Patent Publication Number: US-10309189-B1

Title: Downhole bridge plugs reinforcing rings and reinforcing ring fabrication methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application No. 62/312,545, filed Mar. 24, 2016 and entitled DOWNHOLE BRIDGE PLUGS, REINFORCING RINGS AND REINFORCING RING FABRICATION METHODS, which provisional application is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     Illustrative embodiments of the disclosure generally relate to downhole bridge plugs for plugging a subterranean well. More particularly, illustrative embodiments of the present disclosure relate to downhole bridge plugs having a pair of slip assemblies characterized by enhanced grip strength, slip assemblies characterized by enhanced grip strength and methods of fabricating slip assemblies with enhanced grip strength. 
     BACKGROUND 
     The background description provided herein is solely for the purpose of generally presenting the context of the illustrative embodiments of the disclosure. Aspects of the background description are neither expressly nor impliedly admitted as prior art against the claimed subject matter. 
     In the production of fluids such as hydrocarbons from a subterranean well, it may be desirable to selectively seal or plug the well at various locations. For example, in hydrocarbon (oil and/or gas) production wells, it may be necessary or desirable to seal off a lower hydrocarbon-producing formation during the extraction of hydrocarbons from an upper hydrocarbon-producing formation. In other applications, it may be necessary or desirable to isolate the bottom of the well from the wellhead. Downhole bridge plugs are extensively used in such applications to establish a removable seal in the well. 
     A conventional downhole bridge plug may include a central mandrel on which is provided at least one expandable sealing element. An annular cone and a ridged slip assembly may be provided on the mandrel on each side of the sealing element or elements. The bridge plug may be set in place between adjacent hydrocarbon-producing fractions in the well casing by initially running the bridge plug to the desired location in the casing on a tubing string or using an alternative method and then sliding the slip assemblies onto the respective cones using a hydraulic or other setting tool, causing the slip assemblies to expand against the interior of the casing as they travel on the cones. Simultaneously, the cones move inwardly toward each other and against the sealing element, causing the cones and the sealing element to expand outwardly against the well casing. Therefore, the slip assemblies, the cones and the sealing elements together form a fluid-tight seal to prevent movement of fluids from one fraction to another within the well. When it is desired to re-establish fluid communication between the fractions in the well, the downhole bridge plug may be removed from the well casing. A backup ring on the mandrel between each cone and the sealing element or elements may reinforce the sealing element or elements after expansion against the casing. 
     One type of downhole bridge plug, commonly known as a drillable bridge plug, can be removed from the well casing by drilling or milling the bridge plug rather than by retrieving the plug from the casing. In this process, a milling cutter or drill bit is extended through the casing and rotated to grind the plug into fragments until the plug no longer seals the well casing. Drillable bridge plugs may be constructed of a drillable metal, engineering-grade plastic or composite material that can be drilled or ground into fragments by the milling cutter or drill bit. 
     One drawback of conventional downhole bridge plugs is that the slip assemblies may inadequately reinforce the cones against the sealing element or elements in the casing after the plug expansion process. This may allow the cones and the sealing element or elements to slip on the mandrel during application of pressure to the plug. A common drawback of conventional drillable bridge plugs is that during milling or drilling and grinding of the plug, the mandrel has a tendency to rotate or spin with the cutter or drill bit while the sealing elements, cones and/or other outer sealing components of the plug remain stationary against the interior surface of the well casing. This effect may reduce drilling efficiency and prolong the time which is necessary to remove the plug from the well bore. 
     Accordingly, downhole bridge plugs having a pair of slip assemblies characterized by enhanced grip strength, slip assemblies characterized by enhanced grip strength and methods of fabricating slip assemblies with enhanced grip strength may be desirable for some applications. 
     SUMMARY 
     The disclosure is generally directed to downhole bridge plugs. An illustrative embodiment of the downhole bridge plugs includes a mandrel, at least one sealing element provided on the mandrel and at least one backup ring provided on the mandrel on at least one side of the at least one sealing element. The at least one backup ring includes a first backup ring portion having a first backup ring portion body with a first outer ring section, a first inner ring section and a first spiraled ring groove separating the first outer ring section from the first inner ring section. The first inner ring section and the first outer ring section may be expandable partially circumferentially outwardly responsive to outward pressure applied to the first inner ring section. A second backup ring portion may be disposed adjacent to the first backup ring portion. The second backup ring portion may have a second backup ring portion body with a second outer ring section, a second inner ring section and a second spiraled ring groove separating the second outer ring section from the second inner ring section. The second inner ring section and the second outer ring section may be expandable partially circumferentially outwardly responsive to outward pressure applied to the second inner ring section. A pair of pressure-applying elements may be provided on the mandrel on respective sides of the at least one sealing element and the at least one backup ring, respectively. Each of the pair of pressure-applying elements may include a cone and a slip assembly engaging the cone. The slip assembly may have a reinforcing ring which may include a ring wall, a plurality of ring ridges protruding from the ring wall and a plurality of ring grooves between the plurality of ring ridges. A mandrel cap may engage one of the pair of pressure-applying elements. 
     Illustrative embodiments of the disclosure are further generally directed to backup rings for a downhole bridge plug. An illustrative embodiment of the backup rings includes a first backup ring portion having a first backup ring portion body with a first outer ring section, a first inner ring section and a first spiraled ring groove separating the first outer ring section from the first inner ring section. The first inner ring section and the first outer ring section may be expandable partially circumferentially outwardly responsive to outward pressure applied to the first inner ring section. A second backup ring portion may be disposed adjacent to the first backup ring portion. The second backup ring portion may have a second backup ring portion body with a second outer ring section, a second inner ring section and a second spiraled ring groove separating the second outer ring section from the second inner ring section. The second inner ring section and the second outer ring section may be expandable partially circumferentially outwardly responsive to outward pressure applied to the second inner ring section. 
     The disclosure is further generally directed to methods of fabricating a reinforcing ring of a pressure-applying element for a downhole bridge plug. An illustrative embodiment of the methods includes placing a plurality of reinforcing ring sections in a mold, closing the mold, injecting a liquid molding material into the mold inside and around the reinforcing ring sections, forming a ring insert by curing the liquid molding material and removing the reinforcing ring from the mold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will now be made, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a side perspective view of an illustrative embodiment of the downhole bridge plugs; 
         FIG. 2  is a longitudinal sectional view of an illustrative embodiment of the downhole bridge plugs, with the plug shown in a pre-expanded, well casing-disengaging configuration; 
         FIG. 3A  is a side view of a typical mandrel of an illustrative embodiment of the downhole bridge plugs; 
         FIG. 3B  is a side view of a typical mandrel cap or bottom sub of an illustrative embodiment of the downhole bridge plugs; 
         FIG. 3C  is a front view of the mandrel, taken along viewing lines  3 C- 3 C in  FIG. 3A ; 
         FIG. 3D  is a rear view of the mandrel, taken along section lines  3 D- 3 D in  FIG. 3B ; 
         FIG. 4A  is a longitudinal sectional view of a typical cone element for a slip assembly of an illustrative embodiment of the downhole bridge plugs; 
         FIG. 4B  is an end view, taken along viewing lines  4 B- 4 B in  FIG. 4A , of the cone element for the slip assembly; 
         FIG. 5  is a side view of a typical sealing element of the downhole bridge plugs; 
         FIG. 6  is an end view of the sealing element; 
         FIG. 7  is a side view of a typical reinforcing ring of each slip assembly; 
         FIG. 8  is a side view of the reinforcing ring with interior components of the reinforcing ring illustrated in phantom; 
         FIG. 9  is a cross-sectional view of the reinforcing ring; 
         FIG. 10  is a cross-sectional view of the reinforcing ring of the slip assembly with a typical ring insert seated in and threadably attached to the reinforcing ring; 
         FIG. 11  is a perspective view of the reinforcing ring and ring insert; 
         FIG. 12  is a perspective view of a typical molded ring insert of a multi-sectioned reinforcing ring; 
         FIG. 13  is a perspective view of the multi-sectioned reinforcing ring with a molded ring insert and multiple ring sections on the ring insert in typical fabrication of the molded ring insert; 
         FIG. 14  is an outer perspective view of a typical ring section of the multi-sectioned reinforcing ring; 
         FIG. 15  is an inner perspective view of the ring section; 
         FIG. 16  is a side perspective view of the ring section; 
         FIG. 17  is a longitudinal sectional view of the molded ring insert; 
         FIG. 18A  is an exploded side view of the multi-sectioned reinforcing ring with the molded ring insert and ring sections on the ring insert; 
         FIG. 18B  is a sectional view of the multi-sectioned reinforcing ring; 
         FIG. 19A  is a longitudinal sectional view of the downhole bridge plug disposed in a well casing, with the lower cone, sealing element and upper cone disengaging the well casing in the pre-expanded configuration of the downhole bridge plug; 
         FIG. 19B  is a longitudinal sectional view of the downhole bridge plug with a setting shaft deployed in place and coupled to the mandrel cap preparatory to deployment of the downhole bridge plug in the expanded configuration against the well casing; 
         FIG. 19C  is a longitudinal sectional view of the downhole bridge plug deployed in the expanded configuration and the lower cone, sealing element and upper cone engaging the well casing; 
         FIG. 20  is a flow diagram of an illustrative embodiment of the reinforcing ring fabrication methods; 
         FIG. 21  is a side view of a typical outer backup ring portion of a backup ring suitable for implementation of the downhole bridge plug; 
         FIG. 22  is an outer surface view of the outer backup ring portion; 
         FIG. 23  is a side view of a typical inner backup ring portion of the backup ring; 
         FIG. 24  is an outer surface view of the outer backup ring portion; 
         FIG. 25  is an exploded side view of the backup ring, more particularly illustrating typical pinning of the outer backup ring portion to the inner backup ring portion in assembly of the backup ring; 
         FIG. 26  is an inner surface view of the backup ring; 
         FIG. 27  is a perspective view of an alternative illustrative embodiment of the downhole bridge plugs; 
         FIG. 28  is a longitudinal sectional view of the downhole bridge plug illustrated in  FIG. 27 ; 
         FIG. 28A  is a sectional view illustrating typical interlocking of a pair of downhole bridge plugs to prevent rotation of the downhole bridge plugs during drilling and removal of the plugs from a wellbore; 
         FIG. 29  is an exploded sectional view illustrating mating of a typical sealing element and backup ring suitable for implementation o the downhole bridge plug illustrated in  FIG. 27 ; and 
         FIG. 30  is a longitudinal sectional view of the downhole bridge plug illustrated in  FIG. 27 , deployed in the expanded configuration and the lower cone, sealing element and upper cone engaging the well casing. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to practice the disclosure and are not intended to limit the scope of the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. As used herein, relative terms such as “upper” and “lower” are intended to be used in an illustrative and not a limiting sense. In some applications, therefore, those elements which are identified as “upper” may be located beneath those elements which are identified as “lower” in the following detailed description. As used herein, the terms “upper” and “proximal” are intended to denote the end of a component which is closer to the well surface and the terms “lower” and “distal” are intended to denote the end of a component which is farther from the well surface. 
     Referring initially to  FIGS. 1-11, 19A-19C and 21-26  of the drawings, an illustrative embodiment of the downhole bridge plug is generally indicated by reference numeral  1 . As illustrated in  FIG. 2 , the downhole bridge plug  1  may include a mandrel  2  which may include any suitable type of rigid drillable material including but not limited to metal, composite material and/or engineering-grade plastic. The mandrel  2  may have a mandrel base  3  which may be generally cylindrical in shape. A mandrel shaft  4 , which may be generally elongated and cylindrical with a longitudinal mandrel shaft bore  9 , may extend from the mandrel base  3 . As illustrated in  FIGS. 3A and 3C , a mandrel shaft groove  10  may extend into the exterior surface of the mandrel shaft  4 , in parallel relationship to the longitudinal axis of the mandrel shaft  4 , for purposes which will be hereinafter described. In some embodiments, the mandrel shaft groove  10  may be elongated and generally U-shaped in cross-section. The mandrel shaft groove  10  may extend along at least a portion of the length of the mandrel shaft  4 . In typical application of the downhole bridge plug  1 , which will be hereinafter described, a running-in tool  100  ( FIGS. 19A-19C ) may operably engage the mandrel  2  for purposes which will be hereinafter described. As illustrated in  FIG. 2 , in some embodiments, a pair of spaced-apart cone pin openings  5  may extend into the mandrel shaft  4  for purposes which will be hereinafter described. 
     As further illustrated in  FIG. 2 , a mandrel cap  12  may engage the mandrel shaft  4  of the mandrel  2 . The mandrel cap  12  may include a mandrel cap base  13  which may be generally cylindrical. A mandrel cap wall  14  may extend from the mandrel cap base  13 . A mandrel cap bore  15  may extend through the mandrel cap base  13 . The mandrel cap wall  14  may form a mandrel cap interior  16  which communicates with the mandrel cap bore  15  of the mandrel cap base  13 . In the assembled downhole bridge plug  1 , the mandrel cap interior  16  may accommodate the mandrel shaft  4  of the mandrel  2 . Accordingly, the mandrel cap  12  may be positional with respect to the mandrel  2  between a pre-expanded configuration illustrated in  FIGS. 2 and 19A  and an expanded configuration illustrated in  FIG. 19C  for purposes which will be hereinafter described. 
     As illustrated in  FIGS. 19A and 19B , in some embodiments, at least one mandrel cap coupling pin  11  may normally couple the mandrel cap  12  to the mandrel shaft  4  of the mandrel  2 . The mandrel cap coupling pin  11  may normally secure the mandrel cap  12  in the pre-expanded configuration with respect to the mandrel  2 . Accordingly, the intact mandrel cap coupling pin  11  may normally extend through a mandrel cap pin opening  26  in the mandrel cap wall  14  of the mandrel cap  12  and through a registering mandrel pin opening  6  in the mandrel shaft  4  of the mandrel  2 . Responsive to actuation of the running-in tool  100 , as will be hereinafter described, the mandrel coupling pin  11  may be sheared as the mandrel shaft  4  is displaced in the mandrel cap interior  16  of the mandrel cap  12  from the pre-expanded configuration of  FIG. 19A  to the expanded configuration of  FIG. 19C , for purposes which will be hereinafter described. 
     As illustrated in  FIG. 2 , in some embodiments, an anti-rotation pin slot  8  may be provided in the distal or extending end of the mandrel shaft  4  of the mandrel  2 . An anti-rotation pin opening  17  may be provided in the mandrel cap wall  14  at the distal or extending end of the mandrel cap interior  16 . An anti-rotation pin  21  may extend through the anti-rotation pin opening  17 . The purpose of the anti-rotation pin slot  8 , the anti-rotation pin opening  17  and the anti-rotation pin  21  will be hereinafter described. 
     The mandrel cap  12  may be configured for coupling to a lower tubing string  94  ( FIGS. 19A-19C ) according to any suitable technique which is known by those skilled in the art. As illustrated in  FIGS. 1 and 2 , in some embodiments, a mandrel cap lock  18   a  may extend from the mandrel cap  12 . The mandrel cap lock  18   a  may include a curved or semicircular major cam lock flange  19  having a curved major flange surface  20  which slopes away from the end of the mandrel cap base  13 . A major flange tab  22  ( FIG. 1 ) may extend from the major flange surface  20  at the extending or distal end of the major cam lock flange  19 . A curved or semicircular minor cam lock flange  23  may extend from the mandrel base  3  in generally adjacent and diametrically-opposed relationship to the major cam lock flange  19 . The minor cam lock flange  23  may have a generally curved minor flange surface  24 . A minor flange tab  25  may extend from the minor flange surface  24  at the extending or distal end of the minor cam lock flange  23 . As further illustrated in  FIGS. 1 and 2 , the major cam lock flange  19  may protrude beyond the minor cam lock flange  23 . 
     A tubing string lock  95  ( FIGS. 19A-9C ) which is companion or complementary in design to the mandrel cap lock  18   a  may be provided on the lower tubing string  94 . Accordingly, the mandrel cap  12  may be selectively coupled to the lower tubing string  94  by interlocking engagement of the mandrel cap lock  18   a  with the companion or complementary tubing string lock  95  on the lower tubing string  94 . Alternative techniques known by those skilled in the art, including but not limited to threads, couplings and/or pins, may be used in addition to or instead of the mandrel cap lock  18   a  and the tubing string lock  95  to facilitate coupling of the mandrel cap  12  with the lower tubing string  94 . 
     The mandrel  2  may be configured for coupling to the running-in tool  100  according to any suitable technique which is known by those skilled in the art. As illustrated in  FIG. 2 , in some embodiments, a tool lock  18   b  may extend from the mandrel base  3 . The tool lock  18   b  may have a design which is the same as or similar to that of the mandrel cap lock  18   a , with like numerals designating like components. A running-in tool lock  101  ( FIGS. 19A-19C ) which is companion or complementary in design to the tool lock  18   b  may be provided on the running-in tool  100 . Accordingly, as illustrated in  FIGS. 19A-19C , in typical application of the downhole bridge plug  1 , which will be hereinafter described, the running-in tool  100  may be selectively coupled to the mandrel  2  by interlocking engagement of the running in tool lock  101  on the running-in tool  100  with the companion or complementary tool lock  18   b  on the mandrel base  3 . The running-in tool  100  may be coupled to an upper tubing string (not illustrated) to facilitate placement and deployment of the assembly  1  in a well casing  80  in use of the assembly  1 , as will be hereinafter described. Alternative techniques known by those skilled in the art, including but not limited to threads, couplings and/or pins, may be used in addition to or instead of the tool lock  18   b  and the running-in tool lock  101  to facilitate coupling of the mandrel  2  with the running-in tool  100 . 
     A distal or lower pressure-applying element, such as an annular lower slip assembly  28   a  having a reinforcing ring  29 , may be provided on the mandrel shaft  4  of the mandrel  2  adjacent to the mandrel cap  12 . A proximal or upper pressure-applying element, such as an annular upper slip assembly  28   b , also having a reinforcing ring  29 , may be provided on the mandrel shaft  4  of the mandrel  2  generally adjacent to the mandrel base  3 . An annular proximal or lower cone  72   a  may be provided on the mandrel shaft  4  in engagement with the lower slip assembly  28   a . An annular distal or upper cone  72   b  may be provided on the mandrel shaft  4  in engagement with the upper slip assembly  28   b . A lower backup ring  160   a  may be provided on the mandrel shaft  4  in engagement with the lower cone  72   a . An upper backup ring  160   b  may be provided on the mandrel shaft  4  in engagement with the upper cone  72   b . In some embodiments, each of the lower backup ring  160   a  and the upper backup ring  160   b  may have a structure which is the same as or similar to that described in U.S. patent application Ser. No. 14/794,890, filed Jul. 9, 2015, now U.S. Pat. No. 9,784,066, issued Oct. 10, 2017, and entitled DOWNHOLE BRIDGE PLUG OR PACKER ASSEMBLIES, which patent application is incorporated by reference herein in its entirety. 
     Referring next to  FIGS. 21-26  of the drawings, a typical design for each of the lower backup ring  160   a  and the upper backup ring  160   b  ( FIG. 2 ) is indicated by reference numeral  160  in  FIG. 25 . Each of the upper backup ring  160   a  and the lower backup ring  160   b  may include an outer backup ring portion  136  ( FIGS. 21 and 22 ) and an inner backup ring portion  176  ( FIGS. 23 and 24 ). The outer backup ring portion  136  may include an annular outer backup ring portion body  137  which may include rubber or other elastomeric material and through which extends a ring opening  141 . In some embodiments, the outer backup ring portion body  137  may have a continuous unitary or one-piece construction and may include PEEK (polyether ether ketone), for example and without limitation. The outer backup ring portion body  137  may have an annular exterior engaging ring surface  138  and an annular ring opening edge  142  which encircles and faces the ring opening  141 . As illustrated in  FIG. 21 , a beveled outer ring surface  139  and a beveled inner ring surface  140  may extend or taper inwardly toward each other from the exterior engaging ring surface  138  to the ring opening edge  142 . In the assembled downhole bridge plug  1 , the outer ring surface  139  of the upper backup ring  160   a  faces outwardly and is engaged by the corresponding upper cone  72   b , whereas the outer ring surface  139  of the lower backup ring  160   b  faces outwardly and is engaged by the lower cone  72   a . The inner ring surface  140  of the outer backup ring portion  136  of the upper backup ring  160   a  and the inner ring surface  140  of the outer backup ring portion  136  of the lower backup ring  160   b  face inwardly and engage the corresponding inner backup ring portion  176 , as illustrated in  FIG. 25 . 
     As illustrated in  FIG. 22 , a single spiraled, multi-segmented ring groove  190  is provided in the outer backup ring portion body  137  of the outer backup ring portion  136  of each backup ring  160 . As illustrated in  FIG. 22 , the ring groove  190  may divide the outer backup ring portion body  137  into an inner ring section  137   a  and an outer ring section  137   b . Accordingly, responsive to outward pressure applied to the inner ring section  137   a , the inner ring section  137   a  and the outer ring section  137   b  may be partially circumferentially expandable outwardly for purposes which will be hereinafter described. As used herein, “partially circumferentially outwardly” means that the inner ring section  137   a  and the outer ring section  137   b  may be expandable outwardly along a portion of the are or curvature of the outer backup ring portion body  137 , such as 180 degrees, for example and without limitation. The depth of the spiraled ring groove  190  may extend from the engaging ring surface  138  through part of the thickness of the outer backup ring portion body  137  to the inner ring surface  140 . As illustrated in  FIG. 21 , the spiraled ring groove  190  may include an elongated main groove segment  191  which may be generally straight or axial in side view of the outer backup ring body  136  and extends along a portion of the circumference of the engaging ring surface  138 ; a generally curved inner surface groove segment  192  ( FIG. 22 ) the length of which extends from the main groove segment  191  along a portion of the inner ring surface  140  to the ring opening edge  142 ; and a generally curved or straight outer surface groove segment  193  ( FIG. 22 ) the length of which extends from the main groove segment  191  along a portion of the outer ring surface  139  to the ring opening edge  142 . The main groove segment  191  may have an outer main groove segment end  191   a  ( FIG. 21 ) at the outer ring surface  139  and an inner main groove segment end  191   b  ( FIG. 22 ) at the inner ring surface  140 . In some embodiments, from the outer main groove segment end  191   a  to the inner main groove segment end  191   b , the main groove segment  191  may traverse about 180 degrees of the circumference of the engaging ring surface  138 . 
     The inner surface groove segment  192  ( FIG. 22 ) of the spiraled ring groove  190  may extend lengthwise from the engaging ring surface  138  to the ring opening edge  142 . As particularly illustrated in  FIG. 22 , the inner surface groove segment  192  may be generally tangential with respect to both the engaging ring surface  138  and with respect to the ring opening edge  142 . At the engaging ring surface  138 , the inner surface groove segment  192  may communicate with the inner main groove segment end  191   b  of the main groove segment  191 . 
     As further illustrated in  FIG. 22 , the outer surface groove segment  193  of the spiraled ring groove  190  may extend lengthwise from the engaging ring surface  138  to the ring opening edge  142 . At the engaging ring surface  138 , the outer surface groove segment  193  may communicate with the outer main groove segment end  191   a  ( FIG. 21 ) of the main groove segment  191 . Therefore, the main groove segment  191 , the inner surface groove segment  192  and the outer surface groove segment  193  of the spiraled ring groove  190  may be contiguous with each other. As illustrated in  FIG. 22 , the spiraled ring groove  190  divides a portion of the outer backup ring portion body  137  into the inner ring section  137   a  and the circumferentially expandable outer ring section  137   b . Accordingly, application of outwardly-directed pressure to the inner ring section  137   a  of the outer backup ring portion body  137  facilitates uniform outward circumferential expansion of the expandable outer ring section  137   b  from the inner ring section  137   a , for purposes which will be hereinafter described. 
     At least one retainer pin opening  144  may extend into the outer ring surface  139  of the outer backup ring portion body  137 . As illustrated in  FIG. 25 , a shear-able ring retainer pin  145  may be seated in the retainer pin opening  144  and in a corresponding registering pin opening  75  ( FIG. 4B ) in the corresponding adjacent lower cone  72   a  or upper cone  72   b . The ring retainer pin  145  may normally retain the upper backup ring  160   a  and the lower backup ring  160   b  in the pre-expanded configuration during installation of the downhole bridge plug  1  in the well casing  52  and prior to expansion of the downhole bridge plug  1 . 
     As illustrated in  FIG. 25 , at least one outer coupling retainer pin opening  147  may extend through the outer backup ring body portion  137  from the outer ring surface  139  to the inner ring surface  140  of the outer backup ring portion  136 . As illustrated in  FIG. 22 , the outer coupling retainer pin opening  147  may be disposed about 120 degrees relative to the retainer pin opening  144 . As further illustrated in  FIG. 25 , a coupling retainer pin  184  may be inserted in and may extend through the outer coupling retainer pin opening  147 . The coupling retainer pin  184  may couple the outer backup ring portion  136  to the inner backup ring portion  176  of each backup ring  160 , typically as will be hereinafter described. The coupling retainer pin  184  may prevent premature expansion of the corresponding upper backup ring  160   a  and lower backup ring  160   b  as well as maintain proper orientation of the outer backup ring portion  136  and the inner backup ring portion  176  relative to each other in the upper backup ring  160   a  and the lower backup ring  160   b.    
     In some embodiments, at least one fluid emission channel (not illustrated) may extend into the engaging ring surface  138  of the outer backup ring portion body  137 . The fluid emission channel may traverse the width of the outer backup ring portion body  137  from the outer ring surface  139  to the inner ring surface  140 . The fluid emission channel may facilitate emission of fluids from the outer backup ring portion body  137  upon expansion of the downhole bridge plug  1 . 
     As illustrated in  FIGS. 23 and 24 , the inner backup ring portion  176  of each backup ring  160  may include an annular inner backup ring portion body  177  which may include rubber and/or other elastomeric material. In some embodiments, the inner backup ring portion body  177  may have a continuous unitary or one-piece construction and may include PEEK (polyether ether ketone), for example and without limitation. A ring opening  181  that registers with the ring opening  141  ( FIGS. 21 and 22 ) of the outer backup ring portion  136  extends through the inner backup ring portion body  177 . The inner backup ring portion body  177  may have an annular exterior engaging ring surface  178  and an annular interior ring opening edge  182  which faces the ring opening  181 . A beveled inner backup ring surface  180  ( FIG. 23 ) may extend or taper from the exterior engaging ring surface  178  to the ring opening edge  182  in the ring opening  181 . A beveled annular outer ring surface  179   m   179  may extend or taper from the engaging ring surface  178 . An annular ring lip  174  may protrude from the outer ring surface  179 . A beveled annular ring opening surface  186  may extend from the ring opening edge  182  through the ring lip  174  and faces the ring opening  181 . In the assembled downhole bridge plug  1 , the outer ring surface  179  of the inner backup ring portion  176  faces outwardly and is engaged by the inner ring surface  140  of the outer backup ring portion  136 , as illustrated in  FIG. 25 , whereas the inner backup ring surface  180  of the inner backup ring portion  176  faces inwardly and engages the sealing element  64  ( FIG. 2 ). 
     A single spiraled ring groove  170  extends along the inner backup ring portion body  177  of the inner backup ring portion  176 . As illustrated in  FIG. 24 , the spiraled ring groove  170  may divide the backup ring body  177  into an inner ring section  177   a  and an outer ring section  177   b . Accordingly, responsive to outward pressure applied to the inner ring section  177   a , the inner ring section  177   a  and the outer ring section  177   b  may be partially circumferentially expandable outwardly for purposes which will be hereinafter described. As used herein, “partially circumferentially outwardly” means that the inner ring section  177   a  and the outer ring section  177   b  may be expandable outwardly along a portion of the arc or curvature of the backup ring body  177 , such as 180 degrees, for example and without limitation. The spiraled ring groove  170  may include a main groove segment  171  which extends along the engaging ring surface  178 , an inner surface groove segment  172  which extends from the main groove segment  171  along the inner backup ring surface  180 , an interior groove segment  175  ( FIG. 24 ) which extends from the inner surface groove segment  172  along the ring opening surface  186  and an outer surface groove segment  173  which extends along the outer ring surface  179  from the interior groove segment  175  back to the main groove segment  171 . As illustrated in  FIG. 23 , the main groove segment  171  of the spiraled ring groove  170  may be generally straight or axial in side view of the inner backup ring portion  176  and extends along a portion of the circumference of the engaging ring surface  178 . 
     The inner surface groove segment  172  of the spiraled ring groove  170  may be generally curved and extends lengthwise from the main groove segment  171  along a portion of the inner backup ring surface  180  to the ring opening surface  186 . As particularly illustrated in  FIG. 24 , the inner surface groove segment  172  may be generally tangential with respect to both the engaging ring surface  178  and the ring opening edge  182 . 
     The outer surface groove segment  173  of the spiraled ring groove  170  may be generally curved and extends lengthwise from the inner surface groove segment  172  along a portion of the outer ring surface  179  and may terminate at the ring lip  174 . 
     The interior groove segment  175  of the spiraled ring groove  170  may extend lengthwise from the outer surface groove segment  173  along the ring opening surface  186  from the inner surface groove segment  172  in the inner backup ring surface  180  to the outer surface groove segment  173  at the ring lip  174 . In some embodiments, the main groove segment  171 , the inner surface groove segment  172 , the outer surface groove segment  173  and the interior groove segment  175  of the spiraled ring groove  170  may be contiguous with each other and may traverse about 180 degrees of the circumference of the inner backup ring portion body  177 . Accordingly, as illustrated in  FIG. 24 , the spiraled ring groove  170  divides a portion of the inner backup ring portion body  177  into the inner ring section  177   a  and the expandable outer ring section  177   b . Therefore, application of outwardly-directed pressure to the backup ring body  177  facilitates uniform outward circumferential expansion of the expandable outer ring section  177   b  from the inner ring section  177   a  against the well casing  152  ( FIG. 16 ) to seal adjacent fractions from each other, as was heretofore described. 
     As illustrated in  FIGS. 23 and 24 , at least one inner coupling retainer pin opening  183  may extend into the beveled outer ring surface  179  of the inner backup ring portion body  177 . As illustrated in  FIG. 24 , the inner coupling retainer pin opening  183  may be disposed generally at or near the junction where the inner surface groove segment  172  of the spiraled ring groove  170  meets the engaging ring surface  178  of the inner backup ring portion body  177 . 
     As illustrated in  FIG. 25 , each backup ring  160  may be assembled by initially orienting the outer backup ring portion  136  and the inner backup ring portion  176  such that the beveled outer ring surface  179  on the inner backup ring portion  176  faces the complementary inner ring surface  140  on the outer backup ring portion  136 . The outer backup ring portion  136  and/or the inner backup ring portion  176  is rotated until the outer coupling retainer pin opening  147  in the outer backup ring portion  136  aligns or registers with the companion inner coupling retainer pin opening  183  in the inner backup ring portion  176 . The ring lip  174  on the outer backup ring portion  176  is inserted through the ring opening  141  of the outer backup ring portion  136  as the beveled outer ring surface  179  on the inner backup ring portion  176  engages the companion beveled inner ring surface  140  on the outer backup ring portion  136 . Accordingly, as illustrated in  FIG. 26 , the spiraled ring groove  170  in the inner backup ring portion  176  traverses approximately a first half of the backup ring  160 , whereas the spiraled ring groove  190  in the outer backup ring portion  136  traverses approximately a second half of the backup ring  160 . Therefore, in the assembled lower backup ring  160   a  and upper backup ring  160   b , the outer backup ring portion  136  may be oriented about 180 degrees relative to the inner backup ring portion  176  such that the spiral ring groove  190  of the outer backup ring portion  136  does not overlap the spiral ring groove  170  of the inner backup ring portion  176 , as further illustrated in  FIG. 26 . The coupling retainer pin  184  maintains the outer backup ring portion  136  in position relative to the inner backup ring portion  176 . 
     As illustrated in  FIG. 2 , an annular sealing element  64 , which will be hereinafter described, may be provided on the mandrel shaft  4  between the lower backup ring  160   a  and the upper backup ring  160   b . In some embodiments, the sealing element  64  may include rubber and/or other elastomeric material. As illustrated in  FIGS. 5 and 6 , in some embodiments, the sealing element  64  may include a generally cylindrical sealing element wall  65  which defines a longitudinal sealing element bore  66 . A sealing element interior surface  67  of the sealing element wall  65  may face the sealing element bore  66 . A longitudinal sealing element ridge  68  may protrude from the sealing element interior surface  67  into the sealing element bore  66 . The longitudinal sealing element ridge  68  may traverse at least a portion of the length of the sealing element  64 . The longitudinal sealing element ridge  68  may have a cross-sectional size and shape which are generally complementary to the cross-sectional size and shape of the mandrel shaft groove  10  ( FIG. 3 ) in the mandrel shaft  4  of the mandrel  2 . Accordingly, as illustrated in  FIG. 2 , when the sealing element  64  is placed on the mandrel shaft  4 , the sealing element ridge  68  inserts into the companion mandrel shaft groove  10  ( FIGS. 3A and 3C ) to prevent rotation of the sealing element  64  relative to the mandrel  2  for purposes which will be hereinafter described. As illustrated in  FIG. 5 , in some embodiments, a circumferential sealing element notch  69  may extend into the sealing element interior surface  67 . The sealing element ridge  68  may include a pin, bump, key or any other type of protuberance which extends from, engages or extends into the sealing element interior surface  67  and inserts into the mandrel shaft groove  10 . 
     A typical design for each of the lower cone  72   a  and the upper cone  72   b  is indicated by reference numeral  72   a, b  in  FIGS. 4A and 4B . The lower cone  72   a  and the upper cone  72   b  may have the same or similar design. The cones  72   a ,  72   b  may include a generally conical cone wall  73 . The cone wall  73  may define a longitudinal cone bore  78 . The cone wall  73  may have a tapered inner cone wall surface  74 , a straight outer cone wall surface  76 , and a straight cone wall surface  79  and a tapered cone wall surface  82  which extend from the inner cone wall surface  74  to the outer cone wall surface  76 . An annular straight interior cone wall surface  81  may extend from the inner cone wall surface  74  to the outer cone wall surface  76  in facing relation to the cone bore  78 . A longitudinal cone pin opening  77   a  may extend into the interior cone wall surface  81  of the cone wall  73  in facing and communicating relationship to the cone bore  78 . The cone pin opening  77   a  may traverse at least a portion of the length of the cone  72   a ,  72   b . As illustrated in  FIG. 4A , in some embodiments, at least one radial cone pin opening  83  may extend through the cone wall  73  for purposes which will be hereinafter described. 
     As illustrated in  FIG. 2 , when each of the lower cone  72   a  and the upper cone  72   b  is placed on the mandrel shaft  4 , a cone pin  77  may insert into and may be glued and/or otherwise secured in the cone pin opening  77   a  in the corresponding lower cone  72   a  or upper cone  72   b , and the cone pin  77  may insert into the companion mandrel shaft groove  10  ( FIGS. 3A and 3C ) in the exterior surface of the mandrel shaft  4  of the mandrel  2  to prevent rotation of the lower cone  72   a  and the upper cone  72   b  relative to the mandrel  2 , for purposes which will be hereinafter described. As further illustrated in  FIG. 2 , the inner cone wall surface  74  of the lower cone  72   a  may engage the outer backup ring portion  136  of the adjacent lower backup ring  160   a . Likewise, the inner cone wall surface  74  of the upper cone  72   b  may engage the outer backup ring portion  136  of the adjacent upper backup ring  160   b . As illustrated in  FIGS. 4A and 4B , in some embodiments, multiple pin openings  75  may extend into the inner cone wall surface  74  of each of the lower cone  72   a  and the upper cone  72   b . Registering pin openings (not illustrated) may extend into the facing outer surface in the outer backup ring portion  136  of the lower backup ring  160   a  and upper backup ring  160   b , respectively. A ring retainer pin  145  ( FIG. 2 ) may insert into the pin opening  75  ( FIGS. 4A and 4B ) in the corresponding lower cone  72   a  and the upper cone  72   b  and the interfacing retainer pin opening  144  ( FIGS. 21 and 25 ) in the outer ring surface  139  of the outer backup ring portion  136  of the corresponding lower backup ring  160   a  and upper backup ring  160   b  to secure the lower backup ring  160   a  to the lower cone  72   a  and the upper backup ring  160   b  to the upper cone  72   b . As illustrated in  FIGS. 2 and 19A , in some embodiments, a cone pin  90  may be extended through the cone pin opening  83  ( FIG. 4A ) in the cone wall  73  of each of the lower cone  72   a  and the upper cone  72   b  and into the corresponding registering cone pin opening  5  ( FIG. 3 ) in the mandrel shaft  4  of the mandrel  2  to secure the lower cone  72   a  and the upper cone  72   b  on the mandrel shaft  4 . The cone pin  77  may include a pin, bump, key or any other type of protuberance which extends from, engages or extends into the corresponding lower cone  72   a  or upper cone  72   b  and inserts into the mandrel shaft groove  10 . 
     As illustrated in  FIGS. 7-9 , the reinforcing ring  29  of each of the lower slip assembly  28   a  and the upper slip assembly  28   b  may include an annular reinforcing ring wall  30  which may be generally cylindrical and forms a reinforcing ring bore  35  ( FIG. 9 ). In some embodiments, the reinforcing ring wall  30  may be a continuous, one-piece construction, as illustrated in  FIGS. 7 and 8 . In other embodiments, the reinforcing ring wall  30  may be divided into multiple adjacent ring sections  48 , connected by at least one frangible connection  62 , as illustrated in  FIG. 11 i    and will be hereinafter further described. As illustrated in  FIG. 10 , the reinforcing ring wall  30  may have an inner reinforcing ring wall end  30   a  and an outer reinforcing ring wall end  30   b . Multiple adjacent, spaced-apart, concentric ring ridges  31  may protrude from an exterior surface of the reinforcing ring wall  30 . Concentric ring grooves  36  may be defined between the adjacent ring ridges  31 . An annular ring shoulder  32  may be provided in an interior surface of the reinforcing ring wall  30  at the inner reinforcing ring wall end  30   a . An annular ring flange  33  may protrude from the interior surface of the reinforcing ring wall  30  at the outer reinforcing ring wall end  30   b . Ring threads  34  ( FIG. 9 ) may protrude from the interior surface of the reinforcing ring wall  30  adjacent to the ring flange  33 . 
     As illustrated in  FIG. 10 , a ring insert  38  may be inserted in the ring bore  35  of the reinforcing ring  29 . In some embodiments, the ring insert  38  may include a ring insert wall  39  having an inner ring insert wall end  39   a  and an outer ring insert wall end  39   b . The ring insert wall  39  may have a straight insert wall portion  44  which extends from the outer ring insert wall end  39   b  and a tapered wall portion  45  which extends from the straight wall portion  44  to the inner ring insert wall end  39   a . The ring insert wall  39  may form a ring insert interior  43 . An annular ring insert flange  42  may protrude outwardly from the inner ring insert wall end  39   a  of the ring insert wall  39 . The ring insert flange  42  may engage the inner reinforcing ring wall end  30   a  of the reinforcing ring wall  30  in meshing relation to the ring shoulder  32  of the reinforcing ring  29 . An annular flange receiving groove  40  may be provided in the outer reinforcing ring wall end  39   b  of the ring insert wall  39 . The flange receiving groove  40  may receive the companion ring flange  33  on the reinforcing ring  29 . The reinforcing ring  29  may threadably engage the ring insert  38  at the ring threads  34  ( FIG. 9 ). A lip receiving groove  41  may be provided in the outer surface of the ring insert wall  39  adjacent to the flange receiving groove  40 . Ring insert threads  70  may be provided in the lip receiving groove  41  and along the exterior length of the ring insert wall  39 . As illustrated in  FIG. 10 , the ring insert threads  70  may mesh with companion ring threads  34  provided in the interior surface of the ring wall  30  of each reinforcing ring  29  to secure the reinforcing ring  29  on the ring insert  38 . In some embodiments, the ring insert threads  70  may be provided along substantially the entire exterior length of the ring insert wall  39  and the ring threads  34  may be provided along substantially the entire length of the ring wall  30  of the reinforcing ring  29 . In some embodiments, a bonding resin (not illustrated) may be applied to the ring threads  34  and the ring insert threads  70  and cured to achieve a strong bond between the reinforcing ring  29  on the ring insert  38 . In some embodiments, the ring insert  38  may include a composite material and/or other non-metallic drillable material which is consistent with the functional requirements of the slip assemblies  28   a ,  28   b.    
     The reinforcing ring  29  may be fabricated using a conventional injection-molding process, which will be hereinafter described. The reinforcing ring  29  may include any suitable type of rigid drillable material including but not limited to metal, composite material and/or engineering-grade plastic. For example and without limitation, in some embodiments, the reinforcing ring  29  may include cast iron. After it is cured, the sectioned reinforcing ring  29  may be removed from the mold (not illustrated). As illustrated in  FIGS. 11 and 13 , the sectioned reinforcing ring  29  may include multiple, adjacent ring sections  48 , each of which corresponds to a radial portion of the reinforcing ring  29 . Each ring section  48  may include multiple ring ridges  31  and intervening ring grooves  36  between the ring ridges  31 . 
     In typical application, the downhole bridge plug  1  may be used as a permanent packer, a retrievable packer or a drillable plug, for example and without limitation. The upper slip assembly  28   b  may be placed on the mandrel shaft  4  of the mandrel  2 , typically by extending the mandrel shaft  4  through the ring insert interior  43  ( FIG. 10 ) of the ring insert  38 , until the outer ring wall end  30   b  on the ring wall  30  of the reinforcing ring  29  engages the mandrel base  3  of the mandrel  2 . The upper cone  72   b  may then be placed on the mandrel shaft  4 . The cone pin  77  ( FIG. 2 ) may be inserted in the cone pin opening  77   a  ( FIG. 4A ) in the upper cone  72   b  and in the mandrel shaft groove  10  ( FIGS. 3A and 3C ) to prevent rotation of the upper cone  72   b  on the mandrel  2 . The outer backup ring portion  136  of the upper backup ring  160   b  may then be placed on the mandrel shaft  4 , and the ring retainer pins  145  may be inserted in the respective pin openings  75  ( FIG. 4B ) in the inner cone wall surface  74  of the upper cone  72   b  and the respective registering retainer pin openings  144  ( FIG. 21 ) in the outer ring surface  139  of the outer backup ring portion  136 . The inner backup ring portion  176  of the upper backup ring  160   b  may be placed on the mandrel shaft  4  against the outer backup ring portion  136 . 
     Next, the sealing element  64  may be placed on the mandrel  2  by inserting the mandrel shaft  4  of the mandrel  2  through the sealing element bore  66  ( FIG. 6 ) until the sealing element  64  engages the inner backup ring portion  176  of the upper backup ring  160   b . As illustrated in  FIG. 2 , the sealing element ridge  68  provided on the sealing element  64  may simultaneously be inserted into and slid along the mandrel shaft groove  10  ( FIGS. 3A and 3C ) provided in the mandrel shaft  4  of the mandrel  2 . The inner backup ring portion  176  of the lower backup ring  160   a  may next be placed on and slid along the mandrel shaft  4  against the sealing element  64 , and the outer backup ring portion  136  of the lower backup ring  160   a  may be placed on and slid along the mandrel shaft  4  against the inner backup ring portion  176 . 
     The lower cone  72   a  may be placed on the mandrel shaft  4  of the mandrel  2 . The lower cone  72   a  may be slid along the mandrel shaft  4  until the inner cone wall surface  74  of the cone wall  73  engages the outer backup ring portion  136  of the lower backup ring  160   a . The ring retainer pins  145  may be inserted in the respective pin openings  75  ( FIG. 4B ) in the inner cone wall surface  74  of the lower cone  72   a  and the respective registering retainer pin openings  144  ( FIG. 25 ) in the outer backup ring portion  136 . The cone pin  90  may be extended through the cone pin opening  83  ( FIG. 4A ) in the cone wall  73  of each of the lower cone  72   a  and the upper cone  72   b  and into the corresponding registering cone pin opening  5  ( FIG. 2 ) in the mandrel shaft  4  of the mandrel  2 . 
     The lower slip assembly  28   a  may be placed on the mandrel shaft  4 , typically by extending the mandrel shaft  4  through the ring insert interior  43  ( FIG. 10 ) of the ring insert  38 , and sliding the lower slip assembly  28   a  along the mandrel shaft  4  until the ring insert  38  receives and engages the tapered cone wall surface  82  of the cone wall  73  of the lower cone  72   a . The mandrel cap  12  may then be pinned to the mandrel shaft  4  of the mandrel  2  by inserting the mandrel coupling pin or pins  11  ( FIGS. 19A-19C ) through the respective mandrel cap pin opening or openings  26  in the mandrel cap wall  14  of the mandrel cap  12  and the registering mandrel pin opening or openings  6  in the mandrel shaft  4  of the mandrel  2 . 
     The running-in tool  100  ( FIGS. 19A-19C ) may be coupled to the mandrel base  3  of the mandrel  2  typically by interlocking the running-in tool lock  101  on the running-in tool  100  with the companion tool lock  18   b  on the mandrel base  3 . In like manner, the lower tubing string  94  may be coupled to the mandrel cap  12  typically by interlocking the tubing string lock  95  on the lower tubing string  94  with the companion mandrel cap lock  18   a  on the mandrel cap  12 . An upper tubing string (not illustrated) may be coupled to the running-in tool  100  typically by threading, pinning and/or other suitable technique known by those skilled in the art. 
     As illustrated in  FIGS. 19A-19C , in typical application, the downhole bridge plug  1  may be placed in a well casing  80  which extends into a subterranean fluid-producing well (not illustrated) such as an oil and/or gas well, for example and without limitation, between two adjacent production fractions in the well to seal the fractions from each other and prevent flow of fluid between the fractions. Accordingly, the upper tubing string may be inserted in the well casing  80  with the running-in tool  100  and the mandrel  2  coupled thereto, the mandrel cap  12  coupled to the mandrel shaft  4  of the mandrel  2  typically via the mandrel coupling pin or pins  11  and the lower tubing string  94  coupled to the mandrel cap  12 . In some applications, the well casing  80  may be oriented in a vertical position in the well in which case the lower slip assembly  28   a , the lower cone  72   a  and the lower backup ring  160   a  may be oriented beneath the sealing element  64  and the upper slip assembly  28   b , the upper cone  72   b  and the upper backup ring  160   b  may be oriented above the sealing element  64 . In other applications, the well casing  80  may be oriented in a horizontal or diagonal position. 
     Deployment of the downhole bridge plug  1  from the pre-expanded to the expanded configuration may be as follows. As illustrated in  FIG. 19B , a setting shaft  104  may be inserted through the mandrel shaft bore  9  of the mandrel shaft  4  and through the mandrel cap interior  16  and into the mandrel cap bore  15  of the mandrel cap  12 . One or more shaft pins  106  may be extended through one or more shaft pin openings  27  in the mandrel cap bore  13  of the mandrel cap  12  and into one or more respective registering shaft pin openings (not numbered) in the setting shaft  104 . A hydraulic setting tool (not illustrated), which may be conventional, may next be operated to pull the setting shaft  104 , which in turn pulls the mandrel cap  12  along the mandrel shaft  4  such that the mandrel cap  12  impinges against the lower slip assembly  28   a  as the mandrel coupling pin or pins  11  is/are sheared. This action pushes the lower slip assembly  28   a  onto the lower cone  72   a , as indicated by the arrow  91  in  FIG. 19A . Simultaneously, the running-in tool  100  may push the upper slip assembly  28   b  onto the upper cone  72   b , as indicated by the arrow  92  in  FIG. 19A . Therefore, the lower cone  72   a  pushes or expands the lower slip assembly  28   a  outwardly until the ring ridges  31  on the reinforcing ring  29  of the lower slip assembly  28   a  and the lower backup ring  160   a  engage the interior surface of the well casing  80 . In like manner, the upper cone  72   b  pushes or expands the upper slip assembly  28   b  outwardly until the ring ridges  31  on the reinforcing ring  29  of the upper slip assembly  28   b  and the upper backup ring  160   b  engage the interior surface of the well casing  80 . The sealing element  64  is compressed between the lower backup ring  160   a  and the upper backup ring  160   b  and expands circumferentially outwardly to engage the interior surface of the well casing  80 . In some applications, the frangible connection  62  ( FIG. 11 ) between adjacent ring sections  48  of each reinforcing ring  29  may break as the ring sections  48  are wedged away from each other on the respective lower cone  72   a  and upper cone  72   b . As each cone pin  90  is sheared, as illustrated in  FIG. 19C , the lower cone  72   a  and the upper cone  72   b  travel along the mandrel  2  against the lower backup ring  160   a  and the upper backup ring  160   b , respectively. This action compresses the sealing element  64 , the lower backup ring  160   a  and the upper backup ring  160   b  between the lower slip assembly  28   a  and the upper slip assembly  28   b . Consequently, the sealing element  64  circumferentially expands outwardly and engages the interior surface of the well casing  80 , forming a fluid-tight seal between the downhole bridge plug  1  and the well casing  80 . The lower slip assembly  28   a , the lower backup ring  160   a , the upper backup ring  160   b  and the upper slip assembly  28   b  may expand outwardly and engage the interior surface of the well casing  80 , reinforcing and preventing movement of the sealing element  64  as pressure is subsequently placed on the downhole bridge plug  1  during well operations. The lower cone  72   a  applies outward pressure against the beveled outer backup ring surface  139  ( FIG. 25 ) on the outer backup ring portion  136  of the lower backup ring  160   a , and the upper cone  72   b  likewise applies outward pressure against the beveled outer backup ring surface  139  on the outer backup ring portion  136  of the upper backup ring  160   b . Consequently, the inner ring section  137   a  ( FIG. 22 ) and the outer ring section  137   b  of the outer backup ring portion  136  expand partially circumferentially outwardly to engage the interior surface of the well casing  80 , as illustrated in  FIG. 19C . In like manner, the sealing element  64  applies outward pressure against the beveled inner backup ring surface  180  ( FIG. 25 ) on the inner backup ring portion  176  of each of the lower backup ring  160   a  and the upper backup ring  160   b . Consequently, the inner ring section  177   a  ( FIG. 24 ) and the outer ring section  177   b  of the inner backup ring portion  176  expand partially circumferentially outwardly to engage the interior surface of the well casing  80 . The reinforcing ring  29  of each of the lower slip assembly  28   a  and the upper slip assembly  28   b  engages the well casing  80  with a grip strength greater than that which can be attained using conventional slip assembly designs. As further illustrated in  FIG. 19C , a ball  120  may be dropped down the tubing string and onto a ball seat (not numbered) in the mandrel base  3  of the mandrel  2  to seal the portion of the well casing  80  below or distal to the downhole bridge plug  1 . Fracking and/or other operations may then be carried out on the reservoir sections which are above or proximal to the downhole bridge plug  1 . 
     In some applications, when removal of the downhole bridge plug  1  from the well casing  80  is desired, a drill bit or milling cutter (not illustrated) may be inserted through the well casing  80  and operated to grind the downhole bridge plug  1  into fragments according to the knowledge of those skilled in the art. It will be appreciated by those skilled in the art that during drilling or cutting of the downhole bridge plug  1 , the mandrel  2  is locked in place with the sealing element  64  and each of the lower backup ring  160   s , the upper backup ring  160   b , the lower cone  72   a  and the upper cone  72   b , since the sealing element ridge  68  ( FIG. 6 ) on the sealing element  64  and the cone pin  77  ( FIG. 2 ) in the cone pin opening  77   a  of each of the lower cone  72   a  and the upper cone  72   b  protrude into the mandrel shaft groove  10  ( FIG. 3A ) in the mandrel shaft  4  of the mandrel  2 . As illustrated in  FIG. 19C , in the expanded configuration of the downhole bridge plug  1 , the anti-rotation pin slot  8  in the distal or extending end of the mandrel shaft  4  receives the anti-rotation pin  21  in the anti-rotation pin opening  17  of the mandrel cap wall  14 . This expedient prevents rotation of the mandrel  2  and the mandrel cap  12  relative to each other during cutting of the downhole bridge plug  1 . Therefore, because the mandrel  2  does not spin with the milling cutter or drill bit, speed and efficiency in cutting and removal of the downhole bridge plug  1  from the well casing  80  is enhanced. In some applications, the downhole bridge plug  1  may be used with a permanent packer or a retrievable packer. 
     It will be appreciated by those skilled in the art that the typically one-piece solid construction between the mandrel base  3  and the mandrel shaft  4  of the mandrel  2  enhances the structural strength and integrity of the downhole bridge plug  1 . Thus, the mandrel base  3  applies the typically downward pressure against the upper slip assembly  28   b  as the setting shaft  104  applies the mandrel cap  12  with the typically upward pressure against the lower slip assembly  28   a  with sufficient force to ensure maximum longitudinal compression, radial expansion and exertion of the sealing element  64  against the interior surface of the well casing  80 . Therefore, an optimum fluid-tight seal against the well casing  80  is ensured throughout deployment of the downhole bridge plug  1 . 
     Referring next to  FIGS. 11-18B  of the drawings, in some embodiments, the reinforcing ring  29  of each of the lower slip assembly  28   a  and the upper slip assembly  28   b  may be multi-sectional and may be fabricated using an injection molding process. As illustrated in  FIG. 12 , multiple wall slots  55  may be provided in the tapered wall portion  45  of the ring insert wall  39 . The wall slots  55  may partially divide the mold body wall  52  into multiple adjacent mold sections  56 . A pair of spaced-apart insert partitions  58  may extend along opposite edges of each ring section  56 . Insert cavities  116  ( FIG. 17 ) may be formed by and between the adjacent insert partitions  58 . Multiple, adjacent insert ring ridges  60  may extend between the insert partitions  58  in the insert cavity  116  of each insert section  56 . Insert ring grooves  61  may extend between the adjacent insert ring ridges  60 . 
     As illustrated in  FIGS. 11 and 14-16 , the sectioned reinforcing ring  29  may include multiple, adjacent ring sections  48 , each of which corresponds to a radial portion of the reinforcing ring  29 . Each ring section  48  may include a ring wall  30  having multiple ring ridges  31  and intervening ring grooves  36  between the ring ridges  31 . 
     The sectioned reinforcing ring  29  may be fabricated by initially fabricating the ring sections  48  typically by injection molding. The ring sections  48  may then be placed in an injection mold (not illustrated) for fabrication of the ring insert  38 . In some embodiments, the ring sections  48  may be attached to the injection mold by extending  6  fasteners (not illustrated) through respective fastener openings  37  ( FIG. 14 ) in the respective ring sections  48  and threading the fasteners into respective fastener openings (not illustrated) in the mold. 
     A liquid molding material (not illustrated) which will form the ring insert  38  may next be injected into the mold. The liquid molding material may include any suitable type of rigid drillable material including but not limited to metal, composite material and/or engineering-grade plastic. The liquid molding material flows within and around the ring sections  48 . As illustrated in  FIGS. 13 and 17 , the liquid molding material cures and forms the ring insert  38 . After the sectioned reinforcing ring  29  is removed from the mold, the wall slots  55  may be cut into the tapered wall portion  45  in the ring insert wall  39  of the ring insert  38 . The sectioned reinforcing rings  29  of the lower slip assembly  28   a  and the upper slip assembly  28   b  may then be assembled in the downhole bridge plug  1 , typically as was heretofore described. 
     Application of the downhole bridge plug  1  having the lower slip assembly  28   a  and the upper slip assembly  28   b  may be as was heretofore described with respect to the downhole bridge plug  1  in  FIGS. 19A-19C . The ring sections  48  may enhance outward radial expansion of each reinforcing ring  29  against the interior surface of the well casing  80  upon actuation of the running-in tool  100  and the mandrel cap  12  and radial expansion of the sealing element  64  against the well casing  80 . 
     Referring next to  FIG. 20  of the drawings, a flow diagram  2100  of an illustrative embodiment of the reinforcing ring fabrication methods is illustrated. Multiple reinforcing ring sections of a reinforcing ring may initially be fabricated using conventional injection molding and/or other techniques. At block  2102 , the multiple reinforcing ring sections of the reinforcing ring may be placed in a mold. At block  2104 , the mold may be closed. At block  2106 , a liquid molding material may be injected into the mold inside and around the ring sections. The liquid molding material may include metal, composite material and/or engineering-grade plastic, for example and without limitation. At block  2108 , a ring insert may be formed by curing the liquid molding material. At block  2110 , the reinforcing ring may be removed from the mold. 
     Referring next to  FIGS. 27-30  of the drawings, an alternative illustrative embodiment of the downhole bridge plugs is generally indicated by reference numeral  1   a , where like reference numerals designate like elements to those of the downhole bridge plug  1  that was heretofore described with respect to  FIGS. 1-26 . The downhole bridge plug  1   a  may include an upper sealing element  264  which is provided on the mandrel shaft  204  of the mandrel  202 . The upper sealing element  264  may directly engage the upper cone  72   b . Accordingly, the upper backup ring (not illustrated) may be omitted from between the upper sealing element  264  and the upper cone  72   b . A lower sealing element  296  may be provided on the mandrel shaft  204  in engagement with the upper sealing element  264 . The upper backup ring  160   a  may be interposed between the lower cone  72   a  and the lower sealing element  296 . 
     As illustrated in  FIG. 29 , the upper sealing element  264  may include an upper sealing element wall  265  which may be generally elongated and cylindrical. The upper sealing element wall  265  may have a proximal wall bevel  265   a  and a distal wall bevel  265   b . The upper sealing element wall  265  may form an upper sealing element bore  266  which traverses the length of the upper sealing element  264 . The upper sealing element bore  266  may be suitably sized to accommodate the mandrel shaft  4  of the mandrel  2 . The upper sealing element bore  266  may have a sealing element bore surface  267 . A longitudinal sealing element ridge  268  may protrude from the sealing element bore surface  267 . The sealing element ridge  268  may traverse at least a portion of the length of the upper sealing element  264 . In assembly of the downhole bridge plug  1   a , the sealing element ridge  268  may insert into the companion mandrel shaft groove  10  (FIG. ( FIG. 3C ) in the mandrel shaft  4  of the mandrel  2 , as was heretofore described with respect to the downhole bridge plug  1 . 
     As further illustrated in  FIG. 29 , the lower sealing element  296  of the downhole bridge plug  1  may include a lower sealing element wall  297  which may be generally cylindrical or annular. A lower sealing element seat  299  and a beveled sealing element wall bevel  297   a  may be provided in opposite ends of the lower sealing element wall  297 . The lower sealing element seat  299  may be suitably sized and configured to receive and accommodate the distal wall bevel  265   b  of the upper sealing element  264  in engaging relationship thereto in assembly of the downhole bridge plug  1 . The sealing element wall bevel  297   a  may be suitably sized and angled to engage the inner backup ring portion  176  of the lower backup ring  160   a  in the assembled downhole bridge plug  1 . 
     The lower sealing element wall  297  of the lower sealing element  296  may form a lower sealing element bore  298  which traverses the length of the lower sealing element  296 . The lower sealing element bore  298  may be suitably sized to accommodate the mandrel shaft  4  of the mandrel  2 . The lower sealing element bore  298  may have a sealing element bore surface  297 T. A longitudinal sealing element ridge  297   c  may protrude from the sealing element bore surface  297   b . The sealing element ridge  297   c  may traverse at least a portion of the length of the lower sealing element  296 . In assembly of the downhole bridge plug  1   a , the sealing element ridge  297   c  may insert into the companion mandrel shaft groove  10  (FIG. ( FIG. 3C ) in the mandrel shaft  4  of the mandrel  2 , as was heretofore described with respect to the downhole bridge plug  1 . 
     As illustrated in  FIGS. 28 and 30 , in some embodiments, a threaded shear insert  262  may be seated in the mandrel cap bore  15  adjacent to the mandrel cap interior  16  of the mandrel cap  12 . The threaded shear insert  262  may be secured in the mandrel cap interior  16  via pins, threads, welding and/or other attachment technique known by those skilled in the art. For example and without limitation, in some embodiments, at least one radial insert retainer pin opening  270  may extend through the mandrel cap base  13  of the mandrel cap  12 . An insert retainer pin  271  may extend through the insert retainer pin opening  270 . The insert retainer pin  271  may be seated in a corresponding pin cavity (not numbered) provided in the threaded shear insert  262 . The threaded shear insert  262  may have interior shear insert threads  263 . In setting of the downhole bridge plug  1 , a setting shaft (not illustrated) may be inserted through the mandrel shaft bore  9  of the mandrel shaft  4  and the mandrel cap interior  16  of the mandrel cap  12 , as was heretofore described with respect to the setting shaft  104  in  FIG. 19B . The setting shaft  104  may be threadably engaged with the shear insert threads  263  in the threaded shear insert  262  to deploy the downhole bridge plug  1   a  from the pre-expanded configuration to the expanded configuration, as was heretofore described with respect to  FIGS. 19A-19C . The setting shaft  104  may be subsequently removed from the mandrel shaft bore  9  and mandrel cap interior  16  by reverse or downward movement of the setting shaft  104 , thus typically facilitating shearing of the insert retainer pin or pins  271  and detachment of the threaded shear insert  262  from the mandrel cap bore  15  of the mandrel cap  12 . 
     In typical application of the downhole bridge plug  1   a , the upper slip assembly  28   b  and the upper cone  72   b  may be sequentially placed on the mandrel shaft  4  of the mandrel  2 . Next, the upper sealing element  264  may be placed on the mandrel  2  by inserting the mandrel shaft  4  of the mandrel  2  through the sealing element bore  266  ( FIG. 6 ) until the proximal wall bevel  265   a  on the upper sealing element  264  engages the inner backup ring portion  176  of the upper backup ring  160   b . As illustrated in  FIG. 28 , the sealing element ridge  268  provided on the upper scaling element  264  may simultaneously be inserted into and slid along the mandrel shaft groove  10  ( FIGS. 3A and 3C ) provided in the mandrel shaft  4  of the mandrel  2 . 
     The lower sealing element  296  may next be placed on the mandrel  2  by inserting the mandrel shaft  4  of the mandrel  2  through the lower sealing element bore  298  ( FIG. 29 ) until the lower sealing element seat  299  in the lower sealing element  296  receives and engages the complementary-shaped distal wall bevel  265   b  on the upper sealing element  264 . As illustrated in  FIG. 28 , the sealing element ridge  297   c  provided on the lower sealing element  296  may simultaneously be inserted into and slid along the mandrel shaft groove  10  ( FIGS. 3A and 3C ) provided in the mandrel shaft  4  of the mandrel  2 . 
     The inner backup ring portion  176  of the lower backup ring  160   a  may next be placed on and slid along the mandrel shaft  4  against the sealing element wall bevel  297   a  on the lower sealing element  296 , and the outer backup ring portion  136  of the lower backup ring  160   a  may be placed on and slid along the mandrel shaft  4  against the inner backup ring portion  176 . 
     The lower cone  72   a  may be placed on the mandrel shaft  4  of the mandrel  2 . The lower cone  72   a  may be slid along the mandrel shaft  4  until the inner cone wall surface  74  of the cone wall  73  engages the outer backup ring portion  136  of the lower backup ring  160   a . In some embodiments, ring retainer pins  145  may be inserted in the respective pin openings  75  ( FIG. 4B ) in the inner cone wall surface  74  of the lower cone  72   a  and the respective registering retainer pin openings  144  ( FIG. 25 ) in the outer backup ring portion  136 . A cone pin  90  may be extended through the cone pin opening  83  ( FIG. 4A ) in the cone wall  73  of each of the lower cone  72   a  and the upper cone  72   b  and into the corresponding registering cone pin opening  5  ( FIG. 2 ) in the mandrel shaft  4  of the mandrel  2 . 
     The lower slip assembly  28   a  may be placed on the mandrel shaft  4 , typically by extending the mandrel shaft  4  through the ring insert interior  43  ( FIG. 10 ) of the ring insert  38 , and sliding the lower slip assembly  28   a  along the mandrel shaft  4  until the ring insert  38  receives and engages the tapered cone wall surface  82  of the cone wall  73  of the lower cone  72   a . The mandrel cap  12  may then be pinned to the mandrel shaft  4  of the mandrel  2  by inserting the mandrel coupling pin or pins  11  ( FIGS. 19A-19C ) through the respective mandrel cap pin opening or openings  26  in the mandrel cap wall  14  of the mandrel cap  12  and the registering mandrel pin opening or openings  6  in the mandrel shaft  4  of the mandrel  2 . 
     Application of the downhole bridge plug  1   a  may be as was heretofore described with respect to the downhole bridge plug  1  in  FIGS. 19A-19C . Upon deployment of the downhole bridge plug  1   a  from the pre-expanded configuration ( FIG. 28 ) to the expanded configuration ( FIG. 30 ), the lower slip assembly  28   a  traverses the lower cone  72   a  and engages the lower backup ring  160   a , which in turn engages the lower sealing element  296 . The lower slip assembly  28   a  and the lower backup ring  160   a  expand outwardly to engage the well casing  80 , as was heretofore described. Simultaneously, the upper slip assembly  28   b  traverses the upper cone  72   b  and engages the upper sealing element  264 , and the upper slip assembly  28   b  expands outwardly to engage the well casing  80 . The upper sealing element  264  and the lower sealing element  296  are compressed between the upper cone  72   b  and the lower backup ring  160   a , expanding outwardly to engage the well casing  80 . In some applications, after use, a drill bit or milling cutter (not illustrated) may be inserted through the well casing  80  and operated to grind the downhole bridge plug  1   a  into fragments to remove the downhole bridge plug  1   a  from the well casing  80 , as was heretofore described. 
     As illustrated in  FIG. 28 , an annular lower cone receptacle  274  may be provided in the end surface of the mandrel cap wall  14  of the mandrel cap  12  which faces the lower slip assembly  28   a . An upper cone receptacle  276  may in like manner be provided in the end surface of the mandrel base  3  of the mandrel  2  which faces the upper slip assembly  28   b . The lower cone receptacle  274  and the upper cone receptacle  276  may be configured to receive and accommodate the lower cone  72   a  and the upper cone  72   b , respectively, in the expanded configuration of the downhole bridge plug  1   a.    
     As illustrated in  FIG. 28A , during their removal from the well casing  80 , the downhole bridge plugs  1   a  may sequentially drop in the well casing  80  as each downhole bridge plug  1   a  is drilled or cut and consequently disengages the interior surface of the well casing  80 . Accordingly, the partially removed downhole bridge plug  1   a  which is being cut may drop in the well casing  80  such that the mandrel cap lock  18   a  on the mandrel cap  12  of the partially-cut downhole bridge plug  1   a  engages and interlocks with the companion tool lock  18   b  on the mandrel  2  of the next succeeding, typically lower downhole bridge plug  1   a . Thus, the downhole bridge plugs  1   a  will not rotate relative to each other as cutting continues to remove the downhole bridge plugs  1   a  from the well casing  80 . This feature may also characterize the downhole bridge plugs  1  which were heretofore described with respect to  FIGS. 1-26  in their removal from the well casing  80 . 
     While the preferred embodiments of the disclosure have been described above, it will be recognized and understood that various modifications can be made in the disclosure and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the disclosure.