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BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    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 the 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. 
         [0003]    2. Description of Related Art 
         [0004]    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. 
         [0005]    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. 
         [0006]    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 expand radially outward against the inside of the casing to anchor the packer, or bridge plug, so that the downhole tool will not move relative to the casing. Once set, additional force, in the form of increased hydraulic pressure, is commonly applied to further set the downhole tool. Unfortunately, the increased pressure commonly causes the downhole tool to slip up or down the casing. 
         [0007]    To prevent slipping of the downhole tool, cylindrically shaped inserts, or buttons, are secured to the slip segments to enhance the ability of the slip segments to engage the well casing. The buttons must be of sufficient hardness to be able to partially penetrate, or bite into the surface of the well casing, which is typically steel. Unfortunately, the buttons will occasionally disintegrate under increased force, or higher pressures, thereby allowing the downhole tool to slide within the well. 
         [0008]    Alternatively, the slip segments may have a plurality of wickers positioned about them to engage and secure the slip segments within the casing. The wickers must be sufficiently hard to engage and deformably cut into the well casing. Unfortunately, the amount of force required to cause the plurality of wickers to engage the well casing is significant, and often exceeds that of a setting tool. Thus, until sufficient force is exerted upon the wickers, the wickers may not fully engage the casing, thereby allowing the tool to slide significant distances within the well prior to engaging the casing. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with one embodiment of the invention there is provided a slip ring for anchoring a downhole tool in a wellbore casing having an inner wall, the slip ring comprising two or more slip segments, two or more grooves and a plurality of generally circumferentially extending wickers. The slip segments are integrally formed into the slip ring and each slip segment has an outer surface. The grooves are grooves longitudinally positioned between the slip segments. A first portion of the grooves define fracture channels such that the slip segments are frangiblely connected together. The slip segments will separate along the first portion of the grooves upon application of a predetermined primary radial force. The generally circumferentially extending wickers are located upon each the outer surfaces of the slip segments. Each wicker has a cutting edge. Each slip segment has a longitudinally extending centerline and each slip segment and each wicker is configured such that, upon expansion of the slip ring in the casing, a contact point on the cutting edge and at or near the centerline will meet the casing before any portion of the cutting edge at or near the groove. 
         [0010]    In accordance with another embodiment of the invention there is provide a method of anchoring a downhole tool in a wellbore casing comprising:
       introducing the downhole tool into the casing wherein the downhole tool has a mandrel, a slip ring positioned on the mandrel and a slip wedge positioned on the mandrel, wherein the slip ring comprises:
           two or more slip segments integrally formed into the slip ring to produce a central aperture adapted to receive the mandrel, the slip segments having an outer surface and;   two or more grooves longitudinally positioned between the slip segments, wherein a first portion of the grooves define fracture channels such that the slip segments are frangiblely connected together and the slip segments will separate along the first portion of the grooves upon application of a predetermined primary radial force; and   a plurality of generally circumferentially extending wickers upon the outer surface wherein each wicker has a cutting edge; and wherein each slip segment has a longitudinally extending centerline; and wherein each slip segment and each wicker is configured such that, upon expansion of the slip ring in the casing, a contact point on the cutting edge and at or near the centerline will meet the casing before any portion of the cutting edge at or near the groove;   
           positioning the downhole tool at a desired location;   applying a setting force to the downhole tool such that the slip wedge engages the slip ring so as to provide a radial force at least equal to the predetermined primary radial force to the slip ring and thus causing the contact point to penetrate the casing; and   increasing the radial force applied to the slip ring such that the majority of the cutting edge penetrates the casing.       
 
         [0018]    In accordance with yet another embodiment of the invention there is provided slip ring for anchoring a downhole tool in a wellbore casing having an inner wall, the slip ring comprising four or more slip segments, two or more primary grooves, two or more secondary grooves and a plurality of anchors. The slip segments are integrally formed into the slip ring and each slip segment has an outer surface. The primary grooves are longitudinally positioned between the slip segments. The primary grooves define fracture channels such that the slip segments are frangiblely connected and the slip segments will separate along the primary grooves into pairs upon application of a predetermined primary radial force. The secondary grooves are longitudinally positioned between the slip segments forming the pairs. The secondary grooves define fracture channels such that the pairs of slip segments are frangiblely connected and will separate upon application of a predetermined secondary radial force and wherein the predetermined secondary radial force is greater than the predetermined primary radial force. The anchors are located upon the outer surface. Each slip segment has a longitudinally extending centerline. Each slip segment and each wicker is configured such that, upon expansion of the slip ring by the predetermined primary radial force in the casing, the anchors near will meet the inner wall of the casing. 
         [0019]    In accordance with still another embodiment of the invention there is provide a method of anchoring a downhole tool in a wellbore casing comprising:
       introducing the downhole tool into the casing wherein the downhole tool has a mandrel, a slip ring positioned on the mandrel and a slip wedge positioned on the mandrel, wherein the slip ring comprises:
           four or more slip segments integrally formed into the slip, wherein each slip segment has an outer surface;   two or more primary grooves longitudinally positioned between the slip segments wherein the primary grooves define fracture channels such that the slip segments are frangiblely connected and the slip segments will separate along the primary grooves into pairs upon application of a predetermined primary radial force;   two or more secondary grooves longitudinally positioned between the slip segments forming the pairs wherein the secondary grooves define fracture channels such that the pairs of slip segments are frangiblely connected and will separate upon application of a predetermined secondary radial force wherein the predetermined secondary radial force is greater than the predetermined primary radial force; and   a plurality anchors upon the outer surface; and wherein each slip segment has a longitudinally extending centerline; and wherein each slip segment and each wicker is configured such that, upon expansion of the slip ring by the predetermined primary radial force in the casing, the anchors near will meet the inner wall of the casing;   
           positioning the downhole tool at a desired location; and   applying a setting force to the downhole tool such that the slip wedge engages the slip ring so as to provide a radial force at least equal to the predetermined primary radial force to the slip ring and thus causing the anchors to penetrate the casing.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a cross-section of a downhole tool disposed in a well with a slip assembly. 
           [0028]      FIG. 2  is a cross-section of an alternative downhole tool disposed in a well with a slip assembly. 
           [0029]      FIG. 3  is a bottom perspective view of a slip ring in accordance with one embodiment of the current invention. 
           [0030]      FIG. 4  is a top perspective view of the slip ring in accordance with the embodiment of  FIG. 4 . 
           [0031]      FIG. 5  is a top view of the slip ring of the embodiment of  FIGS. 3 and 4   
           [0032]      FIG. 6  is a cross-sectional view of the slip ring taken along section  6 - 6  of  FIG. 5 . 
           [0033]      FIG. 7  is an enlargement of a slip segment of the embodiment of  FIGS. 3-6 . The slip segment is shown having a wicker having a standard radius and is shown in contact with a casing. 
           [0034]      FIG. 8  is an enlargement of a slip segment of the embodiment of  FIGS. 3-6 . The slip segment is shown having a wicker having a peak and is shown in contact with a casing. 
           [0035]      FIG. 9  is a detailed view of a slip segment of the embodiments of  FIGS. 3-6 , illustrating the substandard radius. 
           [0036]      FIG. 10  is a bottom perspective view of a slip ring in accordance with another embodiment of the current invention. 
           [0037]      FIG. 11  is an enlargement of a slip segment of the embodiment of  FIG. 10 . The slip segment is shown having a wicker having a sub-standard radius and is shown in contact with a casing. 
           [0038]      FIG. 12  is a bottom perspective view of a slip ring in accordance with yet another embodiment of the current invention. 
           [0039]      FIG. 13  is a top view of the slip ring in accordance with the embodiment of  FIG. 12 . 
           [0040]      FIG. 14  is an enlargement of a slip segment of the embodiment of  FIGS. 12 and 13 . The slip segment is shown having a wicker having a casing radius and is shown in contact with a casing. 
           [0041]      FIG. 15  is an enlargement of a slip segment of the embodiment of  FIGS. 12 and 13 . The slip segment is shown having a wicker having a sub-standard radius and is shown in contact with a casing. 
           [0042]      FIG. 16  is a bottom perspective view of a slip ring in accordance with still another embodiment of the current invention. 
           [0043]      FIG. 17  is an enlargement of a slip segment of the embodiment of  FIG. 16 . The slip segment is shown having a wicker having a casing radius and is shown in contact with a casing. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    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 . 
         [0045]    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. 
         [0046]    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 typically identical, and only the orientation and position on downhole tool  18  are different. 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 as being pinned into place with pins  46 . 
         [0047]    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 . 
         [0048]    Slip ring  38 , shown in  FIGS. 3-6 , is an expandable slip ring  38  and has a plurality of slip segments  48 . Slip segments  48  are separated by a groove  50 , which is also a fracture channel  52 . Groove  50  and fracture channel  52  is longitudinally or axially positioned between slip segments  48  and provides a weakened point in slip ring  38  for slip segments  48  to break apart from each other when sufficient forces are radially exerted on the interior of slip ring  38 . Thus, the slip segments are frangiblely connected together and the slip segments will separate along grooves  50  when a predetermined radial force is applied. Without limiting the invention, slip ring  38  may include a plurality of slip segments  48 . Collectively, all slip segments  48  make up a circumferential slip ring  38 . Preferably, slip ring  38  has at least one circumferential pair of slip segments  48  with at least one fracture channel  52  positioned therebetween. As illustrated in  FIGS. 3-5 , slip ring  38  has eight slip segments  48 . Slip ring  38  also has first or top end  82  and second or bottom end  84 . First end  82  is adapted to receive slip wedge  40 . 
         [0049]    As illustrated in  FIGS. 3-6 , slip ring  38  is a one piece or unitary slip ring; that is, the slip ring is integrally formed from a single material without the need to bond individually formed segments together or hold individually formed segments together by the use of frangible retaining rings. Although slip ring  38  is illustrated as a fracturable unitary slip ring, it is within the scope of the invention to form slip ring  38  from separate slip segments  48 . In this configuration, all of slip segments  48  typically are secured by frangible retaining rings; however, they can be bonded together by a frangible material. 
         [0050]    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  34  and other components of the tool may likewise be made from drillable materials. 
         [0051]    Preferably, each slip segment  48  has defined at least one anchor on outer surface  120  thereof. As illustrated, the anchors are a plurality of wickers  54  defined on the outer surface  120  of each slip segment  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. 3-6  shows each slip segment  48  having five wickers defined thereon. As illustrated, wicker  54  generally circumferentially extends across outer surface  120 . 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. 
         [0052]    As can be seen best from  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 having an inner diameter  60  of about 4.04 inches (10.26 centimeters). In this example, outer diameter  58  of slip ring  38  is about 3.5 inches (8.89 centimeters) and height  80  of about 1.95 inches (4.95 centimeters). 
         [0053]    Wickers  54  are positioned on slip segment  48  such that a contact point  57  on each cutting edge  56  first contacts casing inner wall  16 . In other words, when a predetermined radial force separates the slip segments  48  and radially expands them, contact point  57  will meet the casing before any portion of said cutting edge  56  at or near the groove. Thereby, upon separation the contact point will initially exert all the force upon casing inner wall  16  for the wicker. Thus, the initial biting capability of slip segment  48  is improved and when pressure is applied to the plug it allows the wicker to bite deeper and subsequently for more area to penetrate and/or deformably cut into casing inner wall  16 . The initial penetration and/or deformation of casing inner wall  16  by cutting edge  56  is hereinafter called “bite”. It has been found that wicker penetration can be an issue for harder casings, such as P-110 grade and harder. More wicker area requires more force to start the bite into the casing. Accordingly, in one embodiment of the invention, wickers  54  are made to have a cutting edge with only a few contact points, which will meet the casing before the rest of the cutting edge, then the wicker area for the initial bite into the casing will be less and will require less force than for penetration of the entire cutting edge at once. This action securely anchors downhole tool  18  for harder casings grades. Casing grades are the industry standardized measures of casing-strength properties. Since most oilfield casing is of approximately the same chemistry (typically steel), and differs only in the heat treatment applied, the grading system provides for standardized strengths of casing to be manufactured and used in wellbores. 
         [0054]    In accordance with the above description, the initial bite area or contact point  57  of cutting edge  56  is less than a third of the circumferential length of cutting edge  56  across slip segment  48  and contacts the casing inner wall  16  before other portions of the wicker. Preferably, the initial bite area or contact point  57  is less than a forth of the circumferential length of cutting edge  56 . Generally, this bite area will be in the central one-third or central quarter section of cutting edge  56 . Preferably, the bite area will be a set of contact points, with one or two such contact points being more preferable. As can be seen in  FIGS. 7 ,  8  and  11 , contact point  57  can be a single contact point or a double contact point located at or near the longitudinal or axial centerline  49  of slip segment  48 , which contacts the casing inner wall  16  before portions of the cutting edge  56  at or near the groove.\. By “at or near the centerline” it is meant within about one-fourth of cutting edge length to either side of centerline  49 , and more preferably within one-sixth of the cutting edge length to either side of centerline  49  and more preferably within in one-eighth of the cutting edge length to either side of the centerline  49 . Where there is a single contact point  57  on cutting edge  56 , it is more preferable that contact point  57  be located at or adjacent to centerline  49 . By “at or near the groove” it is generally meant that portion of the cutting edge  56  which is not at or near the centerline and preferably includes at least that portion of the cutting edge  56  which is within about one-fourth the cutting edge length from the groove  50  and fracture channel  52 . 
         [0055]    Turning now to  FIGS. 5 ,  7  and  9 , a contact point  57  is provided for on cutting edge  56  by adjusting the curvature of cutting edge  56 . As can best be seen in  FIG. 9 , inner wall  16  of casing  14  has a circular curvature with a radius  90 . As can best be seen from  FIGS. 5 and 9 , prior to separation of slip segment  48 , outer surface  120  of slip ring  38  has an overall circular shape such that it forms a generally circular curvature with a radius  92 . Thus, slip segments  48  make up a generally circular slip ring  38  with each slip segment making up a portion of the circle represented by angle  72  between first slip segment edge  74  and second slip segment edge  76 . Generally, there will be at least two slip segments  48  and thus angle  72  will be 180° or less. As illustrated in  FIG. 5 , angle  72  is about 45°. 
         [0056]    In order to provide for contact point  57 , cutting edge  56  has an arcuate or circular curvature which differs from the overall circular shape of the slip ring. Generally cutting edge  54  can have an arcuate or circular curvature having a radius  93  less than the radius  90  of inner wall  16 . Generally, radius  93  can be less than or equal to radius  92  of the overall circular shape of the slip ring and preferably is less than radius  92  of the slip ring. Typically, the radius  93  can be at least 3% shorter than radius  90  of inner wall  16  and generally will be no more than 10% shorter than radius  90  of inner wall  16 , can be at least 5% shorter than radius  90  and can be no more than 8% shorter than radius  90 . Thus, upon separation, cutting edge  56  will meet inner wall  16  at a contact point  57 . As illustrated in  FIG. 8 , cutting edge  56  can be defined by two intersecting arcs having differing center points such that a generally pointed cutting edge is formed having a peak  59 , which is also contact point  57 . 
         [0057]    As will be understood, each wicker  54  will generally have a cutting edge  56  having a contact point  57 . Thus, in the case of the embodiment illustrated in  FIG. 3-7 , there will be five wickers on each slip segment  48  with each wicker having a cutting edge  56  with a contact point  57 . Accordingly, there will be five contact points per slip segment. The contact points across the wickers on a slip segment can be aligned to be in the same position relative to centerline  49  or can be staggered so as to vary in distance from centerline  49 . As will be appreciated, the reduction of the bite service area from substantially the entire area of the five cutting edges to five contact points substantially reduces the force need to bite into the casing. 
         [0058]    Turning now to  FIGS. 10 and 11 , 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 . Generally, longitudinal channels  96  will not be fracture channels; that is, they will not be designed to fracture under the force and pressures exerted on the slip ring while in use downhole. Each longitudinal channel  96  is defined by a pair of edges, first edge  97  and second edge  98 . Longitudinal channel  96  run along the centerline  49  of slip segment  48  and divides wicker  54 . Longitudinal channel  96  provide for additional non-continuous wicker segments and, thus creates two contact points  57  on cutting edge  56 . One located at first edge  97  and one located at second edge  98 . 
         [0059]    Another embodiment of the invention is illustrated in  FIGS. 12-14 . A first portion of grooves  50  are primary fracture channels  100 . A second portion of grooves  50  are secondary fracture channels  102 . Primary fracture channels  100  fracture upon application of a predetermined primary radial force. Secondary fracture channels fracture upon application of a predetermined secondary radial force, which is greater than the predetermined primary radial force. Fracture channels  100  and  102  are configured so that upon application of the predetermined primary radial force the slip segments  48  split into segment pairs  104 , as can be best seen in  FIG. 14 . Thus, it can be determined which sections will be in pairs. 
         [0060]    In one embodiment illustrated in  FIG. 14 , the pairs of segments are configured such that the radius of cutting edge cutting edge  56  for each wicker on a pair is able to be evenly set against casing inner wall  16 . Thus, each cutting edge is nearly equal in the force exerted upon the casing inner wall  16 . This can be achieved by having each cutting edge lay along a circle having a radius equal to the radius of casing inner wall  16 . Generally, this embodiment will be useful in casings with hardness of less than P-100 grade. 
         [0061]    In the embodiment illustrated in  FIG. 15 , each cutting edge is designed with contact points  57  as described above. Thus, each pair initially bite into the casing at contact points  57  such that each pair initially bites into the casing at or near the centerline instead of at the portion of the cutting edge  56  at or near the groove. Generally, this embodiment will be useful in casings with hardness of P-100 grade or higher. 
         [0062]    In the embodiment illustrated in  FIGS. 16 and 17 , the slip rings use a plurality of inserts or buttons  110  as anchors instead of wickers. Buttons  110  are secured to outer surface  120  of slip ring  38  by adhesive, or by other means known to those skilled in the art. Buttons  110  extend radially outward from outer surface  54 , and are positioned to engage casing  14 , or in particular, an inner wall  16  of casing  14 , in response to the predetermined primary radial force. There is at least one button  110  secured to and carried by each slip segment  48  of slip ring  38 . Generally, there will be multiple circumferential pairs of buttons carried by each slip segment  48 , as illustrated. The circumferential pairs of button comprise inner button  112  and outer button  114 . 
         [0063]    Buttons  110  are comprised of a material having sufficient hardness to penetrate or bite into casing  14 . Each button  110  has button edge  116  defining the point of engagement for button  58  with casing  14 . Segment pairs  104  are configured such that the buttons  110  initially bite into casing  14  at the portion  122  of button edge  116  closest to centerline  49  or segment pair center  118 , instead of along the portion  124  of button edge  116  closest to secondary fracture channel  102  or primary fracture channel  100 . 
         [0064]    Preferably, buttons  110  are made from a material selected from the group consisting of tungsten carbide, ceramic, metallic-ceramic, zirconia-ceramic titanium, molybdenum, nickel and combinations thereof. Additionally, buttons  110  may be, for example, similar in material and form as those described in U.S. Pat. No. 5,984,007, which is incorporated by reference herein. Buttons  110  may be made from any material that can pierce the casing or is harder than the casing grade utilized for casing  14 . 
         [0065]    In operation, downhole tool  18  is introduced into the wellbore and casing  14 . Downhole tool  18  is then positioned at the desired depth or location by a setting tool, such as a wireline. The wireline exerts an initial or setting force upon slip assembly  36 , causing slip wedge  40  and slip ring  38  to move relative to one another, which exerts a 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 segment  48  against casing inner wall  16 . As the radial force is increased, contact point  57  of cutting edge  56  of wickers  54  bite into casing inner wall  16 . As the force continues or increases, the remaining part of wickers  54  penetrate into casing inner wall  16 , thus setting downhole tool  18 . Additionally, where segment pairs  104  have been used, the setting force is sufficient to result in the radial force exerted on slip ring  38  being at least equal to the predetermined primary radial force but generally less than the predetermined secondary radial force. After the contact points  57  have bit into the casing, wickers  54  can be fully set into the casing under operation of a radial force less than the predetermined secondary radial force or the radial force can be increased to or above the predetermined secondary force. Thus, fraturing the secondary fracture channels during setting of the remaining portion of wickers  54 . 
         [0066]    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:
This invention particularly relates to improving the engagement of the slip elements within a casing or tubing. Particularly, the invention is directed to improving the penetration of anchors on slip elements to better set downhole tools. Generally, in one aspect, the invention relies on decreasing the contact surface of the cutting edge of the anchor during the initial penetration of the anchor into the casing.