  130 . Further, the inner diameter of upper retainer ring  56  is not required to be equal to the inner diameter of lower retainer ring  58 . Likewise, the shape of upper flare portion  157  is not required to be the same shape as lower flare portion  159 . Additionally, the expandable casing  30 ,  130  may be disposed in a cased wellbore as opposed to an open-hole wellbore. Thus, the term “wellbore” as used herein includes a cased wellbore as well as an opened-hole wellbore. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.

Summary:
The expandable casing packing element systems for cased and open-hole wellbores include an expandable casing member having a sealing device comprising a sealing element disposed between at least two retainer rings. The retainer rings have flat cross-sections and the sealing element is forced radially outward by the expansion of the expandable casing against the two retainer rings such that the sealing element protrudes outwardly beyond the retainer rings and engages the wall of a wellbore in three locations. The retainer rings can also include flares that extend outwardly from the body of the expandable casing to which they are attached. As the expandable casing is expanded, the flares are forced inward to compress the sealing element which is then extruded radially outward through a gap between the two retainer rings to engage and seal off the wellbore.