Patent Publication Number: US-6708770-B2

Title: Drillable bridge plug

Description:
1. CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/844,512, filed Apr. 27, 2001, entitled “Drillable Bridge Plug,” which is a continuation-in-part U.S. patent application Ser. No. 09/608,052, filed Jun. 30, 2000 is now U.S. Pat. No. 6,491,108, entitled “Drillable Bridge Plug,” both of which are incorporated herein in their entireties by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     2. Field of the Invention 
     This invention relates generally to methods and apparatus for drilling and completing subterranean wells and, more particularly, to methods and apparatus for a drillable bridge plug, frac plug, cement retainer, and other related downhole apparatus, including apparatus for running these downhole apparatus. 
     3. Description of Related Art 
     There are many applications in well drilling, servicing, and completion in which it becomes necessary to isolate particular zones within the well. In some applications, such as cased-hole situations, conventional bridge plugs such as the Baker Hughes model T, N1, NC1, P1, or S wireline-set bridge plugs are inserted into the well to isolate zones. The bridge plugs may be temporary or permanent; the purpose of the plugs is simply to isolate some portion of the well from another portion of the well. In some instances perforations in the well in one portion need to be isolated from perforations in another portion of the well. In other situations there may be a need to use a bridge plug to isolate the bottom of the well from the wellhead. There are also situations where these plugs are not used necessarily for isolation but instead are used to create a cement plug in the wellbore which may be used for permanent abandonment. In other applications a bridge plug with cement on top of it may be used as a kickoff plug for side-tracking the well. 
     Bridge plugs may be drillable or retrievable. Drillable bridge plugs are typically constructed of a brittle metal such as cast iron that can be drilled out. One typical problem with conventional drillable bridge plugs is that without some sort of locking mechanism, the bridge plug components tend to rotate with the drill bit, which may result in extremely long drill-out times, excessive casing wear, or both. Long drill-out times are highly undesirable as rig time is typically charged for by the hour. 
     Another typical problem with conventional drillable plugs is that the conventional metallic construction materials, even though brittle, are not easy to drill through. The plugs are generally required to be quite robust to achieve an isolating seal, but the materials of construction may then be difficult to drill out in a reasonable time. These typical metallic plugs thus require that significant weight be applied to the drill-bit in order to drill the plug out. It would be desirable to create a plug that did not require significant forces to be applied to the drill-bit such that the drilling operation could be accomplished with a coiled tubing motor and bit; however, conventional metallic plugs do not enable this. 
     In addition, when several plugs are used in succession to isolate a plurality of zones within the wellbore, there may be significant pressures on the plug from either side. It would be desirable to design an easily drilled bridge plug that is capable of holding high differential pressures on both sides of the plug. Also, with the potential for use of multiple plugs in the same wellbore, it would be desirable to create a rotational lock between plugs. A rotational lock between plugs would facilitate less time-consuming drill outs. 
     Additionally, it would be desirable to design an easily drillable frac plug that has a valve to allow fluid communication through the mandrel. It would be desirable for the valve to allow fluid to flow in one direction (e.g. out of the reservoir) while preventing fluid from flowing in the other direction (into the reservoir). It is also desired to design an easily drillable cement retainer that includes a mandrel with vents for circulating cement slurry through the tool. 
     Finally, it is desired to provide a wire line adapter kit that will facilitate the running of the drillable downhole tool, but still be releasable from the tool. Once released, the wire line adapter kit should be retrievable thus allowing the downhole tool to be drilled. Preferably, the wire line adapter kit should leave little, if any, metal components downhole, thus reducing time milling and/or drilling time to remove plugs. 
     The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above. 
     SUMMARY OF THE INVENTION 
     In one embodiment a subterranean apparatus is disclosed. The apparatus may include a mandrel having an outer surface and a non-circular cross-section and a packing element arranged about the mandrel, the packing element having a non-circular inner surface such that rotation between the mandrel and the packing element is precluded. The mandrel may include non-metallic materials, for example carbon fiber. 
     In one embodiment, the apparatus exhibits a non-circular cross-section that is hexagonally shaped. The interference between the non-circular outer surface of the mandrel and the inner surface of the packing element comprise a rotational lock. 
     In one embodiment the apparatus includes an anchoring assembly arranged about the mandrel, the anchoring assembly having a non-circular inner surface such that rotation between the mandrel and the anchoring assembly is precluded. The anchoring assembly may further include a first plurality of slips arranged about the non-circular mandrel outer surface, the slips being configured in a non-circular loop such that rotation between the mandrel and the slips is precluded by interference between the loop and the mandrel outer surface shape. The first plurality of slips may include non-metallic materials. The first plurality of slips may each include a metallic insert mechanically attached to and/or integrally formed into each of the plurality of slips wherein the metallic insert is engagable with a wellbore wall. The anchoring assembly may also include a first cone arranged about the mandrel, the first cone having a non-circular inner surface such that rotation between the mandrel and the first cone is precluded by interference between the first cone inner surface shape and the mandrel outer surface shape. The first plurality of slips abuts the first cone, facilitating radial outward movement of the slips into engagement with a wellbore wall upon traversal of the plurality of slips along the first cone. In this embodiment, the first cone may include non-metallic materials. At least one shearing device may be disposed between the first cone and the mandrel, the sharing device being adapted to shear upon the application of a predetermined force. 
     The anchoring assembly of the apparatus may further include a second plurality of slips arranged about the non-circular outer surface of the mandrel, the second plurality of slips, the slips being configured in a non-circular loop such that rotation between the mandrel and the slips is precluded by interference between the loop and the mandrel outer surface shape. The second plurality of slips may include non-metallic materials. The second plurality of slips may each include a metallic insert mechanically attached to and/or integrally formed therein with the metallic inserts being engagable with the wellbore wall. The anchoring assembly may also include a second collapsible cone arranged about the non-circular outer surface of the mandrel, the second collapsible cone having a non-circular inner surface such that rotation between the mandrel and the second cone is precluded by interference between the second cone inner surface shape and the mandrel outer surface shape, wherein the second plurality of slips abuts the second collapsible cone, facilitating radial outward movement of the slips into engagement with the wellbore wall upon traversal of the plurality of slips along the second collapsible cone. The second collapsible cone may include non-metallic materials. The second collapsible cone may be adapted to collapse upon the application of a predetermined force. The second collapsible cone may include at least one metallic insert mechanically attached to and/or integrally formed therein, the at least one metallic insert facilitating a locking engagement between the cone and the mandrel. The anchoring assembly may include at least one shearing device disposed between the second collapsible cone and the mandrel, the at least one shearing device being adapted to shear upon the application of a predetermined force. 
     In one embodiment the packing element is disposed between the first cone and the second collapsible cone. In one embodiment a first cap is attached to a first end of the mandrel. The first cap may include non-metallic materials. The first cap may be attached to the mandrel by a plurality of non-metallic pins. 
     In one embodiment the first cap may abut a first plurality of slips. In one embodiment the packing element includes a first end element, a second end element, and a elastomer disposed therebetween. The elastomer may be adapted to form a seal about the non-circular outer surface of the mandrel by expanding radially to seal with the wall of the wellbore upon compressive pressure applied by the first and second end elements. 
     In one embodiment the apparatus may include a second cap attached to a second end of the mandrel. The second cap may include non-metallic materials. The second cap may be attached to the mandrel by a plurality of non-metallic pins. In this embodiment, the second cap may abut a second plurality of slips. In one embodiment the first end cap is adapted to rotationally lock with a second mandrel of a second identical apparatus such as a bridge plug. 
     In one embodiment the apparatus includes a hole in the mandrel extending at least partially therethrough. In another embodiment the hole extends all the way through the mandrel. In the embodiment with the hole extending all the way therethrough, the mandrel may include a valve arranged in the hole facilitating the flow of cement or other fluids, gases, or slurries through the mandrel, thereby enabling the invention to become a cement retainer. 
     In one embodiment there is disclosed a subterranean apparatus including a mandrel having an outer surface and a non-circular cross-section, and an anchoring assembly arranged is about the mandrel, the anchoring assembly having a non-circular inner surface such that rotation between the mandrel and the anchoring assembly is precluded as the outer surface of the mandrel and inner surface of the packing element interfere with one another in rotation. 
     In one embodiment there is disclosed a subterranean apparatus including a mandrel; a first cone arranged about an outer diameter of the mandrel; a first plurality of slips arranged about first cone; a second cone spaced from the first cone and arranged about the outer diameter of the mandrel; a second plurality of slips arranged about the first cone; a metallic insert disposed in an inner surface of the second cone and adjacent to the mandrel; a packing element disposed between the first and second cones; with the first and second pluralities of slips being lockingly engagable with the wall of a wellbore and the metallic insert being lockingly engagable with the mandrel. In this embodiment the second cone may be collapsible onto the mandrel upon the application of a predetermined force. The mandrel, cones, and slips may include non-metallic materials. In addition, a cross-section of the mandrel is non-circular and the inner surfaces of the cones, slips, and packing element are non-circular and may or may not match the outer surface of the mandrel. 
     In one embodiment there is disclosed a slip assembly for use on subterranean apparatus including: a first cone with at least one channel therein; a first plurality of slips, each having an attached metallic insert, the first slips being arranged about the first cone in the at least one channel of the first cone; a second collapsible cone having an interior surface and an attached metallic insert disposed in the interior surface; a second plurality of non-metallic slips, each having an attached metallic insert, the second slips being arranged about the second cone; with the second non-metallic collapsible cone being adapted to collapse upon the application of a predetermined force. In this embodiment the first and second pluralities of slips are adapted to traverse first and second cones until the slips lockingly engage with a wellbore wall. The insert of the second non-metallic cone is adapted to lockingly engage with a mandrel upon the collapse of the cone. Each of first and second cones and first and second pluralities of slips may include non-metallic materials. 
     There is also disclosed a method of plugging or setting a packer in a well. The method may include the steps of: running an apparatus into a well, the apparatus comprising a mandrel with a non-circular outer surface and a packing element arranged about the mandrel; setting the packing element by the application force delivered from conventional setting tools and means including, but not limited to: wireline pressure setting tools, mechanical setting tools, and hydraulic setting tools; locking the apparatus in place within the well; and locking an anchoring assembly to the mandrel. According to this method the apparatus may include a first cone arranged about the outer surface of the mandrel; a first plurality of slips arranged about the first cone; a second cone spaced from the first cone and arranged about the outer diameter of the mandrel; a second plurality of slips arranged about the second cone; a metallic insert disposed in an inner surface of the second cone and adjacent to the mandrel; with the first and second pluralities of slips being lockingly engagable with the wall of a wellbore and the metallic insert being lockingly engagable with the mandrel. The first and second cones may include a plurality of channels receptive of the first and second pluralities of slips. Also according to this method, the step of running the apparatus into the well may include running the apparatus such as a plug on wireline. The step of running the apparatus into the well may also include running the apparatus on a mechanical or hydraulic setting tool. The step of locking the apparatus within the well may further include the first and second pluralities of slips traversing the first and second cones and engaging with a wall of the well. The step of locking the anchoring assembly to the mandrel may further include collapsing the second cone and engaging the second cone metallic insert with the mandrel. 
     There is also disclosed a method of drilling out a subterranean apparatus such as a plug including the steps of: running a drill into a wellbore; and drilling the apparatus; where the apparatus is substantially non-metallic and includes a mandrel having a non-circular outer surface; and a packing element arranged about the mandrel, the packing element having a non-circular inner surface matching the mandrel outer surface. According to this method, the step of running the drill into the wellbore may be accomplished by using coiled tubing. Also, drilling may be accomplished by a coiled tubing motor and bit. 
     In one embodiment there is disclosed an adapter kit for a running a subterranean apparatus including: a bushing adapted to connect to a running tool; a setting sleeve attached to the bushing, the setting sleeve extending to the subterranean apparatus; a setting mandrel interior to the setting sleeve; a support sleeve attached to the setting mandrel and disposed between the setting mandrel and the setting sleeve; and a collet having first and second ends, the first end of the collet being attached to the setting mandrel and the second end of the collet being releasably attached to the subterranean apparatus. According to this adapter kit the subterranean apparatus may include an apparatus having a packing element and an anchoring assembly. The subterranean apparatus may include a plug, cement retainer, or packer. The anchoring assembly may be set by the transmission of force from the setting sleeve to the anchoring assembly. In addition, the packing element may be set by the transmission of force from the setting sleeve, through the anchoring assembly, and to the packing element. According to this embodiment the collet is locked into engagement with the subterranean apparatus by the support sleeve in a first position. The support sleeve first position may be facilitated by a shearing device such as shear pins or shear rings. The support sleeve may be movable into a second position upon the application of a predetermined force to shear the shear pin. According to this embodiment, the collet may be unlocked from engagement with the subterranean apparatus by moving the support sleeve to the second position. 
     In one embodiment there is disclosed a bridge plug for use in a subterranean well including: a mandrel having first and second ends; a packing element; an anchoring assembly; a first end cap attached to the first end of the mandrel; a second end cap attached to the second end of the mandrel; where the first end cap is adapted to rotationally lock with the second end of the mandrel of another bridge plug. According to this embodiment, each of mandrel, packing element, anchoring assembly, and end caps may be constructed of substantially non-metallic materials. 
     In some embodiments, the first and/or the second plurality of slips of the subterranean apparatus include cavities that facilitate the drilling out operation. In some embodiments, these slips are comprised of cast iron. In some embodiments, the mandrel may be comprised of a metallic insert wound with carbon fiber tape. 
     Also disclosed is a subterranean apparatus comprising a mandrel having an outer surface and a non-circular cross section, an anchoring assembly arranged about the mandrel, the anchoring assembly having a non-circular inner surface, and a packing element arranged bout the mandrel. 
     In some embodiments, an easily drillable frac plug is disclosed having a hollow mandrel with an outer surface and a non-circular cross-section, and a packing element arranged about the mandrel, the packing element having a non-circular inner surface such that rotation between the mandrel and the packing element is precluded, the mandrel having a valve for controlling flow of fluids therethrough. In some embodiments, the mandrel may be comprised of a metallic insert wound with carbon fiber tape. In some embodiments, a method of drilling out a frac plug is described. 
     A wire line adapter kit for running subterranean apparatus is also described as having a adapter bushing to connect to a setting tool, a setting sleeve attached to the adapter bushing, a crossover, a shear ring, a rod, and a collet releasably attached to the subterranean apparatus. In other aspects, the wire line adapter kit comprises a adapter bushing, a crossover, a body having a flange, a retainer, and a shear sleeve connected to the flange, the shear sleeve having tips. 
     In some embodiments, a composite cement retainer ring is described having a hollow mandrel with vents, a packing element, a plug, and a collet. 
     In some embodiments, a subterranean apparatus is disclosed comprising a mandrel having an outer surface and a non-circular cross-section, such as a hexagon; an anchoring assembly arranged about the mandrel, the anchoring assembly having a non-circular inner surface such that rotation between the mandrel and the anchoring assembly is precluded; and a packing element arranged about the mandrel, the packing element having a non-circular inner surface such that rotation between the mandrel and the packing element is precluded. The outer surface of the mandrel and the inner surface of the packing element exhibit matching shapes. Further, the mandrel may be comprised of non-metallic materials, such as reinforced plastics, or metallic materials, such as brass, or may be circumscribed with thermoplastic tape or reinforced with carbon fiber. In some embodiments, the non-circular inner surface of the packing element matches the mandrel outer surface. 
     In some embodiments, the anchoring assembly comprises a first plurality of slips arranged about the non-circular mandrel outer surface, the slips being configured in a non-circular loop such that rotation between the mandrel and the first plurality of slips is precluded by interference between the loop and the mandrel outer surface shape. The anchoring assembly may comprise a slip ring surrounding the first plurality of slips to detachably hold the first plurality of slips about the mandrel. The slips may be comprised of cast iron, and may contain a cavity and may contain a wickered edge. 
     Also described is are first and second cones arranged about the mandrel, the first cone comprising a non-circular inner surface such that rotation between the mandrel and the first and second cones is precluded by interference between the first or second cone inner surface shape and the mandrel outer surface shape. The cones may have a plurality of channels to prevent rotation between the cones and the slips. The cones may be comprised of non-metallic materials. The anchoring devices may comprise a shearing device, such as a pin. Also described is a second plurality of slips, which may be similar to the first plurality of slips described above. A packing element may be disposed between the first cone and the second cone. The apparatus may have a first and second end cap attached to either end of the mandrel in various ways. Additional components, such as a booster ring, a lip, an O-ring, and push rings are also described in some embodiments. 
     In other aspects, a subterranean apparatus is described as a frac plug having a hollow mandrel with a non-circular cross-section; and a packing element arranged about the mandrel, the packing element having a non-circular inner surface such that rotation between the mandrel and the packing element is precluded, the mandrel having a valve for controlling flow of fluids therethrough. The mandrel may have a first internal diameter, a second internal diameter being smaller than the first internal diameter, and a connecting section connecting the first internal diameter and the second internal diameter. The apparatus may have a ball, the connecting section defining a ball seat, the ball adapted to rest in the ball seat thus defining a ball valve to allow fluids to flow in only one direction through the mandrel, the ball valve preventing fluids from flowing in an opposite direction. In some embodiments, the mandrel is comprised of a metallic core wound with carbon fiber tape. The mandrel may have grooves on an end to facilitate the running of the apparatus. Further, the mandrel and the inner surface of the packing element may exhibit matching shapes to precluded rotation between the mandrel and the packing element as the outer surface of the mandrel and the inner surface of the packing element interfere with one another in rotation. The mandrel is described as being metallic or non-metallic. 
     In some aspects, a method of controlling flow of fluids in a portion of a well is described using the frac plug as well as a method of milling and/or drilling out a subterranean apparatus. 
     Also disclosed are wire line adapter kits for running a subterranean apparatus. One embodiment includes a adapter bushing, a setting sleeve, a crossover, a shear ring, a collet, and a rod. One embodiment includes a adapter bushing, a setting sleeve, a body, a retainer, and a shear sleeve. 
     A cement retainer is also described having a non-circular, hollow mandrel with radial vents for allowing fluid communication from an inner surface of the mandrel to an outer surface of the apparatus, a packing element, a plug, and a collet. 
     A subterranean apparatus is described having a mandrel, a packing element, an anchoring assembly, a first end cap attached to the first end of the mandrel, and a second end cap attached to the second end of the mandrel, wherein the first end cap is adapted to rotationally lock with a top end of another mandrel. Various components of all embodiments are described as comprised of metallic or non-metallic components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features and aspects of the invention will become further apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a simplified view of a subterranean apparatus and adapter kit assembly positioned in a wellbore according to one embodiment of the present invention. 
     FIG. 2 is a top cross-sectional view of the subterranean apparatus through the upper slip and cone, according to FIG.  1 . 
     FIG. 3 is a top view of a slip ring according to one embodiment of the disclosed method and apparatus. 
     FIG. 4 is a side view of a cone assembly according to one embodiment of the disclosed method and apparatus. 
     FIG. 5 is a simplified view of the subterranean apparatus and adapter kit according to FIG. 1, shown in a second position. 
     FIG. 6 is a simplified view of the subterranean apparatus and adapter kit according to FIG. 1, shown in a third position. 
     FIG. 7 is a simplified view of the subterranean apparatus and adapter kit according to FIG. 1, shown in a fourth position. 
     FIG. 8 is a simplified view of the subterranean apparatus and adapter kit according to FIG. 1, shown in a fifth position. 
     FIG. 9 is a simplified view of the subterranean apparatus and adapter kit according to FIG. 1, shown in a sixth position. 
     FIG. 10 is a simplified view of the subterranean apparatus and adapter kit according to FIG. 1, shown in a seventh position. 
     FIG. 11 is a simplified view of a subterranean apparatus and adapter kit assembly positioned in a wellbore according to one embodiment of the present invention. 
     FIG. 12 is a simplified view of the subterranean apparatus assembly and adapter kit according to FIG. 11, shown in a second position. 
     FIG. 13 is a simplified view of the subterranean apparatus assembly and adapter kit according to FIG. 11, shown in a third position. 
     FIG. 13A is a cross-sectional view of the subterranean apparatus assembly according to FIG. 13 taken along line A—A. 
     FIG. 14 is a top cross-sectional view of the subterranean apparatus through the mandrel and packing element, an alternative embodiment of the present invention. 
     FIG. 15 is a top cross-sectional view of the subterranean apparatus through the mandrel and packing element, according to an alternative embodiment of the present invention. 
     FIG. 16 is a top cross-sectional view of the subterranean apparatus through the mandrel and packing element, according to another alternative embodiment of the present invention. 
     FIG. 17 is a top cross-sectional view of the subterranean apparatus through the mandrel and packing element, according to another alternative embodiment of the present invention. 
     FIG. 18 is a sectional view of the subterranean apparatus according to another alternative embodiment of the present invention. 
     FIG. 19 is a sectional view of the subterranean apparatus according to another alternative embodiment of the present invention. 
     FIG. 20 is a sectional view of the subterranean apparatus according to another alternative embodiment of the present invention. 
     FIGS. 21A-21D show sectional views of the slips of one embodiment of the present invention. 
     FIG. 21A shows a side view of a slip of one embodiment of the present invention. 
     FIG. 21B shows a cross-section of a slip having a cavity of on e embodiment of the present invention. 
     FIG. 21C shows a bottom view of a slip of one embodiment of the present invention. 
     FIG. 21D shows a top view of a slip of one embodiment of the present invention. 
     FIG. 22 shows a simplified view of a subterranean apparatus according to one embodiment of the present invention. 
     FIG. 23 is a simplified view of a subterranean apparatus and adapter kit assembly according to one embodiment of the present invention. 
     FIG. 24 shows a simplified view of a subterranean apparatus and adapter kit assembly according to one embodiment of the present invention. 
     FIG. 25 is a simplified view of a subterranean apparatus and adapter kit assembly according to one embodiment of the present invention. 
     FIG. 26 shows simplified view of a subterranean apparatus and adapter kit assembly according to one embodiment of the present invention. 
     FIG. 27 is a simplified view of a subterranean apparatus and adapter kit assembly according to one embodiment of the present invention. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, that will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     Turning now to the drawings, and in particular to FIGS. 1 and 13, a subterranean plug assembly  2  in accordance with one embodiment of the disclosed method and apparatus is shown. Plug assembly  2  is shown in the running position in FIGS. 1 and 13. Plug assembly  2  is shown as a bridge plug, but it may be modified as described below to become a cement retainer or other plug. Plug assembly  2  includes a mandrel  4  constructed of non-metallic materials. The non-metallic materials may be a composite, for example a carbon fiber reinforced material or other material that has high strength yet is easily drillable. Carbon fiber materials for construction of mandrel  4  may be obtained from ADC Corporation and others, for example XC-2 carbon fiber available from EGC Corporation. Mandrel  4  has a non-circular cross-section as shown in FIG.  2 . The cross-section of the embodiment shown in FIGS. 1-13 is hexagonal; however, it will be understood by one of skill in the art with the benefit of this disclosure that any non-circular shape may be used. Other non-circular shapes include, but are not limited to, an ellipse, a triangle, a spline, a square, or an octagon. Any polygonal, elliptical, spline, or other non-circular shape is contemplated by the present invention. FIGS. 14-17 disclose some of the exemplary shapes of the cross-section of mandrel  4  and the outer components. FIG. 14 discloses a hexagonal mandrel  4 , FIG. 15 discloses an elliptical mandrel  4 , FIG. 16 discloses a splined mandrel  4 , and FIG. 17 discloses a semi-circle and flat mandrel. In one embodiment mandrel  4  may include a hole  6  partially therethrough. Hole  6  facilitates the equalization of well pressures across the plug at the earliest possible time if and when plug assembly  2  is drilled out. One of skill in the art with the benefit of this disclosure will recognize that it is desirable in drilling operations to equalize the pressure across the plug as early in the drilling process as possible. 
     Mandrel  4  is the general support for each of the other components of plug assembly  2 . The non-circular cross-section exhibited by mandrel  4  advantageously facilitates a rotational lock between the mandrel and all of the other components (discussed below). That is, if and when it becomes necessary to drill out plug assembly  2 , mandrel  4  is precluded from rotating with the drill, the non-circular cross-section of mandrel  4  prevents rotation of the mandrel with respect to the other components which have surfaces interfering with the cross-section of the mandrel. 
     Attached to a first end  8  of mandrel  4  is a first end cap  10 . First end cap  10  is a non-metallic composite that is easily drillable, for example an injection molded phenolic or other similar material. First end cap  10  may be attached to mandrel  4  by a plurality of non-metallic composite pins  12 , and/or attached via an adhesive. Composite pins  12  are arranged in different planes to distribute any shear forces transmitted thereto. First end cap  10  prevents any of the other plug components (discussed below) from sliding off first end  8  of mandrel  4 . First end cap  10  may include a locking mechanism, for example tapered surface  14 , that rotationally locks plug assembly  2  with another abutting plug assembly (not shown) without the need for a third component such as a key. This rotational lock facilitates the drilling out of more than one plug assembly when a series of plugs has been set in a wellbore. For example, if two plug assemblies  2  are disposed in a wellbore at some distance apart, as the proximal plug is drilled out, any remaining portion of the plug will fall onto the distal plug, and first end cap  10  will rotationally lock with the second plug to facilitate drilling out the remainder of the first plug before reaching the second plug. In the embodiment shown in the figures, first end cap  10  exhibits an internal surface matching the non-circular cross-section of mandrel  4  which creates a rotational lock between the end cap and mandrel; however, the internal surface of the first end cap  10  may be any non-circular surface that precludes rotation between the end cap and mandrel  4 . For example, the internal surface of first end cap  10  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still advantageously precluded without the need for a third component such as a key. 
     First end cap  10  abuts an anchoring assembly  16 . Anchoring assembly  16  includes a first plurality of slips  18  arranged about the outer diameter of mandrel  4 . Slips  18  are arranged in a ring shown in FIG. 3 with the slips being attached to one another by slip ring  20 . In the embodiment shown in FIG. 3, there are six slips  18  arranged in a hexagonal configuration to match the cross-section of mandrel  4 . It will be understood by one of skill in the art with the benefit of this disclosure that slips  18  may be arranged in any configuration matching the cross-section of mandrel  4 , which advantageously creates a rotational lock such that slips  18  are precluded from rotating with respect to mandrel  4 . In addition, the number of slips may be varied and the shape of slip ring may be such that rotation would be allowed between the slips and the mandrel—but for the channels  99  (discussed below). Further, the configuration of slip ring  20  may be any non-circular shape that precludes rotation between slips  18  and mandrel  4 . For example, the slip ring  20  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. Each of slips  18  is constructed of non-metallic composite materials such as injection molded phenolic, but each slip also includes a metallic insert  22  disposed in outer surface  23 . Metallic inserts  22  may each have a wicker design as shown in the figures to facilitate a locked engagement with a casing wall  24 . Metallic inserts  22  may be molded into slips  18  such that slips  18  and inserts  22  comprise a single piece as shown in FIG. 1; however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  22  may also be mechanically attached to slips  18  by a fastener, for example screws  23 . Metallic inserts  22  are constructed of low density metallic materials such as cast iron, which may heat treated to facilitate surface hardening such that inserts  22  can penetrate casing  24 , while maintaining small, brittle portions such that they do not hinder drilling operations. Metallic inserts  22  may be integrally formed with slips  18 , for example, by injection molding the composite material that comprises slips  18  around metallic insert  22 . 
     Anchoring assembly  16  also includes a first cone  26  arranged adjacent to the first plurality of slips  18 . A portion of slips  18  rest on first cone  26  as shown in the running position shown in FIGS. 1 and 13. First cone  26  comprises non-metallic composite materials such as phenolics that are easily drillable. First cone  26  includes a plurality of metallic inserts  28  disposed in an inner surface  30  adjacent mandrel  4 . In the running position shown in FIGS. 1 and 13, there is a gap  32  between metallic inserts  28  and mandrel  4 . Metallic inserts  28  may each have a wicker design as shown in the figures to facilitate a locked engagement with mandrel  4  upon collapse of first cone  26 . Metallic inserts  28  may be molded into first cone  26  such that first cone  26  and metallic inserts  28  comprise a single piece as shown in FIG. 1; however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  28  may also be mechanically attached to first cone  26  by a fastener, for example screws  27 . Metallic inserts  28  may be constructed of low density metallic materials such as cast iron, which may be heat treated to facilitate surface hardening sufficient to penetrate mandrel  4 , while maintaining small, brittle portions such that the inserts do not hinder drilling operations. For example, metallic inserts  28  may be surface or through hardened to approximately plus or minus fifty-five Rockwell C hardness. Metallic inserts  28  may be integrally formed with first cone  26 , for example, by injection molding the composite material that comprises first cone  26  around metallic inserts  28  as shown in FIG. 1; however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  28  may also be mechanically attached to first cone  26  by a fastener, for example screws  27 . Inner surface  30  of first cone  26  may match the cross-section of mandrel  4  such that there is an advantageous rotational lock therebetween. In the embodiment shown in FIGS. 2 and 4, inner surface  30  is shaped hexagonally to match the cross-section of mandrel  4 . However, it will be understood by one of skill in the art with the benefit of this disclosure that inner surface  30  of cone  26  may be arranged in any configuration matching the cross-section of mandrel  4 . The matching of inner surface  30  and mandrel  4  cross-section creates a rotational lock such that mandrel  4  is precluded from rotating with respect to first cone  26 . In addition, however, the inner surface  30  of the first cone  26  may not match and instead may be any non-circular surface that precludes rotation between the first cone and mandrel  4 . For example, the inner surface  30  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still advantageously precluded without the need for a third component such as a key. 
     As shown in FIG. 4, first cone  26  includes a plurality of slots  32  disposed therein, for example six slots. Slots  32  weaken first cone  26  such that the cone will collapse at a predetermined force. The predetermined collapsing force on first cone  26  may be, for example, approximately 4500 pounds; however, first cone  26  may be designed to collapse at any other desirable force. When first cone  26  collapses, as shown in FIGS. 7 and 12, metallic inserts  28  penetrate mandrel  4  and preclude movement between anchoring assembly  16  and mandrel  4 . As shown in FIGS. 1 and 13, one or more shearing devices, for example shear pins  38 , may extend between first cone  26  and mandrel  4 . Shear pins  38  preclude the premature setting of anchoring assembly  16  in the wellbore during run-in. Shear pins  38  may be designed to shear at a predetermined force. For example, shear pins  38  may shear at a force of approximately 1500 pounds; however, shear pins  38  may be designed to shear at any other desirable force. As shear pins  38  shear, further increases in force on first cone  26  will cause relative movement between first cone  26  and first slips  18 . FIG. 6 shows the shearing of shear pins  38 . The relative movement between first cone  26  and first slips  18  causes first slips  18  to move in a radially outward direction and into engagement with casing wall  24 . At some point of the travel of slips  18  along first cone  26 , slip ring  20  will break to allow each of slips  18  to engage casing wall  24 . For example, slip ring  20  may break between 1500 and 3000 pounds, with slips  18  being fully engaged with casing wall  24  at 3000 pounds. FIGS. 6 and 12 show plug assembly  2  with slips  18  penetrating casing wall  24 . FIG. 4 also discloses a plurality of channels  99  formed in first cone  26 . Each of channels  99  is associated with its respective slip  18 . Channels  99  advantageously create a rotational lock between slips  18  and first cone  26 . 
     First cone  26  abuts a gage ring  40 . Gage ring  40  may be non-metallic, comprised, for example, of injection molded phenolic. Gage ring  40  prevents the extrusion of a packing element  42  adjacent thereto. Gage ring  40  includes a non-circular inner surface  41  that precludes rotation between the gage ring and mandrel  4 . For example inner surface  41  may be hexagonal, matching a hexagonal outer surface of mandrel  4 , but inner surface  41  is not limited to a match as long as the shape precludes rotation between the gage ring and the mandrel. 
     Packing element  42  may include three independent pieces. Packing element  42  may include first and second end elements  44  and  46  with an elastomeric portion  48  disposed therebetween. First and second end elements  44  and  46  may include a wire mesh encapsulated in rubber or other elastomeric material. Packing element  42  includes a non-circular inner surface  50  that may match the cross-section of mandrel  4 , for example, as shown in the figures, inner surface  50  is hexagonal. The match between non-circular surface  50  of packing element  42  and the cross-section of mandrel  4  advantageously precludes rotation between the packing element and the mandrel as shown in any of FIGS. 14-17. However, the non-circular surface  50  of packing element  42  may be any non-circular surface that precludes rotation between the packing element and mandrel  4 . For example, the surface  50  may be hexagonal, while mandrel  4  has an outer surface that is octagonal, but rotation between the two is still precluded. Packing element  42  is predisposed to a radially outward position as force is transmitted to the end elements  44  and  46 , urging packing element  42  into a sealing engagement with casing wall  24  and the outer surface of mandrel  4 . Packing element  42  may seal against casing wall  24  at, for example, 5000 pounds. 
     End element  46  of packing element  42  abuts a non-metallic second cone  52 . Second cone  52  includes non-metallic composite materials that are easily drillable such as phenolics. Second cone  52  is a part of anchoring assembly  16 . Second cone  52 , similar to first cone  26 , may include a non-circular inner surface  54  matching the cross-section of mandrel  4 . In the embodiment shown in the figures, inner surface  54  is hexagonally shaped. The match between inner surface  54  precludes rotation between mandrel  4  and second cone  52 . However, inner surface  54  may be any non-circular surface that precludes rotation between second cone  52  and mandrel  4 . For example, inner surface  54  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. In one embodiment, second cone  52  does not include any longitudinal slots or metallic inserts as first cone  26  does; however, in an alternative embodiment second cone  52  does include the same elements as first cone  26 . Second cone  52  includes one or more shearing devices, for example shear pins  56 , that prevent the premature setting of a second plurality of slips  58 . Shear pins  56  may shear at, for example approximately 1500 pounds. FIG. 4 also discloses that second cone  52  includes a plurality of channels  99  formed therein. Each of channels  99  is associated with its respective slip  58 . Channels  99  advantageously create a rotational lock between slips  58  and second cone  52 . 
     Anchoring assembly  16  further includes the second plurality of slips  58  arranged about the outer diameter of mandrel  4  in a fashion similar to the first plurality of slips  18  shown in FIG.  3 . Slips  58  (as slips  18  in FIG. 3) are arranged in a ring with the slips being attached to one another by slip ring  60 . Similar to the embodiment shown in FIG. 3, there are six slips  58  arranged in a hexagonal configuration to match the cross-section of mandrel  4 . It will be understood by one of skill in the art with the benefit of this disclosure that slips  58  may be arranged in any configuration matching the cross-section of mandrel  4 , which advantageously creates a rotational lock such that slips  58  are precluded from rotating with respect to mandrel  4 . Further, the configuration of slip ring  60  may be any non-circular shape that precludes rotation between slips  58  and mandrel  4 . For example, the slip ring  60  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. In addition, the number of slips may be varied and the shape of slip ring may be such that rotation would be allowed between the slips and the mandrel—but for the channels  99 . Each of slips  58  may be constructed of non-metallic composite materials, but each slip also includes a metallic insert  62  disposed in outer surface  63 . Metallic inserts  62  may each have a wicker design as shown in the figures to facilitate a locked engagement with a casing wall  24 . Metallic inserts  62  may be molded into slips  58  such that slips  58  and inserts  62  comprise a single piece as shown in FIG. 1; however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  62  may also be mechanically attached to slips  58  by a fastener, for example screws  65 . Metallic inserts  62  may be constructed of low density metallic materials such as cast iron, which may heat treated to facilitate hardening such that inserts  62  can penetrate casing  24 , while maintaining small, brittle portions such that they do not hinder drilling operations. For example, metallic inserts  62  may be hardened to approximately plus or minus fifty-five Rockwell C hardness. Metallic inserts  62  may be integrally formed with slips  58 , for example, by injection molding the composite material that comprises slips  58  around metallic insert  62 . 
     Adjacent slips  58  is a ring  64 . Ring  64  is a solid non-metallic piece with an inner surface  66  that may match the cross-section of mandrel  4 , for example inner surface  66  may be hexagonal. However, inner surface  66  may be any non-circular surface that precludes rotation between ring  64  and mandrel  4 . For example, inner surface  66  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded Ring  64 , like the other components mounted to mandrel  4 , may have substantially circular outer diameter. The match between inner surface  66  and the cross-section of mandrel  4  advantageously precludes rotation between ring  64  and mandrel  4 . 
     Ring  64  abuts a second end cap  68 . Second end cap  68  may be a non-metallic material that is easily drillable, for example injection molded phenolic or other similar material. Second end cap  68  may be attached to mandrel  4  by a plurality of non-metallic composite pins  70 , and/or attached via an adhesive. Composite pins  70  are arranged in different planes to distribute any shear forces transmitted thereto. Second end cap  68  prevents any of the other plug components (discussed above) from sliding off second end  72  of mandrel  4 . In the embodiment shown in the figures, second end cap  68  exhibits an internal surface matching the non-circular cross-section of mandrel  4  which creates a rotational lock between the end cap and mandrel; however, the internal surface of the second end cap  68  may be any non-circular surface that precludes rotation between the end cap and mandrel  4 . For example, the internal surface of second end cap  68  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. Second end  72  of mandrel  4  may include a locking mechanism, for example tapered surface  74 , that rotationally locks plug assembly  2  with another abutting plug assembly (not shown). Tapered surface  74  is engagable with tapered surface  14  of end cap  10  such that rotation between two plugs  2  is precluded when surfaces  74  and  14  are engaged. 
     Second end  72  of plug  2  includes two grooves  76  extending around mandrel  4 . Grooves  76  are receptive of a collet  78 . Collet  78  is part of an adapter kit  80 . Adapter kit  80  includes a bushing  82  receptive of a setting tool  500  (not shown in FIG. 1, but shown in FIGS.  11 - 13 ). Bushing  82  is receptive, for example of a Baker E-4 wireline pressure setting assembly (not shown), but other setting tools available from Owen and Schlumberger may be used as well. The setting tools include, but are not limited to: wireline pressure setting tools, mechanical setting tools, and hydraulic setting tools. Adjacent bushing  82  is a setting sleeve  84 . Setting sleeve  84  extends between the setting tool (not shown) and bridge plug  2 . A distal end  86  of setting sleeve  84  abuts ring  64 . Adapter kit  80  exhibits a second connection point to the setting tool (not shown) at the proximal end  88  of a setting mandrel  90 . Setting mandrel  90  is part of adapter kit  80 . Setting sleeve  84  and setting mandrel  90  facilitate the application of forces on plug  2  in opposite directions. For example setting sleeve  84  may transmit a downward force (to the right as shown in the figures) on plug  2  while setting mandrel  90  transmits an upward force (to the left as shown in the figures). The opposing forces enable compression of packing element  42  and anchoring assembly  16 . Rigidly attached to setting mandrel  90  is a support sleeve  92 . Support sleeve  92  extends the length of collet  78  between setting sleeve  84  and collet  78 . Support sleeve  92  locks collet  78  in engagement with grooves  76  of mandrel  4 . Collet  78  may be shearably connected to setting mandrel  90 , for example by shear pins  96  or other shearing device such as a shear ring (not shown). 
     It will be understood by one of skill in the art with the benefit of this disclosure that one or more of the non-metallic components may include plastics that are reinforced with a variety of materials. For example, each of the non-metallic components may comprise reinforcement materials including, but not limited to, glass fibers, metallic powders, wood fibers, silica, and flour. However, the non-metallic components may also be of a non-reinforced recipe, for example, virgin PEEK, Ryton, or Teflon polymers. Further, in some embodiments, the non-metallic components may instead be metallic component to suit a particular application. In a metallic-component situation, the rotational lock between components and the mandrel remains as described above. 
     Operation and setting of plug  2  is as follows. Plug  2 , attached to a setting tool via adapter kit  80 , is lowered into a wellbore to the desired setting position as shown in FIGS. 1 and 13. Bushing  82  and its associated setting sleeve  84  are attached to a first portion of the setting tool (not shown) which supplies a downhole force. Setting mandrel  90 , with its associated components including support sleeve  92  and collet  78 , remain substantially stationary as the downhole force is transmitted through setting sleeve  84  to ring  64 . The downhole force load is transmitted via setting sleeve  84  and ring  64  to shear pins  56  of second cone  52 . At a predetermined load, for example a load of approximately 1500 pounds, shear pins  56  shear and packing element  42  begins its radial outward movement into sealing engagement with casing wall  24  as shown in FIG.  5 . As the setting force from setting sleeve  84  increases and packing element  42  is compressed, second plurality of slips  58  traverses second cone  52  and eventually second ring  60  breaks and each of second plurality of slips  58  continue to traverse second cone  52  until metallic inserts  62  of each penetrates casing wall  24  as shown in FIGS. 6 and 12. Similar to the operation of anchoring slips  58 , the load transmitted by setting sleeve  84  also causes shear pins  38  between first cone  26  and mandrel  4  to shear at, for example, approximately 1500 pounds, and allow first plurality of slips  18  to traverse first cone  26 . First plurality of slips  18  traverse first cone  26  and eventually first ring  25  breaks and each of first plurality of slips  18  continue to traverse first cone  26  until metallic inserts  22  of each penetrates casing wall  24 . Force supplied through setting sleeve  84  continues and at, for example, approximately 3000 pounds of force, first and second pluralities of slips  18  and  58  are set in casing wall  24  as shown in FIGS. 6 and 12. 
     As the force transmitted by setting sleeve  84  continues to increase, eventually first cone  26  will break and metallic cone inserts  28  collapse on mandrel  4  as shown in FIGS. 7 and 12. First cone  26  may break, for example, at approximately 4500 pounds. As metallic inserts  28  collapse on mandrel  4 , the wickers bite into mandrel  4  and lock the mandrel in place with respect to the outer components. Force may continue to increase via setting sleeve  84  to further compress packing element  42  into a sure seal with casing wall  24 . Packing element  42  may be completely set at, for example approximately 25,000 pounds as shown in FIG.  8 . At this point, setting mandrel  90  begins to try to move uphole via a force supplied by the setting tool (not shown), but metallic inserts  28  in first cone  26  prevent much movement. The uphole force is transmitted via setting mandrel  90  to shear pins  96 , which may shear at, for example 30,000 pounds. Referring to FIGS. 9 and 11, as shear pins  96  shear, setting mandrel  90  and support sleeve  92  move uphole. As setting mandrel  90  and support sleeve  92  move uphole, collet  78  is no longer locked, as shown in FIGS. 10 and 11. When collet  78  is exposed, any significant force will snap collet  78  out of recess  76  in mandrel  4  and adapter kit  80  can be retrieved to surface via its attachment to the setting tool (not shown). 
     With anchoring assembly  16 , packing element  42 , and first cone metallic insert  28  all set, any pressure build up on either side of plug  2  will increase the strength of the seal. Pressure from uphole may occur, for example, as a perforated zone is fractured. 
     In an alternative embodiment of the present invention shown in FIGS. 18-20, hole  6  in mandrel  4  may extend all the way through, with a valve such as valves  100 ,  200 , or  300  shown in FIGS. 18-20, being placed in the hole. The through-hole and valve arrangement facilitates the flow of cement, gases, slurries, or other fluids through mandrel  4 . In such an arrangement, plug assembly  2  may be used as a cement retainer  3 . In the embodiment shown in FIG. 18, a flapper-type valve  100  is disposed in hole  6 . Flapper valve  100  is designed to provide a back pressure valve that actuates independently of tubing movement and permits the running of a stinger or tailpipe  102  below the retainer. Flapper valve  100  may include a flapper seat  104 , a flapper ring  106 , a biasing member such as spring  108 , and a flapper seat retainer  110 . Spring  108  biases flapper ring  106  in a close position covering hole  6 ; however a tail pipe or stinger  102  may be inserted into hole  6  as shown in FIG.  18 . When tailpipe  102  is removed from retainer  3 , spring  108  forces flapper seat  104  closed. In the embodiment shown in FIG. 19, a ball-type valve  200  is disposed in hole  6 . Ball valve  200  is designed to provide a back pressure valve as well, but it does not allow the passage of a tailpipe through mandrel  4 . Ball valve  200  may include a ball  204  and a biasing member such as spring  206 . Spring  206  biases ball  204  to a closed position covering hole  6 ; however, a stinger  202  may be partially inserted into the hole as shown in FIG.  19 . When stinger  202  is removed from retainer  3 , spring  206  forces ball  204  to close hole  6 . In the embodiment shown in FIG. 20, a slide valve  300  is disposed in hole  6 . Slide valve  300  is designed to hold pressure in both directions. Slide valve  300  includes a collet sleeve  302  facilitating an open and a closed position. Slide valve  300  may be opened as shown in FIG.  20 . by inserting a stinger  304  that shifts collet sleeve  302  to the open position. As stinger  304  is pulled out of retainer  3 , the stinger shifts collet sleeve  302  back to a closed position. It will be understood by one of skill in the art with the benefit of this disclosure that other valve assemblies may be used to facilitate cement retainer  3 . The embodiments disclosed in FIGS. 18-20 are exemplary assemblies, but other valving assemblies are also contemplated by the present invention. 
     Because plug  2  may include non-metallic components, plug assembly  2  may be easily drilled out as desired with only a coiled tubing drill bit and motor. In addition, as described above, all components are rotationally locked with respect to mandrel  4 , further enabling quick drill-out. First end cap  10  also rotationally locks with tapered surface  74  of mandrel  4  such that multiple plug drill outs are also advantageously facilitated by the described apparatus. 
     To further facilitate the drilling out operation, slip  18  and/or slip  58  may include at least one internal cavity. FIGS. 21A-21D illustrate slip  18  or slip  58  having a cavity  33 . As previously described, slips  18  are arranged in a ring shown in FIG. 3 with the slips being attached to one another by slip ring  20 . In the embodiment shown in FIG. 3, there are six slips  18  arranged in a hexagonal configuration to match the cross-section of mandrel  4 . It will be understood by one of skill in the art with the benefit of this disclosure that slips  18  may be arranged in any configuration matching the cross-section of mandrel  4 , which advantageously creates a rotational lock such that slips  18  are precluded from rotating with respect to mandrel  4 . In addition, the number of slips may be varied and the shape of slip ring may be such that rotation would be allowed between the slips and the mandrel-but for the channels  99  (discussed previously). Further, the configuration of slip ring  20  may be any non-circular shape that precludes rotation between slips  18  and mandrel  4 . For example, the slip ring  20  may be square, while mandrel  4  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. 
     In this embodiment, each of slips  18  is constructed of a brittle, metallic material such as cast iron; however, as would be understood by one of ordinary skill in the art having the benefit of this disclosure, other materials such as ceramics could be utilized. Further, each slip may include a wickered surface to facilitate a locked engagement with a casing wall  24 . 
     Referring to FIGS. 21A-21D, slip  18  is shown having two lateral cavities  33  in the shape of rectangular slots. FIG. 21A shows a side view of slip  18 . FIG. 21B shows a cross section of slip  18 . In this configuration, the outer wall of cavity  33  runs parallel to the center line shown in FIGS. 1-14; thus this cavity is a lateral cavity. Also, as best shown in FIGS. 21C and 21D, cavities  33  may be comprised of two slots having a rectangular cross section. However, as would be understood by one of ordinary skill in the art having the benefit of this disclosure, cavities  33  are not limited to being rectangular nor lateral. For instance, cavities  33  could have a square, trapezoidal, or circular cross-section. Cavities  33  could also reside as enclosed cubic, rectangular, circular, polygonal, or elliptical cavities within the slip  18 . The cavities  33  could also be vertical, protruding through the wickered surface of the slip  18 , or through the interior ramp  34  (discussed hereinafter), or through both. Further, the cavities  33  need not be lateral; the angle of the cavities in the form of slots could be at any angle. For instance, the outer wall of cavity  33  may run perpendicular to the center line shown in FIGS. 1-14, and thus be a vertical cavity. Further, the cavities  33  in the form of slots do not need to be straight, and could therefore be curved or run in a series of directions other than straight. All cavities  33  need not run in the same direction, either. For example, cavities  33  in the shape of slots could run from side-to-side of the slip  18 , or at some angle to the longitudinal axis. If the cavities  33  are in the form of enclosed voids as described above, all cavities  33  are not required to be of the same geometry. Any known pattern or in random arrangement may be utilized. 
     Although two cavities  33  are shown in slip  18  in FIGS. 21A-D, any number of cavities  33  may be utilized. 
     Cavities  33  are sized to enhance break up of the slip  18  during the drilling out operation. As is known to one of ordinary skill in the art having the benefit of this disclosure, when slip  18  is being drilled, the cavities  33  allow for the slip  18  to break into smaller pieces compared to slips without cavities. Further, enough solid material is left within the slip so as to not compromise the strength of the slip  18  while it is carrying loads. 
     Also shown in FIG. 21B is the interior ramp  34  of the slip  18  that also enhances plug performance under conditions of temperature and differential pressure. Because it is designed to withstand compressive loads between the slip  18  and the weaker composite material of the cone  26  (mating part not shown, but described above) in service, the weaker composite material cannot extrude into cavities  33  of the slip  18 . If this were to occur, the cone would allow the packing element system, against which it bears on its opposite end, to relax. When the packing element system relaxes, its internal rubber pressure is reduced and it leaks. 
     It should also be mentioned that previous the discussion and illustrations of FIGS. 21A-D pertaining to slips  18  are equally applicable to slips  58  as well. 
     Referring to FIG. 22, another embodiment of the present invention is shown as a subterranean Bridge Plug assembly. Bridge Plug assembly  600  includes a mandrel  414  that may be constructed of metallic or non-metallic materials. The non-metallic materials may be a composite, for example a carbon fiber reinforced material, plastic, or other material that has high strength yet is easily drillable. Carbon fiber materials for construction of mandrel  414  may be obtained from ADC Corporation and others, for example XC-2 carbon fiber available from EGC Corporation. Metallic forms of mandrel  414 —and mandrels  4  described previously and shown in FIGS.  1 - 20 —include, but are not limited to, brass, copper, cast iron, aluminum, or magnesium. Further, these metallic mandrels may be circumscribed by thermoplastic tape, such as 0.5-inch carbon fiber reinforced PPS tape QLC4160 supplied by Quadrax Corp. of Portsmouth, R.I., having 60% carbon fiber and 40% PPS resin, or 68% carbon reinforced PEEK resin, model A54C/APC-2A from Cytec Engineered Materials of West Paterson, N.J. or they may be circumscribed by G-10 laminated epoxy and glass cloth or other phenolic material. Alternatively, mandrels  414  and  4  may be constructed utilizing in-situ thermoplastic tape placement technology, in which thermoplastic composite tape is continuously wound over a metal inner core. The tape is then hardened by applying heat using equipment such as a torch. A compaction roller may then follow. The metal inner core may then be removed thus leaving a composite mandrel. 
     Mandrel  414  may have a non-circular cross-section as previously discussed with respect to FIGS.  2  and  14 - 17 , including but not limited to a hexagon, an ellipse, a triangle, a spline, a square, or an octagon. Any polygonal, elliptical, spline, or other non-circular shape is contemplated by the present invention. 
     Mandrel  414  is the general support for each of the other components of Bridge Plug assembly  600 . The non-circular cross-section exhibited by mandrel  414  advantageously facilitates a rotational lock between the mandrel and all of the other components (discussed below). That is, if and when it becomes necessary to drill out bridge plug assembly  600 , mandrel  414  is precluded from rotating with the drill: the non-circular cross-section of mandrel  414  prevents rotation of the mandrel  414  with respect to the other components which have surfaces interfering with the cross-section of the mandrel. 
     Attached to the lower end (the end on the right-hand side of FIG. 22) of mandrel  414  is a lower end cap  412 . Lower end cap  412  may be constructed from a non-metallic composite that is easily drillable, for example an injection molded phenolic, or molded carbon-reinforced PEEK, or other similar materials, or may be metallic in some embodiments. Lower end cap  412  may be attached to mandrel  414  by a plurality of pins  411 , and/or attached via an adhesive, for example. Pins  411  are arranged in different planes to distribute any shear forces transmitted thereto and may be any metallic material, or may be non-metallic composite that is easily drillable, for example an injection molded phenolic, or molded carbon-reinforced PEEK, or other similar materials. Lower end cap  412  prevents any of the other plug components (discussed below) from sliding off the lower end of mandrel  414 . Lower end cap  412  may include a locking mechanism, for example tapered surface  432 , that rotationally locks Bridge Plug assembly  600  with another abutting plug assembly (not shown) without the need for a third component such as a key. This rotational lock facilitates the drilling out of more than one plug assembly when a series of plugs has been set in a wellbore. For example, if two bridge plug assemblies  600  are disposed in a wellbore at some distance apart, then as the proximal plug is drilled out, any remaining portion of the plug will fall onto the distal plug, and lower end cap  412  will rotationally lock with the second plug to facilitate drilling out the remainder of the first plug before reaching the second plug. 
     In the embodiment shown in the figures, lower end cap  412  exhibits an internal surface matching the non-circular cross-section of mandrel  414  which creates a rotational lock between the end cap and mandrel; however, the internal surface of the lower end cap  412  may be any non-circular surface that precludes rotation between the end cap and mandrel  414 . For example, the internal surface of lower end cap  412  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still advantageously precluded without the need for a third component such as a key. 
     Lower end cap  412  abuts an anchoring assembly  433 . Anchoring assembly  433  includes a plurality of first slips  407  arranged about the outer diameter of mandrel  414 . First slips  407  are arranged in a ring as shown in FIG. 3 with the slips being attached to one another by slip rings  406 . As discussed in greater detail above with respect to FIG. 3, first slips  407  may be arranged in any configuration matching the cross-section of mandrel  414 , which advantageously creates a rotational lock such that first slips  407  are precluded from rotating with respect to mandrel  414 . In addition, the number of slips may be varied and the shape of slip ring may be such that rotation would be allowed between the slips and the mandrel-but for the channels  99  (discussed above with respect to FIG.  3 ). Further, the configuration of slip ring  406  may be any non-circular shape that precludes rotation between first slips  407  and mandrel  414 . For example, the slip ring  406  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. 
     Each of first slips  407  may be constructed of non-metallic composite materials such as injection molded phenolic or may be metal such as cast iron. Also, each slip may includes a metallic inserts disposed in outer surface (not shown in FIG. 22, but shown as inserts  22  in FIG.  1 ). These metallic inserts are identical to those discussed above with respect to FIG.  1 . Alternative, each of first slips  407  may be molded to have rough or wickered outer edges  434  to engage the wellbore. The first slips  407  of this embodiment may further include at least one cavity as discussed above with respect to FIGS. 21A-21D. 
     Anchoring assembly  433  also includes a first cone  409  arranged adjacent to the first plurality of slips  407 . A portion of first slips  407  rest on first cone  409  as shown in FIG.  22 . First cone  409  may be comprised of non-metallic composite materials such as phenolics, plastics, or continuous wound carbon fiber that are easily drillable, for example. First cone  409  may also be comprised of metallic materials such as cast iron. 
     Although not shown in this embodiment, first cone  409  may include a plurality of metallic inserts disposed in an inner surface adjacent mandrel  414 , identical to the metallic inserts  28  of cones  26  shown and described in detail with respect to FIG.  1 . In the running position, there is a gap (not shown in FIG. 22, but shown in FIG. 1) between the metallic inserts and mandrel  414 . Metallic inserts  28  (of FIG. 1) may each have a wicker design as shown in the figures to facilitate a locked engagement with mandrel upon collapse of the cone. Metallic inserts  28  may be molded into the first cone  409  such that the first cone  409  and metallic inserts  28  comprise a single piece (as shown with respect to first cone  26  in FIG.  1 ); however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  28  may also be mechanically attached to first cone  26  by a fastener, for example screws  27 . Metallic inserts  28  may be constructed of metallic materials such as cast iron, which may be heat treated to facilitate surface hardening sufficient to penetrate mandrel  414 , while maintaining small, brittle portions such that the inserts do not hinder drilling operations. For example, metallic inserts  28  may be surface or through hardened to approximately plus or minus fifty-five Rockwell C hardness. Metallic inserts  28  may be integrally formed with first cone  409 , for example, by injection molding the composite material that comprises first cone  409  around metallic inserts  28  as shown in FIG. 1; however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  28  may also be mechanically attached to first cone  26  by a fastener, for example screws  27 . 
     The inner surface of first cone  409  may match the cross-section of mandrel  414  such that there is an advantageous rotational lock therebetween. As discussed above, the inner surface of cone  409  may be shaped hexagonally to match the cross-section of mandrel  414 ; however, it would be understood by one of ordinary skill in the art with the benefit of this disclosure that the inner surface of cone  409  may be arranged in any configuration matching the cross-section of mandrel  414 . The complementary matching surfaces of the inner surface of cone  409  and the mandrel  414  cross-section creates a rotational lock such that mandrel  414  is precluded from rotating with respect to cone  409 . In addition, however, the inner surface of the cone  409  may not match and instead may be any non-circular surface that precludes rotation between the cone and mandrel  414 . For example, the inner surface of cone  409  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still advantageously precluded without the need for a third component such as a key. 
     First cone  409  may include a plurality of slots disposed therein which weaken first cone  409  at a predetermined force identical to those shown in FIG.  4  and described above. In some embodiments, when first cone  409  collapses, the remaining debris of the first cone tightly surround the mandrel  414  to preclude movement between anchoring assembly  433  and mandrel  414 . In other embodiments, when first cone  409  collapses, metallic inserts  28  (not shown in this embodiment) penetrate mandrel  414  and preclude movement between anchoring assembly  433  and mandrel  414 . One or more shearing devices, for example shear pins  408 , may extend between first cone  409  and mandrel  414 . Shear pins  408  preclude the premature setting of anchoring assembly  433  in the wellbore during run-in. Shear pins  408  may be designed to shear at a predetermined force. For example, shear pins  408  may shear at a force of approximately 1500 pounds; however, shear pins  408  may be designed to shear at any other desirable force. As shear pins  408  shear, further increases in force on first cone  409  will cause relative movement between first cone  409  and first slips  407 . As discussed above with respect to FIG. 6, the relative movement between lower cone  409  and first slips  407  causes first slips  407  to move in a radially outward direction and into engagement with the casing wall. At some point of the travel of first slips  407  along first cone  409 , slip ring  406  will break to allow each of first slips  407  to engage the casing wall. For example, slip ring  406  may break between 1500 and 3000 pounds, with slips  407  being fully engaged with the casing wall at 3000 pounds (similar to that shown in FIGS. 6 and 12.). 
     First cone  409  abuts a push ring  405  in some embodiments. Push ring  405  may be non-metallic, comprised, for example, of molded phenolic or molded carbon reinforced PEEK. Push ring  405  includes a non-circular inner surface that precludes rotation between the push ring  405  and mandrel  414 . For example the inner surface of push ring  405  may be hexagonal, matching a hexagonal outer surface of mandrel  414 . But the inner surface of push ring  405  is not limited to a match as long as the shape precludes rotation between the gage ring and the mandrel. 
     Packing element  410  may include three or four independent pieces. Packing element  410  may include first and second end elements  44  and  46  with an elastomeric portion  48  disposed therebetween. In the embodiments shown in FIG. 22, packing element  410  further includes booster ring  450  disposed between elastomeric portion  48  and first end element  44 . Booster ring  450  may be utilized in high pressure applications to prevent leakage. Booster ring  450  acts to support elastomeric portion  48  of packing element  410  against mandrel  414  in high pressure situations. As described herein, the packing element  410  has a non-constant cross sectional area. During operation, when buckling the packing element  410 , the packing element  410  is subject to uneven stresses. Because the booster ring  450  has a smaller mass than the packing element  410 , the booster ring  450  will move away from the mandrel  414  before the packing element  410 ; thus the booster ring  450  will contact the casing prior to the packing element  410  contacting the casing. This action wedges the packing element tightly against the casing, thus closing any potential leak path caused by the non-constant cross section of the packing element  410 . The packing element  410  may also include a lip (not shown) to which the booster ring  450  abuts in operation. 
     Booster ring  450  includes a non-circular inner surface that may match the cross-section of mandrel  414 , for example, hexagonal. The match between the non-circular surface of booster ring  450  and the cross-section of mandrel  414  advantageously precludes rotation between the packing element and the mandrel as shown in any of FIGS. 14-17. However, the non-circular surface of booster ring  450  may be any non-circular surface that precludes rotation between the booster ring  450  and mandrel  414 . For example, the surface of the booster ring  450  may be hexagonal, while mandrel  414  has an outer surface that is octagonal, but rotation between the two is still precluded. 
     Elastomeric portion  48  of packing element  410  comprises a radial groove to accommodate an O-ring  413  which surrounds mandrel  414 . O-ring  413  assists in securing elastomeric portion  48  at a desired location on mandrel  414 . First and second end elements  44  and  46  may include a wire mesh encapsulated in rubber or other elastomeric material. Packing element  410  includes a non-circular inner surface that may match the cross-section of mandrel  414 , for example, hexagonal. The match between the non-circular surface of packing element  410  and the cross-section of mandrel  414  advantageously precludes rotation between the packing element and the mandrel as shown in any of FIGS. 14-17. However, the non-circular surface of packing element  410  may be any non-circular surface that precludes rotation between the packing element and mandrel  414 . For example, the surface of packing element  410  may be hexagonal, while mandrel  414  has an outer surface that is octagonal, but rotation between the two is still precluded. Packing element  410  is predisposed to a radially outward position as force is transmitted to the end elements  44  and  46 , urging elastomeric portion  48  of packing element  410  into a sealing engagement with the casing wall and the outer surface of mandrel  414 . Elastomeric portion  48  of packing element  410  may seal against the casing wall at, for example, 5000 pounds. 
     End element  46  of packing element  410  abuts a second cone  509 , which may be metallic or non-metallic. Second cone  509  may be comprised of metallic materials that are easily drillable, such as cast iron, or of non-metallic composite materials that are easily drillable such as phenolics, plastics, or continuous wound carbon fiber. Second cone  509  is a part of anchoring assembly  533 . Second cone  509 , similar to first cone  409 , may include a non-circular inner surface matching the cross-section of mandrel  414 . In the embodiment shown in the figures, the inner surface of second cone  509  is hexagonally shaped. The match between inner surface of second cone  509  precludes rotation between mandrel  414  and second cone  509 . However, inner surface of second cone  509  may be any non-circular surface that precludes rotation between second cone  509  and mandrel  414 . For example, inner surface of second cone  509  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. In one embodiment, second cone  509  does not include any longitudinal slots as first cone  409  does; however, in an alternative embodiment second cone  509  does include the same elements as first cone  409 . Second cone  509  includes one or more shearing devices, for example shear pins  508 , that prevent the premature setting of a second plurality of slips  507 . Shear pins  508  may shear at, for example approximately 1500 pounds. 
     As discussed above with respect to the identical cones shown in FIG. 4, second cone  509  may include a plurality of channels formed therein. Each of channel is associated with its respective second slip  507 . The channels ( 99  in FIG. 4) advantageously create a rotational lock between second slips  507  and second cone  509 . 
     Anchoring assembly  533  further includes the second plurality of slips  507  arranged about the outer diameter of mandrel  414  in a fashion similar to that of the first plurality of slips  407 . Second slips  507  (like slips  18  in FIG. 3) are arranged in a ring with the slips being attached to one another by slip ring  506 . Similar to the embodiment shown in FIG. 3, there are six slips  507  arranged in a hexagonal configuration to match the cross-section of mandrel  414 . It will be understood by one of skill in the art with the benefit of this disclosure that second slips  507  may be arranged in any configuration matching the cross-section of mandrel  414 , which advantageously creates a rotational lock such that slips  507  are precluded from rotating with respect to mandrel  414 . Further, the configuration of slip ring  506  may be any shape that precludes rotation between second slips  507  and mandrel  414 . For example, the slip ring  506  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. In addition, the number of slips may be varied and the shape of slip ring may be such that rotation would be allowed between the slips and the mandrel—but for the channels. 
     Each of second slips  507  may be constructed of non-metallic composite materials such as injection molded phenolic or may be metal such as cast iron. Also, each second slip  507  may be molded or machined to have rough or wickered outer edges  534  to engage the wellbore. Each second slips  507  of this embodiment may further include at least one cavity as discussed above with respect to FIGS. 21A-21D. Further, each second slip  507  may include a metallic inserts disposed in outer surface (not shown in FIG. 22, but shown as inserts  22  in FIG.  1 ). The inserts method of attaching the inserts to second slips  507  in this embodiment is identical to that described for inserts  22  in FIG.  1 . 
     Further, although not shown in this embodiment, first cone  409  may include a plurality of metallic inserts disposed in an inner surface adjacent mandrel  414 , identical to the metallic inserts  28  of cones  26  shown and described in detail with respect to FIG.  1 . In the running position, there is a gap (not shown in FIG. 22, but shown in FIG. 1) between metallic inserts  28  and mandrel  414 . Metallic inserts  28  may each have a wicker design as shown in the figures to facilitate a locked engagement with mandrel upon collapse of the cone. Metallic inserts  28  may be molded into the first cone  409  such that the first cone  409  and metallic inserts  28  comprise a single piece (as shown with respect to first cone  26  in FIG.  1 ); however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  28  may also be mechanically attached to first cone  26  by a fastener, for example screws  27 . Metallic inserts  28  may be constructed of low density metallic materials such as cast iron, which may be heat treated to facilitate surface hardening sufficient to penetrate mandrel  414 , while maintaining small, brittle portions such that the inserts do not hinder drilling operations. For example, metallic inserts  28  may be surface or through hardened to approximately plus or minus fifty-five Rockwell C hardness. Metallic inserts  28  may be integrally formed with second cone  509 , for example, by injection molding the composite material that comprises second cone  509  around metallic inserts  28  as shown in FIG. 1; however, as shown in the embodiment shown in FIGS. 11-13, metallic inserts  28  may also be mechanically attached to second cone  509  by a fastener, for example screws  27 . 
     Adjacent second slips  507  is a second push ring  505 . Push ring  505  may be metallic, such as cast iron, or non-metallic, e.g. molded plastic, phenolic, or molded carbon reinforced PEEK. Push ring  505  is a solid piece with an inner surface that may match the cross-section of mandrel  414 . For example the inner surface of push ring  505  may be hexagonal. However, the inner surface of push ring  505  may be any surface that precludes rotation between push ring  505  and mandrel  414 . For example, inner surface of push ring  505  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded Push ring  505 , like the other components mounted to mandrel  414 , may have substantially circular outer diameter. The match between inner surface of push ring  505  and the cross-section of mandrel  414  advantageously precludes rotation between push ring  505  and mandrel  414 . 
     Push ring  505  abuts a upper end cap  502 . Upper end cap  502  may be any easily-drillable material, such as metallic material (cast iron) or non-metallic material (e.g. injection molded phenolic, plastic, molded carbon reinforced PEEK, or other similar material). Upper end cap  502  may be attached to mandrel  414  by a plurality of pins  503 , and/or attached via an adhesive, for example. Pins  503  are arranged in different planes to distribute any shear forces transmitted thereto and may be any metallic material or non-metallic composite that is easily drillable, for example an injection molded phenolic, or molded carbon-reinforced PEEK, or other similar materials. 
     Upper end cap  502  prevents any of the other Bridge Plug components (discussed above) from sliding off the upper end of mandrel  414 . In the embodiment shown in the figures, upper end cap  502  exhibits an internal surface matching the non-circular cross-section of mandrel  414  which creates a rotational lock between the end cap and mandrel; however, the internal surface of the upper end cap  502  may be any non-circular surface that precludes rotation between the end cap and mandrel  414 . For example, the internal surface of upper end cap  502  may be square, while mandrel  414  has an outer surface that is hexagonal or octagonal, but rotation between the two is still precluded. The upper end of mandrel  414  may include a locking mechanism, for example tapered surface  532 , that rotationally locks Bridge Plug assembly  600  with another abutting plug assembly (not shown). Tapered surface  532  is engagable with tapered surface  432  of lower end cap  412  such that rotation between two plugs is precluded when surfaces  532  and  432  are engaged. 
     Attached to the upper end of Bridge Plug  600  is release stud  401 . Release stud  401  is attached to upper cap  502  via pins  503 , previously described. Release stud is typically comprised of brass, although multiple commercially-available materials are available. 
     It will be understood by one of skill in the art with the benefit of this disclosure that one or more of the non-metallic components may include plastics that are reinforced with a variety of materials. For example, each of the non-metallic components may comprise reinforcement materials including, but not limited to, glass fibers, metallic powders, wood fibers, silica, and flour. However, the non-metallic components may also be of a non-reinforced recipe, for example, virgin PEEK, Ryton, or Teflon polymers. Further, in some embodiments, the non-metallic components may instead be metallic component to suit a particular application. In a metallic-component situation, the rotational lock between components and the mandrel remains as described above. 
     Operation and setting of Bridge Plug assembly  600  is as follows. Bridge Plug assembly  600 , attached to the release stud  601  via pins  503 , is lowered into a wellbore to the desired setting position. A setting sleeve (not shown) supplies a downhole force on upper push ring  505  to shear pins  508  of second cone  509 . At a predetermined load, for example a load of approximately 1500 pounds, shear pins—shown as  508  on FIGS.  23 - 26 —shear and the elastomeric portion  48  of packing element  410  begins its radial outward movement into sealing engagement with the casing wall. As the setting force from the setting sleeve (not shown) increases and the elastomeric portion  48  of packing element  410  is compressed, the slip rings  506  break and the second plurality of slips  507  traverse second cone  509 . Eventually each of second plurality of slips  507  continue to traverse second cone  509  until the wickered edges  534  (or metallic inserts, if used) of each slip penetrates the casing wall. 
     Similar to the operation of the second plurality of slips  507 , the load transmitted by the setting sleeve also causes shear pins  408  between first cone  409  and mandrel  414  to shear at, for example, approximately 1500 pounds, and allow first plurality of slips  407  to traverse first cone  409 . First plurality of slips  407  traverse first cone  409  and eventually first ring  406  breaks and each of first plurality of slips  407  continue to traverse first cone  409  until wickered surface  434  (or metallic inserts if used) of each slip penetrates the casing wall. Force supplied through the setting sleeve (not shown) continues and at, for example, approximately 3000 pounds of force, first and second pluralities of slips  407  and  507  are set in the casing wall. 
     In some embodiments, as the force transmitted by the setting sleeve continues to increase, eventually first cone  409  and second cone  509  may deflect around mandrel  414 . In other embodiments metallic cone inserts on first cone  409  and second cone  509  grip the mandrel  414  at this point. In yet other embodiments, the remaining fragments of broken first cone  409  and second cone  509  collapse on the mandrel  414 . First cone  409  and second cone  509  may deflect, for example, at approximately 4500 pounds. As first cone  409  and second cone  509  deflect around mandrel  414 , mandrel  414  is locked in place with respect to the outer components. Force may continue to increase via the setting sleeve to further compress packing element  410  into a sure seal with the casing wall. Packing element  410  may be completely set at, for example approximately 25,000 pounds. 
     In some embodiments, as the force transmitted to the setting sleeve continues to increase, eventually release stud  401  fractures, typically at the point  402  having the smallest diameter. 
     Because Bridge Plug assembly  600  may include non-metallic components, Bridge Plug assembly  600  may be easily drilled or milled out as desired with only a coiled tubing drill bit and motor or with a mill, for example. In addition, as described above, all components are rotationally locked with respect to mandrel  414 , further enabling quick drill-out. Tapered surface  432  of first end cap  412  also rotationally locks with tapered surface  532  of upper end cap  502  such that multiple plug drill outs are also advantageously facilitated by the described apparatus. 
     Referring to FIGS. 23 and 24, another embodiment of the present invention is shown as a subterranean Frac Plug assembly  400 . Construction and operation of the embodiment shown in FIG. 23 is identical to those of the embodiment of FIG. 22 with the exception of the valve system as described below. 
     In the Frac Plug assembly  400  shown in FIGS. 23 and 24, mandrel  414  includes a cylindrical hole  431  therethrough. As shown, cylindrical hole  431  through mandrel  414  is not of uniform diameter: at a given point, the diameter of hole  431  gradually narrows thus creating ball seat  439 . Ball seat  439  may be located toward the upper end of the mandrel  414  as shown in FIG. 23, or on the lower end of the mandrel  414  as shown in FIG.  24 . Resting within ball seat  431  is ball  404 . The combination of the ball  404  resting in ball seat  431  results in the mandrel  414  having an internal ball valve that controls the flow of fluid through Frac Plug assembly  400 . As would be appreciated by one of ordinary skill in the art having the benefit of this disclosure, the ball valve allows fluid to move from one direction and will stop fluid movement from the opposite direction. For instance, in the configurations shown in FIGS. 23 and 24, fluid may pass from right (lower end) to left (upper end) thus allowing fluid to escape from the reservoir to the earth&#39;s surface. Yet fluids are prevented from entering the reservoir. The ball valve comprised of ball  404  and ball seat  431  disclosed in FIGS. 23 and 24 are exemplary assemblies, but other valving assemblies are also contemplated by the present invention. 
     This through-hole and valve arrangement facilitates the flow of cement, gases, slurries, oil, or other fluids through mandrel  414 . One of skill in the art with the benefit of this disclosure will recognize this feature to allow the Frac Plug assembly  400  to be used for multiple purposes. 
     The composition, operation, and setting of the remaining components of this Frac Plug  400  embodiment of the present invention is identical to that of the Bridge Plug of FIG. 22 discussed above. 
     Referring to FIG. 25, the Frac Plug assembly  400  of FIGS. 23 and 24 is shown including a wire line adapter kit. Construction and operation of the embodiment shown in FIG. 25 is identical to those of the embodiment of FIG. 23 with the exception of the wire line adapter kit. The wire line adapter kit is comprised of a collet  427 , a rod  428 , a shear ring  429 , a crossover  430 , an adapter bushing  424 , and a setting sleeve  425 . It will be understood by one of ordinary skill in the art that the following wire line adapter kits may be utilized with any number of subterranean devices, including the Bridge Plug of FIG.  23 . 
     Mandrel  414  in the embodiment shown in FIG. 25 is comprised of continuous carbon fiber wound over a metallic sleeve  419  as described above. In this embodiment, the upper end of mandrel  414  includes grooves  420  extending around mandrel  414 . Grooves  420  are receptive of a collet  427 . Collet  427  is part of a wire line adapter kit. Wire line adapter kit includes an adapter bushing  424  receptive of a setting tool  426 . Adapter bushing  424  is receptive, for example of a Baker E-4 wireline pressure setting assembly (not shown), but other setting tools available from Owen, H.I.P., and Schlumberger may be used as well. The setting tools include, but are not limited to: wireline pressure setting tools, mechanical setting tools, and hydraulic setting tools. Adjacent adapter bushing  424  is a setting sleeve  425 . Setting sleeve  425  extends between the setting tool  426  and frac plug  400  or other subterranean device via adapter. A distal end of setting sleeve  425  abuts push ring  505 . The setting tool  426  also connects to the wire line adapter kit at crossover  430 . Crossover  430  is part of the wire line adapter kit. Setting sleeve  425  and crossover  430  facilitate the application of forces on Frac Plug  400  in opposite directions. For example setting sleeve  425  may transmit a downward force (to the right as shown in the figures) on Frac Plug  400 , while crossover  430  transmits an upward force (to the left as shown in the figures). The opposing forces enable compression of packing element  48  and anchoring assemblies  433  and  533 . Rigidly attached to crossover  430  is a sheer ring  429 . Collet  427  may be shearably connected to crossover  430 , for example by shear ring  429  or other shearing device such as shear pins (not shown). Collet  427  surrounds rod  428 . Rod  428  is also rigidly attached to crossover  430  at its proximal end. The distal end of collet  427  engages grooves  420  of composite mandrel  414 . 
     Returning to the operation of the Frac Plug assembly, once the Frac Plug is set, the crossover  430  begins to try to move uphole via a force supplied by the setting tool  426 . Collet  427  is connected to mandrel  414  via grooves  420 . The uphole force is transmitted via crossover  430  to shear ring  429 , which may shear at, for example 30,000 pounds. As shear ring  429  shears, crossover  430  moves uphole and setting sleeve  425  moves downhole. 
     As crossover  430  and support sleeve  425  move in opposite directions, any small applied force will snap collet  427  out of grooves  420  in mandrel  414 , and the wire line adapter kit can be retrieved to surface via its attachment to the setting tool  426 . In this way, the entire wire line adapter kit is removed from the casing. Therefore, no metal is left down hole. This is advantageous over prior art methods which leave some metal downhole, as any metal left downhole increases the time to drill or mill out the downhole component. Additionally, it has been found that this wire line adapter kit is less expensive to manufacture than prior art units, based on its relatively simple design. 
     Referring to FIG. 26, another embodiment of the present invention is shown as a composite cement retainer  500 . In this embodiment, mandrel  414  is comprised of continuous carbon fiber wound over a metallic sleeve  419 . The metallic sleeve has at least one groove  420  on its distal end for attaching a wire line adapter kit (not shown, but described above with respect to the embodiment shown in FIG.  25 ). In this embodiment, radial holes are drilled in the proximal end of mandrel  414  creating vents  418 . 
     The composite cement retainer  500  of this embodiment comprises the same features as the Frac Plug assembly  400  of FIGS. 23 and 24. Construction and operation of the embodiment shown in FIG. 26 is identical to that of the embodiment of FIG. 25 with the exception of plug  415 , O-ring  416 , collet  417 , and vents  418  in mandrel  414 . In the configuration shown in FIG. 26, vents  418  are in a closed position, i.e., collet  417  acts as a barrier to prevent fluids from moving from inside the mandrel  414  to the outside of the mandrel and vice versa. 
     Once the cement retainer is set—using the identical operation as setting the Frac Plug  400  in previous embodiments—a shifting tool (not shown) may be inserted into the hollow mandrel  414  to grasp collet  417 . The shifting tool may then be moved downwardly to shift collet  417  within the mandrel  414 . Once collet  417  is shifted down in mandrel  414 , fluid communication is possible from the inside to the outside of the mandrel  414  and next to encase the wellbore. Thus, cement slurry may be circulated by pumping cement inside the hollow mandrel  414  at its upper end. The cement travels down the mandrel until the cement contacts plug  415 . Plug  415  prevents the cement from continuing downhole. O-ring  416  seals plug  415  within the mandrel  414 . The cement slurry therefore travels through vents  418  in mandrel  414  and out of the cement retainer  500 . 
     Referring to FIG. 27, another embodiment of the present invention is shown. In this embodiment, composite Frac Plug  400  is identical to that disclosed with respect to FIG. 25 with the exception of the wire line adapter kit. In this embodiment, the wire line adapter kit comprises an adapter bushing  424 , shear sleeve  421  having a flange  441  and tips  440 , a retainer  422 , a body  423 , and a setting sleeve  425 . Shear sleeve  42  is connected to body  423  by retainer  422 . Tips  440  secure the wire line adapter kit to upper end cap  502  of the subterranean device. 
     Once the packing element  410  has been set, body  423  begins to try to move uphole until the tips  440  of shear sleeve  421  shear, which may shear at, for example 30,000 pounds. As tips  440  of shear sleeve  421  shear, body  423  and retainer  422  move uphole. Body  423 , retainer  422 , adapter bushing  424 , shear sleeve  421 , and setting sleeve  425  of the wire line adapter kit move uphole and can be retrieved to the surface via attachment to the setting tool  426 . Because only the tips  440  of the shear sleeve remain in the downhole device, less metal is left in the casing than when using known wire line adapter kits. When the downhole component is subsequently milled out, the milling process is not hampered by excessive metal remaining in the downhole device from the wire line adapter kit, as is the problem in the prior art. 
     While the embodiments shown in FIGS. 25-27 show the wire line adapter kits attached to the frac plug of FIGS. 23 and 24, these embodiments are not so limited. For instance, the same wire line adapter kits of FIGS. 25-27 may be utilized with any number of subterranean apparatus, such as the drillable bridge plug of FIG. 22, for instance. 
     While the invention may be adaptable to various modifications and alternative forms, specific embodiments have been shown by way of example and described herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Moreover, the different aspects of the disclosed methods and apparatus may be utilized in various combinations and/or independently. Thus the invention is not limited to only those combinations shown herein, but rather may include other combinations. For example, the disclosed invention is also applicable to any permanent or retrievable packer taking advantage of the non-circular surfaces so as to improve the millability of each, the invention is not limited to plugs.