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BACKGROUND 
       [0001]    This invention relates generally to downhole tools for use in oil and gas wellbores, and methods of anchoring such apparatuses within the casing of the wellbore. This invention particularly relates to improving the engagement of slip elements within a casing or tubing. These slip elements are commonly used in setting or anchoring of a downhole drillable packer, bridge plug and frac plug tools. 
         [0002]    In drilling or reworking oil wells, many varieties of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well by pumping cement or other slurry down the tubing, and forcing the slurry around the annulus of the tubing or out into a formation. It then becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well, or for otherwise isolating specific zones in a well. Downhole tools referred to as packers, bridge plugs and frac plugs are designed for these general purposes, and are well known in the art of producing oil and gas. 
         [0003]    Both packers and bridge plugs are used to isolate the portion of the well below the packer or bridge plug from the portion of the well thereabove. Accordingly, packers and bridge plugs may experience a high differential pressure, and must be capable of withstanding the pressure so that the packer or bridge plug seals the well, and does not move in the well after being set. 
         [0004]    Packers and bridge plugs used with a downhole tool both make use of metallic or non-metallic slip assemblies, or slips, that are initially retained in close proximity to a mandrel, These packers and bridge plugs are forced outwardly away from the mandrel upon the downhole tool being set to engage a casing previously installed within an open wellbore. Upon positioning the downhole tool at the desired depth, or position, a setting tool or other means of exerting force, or loading, upon the downhole tool forces the slips to fracture and expand radially outward against the inside of the casing. This action anchors the packer, or bridge plug, so that the downhole tool will not move relative to the casing. 
         [0005]    To prevent slipping of the downhole tool, slip rings with wickers are used to set the downhole tool and engage the well casing. The wickers cut into and deform the inner casing wall. Unfortunately, the outer diameter of the slip rings and wickers is notably smaller than the inner diameter of the casing. Thus, the wickers only partially and unevenly engage the casing wall, thereby allowing the downhole tool to slide within the well. 
       SUMMARY 
       [0006]    In one embodiment, an apparatus for use in a well is provided. The apparatus is for anchoring a downhole tool against a casing disposed in the well. The apparatus comprises a mandrel and a slip assembly. The slip assembly is positioned on the mandrel. The slip assembly has at least one slip ring. There are a plurality of slip banks formed on the slip ring. The slip banks have a groove longitudinally positioned between each circumferential pair of slip banks. The slip ring has an outer diameter about equal to the inner diameter of the casing. 
         [0007]    In another embodiment, a unitary downhole anchor for use in a well having a casing positioned therein is provided. The casing has an inner diameter. The unitary downhole anchor comprises a mandrel and a slip assembly. The slip assembly is positioned on the mandrel. The slip assembly has at least one outwardly expandable slip ring and at least one slip wedge. The slip ring is a unitary slip ring. The slip wedge and slip ring are movable relative to one another when force is applied to the slip assembly, whereby the slip ring will expand radially outward in response to such movement. There are a plurality of slip banks circumferentially defined on the slip ring. The slip ring has at least one circumferential pair of slip banks. The slip banks have a groove longitudinally positioned between each circumferential pair of slip banks. The slip ring has an outer diameter about equal to the nominal inner diameter. 
         [0008]    In yet another embodiment, an evenly setting anchor apparatus for anchoring a downhole tool in a well, the well having a casing secured therein, is provided. The apparatus comprises a mandrel and at least one slip assembly that is positioned on the mandrel. The slip assembly has at least one slip ring and at least one slip wedge. Each slip ring has a plurality of radially expandable slip banks. There are a plurality of wickers defined on each of the slip banks. Each of the wickers has a cutting edge extending therefrom, wherein the wickers are positioned to evenly set against an inner wall of the casing in response to an input force. 
         [0009]    In still another embodiment, a downhole tool anchoring apparatus for use in high-pressure wells is provided. The high-pressure well has a casing and the casing has an inner diameter. The apparatus comprises a mandrel and a slip assembly. The slip assembly is positioned on the mandrel. The slip assembly has at least one slip ring. The slip bank is defined on the slip ring. The slip bank has at least one wicker integrally formed therewith. The wicker is designed to engage and anchor the downhole tool within the casing in the high-pressure well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-section of a downhole tool disposed in a well with a slip assembly. 
           [0011]      FIG. 2  is a cross-section of an alternative downhole tool disposed in a well with a slip assembly. 
           [0012]      FIG. 3  is a bottom perspective view of the slip. 
           [0013]      FIG. 4  is a top perspective view of the slip. 
           [0014]      FIG. 5  is a bottom view of the slip. 
           [0015]      FIG. 6  is a cross-sectional view of the slip taken along section line  6 - 6  of  FIG. 5 . 
           [0016]      FIG. 7  is a detail view of a slip bank taken from  FIG. 5 . 
           [0017]      FIG. 8  is an alternative configuration of the slip from  FIG. 3 . 
           [0018]      FIG. 9  is a bottom perspective view of an alternative slip. 
           [0019]      FIG. 10  is a top perspective view of the alternative slip. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring to the drawings,  FIG. 1  illustrates well  10  having wellbore  12  with casing  14  cemented therein. Casing  14  has inner wall  16 . Downhole tool  18  includes mandrel  20  with an outer surface  22  and an inner surface  24 . 
         [0021]    By way of a non-limiting example, downhole tool  18  illustrated in  FIG. 1  is referred to as a packer, and allows fluid communication therethrough. The packer illustrated may be used as a frac plug. In another non-limiting example, downhole tool  18  illustrated in  FIG. 2  is referred to as bridge plug. For this second non-limiting example, downhole tool  18  has optional plug  26  pinned within mandrel  20  by radially oriented pins  28 . Plug  26  has a seal  30  located between plug  26  and mandrel  20 . Without plug  26 , downhole tool  18  is suited for use as, and referred to as a packer. 
         [0022]    As illustrated in  FIGS. 1 and 2 , spacer ring  32  is mounted to mandrel  20  with a pin  34 . Slip assembly  36  is positioned on and/or disposed about mandrel  20 . Spacer ring  32  provides an abutment, which serves to axially retain slip assembly  36 . As illustrated in  FIGS. 1 and 2 , downhole tool  18  has two slip assemblies  36 , namely a first slip assembly and second slip assembly, depicted in  FIGS. 1 and 2  as first and second slip assemblies  36   a  and  36   b  for ease of reference. Slip assemblies  36   a  and  36   b  provide anchoring for downhole tool  18  to casing  14  within well  10 . The structure of slip assemblies  36   a  and  36   b  is identical, and only the orientation and position on downhole tool  18  are different. As illustrated in  FIG. 2 , each slip assembly  36  includes at least one slip ring  38  and at least one slip wedge  40 . Slip ring  38  has an inclined/wedge-shaped first surface  42  positioned proximate to an inclined/wedge-shaped complementary second surface  44  of slip wedge  40 . Slip assembly  36  is depicted in  FIG. 2  as being pinned into place with pins  46 . 
         [0023]    Slip ring  38 , shown in  FIGS. 3-8 , is an expandable slip ring  38  and has a plurality of slip banks  48 . Slip banks  48  are separated by groove  50 , which is also fracture channel  52 . Groove  50  and fracture channel  52  provide a weakened point in slip ring  38  for slip banks  48  to break apart from each other when sufficient forces are radially exerted on the interior of slip ring  38 . Without limiting the invention, slip ring  38  may include a plurality of slip banks  48 . Slip bank  48  has an outer arcuate edge  53 . Collectively, all slip banks  48  make up a circumferential slip ring  38 . Preferably, slip ring  38  has at least one circumferential pair of slip banks  48  with at least one groove  50  or fracture channel  52  positioned therebetween. As illustrated in  FIGS. 3-8 , slip ring  38  has eight slip banks  48 . Also, as illustrated, slip ring  38  is a unitary slip ring without requiring the use of frangible retaining rings. 
         [0024]    Preferably, each slip bank  48  defines at least one wicker  54  thereon. As illustrated, a plurality of wickers are defined on each slip bank  48 . The number of wickers  54  on each slip bank  48  is determined by the size of casing  14  and the pressure slip ring  38  is designed to resist. The non-limiting example illustrated in  FIGS. 3-7  shows each slip bank  48  having five wickers defined thereon. Wicker  54  has cutting edge  56  extending therefrom and oriented towards casing inner wall  16 . Preferably, wickers  54  are integrally formed from slip ring  38 . In the alternative, wickers  54  may be secured to slip ring  38 , or inserted into slip ring  38  by other means known to those skilled in the art. 
         [0025]    Wicicers  54  are positioned on slip bank  48  such that each cutting edge  56  is able to be evenly set against casing inner wall  16 . Thereby, each cutting edge is nearly equal in the force exerted upon casing inner wall  16 . Thus, each cutting edge  56  is better able to penetrate and/or deformably cut into casing inner wall  16 . This action securely anchors downhole tool  18 . 
         [0026]    Including wickers  54  and cutting edge  56 , slip ring  38  has an outer diameter  58  that is about equal to inner diameter  60  of casing  14 . A non-limiting example is illustrated in  FIGS. 3-7 , where the nominal casing  14  diameter is about 4.5 inches (11.43 centimeters) and the nominal casing inner wall  16  has inner diameter  60  of about 4.04 inches (10.26 centimeters). Similarly, outer diameter  58  is also about between about 3.98 inches (10.1 centimeters) and about 4.04 inches (10.26 centimeters), or about 0.0625 inches (0.159 centimeters), which is about 1/16 th  of an inch. For the purposes of this invention, outer diameter  58  of slip ring  38  is about equal to inner diameter  60  of casing  14 . 
         [0027]    Slip rings  38  are comprised of a drillable material and may be, for example, cast iron or a molded phenolic. Slip rings  38  may be made from other drillable materials such as drillable metals, composites and engineering grade plastics. The remainder of slip assembly  36  and other components of the tool may likewise be made from drillable materials. 
         [0028]    Slip assemblies  36   a  and  36   b  are illustrated in  FIGS. 1 and 2  as being separated by packer element assembly  62 . As illustrated, packer element assembly  62  includes at least one expandable packer element  64 , which is positioned between slip wedges  40 . Packer shoes  66  may provide axial support to the ends of packer element assembly  62 . 
         [0029]    Referring to the example illustrated in  FIGS. 3-10 , slip bank  48  is a portion of a circle having slip bank  48  outer arcuate edge  68  measured between groove centerlines  70 . Outer arcuate edge  68  has angle  72  between first slip bank edge  74  and second slip bank edge  76  of 180° or less. As illustrated in  FIG. 5 , angle  72  is about 45°. 
         [0030]    Regarding  FIG. 6 , a section view of  FIG. 5  is illustrated and provides exemplary angles and measurements for a slip ring  38  designed for use in a 4.5 inch (about 11.43 centimeters) outer diameter casing. In this example, outer diameter  78  of slip ring  38  is about 3.5 inches (8.89 centimeters) and height  80  of about 1.95 inches (4.95 centimeters), Slip ring  38  also has first end  82  and second end  84 . First end  82  is adapted to receive slip wedge  40 . 
         [0031]    Slip ring  38  has true centerline  86  and offset centerline  88 . Offset centerline  88  is the centerline for slip ring  38  after slip banks  48  have been fractured by slip wedge  40 . As illustrated in  FIG. 7 , each slip bank  48  has outer arcuate edge  68  machined with radius  90 . Radius  90  is measured from offset centerline  88 , and for this example, radius  90  is about 2.02 inches. Radius  92  is the radius from the true centerline  86  to center  94  of cutting edge  56  on each slip bank  48  for the unfractured slip ring  38 . 
         [0032]    Regarding  FIG. 8 , an alternative embodiment of slip ring  38  illustrated in  FIG. 3  is depicted. In the alternative version of slip ring  38 , additional longitudinal channels  96  are defined on each cutting edge of each wicker  54 . Longitudinal channels  96  provide for additional non-continuous wicker segments. 
         [0033]    Another alternative embodiment of slip ring  38  is illustrated in  FIGS. 9 and 10 . In this alternative, slip ring  38  is designed for a 5.5 inch (13.97 centimeters) outer diameter casing. In this larger embodiment, an extra row of wickers is included to provide for additional holding power, Slip ring  38  illustrated in  FIGS. 9 and 10  is an example that may be used on a high-pressure well. One non-limiting example of a high-pressure well has a pressure between about 8,000 pounds per square inch (about 55 megapascals) and about 12,000 pounds per square inch (about 83 megapascals). However, wells have pressures greater and lower, and slip rings  38  are also designed for use in other wells. Thus, as previously stated, the number of wickers  54  on each slip bank  48  is determined by the size of casing  14  and the pressure slip ring  38  is designed to resist. 
         [0034]    In operation, downhole tool  18  is positioned at the desired depth or location by a setting tool, such as a wireline. The wireline exerts an initial or first force upon slip assembly  36 , causing slip wedge  40  and slip ring  38  to move relative to one another, which radially exerts an internal radial force upon slip ring  38 . Slip wedge  40  has inclined surface  42  defined thereon. Slip ring  38  radially expands outward as complementary second surface  44  slides against inclined first surface  42  of slip wedge  40 . The sliding effect of complementary second surface  44  against inclined first surface  42  causes slip ring  38  to force cutting edge  56  of wickers  54  defined on slip bank  38  against casing inner wall  16 . As the radial force is increased, cutting edge  56  of wickers  54  penetrate into casing inner wall  16 . This radial force is sufficient to penetrate the casing grade for the particular casing  14  utilized, thereby setting downhole tool  18 . 
         [0035]    Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.

Summary:
A slip for use in the anchoring of a downhole tool in a well casing is provided. The slip&#39;s outer diameter is about equal to the inner diameter of the well casing. The slip is positioned about a mandrel and radially expands upon the application of force. The wickers on the slip deformably engage the casing in response to a force.