Abstract:
An anchoring device to secure a packer assembly within a casing, including a frangible ring having a plurality of grips on an outer circumference, wherein a first end of the frangible ring includes a plurality of circumferentially spaced slots, and an expansion ring having a plurality of castellations configured to engage the slots of the first end of the frangible ring is disclosed. A method to secure a packer assembly in a casing, including engaging a plurality of arcuate segments of a segmented ring with a plurality of slots in a first end of a frangible ring, engaging a plurality of castellations of an expansion ring with the plurality of slots on a second end of the frangible ring, and moving the expansion ring in an axial direction towards the frangible ring and splitting the frangible ring into a plurality of slip segments, thereby radially extending the plurality of slip segments and segmented ring into the casing is also disclosed.

Description:
BACKGROUND OF DISCLOSURE 
       [0001]    1. Field of the Disclosure 
         [0002]    The disclosure relates generally to methods and apparatus for drilling and completing well bores. More specifically, the disclosure relates to methods and apparatus for a permanent anchoring device in a packer assembly. 
         [0003]    2. Background Art 
         [0004]    In the drilling, completing, or reworking of oil wells, a great variety of downhole tools are used. Particularly, downhole tools, referred to as packers and bridge plugs, are designed to isolate certain areas in a wellbore, and are well known in the art of producing oil and gas. Packers and bridge plugs are similar in structure and similar in the method in which they are set in a casing, however, they are designed to perform different functions in a wellbore. A bridge plug may be set in a casing as a lower limit, whereas a packer may be set above the bridge plug as an upper limit forming an isolated zone between the two. It is then possible to pressure down through a bore of the packer to communicate with the isolated region. 
         [0005]    Downhole packers are typically used to seal an annular area formed between two coaxially disposed tubulars within a wellbore. A packer may seal, for example, an annulus formed between production tubing disposed within wellbore casing. Alternatively, some packers seal an annulus between the outside of a tubular and an unlined borehole. Routine uses of packers include the protection of casing from pressure, both well and stimulation pressures, and protection of the wellbore casing from corrosive fluids. Other common uses may include the isolation of formations or of leaks within wellbore casing, squeezed perforation, or multiple producing zones of a well, thereby preventing migration of fluid or pressure between zones. Packers may also be used to hold kill fluids or treating fluids in the casing annulus. 
         [0006]    A downhole packer assembly may be run into a wellbore with a smaller initial outside diameter that then expands externally to seal the wellbore. The two most common forms are the production or test packer and the inflatable packer. Packers employ flexible, elastomeric elements that expand. The expansion of the former may be accomplished by squeezing the elastomeric elements (somewhat doughnut shaped) between two plates, forcing the sides to bulge outward. The expansion of the latter is accomplished by pumping a fluid into a bladder, in much the same fashion as a balloon, but having more robust construction. Packers may be set in cased holes while inflatable packers may be used in open or cased holes. Installing the packer downhole involves running it on a wireline, pipe or coiled tubing. While, some packers may be designed to be removable, others are installed as permanent, and therefore not retrievable. Permanent packers must be drilled out and destroyed to be removed from a wellbore. The pieces of the packer are circulated back to the surface in the drilling fluid. As such, permanent packers are constructed of materials that are easy to drill or mill out. 
         [0007]    Traditional packers include a sealing element having anti-extrusion rings on both upper and lower ends and a series of slips above and/or below the sealing element. Typically, a setting tool would be run with the packer to set the packer. The setting may be accomplished hydraulically due to relative movement created by the setting tool when subjected to applied pressure. This relative movement causes the slips to move up cones and extend into the surrounding tubular casing wall. At the same time, the sealing element may be compressed into sealing contact with the surrounding tubular casing wall. The set position of the packer may be held in place by a body lock ring, which may prevent reversal of the relative movement. 
         [0008]    The terms “packer” and “bridge plug” may be used interchangeably when describing the structure and manner in which they are set in a casing. A significant difference in the functionality of the two is the ability to pressure down through a bore of a packer. For figures and descriptions within, references are made to packers only.  FIG. 1  further illustrates the components of a typical packer assembly  100  as installed in a wellbore  104 . A packer assembly  100  may be set in a well casing  102  lining a wellbore  104  drilled into an oil and gas producing formation  106 . Packer  100  may be connected with a production tubing string  108  leading to a well head, not shown, at the surface end of the well for conducting produced fluids from the well bore  104  to the well head. Casing  102  may be perforated at  110  to allow well fluids, such as oil and gas, to flow from the formation through the casing into the wellbore. Packer  100  may be locked with the wall of casing  102  by upper slips  112  and lower slips  114 . Packer  100  may include a seal  116  which is expanded against the wall of casing  102  by longitudinal compressive forces forming a fluid-tight seal around packer  100 . Seal  116  ensures that the formation pressure is held in wellbore  104  below seal assembly  116  and formation fluids are forced through the bore of packer  100  to flow to the surface through production tubing  108 . 
         [0009]    In the past, various configurations of packer assemblies have been disclosed for use in downhole operations. U.S. Pat. No. 4,753,444 to Jackson et al. discloses a packer having a conventional sealing element located around the outside of a mandrel. Anti-extrusion rings and back-up rings contain the seal element ends and are compressed to radially expand the seal element outwardly into contact with the well casing. U.S. Pat. No. 4,852,649 to Young discloses packers having multiple moving packer elements which distribute stresses across the elements as the packer elements expand to seal the wellbore annulus. In U.S. Pat. No. 5,046,557 to Manderscheid, multiple seal elements are separated with spacers around the exterior surface of a mandrel. The seal elements are hydraulically set to contact the well casing. 
         [0010]    Further, U.S. Pat. No. 3,526,277 to Scott discloses an anchoring means for well bore tools. Disclosed is an expander having oppositely facing conical surfaces which cooperate with a pair of spaced apart sets of slip elements that are independently outwardly movable into anchoring engagement with the well wall. 
         [0011]    Still further, U.S. Pat. No. 4,526,229 to Dickerson discloses a hydraulic packer assembly for sealing an annulus between a well casing and a tubing string inserted within the well casing having a packer and a setting tool. The packer includes a packer body having an internal bore with a seal and gripping members mounted on its exterior surface for engaging the interior surface of the well casing. 
         [0012]    An integral component to the functioning of a downhole packer assembly is the anchoring device which radially expands to engage the casing wall to prevent movement in the wellbore. U.S. Pat. No. 6,164,377, which is assigned to the assignee of the present disclosure, discloses a slip assembly for engaging a downhole tool and preventing it from rotating within a casing. The slip assembly comprises a frangible ring and a plurality of slip pads supported on the ring, the slip pads preferably engaging the downhole tool by a tongue and groove mechanism. In addition, the camming interfaces between each slip pad and the tool comprise planar surfaces. 
         [0013]    In setting the packer assembly in the well casing, an axial force is imparted on a mechanism in the anchoring device to cause a frangible ring to break into a number of individual slip segments. The slip segments are forced out radially to engage the casing wall inner diameter. In the separation of the frangible ring into individual slip segments, and during the subsequent radial expansion, a random and uneven spacing of the slip segments often occurs around the circumference of the casing wall. The uneven spacing between slip segments creates a localized stress pattern that is closely associated with the random contact with the casing wall. 
         [0014]    Additionally, the slip segments disclosed in prior art have a smaller radius of curvature than the casing in which they are set. This geometry causes a contact area between the slip segment and the casing wall to be concentrated at the center plane of each slip segment. The small contact radii of the slip segments creates a scallop effect that must distort the casing or break the slip in additional locations to gain contact area. This configuration may essentially “gouge” into the casing wall or break off corners of the slips in an effort to engage the casing wall. The metal deformation caused by the gouging may further create higher stress areas which may be detrimental to the integrity of the engagement between the packer assembly and the casing wall. 
         [0015]    Accordingly, there exists a need for an anchoring device that forces the slips into the casing wall to distribute the load more uniformly when set in the casing, thereby mitigating excessive gouging of the casing or breaking off of teeth. 
       SUMMARY OF INVENTION 
       [0016]    In one aspect, embodiments disclosed herein relate to an anchoring device to secure a packer assembly within a casing, including a frangible ring having a plurality of grips on an outer circumference, wherein a first end of the frangible ring includes a plurality of circumferentially spaced slots, and an expansion ring having a plurality of castellations configured to engage the slots of the first end of the frangible ring. 
         [0017]    In another aspect, embodiments disclosed herein relate to an anchoring device to secure a packer assembly within a casing, including a frangible ring having a plurality of grips on an outer circumference, wherein a first end and a second end of the frangible ring include a plurality of circumferentially spaced slots, an expansion ring having a plurality of castellations configured to engage the slots of the first end of the frangible ring, and a segmented ring including a plurality of segments configured to engage the slots of the second end of the frangible ring, wherein a curved outer surface of each of the individual arcuate segments of the segmented ring has a radius of curvature that is larger than the radius of curvature of an inner diameter of the casing. 
         [0018]    In another aspect, embodiments disclosed herein relate to a method to secure a packer assembly in a casing, including engaging a plurality of arcuate segments of a segmented ring with a plurality of slots in a first end of a frangible ring, engaging a plurality of castellations of an expansion ring with the plurality of slots on a second end of the frangible ring, and moving the expansion ring in an axial direction towards the frangible ring and splitting the frangible ring into a plurality of slip segments, thereby radially extending the plurality of slip segments and segmented ring into the casing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  shows a section view of a prior art packer assembly as set in a wellbore. 
           [0020]      FIG. 2  shows a partial section view of a prior art packer assembly in an unexpanded condition. 
           [0021]      FIG. 3  shows a section view of a prior art packer assembly in an expanded condition. 
           [0022]      FIG. 4  shows an assembly view of an anchoring device in an unexpanded condition in accordance with embodiments of the present disclosure. 
           [0023]      FIG. 4A  shows a component view of a frangible ring in accordance with embodiments of the present disclosure. 
           [0024]      FIG. 4B  shows a component view of an expansion ring in accordance with embodiments of the present disclosure. 
           [0025]      FIG. 4C  shows an individual segment from a segmented ring in accordance with embodiments of the present disclosure. 
           [0026]      FIG. 4D  shows a section view of an anchoring device in an unexpanded condition in accordance with embodiments of the present disclosure. 
           [0027]      FIG. 5  shows an assembly view of an anchoring device in an expanded condition in accordance with embodiments of the present disclosure. 
           [0028]      FIG. 5A  shows a section view of an anchoring device in an expanded condition in accordance with embodiments of the present disclosure. 
           [0029]      FIG. 6  shows an assembly view of an anchoring device in an unexpanded condition in accordance with embodiments of the present disclosure. 
           [0030]      FIG. 6A  shows a component view of a frangible ring in accordance with embodiments of the present disclosure. 
           [0031]      FIG. 6B  shows a component view of an expansion ring in accordance with embodiments of the present disclosure. 
           [0032]      FIG. 6C  shows a component view of a cone in accordance with embodiments of the present disclosure. 
           [0033]      FIG. 6D  shows a section view of an anchoring device in an unexpanded condition in accordance with embodiments of the present disclosure. 
           [0034]      FIG. 7  shows an assembly view of an anchoring device in an expanded condition in accordance with embodiments of the present disclosure. 
           [0035]      FIG. 7A  shows a section view of an anchoring device in an expanded condition in accordance with embodiments of the present disclosure. 
           [0036]      FIG. 8  shows a view of a load distribution in a casing in accordance with embodiments of the present disclosure. 
           [0037]      FIG. 9  shows a cross-sectional view of a frangible ring in accordance with embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    Downhole packer assemblies are run into a wellbore and set to provide a seal in an annulus between the packer assembly and the casing of the wellbore.  FIGS. 2 and 3  are shown to provide a general description of the engagement between a packer assembly and the wellbore. As mentioned previously, while packers and bridge plugs may be similar in structure, terms and figures used herein reference a packer only. 
         [0039]    Referring to  FIG. 2 , a partial section view of a packer assembly  200  is shown in an unexpanded condition, or after having been run downhole but prior to setting it in a wellbore. The unexpanded condition is defined as the state in which packer assembly  200  is run downhole and before a force is applied to radially expand and engage the casing wall and set packer assembly  200  in the wellbore. Packer assembly  200  includes a central mandrel  204  having a center axis  202  about which other components are mounted. An upper anchoring device  206  and a lower anchoring device  208  are provided adjacent an upper cone  210  and a lower cone  212 , respectively. A sealing element  214  seals an annulus between the packer assembly and the casing wall. The sealing element  214  may be formed of any material known in the art, for example, elastomer or rubber. 
         [0040]    Referring now to  FIG. 3 , a partial section view of a downhole packer assembly  300  is shown in an expanded condition, or after having been set in a wellbore. The expanded condition is defined as the state at which a force has been applied to radially expand and engage the casing wall and set packer assembly  300  in the wellbore. Packer assembly  300  includes a central mandrel  304  having a center axis  302  about which other components are mounted. An axial force is applied to force upper and lower anchor assemblies  306 ,  308  to travel up an inclined surface of upper and lower cone  310 ,  312 , respectively. In traveling on upper and lower cone  310 ,  312 , anchor assemblies  306 ,  308  travel in both an axial and radial direction to engage casing wall  316 . Upper anchoring device  306  and lower anchoring device  308  are shown engaged with casing wall  316 . A sealing element  314  is shown compressed and expanded to create a seal between packer assembly  300  and casing wall  316 . 
         [0041]    In one aspect, embodiments of the present disclosure relate to a downhole tool for sealing tubing or other pipe in a casing of a well. In particular, embodiments disclose an anchoring device for use in a packer assembly. 
         [0042]      FIG. 4  shows an assembly view of an anchoring device  400  of a packer in an unexpanded condition in accordance with an embodiment of the present disclosure. The unexpanded condition is defined as the state in which the packer is run downhole and before a force is applied to radially expand anchoring device  400  into engagement with the casing wall, or when anchoring device  400  is set. Anchoring device  400  may be disposed at a first end and/or a second end of the packer. Anchoring device  400  includes a frangible ring  410 , an expansion ring  420 , and a segmented ring  430 . Segmented ring  430  includes a plurality of arcuate segments disposed adjacent one another, or side by side, thereby forming a ring. Expansion ring  420  and segmented ring  430  are configured to engage frangible ring  410  on opposite ends. 
         [0043]      FIG. 4A  shows a component view of frangible ring  410  in further detail in accordance with an embodiment of the present disclosure. Frangible ring  410  includes slots  411  circumferentially disposed on both a first end  412  and a second end  413 . Slots  411  may be configured as triangular, square, or other appropriate geometry known to one of ordinary skill in the art. Frangible ring  410  is configured to fracture and separate into individual slip segments  414 . The geometry of individual slip segments  414  corresponds to the geometry of slots  411 . For example, slots  411  may be triangular and slip segments  414  may be substantially triangular or trapezoidal on both first end  412  and second end  413 . The triangular or trapezoidal configuration of slip segments  414  engages triangular slots  411  of segmented ring  430 . Frangible ring  410  further comprises grips  415  disposed on an outer circumference for engaging a casing wall. Grips  415  may be configured as teeth or any other devices for gripping a casing wall known to one of ordinary skill in the art. Furthermore, frangible ring  410  may include a shoulder  416  on an inner circumference of frangible ring  410  configured to contact segmented ring  430  ( FIG. 4 ). 
         [0044]    Referring now to  FIG. 4B , a component view of expansion ring  420  is shown in further detail in accordance with an embodiment of the present disclosure. As shown, expansion ring  420  includes a plurality of castellations  421  arranged around a circumference of a first end  422 . Castellations  421  are configured as a tongue and groove type shape to engage slots  411  of first end  412  of frangible ring  410  ( FIG. 4A ). Furthermore, castellations  421  act to wedge into slots  411  of frangible ring  410  when axial force is applied to anchoring device  400  and to split frangible ring  410  into individual slip segments  414  ( FIG. 4A ). In one embodiment, a second expansion ring may engage slots  411  of second end  413  of frangible ring  410  ( FIG. 4A ). 
         [0045]    Now referring to  FIGS. 4 and 4C , a component view of segmented ring  430  is shown in further detail in accordance with an embodiment of the present disclosure. An arcuate segment  431 , which along with a plurality of identical segments  431  form segmented ring  430 , is shown for further clarification. In anchoring device  400 , segmented ring  430  is configured to engage second end  413  of frangible ring  410 . Segment  431  comprises a face  432  which may contact second end  413  of frangible ring  410  and a protrusion  433  configured to engage slot  411  of second end  413  of frangible ring  410 . Protrusion  433  may be triangular to engage triangular slot  411  ( FIG. 4A ). Segment  431  further includes a lip  434  that mates with an inner diameter of frangible ring  410 , and of which an end  436  may contact shoulder  416  of frangible ring  410 . In an unexpanded condition of anchoring device  400 , shoulder  432  and second end  413  of frangible ring  410  are initially at a slight distance apart and are not in contact. Further, protrusion  433  is engaged in slot  411  of second end  413  and lip  434  is in contact with inner diameter of frangible ring  410 . Upon axial compression and radial expansion of anchoring device  400  during setting, protrusion  433  may fully engage slot  411  and face  432  may move to contact second end  413  of frangible ring  410 . Simultaneously, lip  434  moves axially and end  436  may make contact with lip  416  of frangible ring  410  ( FIG. 4A ) thereby forming a common inner diameter in anchoring device  400 . This engagement further serves to create a more stable connection between components of anchoring device  400  in an expanded condition. Furthermore, segmented ring  430  includes grips  435  on an outer surface for engaging a casing wall. Grips  435  may be configured as teeth or any other gripping device known to one of ordinary skill in the art. 
         [0046]      FIG. 4D  shows a section view of anchoring device  400  in accordance with an embodiment of the present disclosure. Anchoring device  400  is shown in an unexpanded condition similar to  FIG. 4 . As shown, expansion ring  420  engages first end  412  of frangible ring  410 , and segmented ring  430  engages second end  413  of frangible ring  410 . Frangible ring  410  and expansion ring  420  are initially in contact, but not yet fully engaged, to provide a travel distance between castellations  421  of expansion ring  420  and slots  411  of frangible ring  410  sufficient to split frangible ring  410  into individual slip segments (not individually illustrated). 
         [0047]    An assembly view of an anchoring device  500  in an expanded condition is shown in  FIG. 5  in accordance with an embodiment of the present disclosure. The expanded condition is defined as the state at which a force has been applied to axially move and radially expand the anchoring device to engage the casing wall and set the anchoring device  500  in the wellbore. As shown, anchoring device  500  includes a frangible ring  510  which has been split into individual slip segments  514 , an expansion ring  520 , and a segmented ring  530 . 
         [0048]    Now referring to  FIG. 5A , a section view of anchoring device  500  in an expanded condition is shown in accordance with an embodiment of the present disclosure similar to  FIG. 5 . When setting anchoring device  500  in a wellbore, axial forces are applied to expansion ring  520  which are further transferred to frangible ring  510 . Initially, castellations (shown in  FIG. 4B ) of expansion ring  520  engage slots (shown in  FIG. 4A ) of frangible ring  510 , and segmented ring  530  engages an opposite end of frangible ring  510 , as well as an inclined surface  540  as shown. Axial force is then applied to expansion ring  520 , causing a compressive force to be applied to both ends of frangible ring  510  by expansion ring  520  on the first end and segmented ring  530  on the second end. This compressive force causes frangible ring  510  to split at weakened points into individual slip segments  514 . As anchoring device  500  is set, segmented ring  530  expands radially outward, traveling on inclined surface  540  before engaging casing wall  550 . Further, slip segments  514  of frangible ring  510  travel in a radially outward and axial direction simultaneously until making contact with casing wall  550 . Slip segments  514  travel both radially outward and axially because of the interaction between the triangular or trapezoidal configuration of the ends of slip segments  514  ( FIG. 4A ) and the triangular slots of frangible ring  510 . Axial movement of expansion ring  520 , as well as axial and radial movement of slip segments  514  and segmented ring  530  continue until anchoring device  500  is set in casing  550 . 
         [0049]    Referring to  FIG. 6 , an assembly view of an anchoring device  600  is shown in accordance with an embodiment of the present disclosure. In the embodiment shown, anchoring device  600  includes a frangible ring  610 , an expansion ring  620 , and a cone  630 . Expansion ring  620  and cone  630  are configured to engage frangible ring  610  on opposite ends. In one embodiment, frangible ring  610  may be formed of cast iron. In alternate embodiments, frangible ring  610  may be formed of a composite material, including aluminum and cast iron. 
         [0050]    Referring to  FIG. 6A , a component view of frangible ring  610  is shown in further detail in accordance with an embodiment of the present disclosure. Frangible ring  610  includes slots  611  circumferentially disposed on a first end  612  and a second end  613 . Slots  611  may be configured as triangular, square, groove or other appropriate geometry known to one of ordinary skill in the art. Frangible ring  610  is configured to fracture and separate into individual slip segments  614  in an expanded condition. Frangible ring  610  includes grips  615  disposed on an outer circumference for engaging a casing wall. Grips  615  may be configured as teeth or any other device for gripping a casing wall known to one of ordinary skill in the art. 
         [0051]    Now referring to  FIG. 6B , a component view of expansion ring  620  is shown in further detail in accordance with an embodiment of the present disclosure. As shown, expansion ring  620  includes a plurality of castellations  621  arranged around a circumference of a first end  622 . Castellations  621  are configured as a tongue and groove type shape to engage slots  611  of first end  612  of frangible ring  610  ( FIG. 6A ). Furthermore, castellations  621  act to wedge into slots  611  of frangible ring  610  when axial force is applied to anchoring device  600  and to split frangible ring  610  into individual segmented slips  614 . In one embodiment, a second expansion ring may engage slots  611  of second end  613  of frangible ring  610  ( FIG. 6A ). 
         [0052]      FIG. 6C  shows a component view of cone  630  in further detail in accordance with an embodiment of the present disclosure. Cone  630  has a tapered outer surface  631  configured to engage an inner surface of second end  613  of frangible ring  610 . During the process of expanding the anchoring device  600 , slip segments  614  are configured to travel axially and radially outward on outer surface  631  and come into engagement with a casing wall (not shown). 
         [0053]    Referring now to  FIG. 6D , a section view of anchoring device  600  is shown in accordance with an embodiment of the present disclosure. Anchoring device  600  is shown in an unexpanded condition similar to  FIG. 6 . As shown, expansion ring  620  engages first end  612  of frangible ring  610 , and cone  630  engages an inner diameter of second end  613  of frangible ring  610 . Frangible ring  610  and expansion ring  620  are initially at a distance away from each other, so as to provide castellations  621  a sufficient travel distance to split frangible ring  610  into a number of individual slip segments. 
         [0054]      FIG. 7  shows an assembly view of anchoring device  700  in an expanded condition in accordance with an embodiment of the present disclosure. The expanded condition is defined as the state at which a force has been applied to radially expand and engage the casing wall and set the anchoring device  700  in the wellbore. Anchoring device  700  includes a frangible ring  710 , shown split into individual slip segments  714 , an expansion ring  720 , and a cone  730 . 
         [0055]    Now referring to  FIG. 7A , a section view of anchoring device  700  in an expanded condition is shown in accordance with an embodiment of the present disclosure similar to  FIG. 7 . When anchoring device  700  is set, axial forces are applied to expansion ring  720  and transferred to frangible ring  710 . Expansion ring  720  forces frangible ring  710  to split at weakened points into individual slip segments  714 . As frangible ring  710  is split into slip segments  714 , the axial force from expansion ring  720  forces slip segments  714  to move in an axial direction and engage an outer surface of cone  730 . Slip segments  714  of frangible ring  710  travel up outer surface  731  of cone  730  until they engage a casing wall  750 . Axial movement of expansion ring  720 , and axial and radial movement of slip segments  714  continue until fully engaged with casing wall  750  and anchoring device  700  is set in the wellbore. 
         [0056]    Embodiments of the present disclosure offer a number of advantages in the engagement of an anchoring device of a packer in a wellbore. In embodiments disclosed herein, the arcuate segments forming the segmented ring have a larger radius of curvature than the casing in which they are set. More specifically, arcuate segments of the segmented ring have an outer curvature, which forms an “outer diameter” when all the arcuate segments are placed adjacent one another to form the segmented ring. Referring back to  FIG. 4C , when the segmented ring  430  is expanded radially, the larger radius of curvatures of the arcuate segments  431  bite into the smaller radius of curvature of the casing at corners  437  resulting in a “corner bite.” That is, corners  437  of arcuate segment  431  engage the casing most aggressively, creating high stress zones in the contact area between arcuate segments  431  and the casing. In one embodiment, the radius of curvature of arcuate segments  431  may be ¼ inch greater than the radius of the casing. In other embodiments, the radius of curvature of arcuate segments  431  may be 1 inch greater than the radius of the casing. One of ordinary skill in the art will appreciate that the difference in the radius of curvature between segments of segmented ring  430  and the casing may vary without departing from the scope of embodiments disclosed herein. Further, the radius of curvature of segments of the segmented ring  430  may vary without depending on, for example, the length or diameter of the casing, so long as the radius of curvature of the segments of the segmented ring  430  is greater than the radius of the casing. Proper sizing of the radius of curvature of arcuate segments  431  would be known to one of ordinary skill in the art. 
         [0057]    Furthermore, referring back to  FIG. 4A , the radius of frangible ring  410  may be smaller than the radius of the casing into which it is set, causing the teeth to engage the pipe on a center line  417  of each slip segment  414 , resulting in a “center bite.” That is, center line  417  of slip segment  414  engages the casing most aggressively, creating high stress zones in the contact area between slip segments  414  and the casing. The combination of high stress areas created by the corner bite and center bite phenomena may be desirable when alternated over an engagement contact area with the casing. 
         [0058]    With the alternating corner bite/center bite effect, the three adjacent pieces (arcuate segment-slip segment-arcuate segment) provide five contact points between the anchoring device and the casing wall, as opposed to the three contacts points provided by previous anchor mechanisms (all center bites). The alternating corner bite/center bite effect results in a more uniform radial load distribution in the casing. Because the loads are no longer concentrated at the centerline of each segment, a complete full circle foot print is created that distributes the contact stresses over the entire contact area between the engaged slip segments, segmented ring, and the casing.  FIG. 8  shows grip indentations on the inside wall of a casing formed by a frangible ring and segmented ring according to embodiments of the present disclosure. The indentations of  FIG. 8  represent a uniform load distribution  800 . As shown, the combination of corner bites  810  and center bites  820  of segmented ring and frangible ring, respectively, provides a more even distribution of stresses along the inner circumference of casing wall. 
         [0059]    In another embodiment, the segmented ring may be configured with a plurality of segments having substantially planar surfaces on inner and/or outer circumferences. The plurality of substantially planar surfaces form a segmented “ring” having a polygonal configuration on the inner and outer circumferences. Anchor assemblies in accordance with this embodiment may present machining and/or assembly limitations due to the planar surfaces. Configured as such, the segmented ring may perform the function of providing corner bites in the casing and help create a more uniform load distribution. 
         [0060]    In embodiments disclosed herein, the frangible ring is split into individual slip segments having a wedge-shaped cross-sectional area as viewed from at least one end of the frangible ring.  FIG. 9  is a representative footprint of a frangible ring  900  as viewed from one end. As is shown, each slip segment  902  has a wedge-shape cross-section. If a plane of a first side  904  and a plane of a second side  906  are extended inward until they intersect  908 , a “radial wedge angle” α is created. Angle α may vary dependent upon the number of slip segments  902  that comprise frangible ring  900 , as well as the outer circumference measurement required of frangible ring  900 . For example, frangible ring  900  may be comprised of 12 slip segments, each having a cross-section wedge angle of about 30 degrees. Further, frangible ring may be comprised of 10 slip segments, each having a cross-section wedge angle of 36 degrees. One of ordinary skill in the art will appreciate the configuration of a wedge-shape cross-section and the ability to vary the radial wedge angle. 
         [0061]    The wedge-shape cross section provides an advantage to the radial engagement between the slip segments of the frangible ring and the casing wall. In the expansion of the anchoring device, the castellations of the expansion ring force the slip segments to move in an axial direction toward the segmented ring. The wedge-shape cross-section of the slip segments forces the slip segments to travel in both an axial and radial direction simultaneously, ensuring a positive engagement between the anchoring device and the casing wall. The ability to vary the radial wedge angle of the slip segments may become an important factor as the diameter of the casing in which the packer is set increases. As mentioned previously, varying the radial wedge angle of the slip segments is related to the number of slip segments forming the frangible ring which correlates to the number of slots cut into ends of the frangible ring. For example, increasing the number of slots cut in each end of the frangible ring provides a larger or steeper radial wedge angle of the slip segments. 
         [0062]    Another advantage presented by embodiments of the present disclosure is the self locking feature of the anchoring device provided by the tongue and groove connection between the expansion ring and the frangible ring. The wedge shaped castellations are in full contact with the slots of the frangible ring and create a stable “full circle” mechanism that is self locking. Furthermore, the tongue and groove geometry helps “distribute” the space created when the frangible ring breaks into small uniform spaces adjacent to each segment instead of allowing a large gap to form on one side of the casing wall. This arranges the expanded slips evenly around the inner circumference of the casing wall rather than having random spaces scattered around the circumference of the casing. 
         [0063]    Furthermore, the self-locking fall circle engagement formed between the segmented ring and frangible ring may help to prevent the extrusion of the sealing element ( FIGS. 2 and 3 ). As mentioned, the sealing element is formed of material such as elastomer or rubber, and therefore may be capable of extruding through cracks in the anchor mechanism. The sealing element interfering with the anchor mechanism may be detrimental to the packer set in the casing as well as the integrity of the seal. Referring now to  FIG. 5 , to prevent or reduce extrusion of the sealing element, the lip  434  of the arcuate segments  431  ( FIG. 4C ) forming the segmented ring  530  advantageously obstructs or closes extrusion spaces  575  created between slip segments  514  when frangible ring  510  is split. Further, the triangle-shaped protrusions of the arcuate segments of the segmented ring are in full contact with the slots of the frangible ring. This engagement creates a stable full circle mechanism preventing the extrusion of the sealing element through radial cracks. Furthermore, the addition of a backup element, which would be known to one of ordinary skill in the art, may be used in conjunction with the aforementioned configuration to prevent extrusion of the sealing element. 
         [0064]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.