Patent Publication Number: US-2022228459-A1

Title: Mandrel assemblies for a plug and associated methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application Ser. No. 62/846,366 filed May 10, 2019, and entitled “Bridge Plug,” which is hereby incorporated herein by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     After a wellbore has been drilled through a subterranean formation, the wellbore may be cased by inserting lengths of pipe (“casing sections”) connected end-to-end /into the wellbore. Threaded exterior connectors known as casing collars may be used to connect adjacent ends of the casing sections at casing joints, providing a casing string including casing sections and connecting casing collars that extends from the surface towards the bottom of the wellbore. The casing string may then be cemented into place to secure the casing string within the wellbore. 
     In some applications, following the casing of the wellbore, a wireline tool string may be run into the wellbore as part of a “plug-n-perf” hydraulic fracturing operation. The wireline tool string may include a perforating gun for perforating the casing string at a desired location in the wellbore, a downhole plug that may be set to couple with the casing string at a desired location in the wellbore, and a setting tool for setting the downhole plug. In certain applications, the downhole plug may comprise a “bridge plug” configured to seal or isolate the portion of the wellbore extending uphole from the bridge plug upon setting of the bridge plug. In other applications, the downhole plug may comprise a “frac plug” that permits fluid flow through a central passage of the frac plug. Once the casing string has been perforated by the perforating gun and the frac plug has been set, a ball or dart may be pumped into the wellbore for landing against the set frac plug, thereby isolating the portion of the wellbore extending uphole from the frac plug. With this uphole portion of the wellbore isolated, the formation extending about the perforated section of the casing string may be hydraulically fractured by fracturing fluid pumped into the wellbore. 
     SUMMARY OF THE DISCLOSURE 
     An embodiment of a plug for sealing a wellbore comprises a mandrel assembly comprising an inner rod and a filament wound outer rod that is separate and distinct from the inner rod and which is formed about the inner rod, and a packer disposed about the mandrel assembly, the packer configured to seal the wellbore in response to the plug being actuated from a first position to a second position, wherein the mandrel assembly is configured to apply a compressive force to the packer as the plug is actuated from the first position to the second position. In some embodiments, the inner rod comprises a pultruded rod and the outer rod comprises a filament wound outer rod. In some embodiments, the inner rod comprises a composite material and the outer rod comprises a glass filament material. In certain embodiments, the outer rod of the mandrel assembly comprises an inner surface and an inner surface feature positioned on the inner surface, and the inner rod of the mandrel assembly comprises an outer surface and an outer surface feature positioned on the outer surface that is in interlocking engagement with the inner surface feature of the outer rod. In certain embodiments, the outer surface feature of the inner rod comprises a protrusion received within the inner surface feature of the outer rod. In some embodiments, an end of the outer rod is configured to couple to a setting tool for actuating the plug from the first position to the second position. In some embodiments, the plug further comprises a slip assembly configured to affix the plug to a string disposed in the wellbore in response to the plug being actuated from the first position to the second position. In some embodiments, the outer rod of the mandrel assembly comprises a first helical pattern formed on an inner surface of the outer rod and which comprises a first helical groove and a first helical ridge, and the inner rod of the mandrel assembly comprises a second helical pattern formed on an outer surface of the inner rod and which comprises a second helical groove and a second helical ridge, wherein the second helical ridge is interlockingly received in the first helical groove. 
     An embodiment for a plug for sealing a wellbore comprises a mandrel assembly comprising an outer rod comprising an inner surface and an inner surface feature positioned on the inner surface, and an inner rod that is separate and distinct from the outer rod and which comprises an outer surface and an outer surface feature positioned on the outer surface that is in interlocking engagement with the inner surface feature of the outer rod, and a packer disposed about the mandrel assembly, the packer configured to seal the wellbore in response to the plug being actuated from a first position to a second position, wherein the mandrel assembly is configured to apply a compressive force to the packer as the plug is actuated from the first position to the second position. In some embodiments, the outer surface feature of the inner rod comprises a protrusion received within the inner surface feature of the outer rod. In some embodiments, the outer surface feature of the inner rod comprises a helical pattern and the inner surface feature of the outer rod comprises a helical pattern. In some embodiments, the first helical pattern comprises a helical ridge that is interlockingly received in a helical groove of the second helical pattern. In certain embodiments, the outer surface feature of the inner rod is configured to increase a surface roughness of the outer surface of the inner rod. In certain embodiments, the inner rod comprises a pultruded rod and the outer rod comprises a filament wound rod. In some embodiments, the inner rod comprises a central passage extending partially through the inner rod. In some embodiments, the plug further comprises a slip assembly configured to affix the plug to a string disposed in the wellbore in response to the plug being actuated from the first position to the second position. 
     An embodiment of a method of assembling a plug for sealing a wellbore comprises (a) forming a first rod of a mandrel assembly of the plug, (b) forming a second rod of the mandrel assembly about the first rod using a filament winding process, and (c) positioning a packer about the second rod, the packer being configured to seal the wellbore in response to the plug being actuated from a first position to a second position, and wherein the mandrel assembly is configured to apply a compressive force to the packer as the plug is actuated from the first position to the second position. In some embodiments, (a) comprises forming the first rod using a protrusion process. In some embodiments, (a) comprises forming an outer surface feature on an outer surface of the first rod, and (b) comprises receiving at least a portion of the outer surface feature of the first rod in an inner surface feature positioned on an inner surface of the second rod. In certain embodiments, the method further comprises (d) positioning a slip assembly about the second rod, the slip assembly configured to affix the plug to a string disposed in the wellbore in response to the plug being actuated from the first position to the second position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of exemplary embodiments of the disclosure, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a schematic, partial cross-sectional view of a system for completing a subterranean well including an embodiment of a downhole plug in accordance with principles disclosed herein; 
         FIG. 2  is a side view of the downhole plug of  FIG. 1  that includes an embodiment of a mandrel assembly in accordance with principles disclosed herein; 
         FIG. 3  is a cross-sectional view along line  3 - 3  of  FIG. 2  of the downhole plug of  FIG. 1 ; 
         FIG. 4  is a side view of an embodiment of an inner rod of the mandrel assembly of  FIG. 2  in accordance with principles disclosed herein; 
         FIG. 5  is a perspective view of the inner rod of  FIG. 4 ; 
         FIG. 6  is a side view of the mandrel assembly of  FIG. 2 ; 
         FIG. 7  is a cross-sectional view along lines  7 - 7  of  FIG. 6  of the mandrel assembly of  FIG. 2 ; and 
         FIG. 8  is a flow chart of an embodiment of a method of assembling a plug for sealing a wellbore in accordance with principles disclosed herein . 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. Further, the term “fluid,” as used herein, is intended to encompass both fluids and gasses. 
     Referring now to  FIG. 1 , a system  10  for completing a wellbore  4  extending into a subterranean formation  6  is shown. In the embodiment of  FIG. 1 , wellbore  4  is a cased wellbore including a casing string  12  secured to an inner surface or wall  8  of the wellbore  4  using cement (not shown). In some embodiments, casing string  12  generally includes a plurality of tubular segments coupled together via a plurality of casing collars. In this embodiment, completion system  10  includes a tool string  20  disposed within wellbore  4  and suspended from a wireline  22  that extends to the surface of wellbore  4 . Wireline  22  comprises an armored cable and includes at least one electrical conductor for transmitting power and electrical signals between tool string  20  and the surface. System  10  may further include suitable surface equipment for drilling, completing, and/or operating completion system  10  such as, for example, derricks, structures, pumps, electrical/mechanical well control components, etc. Tool string  20  is generally configured to perforate casing string  12  to provide for fluid communication between formation  6  and wellbore  4  at predetermined locations to allow for the subsequent hydraulic fracturing of formation  6  at the predetermined locations. 
     In this embodiment, tool string  20  generally includes a cable head  24 , a casing collar locator (CCL)  26 , a direct connect sub  28 , a plurality of perforating guns  30 , a switch sub  32 , a plug-shoot firing head  34 , a setting tool  36 , and a downhole or bridge plug  100  (shown schematically in  FIG. 1 ). Cable head  24  is the uppermost component of tool string  20  and includes an electrical connector for providing electrical signal and power communication between the wireline  22  and the other components (CCL  26 , perforating guns  30 , setting tool  36 , etc.) of tool string  20 . CCL  26  is coupled to a lower end of the cable head  24  and is generally configured to transmit an electrical signal to the surface via wireline  22  when CCL  26  passes through a casing collar of casing string  12 , where the transmitted signal may be recorded at the surface as a collar kick to determine the position of tool string  20  within wellbore  4  by correlating the recorded collar kick with an open hole log. The direct connect sub  28  is coupled to a lower end of CCL  26  and is generally configured to provide a connection between the CCL  26  and the portion of tool string  20  including the perforating guns  30  and associated tools, such as the setting tool  36  and bridge plug  100 . 
     Perforating guns  30  of tool string  20  are coupled to direct connect sub  28  and are generally configured to perforate casing string  12  and provide for fluid communication between formation  6  and wellbore  4 . Particularly, perforating guns  30  include a plurality of shaped charges that may be detonated by a signal conveyed by the wireline  22  from the surface to produce an explosive jet directed against casing string  12 . Perforating guns  30  may be any suitable perforation gun known in the art while still complying with the principles disclosed herein. For example, in some embodiments, perforating guns  30  may comprise a hollow steel carrier (HSC) type perforating gun, a scalloped perforating gun, or a retrievable tubing gun (RTG) type perforating gun. In addition, gun  30  may comprise a wide variety of sizes such as, for example, 2¾″, 3⅛″, or 3⅜″, wherein the above listed size designations correspond to an outer diameter of perforating guns  30 . 
     Switch sub  32  of tool string  20  is coupled between the pair of perforating guns  30  and includes an electrical conductor and switch generally configured to allow for the passage of an electrical signal to the lowermost perforating gun  30  of tool string  20 . Tool string  20  further includes plug-shoot firing head  34  coupled to a lower end of the lowermost perforating gun  30 . Plug-shoot firing head  34  couples the perforating guns  30  of the tool string  20  to the setting tool  36  and bridge plug  100 , and is generally configured to pass a signal from the wireline  22  to the setting tool  36  of tool string  20 . Plug-shoot firing head  34  may also include mechanical and/or electrical components to fire the setting tool  36 . 
     In this embodiment, tool string  20  further includes setting tool  36  and bridge plug  100 , where setting tool  36  is coupled to a lower end of plug-shoot firing head  34  and is generally configured to set or install bridge plug  100  within casing string  12  to isolate desired segments of the wellbore  4 . As will be discussed further herein, once bridge plug  100  has been set by setting tool  36 , an outer surface of bridge plug  100  seals against an inner surface  13  of casing string  12  to restrict fluid communication through wellbore  4  across bridge plug  100 . Additionally, unlike some downhole plugs such as frac plugs, once set, bridge plug  100  is configured to prevent fluid flow both uphole across (e.g., the annulus formed between the inner surface  13  of casing string  12  and an outer surface of bridge plug  100 ) bridge plug  100  (indicated schematically by arrow  15  in  FIG. 1 ) towards the surface of wellbore  4 , and downhole across bridge plug  100  (indicated schematically by arrow  17  in  FIG. 1 ) towards a lower terminal end or toe (not shown) of wellbore  4 . Setting tool  36  of tool string  20  may be any suitable setting tool known in the art while still complying with the principles disclosed herein. For example, in some embodiments, setting tool  36  may comprise a #10 or #20 Baker style setting tool. In addition, setting tool  36  may comprise a wide variety of sizes such as, for example, 1.68 in., 2.125 in., 2.75 in., 3.5 in., 3.625 in., or 4 in., wherein the above listed sizes correspond to the overall outer diameter of the tool. Although bridge plug  100  is shown in  FIG. 1  as incorporated in tool string  20 , bridge plug  100  may be used in other tool strings comprising components differing from the components comprising tool string  20 . For example, in open hole applications, once set, bridge plug  100  may be configured to sealingly engage a wall of a wellbore (e.g., the wall  8  of wellbore  4 ) rather than the inner surface of a casing string (e.g., the inner surface  13  of casing string  12 ). Additionally, in other embodiments, bridge plug  100  may be employed in well systems other than a completion system. For instance, in some embodiments, bridge plug  100  may be used to permanently or temporarily abandon a completed wellbore. 
     Referring to  FIGS. 1-3 , an embodiment of the bridge plug  100  of the tool string  20  of  FIG. 1  is shown in  FIGS. 2, 3 . In the embodiment of  FIGS. 2, 3 , bridge plug  100  has a central or longitudinal axis  105  and generally includes a mandrel assembly  102 , an engagement disk  150 , a pair of clamping members  160 A,  160 B, an elastomeric member or packer  170 , a pair of slip assemblies  200 A,  200 B, and a nose cone  220 . 
     Mandrel assembly  120  of bridge plug  100  is generally configured to interface with a setting tool (e.g., setting tool  36  shown in  FIG. 1 ) to assist in “setting” or actuating bridge plug  100  from a first or run-in position shown in  FIGS. 2, 3  to a second or set position. In this embodiment, mandrel assembly  102  of bridge plug  100  generally includes a first or outer cylindrical member or rod  104  and a second or inner cylindrical member or rod  120  positionable within outer rod  104 . As shown particularly in  FIG. 3 , the outer rod  104  of mandrel assembly  102  has a first end  104 A, a second end  104 B opposite first end  104 A, a central bore or passage defined by a generally cylindrical inner surface  106  extending between ends  104 A,  104 B, and a generally cylindrical outer surface  108  extending between ends  104 A,  104 B. In this embodiment, a first or inner surface pattern or feature  110  is positioned or formed on the inner surface  106  of outer rod  104 , as will be described further herein. 
     In this embodiment, the outer surface  108  of outer rod  104  includes an expanded diameter portion  112  extending from first end  104 A proximal upper end  104 A which forms an annular shoulder  114 . The expanded diameter portion  112  of outer surface  108  may include a plurality of circumferentially spaced apertures  116  (shown in  FIG. 2 ) configured to receive a plurality of connecting members for coupling mandrel assembly  102  with setting tool  36 ; however, in other embodiments, outer rod  104  may not include either expanded diameter portion  112  and/or apertures  116 . The outer surface  108  of outer rod  104  also includes a connector  118  at second end  104 B for coupling mandrel assembly  102  with nose cone  220 . In this embodiment, outer rod  104  of mandrel assembly  102  comprises a non-metallic, glass filament material; however, in other embodiments, outer rod  104  may comprise various materials. Although not included in this embodiment, in other embodiments, the outer surface  108  of outer rod  104  may include a plurality of ratchet teeth for engaging a body lock ring of downhole plug  100  configured for preventing the release of locking bridge plug  100  once plug  100  has been set by setting tool  36 . 
     The inner rod  120  of mandrel assembly  102  has a first end  120 A, a second end  120 B opposite first end  120 A, and a generally cylindrical outer surface  122  extending between ends  120 A,  120 B. In this embodiment, a second or outer surface pattern or feature  124  is positioned or formed on the outer surface  122  of inner rod  104 , as will be described further herein. The outer surface pattern  124  of inner rod  120  is configured to matingly or interlockingly engage the inner surface pattern  110  of outer rod  104  to thereby resist or prevent relative axial movement between outer rod  104  and inner rod  120  following the assembly of mandrel assembly  102 . Particularly, the interlocking engagement between the inner surface pattern  110  of outer rod  104  and the outer surface pattern  124  of inner rod  120  is configured to prevent dislodgement of inner rod  120  from outer rod  104  as mandrel assembly  102  is exposed to elevated pressures in wellbore  4  during the completion of wellbore  4  via completion system  10 . While in this embodiment, outer rod  104  comprises inner surface pattern  110  and inner rod  120  comprises surface pattern  124 , in some embodiments, outer rod  104  may not comprise an inner surface pattern and inner rod  120  may not comprise an outer surface pattern, and instead adhesion resulting from a filament winding process used to form outer rod  104  may serve to lock inner rod  120  with outer rod  104 . 
     Additionally, the inner surface  108  of outer rod  104  sealingly engages the outer surface  122  of inner rod  120  following the assembly of mandrel assembly  102  to prevent fluid communication across a generally cylindrical interface  125  formed between outer rod  104  and inner rod  120 . Particularly, sealing engagement between the inner surface  108  of outer rod  104  and the outer surface  122  of inner rod  120  restricts fluid flow across interface  125  in both a first axial (e.g., parallel with central axis  105 ) direction (indicated schematically by arrow  127  in  FIG. 3 ) from first a first end  125 A of interface  125  to a second end  125 B of interface  125 , and a second axial direction (indicated schematically by arrow  129  in  FIG. 3 ) from second end  125 B to first end  125 A that is opposite of the first direction. Thus, sealing engagement between the inner surface  108  of outer rod  104  and the outer surface  122  of inner rod  120  restricts fluid flow in both axial directions across interface  125 . Additionally, in this configuration, the outer rod  104  is locked to the inner rod  120  such that relative axial movement between inner rod  120  and outer rod  104  in either direction  127  or direction  129  is restricted 
     In this embodiment, the inner rod  120  of mandrel assembly  102  additionally includes a central bore or passage  126  extending from second end  120 B. Particularly, passage  126  of inner rod  120  extends towards, but not entirely to, the first end  120 A of inner rod  120 . As will be described further herein, in some applications, at some point following the setting of bridge plug  100  within wellbore  4 , it may be desirable to permit fluid flow across bridge plug  100  in at least one axial direction. In order to establish fluid flow across the set bridge plug  100 , a portion of the inner rod  120  of mandrel assembly  102  may be drilled or milled out by a downhole tool such that the drilled or milled passage formed by the downhole tool intercepts the central passage  126  of inner rod  120 , thereby permitting fluid flow across bridge plug  100  via central passage  126 . During this drilling or milling operation, central passage  126  may assist with equalizing fluid pressure across bridge plug  100 . Although in this embodiment, inner rod  120  of mandrel assembly  102  includes central passage  126 , in other embodiments, inner rod  120  may not include a central or inner passage. Inner rod  120  may comprise a material having relatively high tensile and shear strengths. In this embodiment, inner rod  120  comprises a non-metallic, composite material; however, in other embodiments, inner rod  120  may comprise fiberglass, magnesium, and other high tensile and shear strengths materials. Thus, in some embodiments, inner rod  120  may comprise a first material while outer rod  104  may comprise a second material that is different from the first material. 
     Engagement disk  150  of bridge plug  100  is disposed about mandrel assembly  102  and has a first end and a second end opposite the first end. In this embodiment, the first end of engagement disk  150  comprises an annular engagement surface  152  configured to engage a corresponding annular engagement surface of setting tool  36  to assist in actuating bridge plug  100  from the run-in position to the set position, as will be discussed further herein. Additionally, engagement disk  150  includes a generally cylindrical inner surface which defines an annular shoulder  154 . In the run-in position of bridge plug  100 , annular shoulder of engagement disk  150  is disposed directly adjacent or contacts shoulder  114  the outer rod  104  of mandrel assembly  102 . 
     Each clamping member  160 A,  160 B of bridge plug  100  is generally annular and is disposed about the outer rod  104  of mandrel assembly  102 . First clamping member  160 A is axially positioned between first slip assembly  200 A and packer  170  while second clamping member  160 B is axially positioned between packer  170  and second slip assembly  200 B. In this embodiment, each clamping member  160 A,  160 B has a generally cylindrical inner surface extending between opposing ends  162  thereof that includes an inner frustoconical surface  164 . Additionally, each clamping member  160 A,  160 B includes a generally cylindrical outer surface extending between ends  162  that includes a plurality of circumferentially spaced planar (e.g., flat) surfaces  166 . Each planar surface  166  extends at an angle relative to the central axis  105  of bridge plug  100 . In some embodiments, friction resulting from contact between the elastomeric material comprising packer  170  and frustoconical surfaces  164  and  164  of clamping members  160 A,  160 B assists in preventing relative rotation between packer  170  and clamping members  160 A,  160 B. 
     Packer  170  of bridge plug  100  is generally annular and disposed about mandrel assembly  102  between clamping members  160 A,  160 B. Packer  170  comprises an elastomeric material and is configured to sealingly engage the inner surface  13  of casing string  12  when bridge plug  100  is set. In this embodiment, packer  170  comprises a generally cylindrical outer surface  172  extending between first and second ends of packer  170 . Outer surface  172  of packer  170  includes a pair of frustoconical surfaces  174  extending from each end of packer  170 , as will be discussed further herein. 
     Slip assemblies  200 A,  200 B of bridge plug  100  are generally configured to engage or “bite into” the inner surface  13  of casing string  12  when bridge plug  100  is actuated into the set position to couple or affix bridge plug  100  to casing string  12 , thereby restricting relative axial movement between bridge plug  100  and casing string  12 . In this embodiment, each slip assembly  200 A,  200 B comprises a plurality of circumferentially spaced arcuate slip segments  202  disposed about the outer rod  104  of mandrel assembly  102 . 
     In some embodiments, one or more annular retainers or inserts may be disposed about the slip segments  202  of each slip assembly  200 A,  200 B In this embodiment, each slip segment  202  includes an inner surface extending between opposing ends  204  of slip segment  202  that includes a planar (e.g., flat) surface  206 . The planar surface  206  of each slip segment  202  extends at an angle relative to central axis  105  of downhole plug  105  and is configured to matingly engage one of the planar surfaces  166  of one of the clamping members  160 A,  160 B. 
     The planar (e.g., flat) interface formed between each corresponding planar surface  166  of clamping members  160 A,  160 B and each planar surface  206  of slip segments  202  restricts relative rotation between clamping members  160 A,  160 B and the slip segments  202  of slip assemblies  200 A,  200 B. Additionally, as will be described further herein, relative axial movement between clamping members  160 A,  160 B and slip assemblies  200 A,  200 B is configured to force the slip segments  202  of slip assemblies  200 A,  200 B radially outwards via the angled or cammed sliding contact between planar surfaces  166  of clamping members  160 A,  160 B and the planar surfaces  206  of the slip segments  202  of slip assemblies  200 A,  200 B. In this embodiment, each slip segment  202  of slip assemblies  200 A,  200 B includes a generally arcuate outer surface extending between opposing ends  204  that includes a plurality of arcuate engagement members  208 . Engagement members  208  are configured to engage or bite into the inner surface  13  of casing string  12  when bridge plug  100  is actuated into the set position to thereby affix bridge plug  100  to casing string  12  at a desired or predetermined location. Thus, engagement members  208  comprise a suitable material for engaging with inner surface  13  of casing string  12  during operations. For example, engagement members  208  may comprise  8620  Chrome-Nickel-Molybdenum alloy, carbon steel, tungsten carbide, cast iron, and/or tool steel. In some embodiments, engagement members  208  may comprise a composite material. However, in other embodiments, slip segments  202  may not include separate engagement members  208 . For example, instead of arcuate engagement members  208 , in some embodiments, each slip segment  202  may comprise one or more cylindrical, ceramic engagement members or inserts configured to physically contact and couple to the inner surface of casing string  12 . Additionally, while in this embodiment bridge plug  100  includes a pair of slip assemblies  200 A,  200 B, in other embodiments, bridge plug  100  may include a single slip assembly or more than two slip assemblies. 
     Nose cone  220  of bridge plug  100  is generally annular and is disposed about the second end  104 B of the outer rod  104  of mandrel assembly  102 . Nose cone  220  has a first end  220 A, a second end  220 B, a central bore or passage  222  defined by a generally cylindrical inner surface  224  extending between ends  220 A,  220 B, and a generally cylindrical outer surface  226  extending between ends  220 A,  220 B. In this embodiment, the inner surface  224  of nose cone  200  includes a connector  228  that releasably or threadably couples with the connector  118  of the outer rod  104  of mandrel assembly  102  to restrict relative axial movement between mandrel assembly  102  and nose cone  220 . In this embodiment, the outer surface  226  of nose cone  220  includes a plurality of axially spaced annular fins  230 . Fins  232  increase the surface area of outer surface  226  to facilitate the creation of turbulent fluid flow around fins  230  when bridge plug  100  is pumped through wellbore  4  along with the other components of tool string  20  to thereby increase the pressure differential in wellbore  4  between the uphole and downhole ends of bridge plug  100 . However, in other embodiments, nose cone  220  of bridge plug  100  may not include fins  230 . 
     Referring to  FIGS. 2-7 ,  FIGS. 4-7  illustrate an embodiment for forming or assembling the mandrel assembly  102  shown in  FIGS. 2, 3 . In the embodiment of  FIGS. 2-7 , inner rod  120  of mandrel assembly  102  is first formed through a pultrusion process until a desired length and outer diameter of inner rod  120  is achieved. Thus, in this embodiment, inner rod  120  comprises a pultruded rod. Following the formation of inner rod  120  via the pultrusion process, the outer surface  122  of inner rod  120  is machined to form outer surface pattern  124 . In this embodiment, outer surface pattern  124  comprises a helical pattern  124  extending the length of inner rod  120  and comprising at least one helical recess or groove  128  and at least one helical protrusion or ridge  130 . A maximum outer diameter  130 D (shown in  FIG. 4 ) of the helical ridge  130  of outer surface pattern  124  is greater than a maximum outer diameter  128 D (shown in  FIG. 4 ) of the helical groove  128 . In other embodiments, the configuration of outer surface pattern  124  may vary. For instance, in other embodiments outer surface pattern  124  may comprise one or more protrusions of various shapes formed on the outer surface  122  of inner rod  120 . In some embodiments, outer surface pattern  124  comprises a protrusion which is at least partially received within the inner surface pattern  110  of outer rod  104 . 
     For example, inner surface pattern  110  may comprise at least one helical recess or groove  119  (shown in  FIG. 7 ) and at least one corresponding helical protrusion or ridge  121  (shown in  FIG. 7 ). The helical ridge  121  of inner surface pattern  110  may have a maximum inner diameter  121 D that is less than a maximum inner diameter  119 D of helical groove  119  of inner surface pattern  110 . Additionally, the maximum inner diameter  121 D of the helical ridge  121  of inner surface pattern  110  may be less than the maximum outer diameter  130 D of the helical ridge  130  of outer surface pattern  124 . 
     In this embodiment, once outer surface pattern  124  is formed on the outer surface  122  of inner rod  120 , glass filaments are uniformly wound about the outer surface  122  of inner rod  120  to thereby form outer rod  104 . In other words, outer rod  104  of mandrel assembly  102  is formed in this embodiment via a filament winding process until a desired outer diameter of outer rod  104  is achieved. The inner surface pattern  110  is formed on the inner surface  106  of outer rod  104  as outer rod  104  is formed via the filament winding process, thereby interlocking the outer surface pattern  124  of inner rod  120  into the inner surface pattern  110  formed on the inner surface  106  of outer rod  104 . Particularly, the helical ridge  130  of the outer surface pattern  124  may be interlockingly received in the helical groove  119  of the inner surface pattern  110 . 
     Once the desired outer diameter of outer rod  104  is achieved via the filament winding process, the outer surface  108  of outer rod  104  is machined to form annular shoulder  114  and circumferentially spaced apertures  116 . In this embodiment, once the outer surface  108  of outer rod  104  is machined to form shoulder  114  and apertures  116 , the formation of mandrel assembly  102  is completed by forming or drilling the central passage  126  of inner rod  120 . As described above, in other embodiments, inner rod  120  of mandrel assembly  102  may not include central passage  126 . 
     As described above, bridge plug  100  is conveyed downhole though wellbore  4  along with the other components of tool string  20 . As tool string  20  is conveyed through wellbore  4 , the position of tool string  20  in wellbore  4  is monitored at the surface via signals generated from CCL  26  and transmitted to the surface using wireline  22 . Once tool string  20  is disposed in a desired location in wellbore  4 , a firing or actuation signal may be transmitted from the surface to tool string  20  to actuate or fire setting tool  36  and thereby actuate bridge plug  100  from the run-in position shown in  FIGS. 2, 3  to the set position. 
     Particularly, in this embodiment, setting tool  36  includes an inner member or mandrel (not shown) that moves axially relative to an outer member or housing of setting tool  36  upon the actuation of tool  36 . The mandrel of setting tool  36  is coupled to the outer rod  104  of the mandrel assembly  102  of bridge plug  100  such that the movement of the mandrel of setting tool  36  pulls mandrel assembly  102  uphole (e.g., towards setting tool  36 ). Additionally, the outer member of setting tool  36  contacts engagement surface  152  of engagement disk  150  to prevent disk  150 , clamping members  160 A,  160 B, packer  170 , and slip assemblies  200 A,  200 B from travelling in concert with mandrel assembly  102 , thereby providing relative axial movement between mandrel assembly  102  and disk  150 , clamping members  160 A,  160 B, packer  170 , and slip assemblies  200 A,  200 B. 
     As mandrel assembly  102  travels uphole towards setting tool  36 , the planar surfaces  166  of clamping members  160 A,  160 B apply a radially outwards force against slip assemblies  200 A,  200 B, respectively, forcing slip segments  202  radially outward towards casing string  12  as planar surfaces  166  of clamping members  160 A,  160 B slide along the planar surfaces  204  of the slip segments  202  of slip assemblies  200 A,  200 B. Slip segments  202  of slip assemblies  200 A,  200 B continue to travel radially outwards until engagement members  206  contact and couple to the inner surface  13  of casing string  12 , locking bridge plug  100  to casing string  12  at the desired location in wellbore  4 . 
     Additionally, upwards travel of mandrel assembly  102  causes the inner frustoconical surfaces  164  of clamping members  160 A,  160 B to apply an axially compressive force against packer  170 . The axially directed compressive force applied to packer  170  forces the outer surface  172  of packer  170  into sealing engagement with the inner surface  13  of casing string  12 . With outer surface  172  of packer  170  sealing against the inner surface  13  of casing string  12 , fluid flow across bridge plug  100  is restricted in both a first or downhole direction  13  (shown in  FIG. 1 ) from an uphole end to a downhole end of bridge plug  100 , and in a second or uphole direction  15  (shown in  FIG. 1 ) from the downhole end to the uphole end of bridge plug  100 . Particularly, sealing engagement between the outer surface  172  of packer  170  and the inner surface  13  of casing string  12 , sealing engagement between an inner surface of packer  170  and the outer surface  108  of the outer rod  104  of mandrel assembly  102 , and sealing engagement between the outer surface  22  of inner rod  120  and the inner surface  106  of outer rod  104  restrict fluid flow across bridge plug  100  in both the uphole and downhole directions  13 ,  15 . In some embodiments, following the actuation of bridge plug  100  into the set position, casing string  12  is pressure tested to confirm the sealing integrity formed between bridge plug  100  and casing string  12 . In certain embodiments, once casing string  12  has been successfully pressure tested, one or more firing signals may be transmitted from the surface to tool string  20  to fire one or more of the perforating guns  30  and thereby perforate casing string  12  at the desired location.. 
     Following the perforation of casing string  12 , setting tool  36  may be disconnected from bridge plug  100 , allowing setting tool  36  and the other components of tool string  20  to be retrieved to the surface of wellbore  4 , with bridge plug  100  remaining at the desired location in wellbore  4 . In some embodiments, a lock ring of bridge plug  100  may retain bridge plug  100  in the set position once setting tool  36  is released from bridge plug  100 . After tool string  20  has been retrieved from the wellbore  4 , fluid is pumped into wellbore  4  from the surface and directed through the perforations previously formed in casing string  12  by one or more of the perforating guns  30 , thereby hydraulically fracturing the formation  6  at the desired location in wellbore  4 . In some embodiments, the hydraulic fracturing process described above is repeated a plurality of times at a plurality of desired locations in wellbore  4  moving towards the surface of wellbore  4  using frac plugs in lieu of bridge plug  100  in order to permit uphole fluid flow through the frac plugs set uphole from bridge plug  100 . Thus, in some embodiments, bridge plug  100  may comprise the lowermost downhole plug installed within the casing string  12 . 
     After the formation  6  has been hydraulically fractured at each desired location in wellbore  4 , a tool may be deployed in wellbore  4  to drill out the bridge plug  100  disposed therein. Particularly, a downhole tool may be deployed through casing string  12  to drill into and through the inner rod  120  of the mandrel assembly  102  of bridge plug  100  from first end  120 . The drill of the downhole tool may cut through inner rod  120  until the drill intercepts passage  126  of inner rod  120 , thereby providing fluid communication between the uphole and downhole ends of bridge plug  100  via passage  126 . 
     Referring to  FIG. 8 , a flowchart of a method  300  of assembling a plug for sealing a wellbore is shown in  FIG. 8 . In some embodiments, method  300  may be practiced with the bridge plug  100  shown in  FIGS. 2-7 . Thus, in describing the features of method  300 , continuing reference will be made to bridge plug  100  shown in  FIGS. 2-7 ; however, it should be appreciated that embodiments of method  300  may be practiced with other devices. 
     Initially, method  300  includes forming a first rod at method block  302 . In some embodiments, method block  302  may include forming the inner rod  120  of mandrel assembly  102  through a pultrusion process until a desired length and outer diameter of inner rod  120  is achieved. In some embodiments, method block  302  may also include machining a surface pattern (e.g., surface pattern  124  of inner rod  120 ) onto an outer surface of the inner rod. In some embodiments, the pattern may be a helical pattern including one or more helical grooves (e.g., helical groove  128 ) and one or more helical ridges (e.g., helical ridge  130 ). 
     Method  300  continues at method block  304  by forming a second rod about the first rod using a filament winding process. In some embodiments, method block  304  may include uniformly winding glass filaments about the outer surface of the formed inner rod (e.g., inner rod  120  of mandrel assembly  102 ) until a desired outer diameter of the outer rod (e.g., outer rod  104  of mandrel assembly  102 ) is achieved. Method block  304  may also include forming a surface pattern on an inner surface of the outer rod as the outer rod is wound about the outer surface of the inner rod. In some embodiments, the surface pattern may be a helical pattern including one or more helical grooves (e.g., helical groove  119 ) and one or more helical ridges (e.g., helical ridge  121 ). 
     Method  300  continues at block  306  by positioning a packer about the second rod, the packer being configured to seal the wellbore in response to the plug being actuated from a first position to a second position. In some embodiments, method block  306  may include positioning packer  170  about the outer surface  108  of the outer rod  104  of mandrel assembly  102 . In some embodiments, method  300  may further include positioning engagement disk  150 , clamping members  160 A,  160 B, and slip assemblies  200 A,  200 B about the outer surface  108  of outer rod  104 . 
     Embodiments disclosed herein include a downhole plug (e.g., bridge plug  100 ) comprising a mandrel assembly (e.g., mandrel assembly  102 ) comprising an inner rod (e.g., inner rod  120 ) and a filament wound outer rod (e.g., outer rod  104 ) that is separate and distinct from the inner rod and which is formed about the inner rod. The downhole plug may also include a packer (e.g., packer  170 ) disposed about the mandrel assembly, the packer configured to seal the wellbore in response to the plug being actuated from a first position to a second position, wherein the mandrel assembly is configured to apply a compressive force to the packer as the plug is actuated from the first position to the second position. 
     By forming the mandrel assembly using a filament winding process the costs associated with manufacturing the mandrel assembly may be minimized (e.g., relative to compression molded mandrel assemblies, etc.). For instance, the number of parts required to form the mandrel assembly may be minimized by utilizing a filament winding process. Additionally, the simplified design offered by the filament wound mandrel assemblies described herein also minimize the number of points at which a failure of the mandrel assembly may occur, thereby increasing the reliability of the mandrel assembly. Further, the seal created by the filament wound mandrel assembly may enable a downhole plug incorporating the mandrel assembly to withstand relatively greater differential pressures across the plug (following setting of the plug) than other designs which may, for instance, rely on elastomeric seals (e.g., O-ring seals, etc.) for forming a seal barrier. 
     While exemplary embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure presented herein. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.