Patent Publication Number: US-8967255-B2

Title: Subsurface release cementing plug

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     When wellbores are prepared for oil and gas production, it is common to cement a casing string within the wellbore. Often, it may be desirable to cement the casing within the wellbore in multiple, separate stages. 
     Conventionally, cementing a casing string within a wellbore is achieved by flowing cement to the bottom of the casing string and upward into the annular space between the casing string and the wellbore walls. In order to preserve the integrity of the cementitious slurry used to cement the casing within the wellbore, “cementing plugs” or “wiper plugs” are used to form a barrier between the cementitious slurry and other servicing fluids and reduce intermixing or intermingling between the cementitious slurry and any other fluid. It may be desirable to employ subsurface release cementing plugs, that is, cementing plugs that are released from a point within the wellbore below the Earth&#39;s surface, in a cementing operation. However, conventional subsurface release plugs are limited in application, for example, because of the relatively large diameter of conventional subsurface release cementing plug systems. 
     Therefore, there is a need for improved subsurface release plugs that may be employed in a wider range of applications. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a subsurface release plug release apparatus comprising a mandrel comprising a bottom plug portion, a top plug portion, a work string attachment portion, a first release portion between the bottom plug portion and the top plug portion, wherein the first release portion comprises a controlled strength segment configured to fail structurally and thereby release the bottom plug portion at a first fluid pressure, and a second release portion between the top plug portion and the work string attachment portion, wherein the second release portion is configured to release the bottom plug portion at a second fluid pressure, wherein the first fluid pressure is less than the second fluid pressure, a bottom plug body disposed about the bottom plug portion of the mandrel, and a top plug body disposed about the top plug portion of the mandrel. 
     Further disclosed herein is a wellbore servicing method comprising positioning a casing defining a flowbore within a wellbore with a subsurface release plug release apparatus disposed within a portion of the casing, the subsurface release plug release apparatus comprising a mandrel comprising a bottom plug portion, a top plug portion, a work string attachment portion, a first release portion between the bottom plug portion and the top plug portion, wherein the first release portion comprises a controlled strength segment configured to fail structurally and thereby release the bottom plug portion at a first fluid pressure, and a second release portion between the top plug portion and the work string attachment portion, wherein the second release portion is configured to release the bottom plug portion at a second fluid pressure, wherein the first fluid pressure is less than the second fluid pressure, a bottom plug body disposed about the bottom plug portion of the mandrel, and a top plug body disposed about the top plug portion of the mandrel, causing the first release portion to release the bottom plug portion by causing structural failure of the controlled strength segment, pumping a cementitious slurry via the flowbore of the casing, causing the second release portion to release the top plug portion, displacing the cementitious slurry from the flowbore of the casing into an annular space between the casing and a wellbore wall, and allowing the cementitious slurry to set. 
     Also disclosed herein is a wellbore servicing method comprising positioning a casing defining a flowbore within a wellbore with a subsurface release plug release apparatus disposed within a portion of the casing, the subsurface release plug release apparatus comprising a mandrel comprising a bottom plug portion, a top plug portion, a work string attachment portion, a first release portion between the bottom plug portion and the top plug portion, wherein the first release portion comprises a controlled strength segment configured to fail structurally and thereby release the bottom plug portion at a first fluid pressure, and a second release portion between the top plug portion and the work string attachment portion, wherein the second release portion is configured to release the top plug portion at a second fluid pressure, wherein the first fluid pressure is less than the second fluid pressure, a bottom plug body disposed about the bottom plug portion of the mandrel, and a top plug body disposed about the top plug portion of the mandrel, pumping a first obturating member to pass through the top plug portion of the mandrel and engage a first seat within the bottom plug portion of the mandrel, applying a fluid pressure to cause the first release portion to release the bottom plug portion by causing structural failure of the first controlled strength segment, pumping a second obturating member to engage a second seat within the top plug portion of the mandrel, and applying a fluid pressure to cause the second release portion to release the top plug portion. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         FIG. 1  is a cut-away illustration of an environment for a wellbore servicing operation. 
         FIG. 2A  is cross-sectional illustration of an embodiment of a subsurface release plug release apparatus. 
         FIG. 2B  is cross-sectional illustration of an alternative embodiment of a subsurface release plug release apparatus. 
         FIG. 3A  is a cross-sectional longitudinal illustration of an embodiment of a mandrel of a subsurface release plug release apparatus. 
         FIG. 3B  is a cross-sectional end-view illustration of an embodiment of a mandrel of a subsurface release plug release apparatus. 
         FIG. 4A  is a cross-sectional illustration of an embodiment of a bottom plug releasing member disposed within a work string. 
         FIG. 4B  is a cross-sectional illustration of an embodiment of a top plug releasing member disposed within a work string. 
         FIG. 5  is a cross-sectional illustration of an embodiment of a collar integrated within a casing. 
         FIG. 6  is a cross-sectional illustration of an embodiment of a bottom plug separated from a subsurface release plug (SRP) release apparatus and disposed within a casing. 
         FIG. 7  is a cross-sectional illustration of an embodiment of a bottom plug separated from a SRP release apparatus and engaging a collar integrated within a casing. 
         FIG. 8  is a cross-sectional illustration of an embodiment of a bottom plug mandrel portion separated from a bottom plug body portion within a casing. 
         FIG. 9  is a cross-sectional illustration of an embodiment of a top plug separated from a SRP release apparatus and disposed within a casing. 
         FIG. 10  is a cross-sectional illustration of an embodiment of a top plug separated from a SRP release apparatus and engaging a bottom plug body integrated within a casing. 
     
    
    
     DETAILED DESCRIPTION 
     Unless otherwise specified, use of the terms “connect,” “engage,” “couple,” “attach,” or any other like term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. 
     Unless otherwise specified, use of the terms “up,” “upper,” “upward,” “up-hole,” “upstream,” or other like terms shall be construed as generally from the formation toward the surface or toward the surface of a body of water; likewise, use of “down,” “lower,” “downward,” “down-hole,” “downstream,” or other like terms shall be construed as generally into the formation away from the surface or away from the surface of a body of water, regardless of the wellbore orientation. Use of any one or more of the foregoing terms shall not be construed as denoting positions along a perfectly vertical axis. 
     Unless otherwise specified, use of the term “subterranean formation” shall be construed as encompassing both areas below exposed earth and areas below earth covered by water such as ocean or fresh water. 
     Disclosed herein are one or more embodiments of a subsurface release plug (SRP) release apparatus, a SRP system, and methods using the same in the performance of a wellbore servicing operation. In an embodiment, such an SRP release apparatus or SRP system may be employed in the placement and cementing of a casing string within a wellbore. 
     Referring to  FIG. 1 , an embodiment of an operating environment in which an SRP release apparatus and/or system may be employed is illustrated. It is noted that although some of the figures may exemplify horizontal or vertical wellbores, the principles of the apparatuses, systems, and methods disclosed may be similarly applicable to horizontal wellbore configurations, conventional vertical wellbore configurations, and combinations thereof. Therefore, the horizontal or vertical nature of any figure is not to be construed as limiting the wellbore to any particular configuration. 
     As depicted in  FIG. 1 , the operating environment generally comprises a wellbore  114  that penetrates a subterranean formation  102  for the purpose of recovering hydrocarbons, storing hydrocarbons, disposing of carbon dioxide, or the like. The wellbore  114  may be drilled into the subterranean formation  102  using any suitable drilling technique. In an embodiment, a drilling or servicing rig comprises a derrick with a rig floor through which a work string  150  (e.g., a drill string, a tool string, a segmented tubing string, a jointed tubing string, or any other suitable conveyance, or combinations thereof) may be positioned within or partially within the wellbore  114 . In an embodiment, the work string  150  may comprise two or more concentrically positioned strings of pipe or tubing (e.g., a first work string may be positioned within a second work string). The drilling or servicing rig may be conventional and may comprise a motor driven winch and other associated equipment for lowering the work string  150  into the wellbore  114 . Alternatively, a mobile workover rig, a wellbore servicing unit (e.g., coiled tubing units), or the like may be used to lower the work string  150  into the wellbore  114 . 
     The wellbore  114  may extend substantially vertically away from the earth&#39;s surface over a vertical wellbore portion, or may deviate at any angle from the earth&#39;s surface  104  over a deviated or horizontal wellbore portion. In alternative operating environments, portions or substantially all of the wellbore  114  may be vertical, deviated, horizontal, and/or curved. 
     In embodiment, the wellbore  114  may be partially cased with a first casing string  120  and partially uncased. The first casing string  120  may be secured into position within the wellbore  114  in a conventional manner with cement  122 , alternatively, the first casing string  120  may be partially cemented within the wellbore  120 , alternatively, the first casing string may be uncemented. In an alternative embodiment, the wellbore  114  may be uncased and uncemented. 
     In the embodiment of  FIG. 1 , a second casing string  160  (hereinafter, casing  160 ) may be positioned within an uncased portion of the wellbore  116 . The casing  160  may be lowered into the wellbore  114  and/or the uncased portion of the wellbore  116  suspended from the work string  150 . In an embodiment, the casing  160  may be suspended from the work string  150  by a liner hanger  140  or the like. The liner hanger  140  may comprise any suitable type or configuration of liner hanger, as will be appreciated by one of skill in the art with the aid of this disclosure. 
     In the embodiment of  FIG. 1 , a SRP release apparatus  200  is disposed at the lower end of the work string  150  and within an upper portion of the casing  160 . Referring to  FIG. 2A , an embodiment of the SRP release apparatus  200  is illustrated. In the embodiment of  FIG. 2A , the SRP release apparatus  200  generally comprises a mandrel  210 , a bottom plug body  270  disposed about a portion of the mandrel  210 , and a top plug body  280  disposed about a portion of the mandrel  210 . 
     In one or more of the embodiments disclosed herein, a SRP release apparatus such as SRP release apparatus  200  may be discussed with reference to one or more figures. In these figures, the illustrated embodiments of the SRP release apparatus are generally oriented such that the upper-most (i.e., the furthest up-hole) end or portion of the SRP release apparatus  200  may be toward the left-hand side of such figure while the lower-most (i.e., the further down-hole) end or portion of the SRP release apparatus  200  may be toward the right-hand side of the figure. It is noted that reference herein to an upper, upper-most, up-hole, lower, lower-most, or down-hole, portion, segment, and/or component should not be construed as so-limiting unless otherwise specified. While the embodiments of a SRP release apparatus may be illustrated in a given configuration or orientation, one of skill in the art with the aid of this disclosure will appreciate that a SRP release apparatus may be suitably otherwise configured or oriented. 
     In the embodiment of  FIG. 2A , the mandrel  210  may be characterized as a generally tubular body defining an axial flowbore  211  having a longitudinal axis. The axial flowbore  211  may be in fluid communication with an axial flowbore  151  defined by the work string  150 . 
     In the embodiment of  FIG. 2A , the mandrel  210  comprises a bottom plug mandrel portion  220 , a first controlled strength segment  230 , a top plug mandrel portion  240 , a second controlled strength segment  250 , and a work string attachment portion  260 . As used herein, a controlled strength segment refers to segment of the mandrel  210  having a strength in a predetermined, desirable threshold and which, when that threshold is exceeded, will fail structurally, thereby resulting in the longitudinal separation of the mandrel  210  at the controlled strength segment. For example, when subjected to a force (e.g., an internally applied fluid differential pressure) greater than the threshold of a controlled strength segment, the controlled strength segment may burst, crack, disintegrate, break, rupture, or the like. In various embodiments, a controlled strength segment may be characterized as exhibiting a strength that is comparatively greater, alternatively, about the same as, alternatively, less than the strength of another controlled strength segment, the remainder of the mandrel, or combinations thereof. 
     In an embodiment, the mandrel  210  may be characterized as comprising regions or segments having strengths that vary in comparison to each other. For example, the mandrel  210  may comprise two or more portions, regions, or segments exhibiting a relatively high strength. The mandrel  210  may also comprise one or more portions, regions, or segments exhibiting relatively intermediate strength in comparison to the high-strength portions. The mandrel  210  may also comprise one or more segments exhibiting relatively low strength in comparison to the intermediate strength portions. In the embodiment of  FIG. 2A , the bottom plug mandrel portion  220 , the top plug mandrel portion  240 , and the work string attachment portion  260  may exhibit the relatively highest strength, the second controlled strength segment  250  may exhibit relatively low strength in comparison to the bottom plug mandrel portion  220 , the top plug mandrel portion  240 , and the work string attachment portion  260 , and the first controlled strength segment  230  may exhibit relatively low strength in comparison to the second controlled strength segment  250 . 
     In an embodiment, the mandrel  210  may be formed from a suitable material. Examples of materials from which the mandrel may be formed include but are not limited to composite materials (examples of which will be discussed herein), metals and metal alloys, phenolic materials, rubbers, hardened plastics, cast materials, ceramic materials, resins, epoxies, or combinations thereof. Composite materials may include a reinforcing agent and a matrix material. In a fiber-based composite, fibers may act as the reinforcing agent. The matrix material may act to keep the fibers in a desired location and orientation and also serve as a load-transfer medium between fibers within the composite. In an embodiment, the materials from which the mandrel  210  is formed may be characterized as drillable materials. 
     In an embodiment, a mandrel having regions, portions, or segments having strengths that vary in comparison to each other, such as mandrel  210 , comprises a fiber-wound composite formed by a fiber-winding process. Referring to  FIGS. 3A and 3B , a fiber-wound mandrel  210  comprising a composite  210 B of fibers a binder wound about a template or spindle  210 A, is illustrated in a side-view of the pipe and an end-view, respectively. The spindle  210 A may comprise a generally tubular body constructed of conventional metal alloys (e.g., steel, such as X65 or X70), cast materials, ceramic materials, resins, epoxies, or combinations thereof. The fibers may comprise assemblies of strings (e.g., windings, mats, meshes, etc.), each string consisting of multiple, intertwined threads. These threads may be synthetic (e.g., Kevlar™), metal alloys (e.g., steel), fiberglass, carbon fiber, nano-fibers, or combinations thereof. 
     The binder surrounds and/or permeates the fibers. Suitable binder materials that may be used in the composite materials described herein may include, but are not limited to, thermosetting resins including orthophthalic polyesters, isophthalic polyesters, phthalic/maelic type polyesters, vinyl esters, thermosetting epoxies, phenolics, cyanates, bismaleimides, nadic end-capped polyimides (e.g., PMR-15), and any combinations thereof. Additional resin matrix materials may include thermoplastic resins including polysulfones, polyamides, polycarbonates, polyphenylene oxides, polysulfides, polyether ether ketones, polyether sulfones, polyamide-imides, polyetherimides, polyimides, polyarylates, liquid crystalline polyester, polyurethanes, polyureas, and any combinations thereof. In an embodiment, the binder material may comprise a two-component resin composition. Suitable two-component resin materials may include a hardenable resin and a hardening agent that, when combined, react to form a cured resin matrix material. Suitable hardenable resins that may be used include, but are not limited to, organic resins such as bisphenol A diglycidyl ether resins, butoxymethyl butyl glycidyl ether resins, bisphenol A-epichlorohydrin resins, bisphenol F resins, polyepoxide resins, novolak resins, polyester resins, phenol-aldehyde resins, urea-aldehyde resins, furan resins, urethane resins, glycidyl ether resins, other epoxide resins, and any combinations thereof. Suitable hardening agents that can be used include, but are not limited to, cyclo-aliphatic amines; aromatic amines; aliphatic amines; imidazole; pyrazole; pyrazine; pyrimidine; pyridazine; 1H-indazole; purine; phthalazine; naphthyridine; quinoxaline; quinazoline; phenazine; imidazolidine; cinnoline; imidazoline; 1,3,5-triazine; thiazole; pteridine; indazole; amines; polyamines; amides; polyamides; 2-ethyl-4-methyl imidazole; and any combinations thereof. In an embodiment, one or more additional components may be added the matrix material to affect the properties of the matrix material. For example, one or more elastomeric components (e.g., nitrile rubber) may be added to increase the flexibility of the resulting matrix material. Not intending to be bound by theory, the binder may act to hold the fibers together and retain the fibers in the desired orientation. In addition, the binder may protect the fibers. One skilled in the art may readily appreciate that the thickness and/or percentage of the binder may varied to meet a desired parameter. 
     In an embodiment, the mandrel  210  may be manufactured by a method comprising passing the fibers through a bath or solution of the binder solution and wrapping the binder-wetted fibers around the spindle  210 A using a fiber wrapping machine or other similar apparatus, as will be appreciated by one of skill in the art viewing this disclosure. In an embodiment, the fibers may be wound via an automated or computed-driven machine, for example, as may be capable of winding the fibers to achieve one or more desired strength parameters or characteristics for the completed mandrel  210 , as will be described herein. This step in the manufacturing process may be performed in a manufacturing shop or other similar facility. The spindle  210 A may be secured at both ends and rotated as the fibers are wrapped around or otherwise applied about the spindle  210 A from one end to the other and back again, continuing in a winding fashion until the fibers have been applied in the desired thickness and/or number of windings. In an embodiment, the fibers may be wound about the spindle  210 A in alternating “hoop” and “helical” layers, where hoop layers refer to fibers wound circumferentially about the spindle  210 A generally perpendicularly to longitudinal axis of the mandrel  210  and helical layers refer to fibers applied generally axially with respect to the longitudinal axis of the mandrel  210 . 
     In an embodiment, one or more desired strength parameters or characteristics for the completed mandrel  210  may be designed and imparted dependent upon the way in which the fibers are applied to the spindle  210 A at various positions or regions along the mandrel, for example, the number of windings of fibers wound around the spindle  210 A, the direction and/or orientation of the fibers, the thickness of the composite  210 B, or combinations thereof. For example, various strength characteristics and/or other mechanical properties may be adjusted by varying the winding angle of the fibers, altering the type and/or characteristics of the fiber material and/or the binder materials employed, or combinations thereof. As such, it is possible to manufacture mandrels having strength characteristics that vary at different portions or segments along the mandrel  210  by ranging the winding angle from about 0° to about −20° with respect to the longitudinal axis of the mandrel  210 , altering the type of fiber, altering the thickness of the individual fibers, altering the thickness in which the fibers are applied, or combinations thereof. In an embodiment, to achieve the regions of varying strength, the fibers may be wound around the spindle  210 A in a first orientation and/or thickness in a first region and a second orientation and/or thickness in a second region, thereby imparting differing strength parameters or characteristics to differing regions of the mandrel  210 . For example, a relatively high strength portion of the mandrel may be wound with high strength carbon fibers and a relatively low strength portion of the mandrel may be wound with a lower strength fiber such as glass fibers. For example, the bias angle, the fiber type, fiber diameter, or combinations thereof may be varied to create areas along the mandrel having specific strength properties. 
     In an alternative embodiment, a mandrel like mandrel  210  having regions, portions, or segments having strengths that vary in comparison to each other may be manufactured by a milling process. In such an embodiment the mandrel  210  may be milled to comprise portions having one or more relatively reduced strength characteristics. For example, the mandrel  210  may comprise portions of reduced thickness, perforations, or other induced points of weakness, as will be appreciated by one of skill in the art viewing this disclosure. 
     In an embodiment, the mandrel  210 , particularly, the work string attachment mandrel portion  260 , may be configured to be connected to the lower end of the work string  150  via a suitable connection, for example, a threaded connection, a hammer joint, a collet, the like, or combinations thereof. 
     In an embodiment, the bottom plug mandrel portion  220  may be configured to receive and engage an obturating member (e.g., a dart or ball, as will be discussed herein). For example, the inner bore of the bottom plug mandrel portion  220  may comprise one or more seats comprising a shoulder, a chamfer, a bevel, or a similar reduction in the diameter of the inner bore surface that will receive and engage an obturating member of a given size and/or configuration. In the embodiment of  FIG. 2A  the inner bore of the bottom plug mandrel portion  220  may comprises two chamfers  222  extending between a greater inner bore diameter and a lesser inner bore diameter. 
     In an embodiment, the bottom plug mandrel portion  220  may be configured to allow pressure equalization between the axial flowbore  211  and the exterior of the mandrel  210 . In the embodiment of  FIG. 2A , the bottom plug mandrel portion  220  comprises ports  224  allowing for the communication of fluid between the axial flowbore  211  and the exterior of the mandrel  210 . 
     In an embodiment, the bottom plug mandrel portion  220  may be configured to be releasably secured to the bottom plug body  270  or vice versa. For example, the bottom plug mandrel portion  220  may comprise a groove or channel configured to receive a snap-ring, a bore configured to receive a shear pin or other frangible member, or the like. In the embodiment of  FIG. 2A , the bottom plug mandrel portion  220  comprises a bore  226  configured to receive a the pin or other frangible member and releasably restrict movement of the bottom plug body  270  with respect to the bottom plug mandrel portion  220 , as will be discussed herein. 
     In an embodiment, the top plug mandrel portion  240  may be configured to receive and engage an obturating member (e.g., a dart or ball, as will be discussed herein). For example, the inner bore of the top plug mandrel portion  240  may comprise one or more seats comprising a shoulder, a chamfer, a bevel, or a similar reduction in the diameter of the inner bore surface that will receive and engage an obturating member of a given size and/or configuration. In the embodiment of  FIG. 2A  the inner bore of the top plug mandrel portion  240  comprises two chamfers  242  extending between a greater inner bore diameter and a lesser inner bore diameter. 
     In an embodiment, the top plug mandrel portion  240  may be configured to secure such an obturating member (e.g., a dart or ball, as will be discussed herein) that engages the seat (e.g., chamfers  242 ) within the inner bore of the top plug mandrel portion  240 . For example, the top plug mandrel portion  240  may comprise one or more recesses, grooves, shoulders, or channels configured to receive an expandable ring, a latch, a snap-ring, a pin, or the like associated with the obturating member. Alternatively, the top plug mandrel portion  240  may comprise a latch, a snap-ring, a pin, or combinations thereof to engage a groove and/or recess of an obturating member. In the embodiment of  FIG. 2A , the top plug mandrel portion  240  comprises a shoulder  244  at the upper end of a recess  248  that is configured to receive an expandable ring or the like and secure an obturating member that engages the seat within the inner bore of the top plug mandrel portion  240 . 
     In an embodiment, the top plug mandrel portion  240  may be configured to engage and be secured to the top plug body  280 . For example, the top plug mandrel portion  240  may comprise a series of shoulders or bevels, a series of threads, a groove or channel configured to receive a snap-ring, a bore configured to receive a pin, or combinations thereof associated with the top plug body  230  (or vice versa). In the embodiment of  FIG. 2A , the top plug mandrel portion  240  comprises a threaded interface  246  along the outer surface thereof configured to engage a complementary threaded interface of the top plug body  280  and restrict movement of the top plug mandrel portion  240  with respect to the top plug body  280 , as will be discussed herein. 
     In the embodiment of  FIG. 2A , the first controlled strength segment  230  may extend circumferentially around the mandrel  210  over a given longitudinal distance. The first control strength segment  230  may be longitudinally disposed along the mandrel between the bottom plug mandrel portion  220  and the top plug mandrel portion  240 . 
     In an embodiment, the first controlled strength segment  230  may be characterized as exhibiting a strength, particularly, a tensile strength, less than the second controlled strength segment  250  and less than the body of the mandrel  210 . In such an embodiment, the first controlled strength segment  230  may fail structurally when subjected to an internally applied fluid differential pressure greater than a given threshold while the second strength segment  250  and the body of the mandrel  210  will not. In an embodiment, the first controlled strength segment  230  may be characterized as having a predetermined tensile strength (referring to the amount of force applied in opposing directions along the longitudinal axis of the mandrel  210 ) that the first controlled strength segment is able to withstand. For example, the first controlled strength segment  230  may fail, causing the mandrel  210  to separate longitudinally, upon application of an internally applied fluid differential pressure greater than a given threshold. In an embodiment, such a threshold may be in the range of from about 800 psi to about 2,500 psi, alternatively, from about 1,000 psi to about 2,000 psi. 
     In the embodiment of  FIG. 2A , the second controlled strength segment  250  may extend circumferentially around the mandrel  210  over a given longitudinal distance. The second controlled strength segment  250  may be longitudinally disposed along the mandrel between the top plug mandrel portion  240  and the work string attachment mandrel portion  260   
     In an embodiment, the second controlled strength segment  250  may be characterized as exhibiting a strength, particularly, a tensile strength, greater than the first controlled strength segment  230  and less than the body of the mandrel  210 . In such an embodiment, the second controlled strength segment  250  may fail structurally when subjected to an internally applied fluid differential pressure greater than a given threshold while the body of the mandrel  210  will not. In an embodiment, the second controlled strength segment  250  may be characterized as having a predetermined tensile strength (referring to the amount of force applied in opposing directions along the longitudinal axis of the mandrel  210 ) that the first controlled strength segment is able to withstand. For example, the second controlled strength segment  250  may fail, causing the mandrel  210  to separate longitudinally, upon application of an internally applied fluid pressure greater than a given threshold. In an embodiment, such a threshold may be in the range of from about 1,500 psi to about 5,500 psi, alternatively, from about 3,000 psi to about 4,000 psi. 
     Referring to  FIG. 2B , an alternative embodiment of an SRP release apparatus  400  comprising an alternative configuration of a mandrel  410  is illustrated. In the embodiment of  FIG. 2B , the mandrel  410  comprises a bottom plug mandrel portion  420 , a first controlled strength segment  430 , a top plug mandrel portion  440  comprising a plurality of collet fingers  463  and a collet releasing sleeve  465 , and a work string attachment portion  460  comprising a collet retainer sleeve  447 . 
     In the embodiment of  FIG. 2B , the mandrel  410  comprises regions or segments having strengths that vary in comparison to each other. For example, in the embodiment of  FIG. 2B , the bottom plug mandrel portion  420 , the top plug mandrel portion  440 , and the work string attachment portion  460  may exhibit the relatively highest strength and the first controlled strength segment  430  may exhibit relatively low strength in comparison to the bottom plug mandrel portion  420 , the top plug mandrel portion  440 , and the work string attachment portion  460 . In the embodiment of  FIG. 2B , the bottom plug mandrel portion  420 , the first controlled strength segment  430 , the top plug mandrel portion  440  and the work string attachment portion  460  may be similarly configurable and similarly operable as disclosed herein (e.g., as discussed with reference to the Figures, including but not limited to  FIG. 1 ). 
     In the embodiment of  FIG. 2B , the top plug mandrel portion  440  may be configured to be connected to the work string attachment portion  460 . For example, in the embodiment of  FIG. 2B , the work string attachment portion  460  comprises a collet retainer sleeve  447  having a shoulder  448  or the like. Also, in the embodiment of  FIG. 2B , the top plug mandrel portion  440  comprises a plurality of collet fingers  463 . The collet fingers  463  may be configured to engage the shoulder  448  in a radially-expanded conformation and to disengage the shoulder  448  in a radially contracted or collapsed conformation. In the embodiment of  FIG. 2B , the collet fingers  463  are held in the radially-expanded conformation by a collet releasing sleeve  465 , thereby retaining the top plug mandrel portion  440  with respect to the work string attachment portion  460 . In an embodiment, the collet releasing sleeve  465  may be longitudinally slidable between a first, relatively upper position, as shown in  FIG. 2B , and a second, relatively lower position. In an embodiment, the collet releasing sleeve  465  may be retained in the first, relatively upper position by a frangible member, such as a shear pin or the like. 
     Referring again to  FIG. 2A , in an embodiment the bottom plug body  270  generally comprises a tubular body defining a bore extending longitudinally therethrough. As shown in  FIG. 2A , the bottom plug body  270  may be configured to receive the bottom plug mandrel portion  220 , which may be positioned within the bore defined by the bottom plug body  270 . In the embodiment of  FIG. 2A , the bottom plug body  270  may be releasably secured to the bottom plug mandrel portion  220 . For example, the bottom plug body  270  may comprise a groove or channel configured to receive a snap-ring, a bore configured to receive a shear pin or other frangible member, or the like. In the embodiment of  FIG. 2A , the bottom plug body  270  comprises a bore  276  configured to receive a frangible member, particularly, shear pin  206  which releasably restricts movement of the bottom plug body  270  with respect to the bottom plug mandrel portion  220 . In an embodiment, the force necessary to cause structural failure of the shear pin  206  may be greater than, alternatively, less than, the force necessary to cause structural failure of the first controlled strength segment  230 . 
     In an alternative embodiment, the bottom plug body  270  may be connected to the bottom plug mandrel portion  220  by a controlled strength area within the bottom plug body  270 , a glue joint having a predetermined strength, a shouldered butt joint having a predetermined strength, or the like. 
     In an embodiment, the bottom plug body  270  may be configured to sealably engage an inner wall of a casing string, such as, casing  160 . For example, in the embodiment of  FIG. 2A , the bottom plug body  270  further comprises one or more wipers  275 . In an embodiment, the wipers  275  may generally be configured to substantially remove, separate, or clean fluids from the inner bore surface of the casing  160 . The wipers  275  may be provided in a suitable number and configuration, as will be appreciated by one of skill in the art viewing this disclosure. For example, the embodiment of  FIG. 2A  illustrates the bottom plug body  270  with four wipers, however more or fewer may be provided. The wipers  275  may extend radially outward from the bottom plug body  270 . As will be appreciated by one of skill in the art viewing this disclosure, the wipers  275  may be sized to sealably and slidably engage the inner bore of a casing string such as casing  160  of a particular size. The wipers  275  may extend outward from the bottom plug body at a suitable angle from the bottom plug body  270 . For example, in the embodiment of the  FIG. 2A , each of the four wipers  275  is angled, thereby forming a conical, cross-section. In an embodiment, the wipers  275  may be formed from a suitable material. Such a suitable material may be characterized as conformable or pliable, for example, such that the wipers  275  may be able to conform to inconsistencies in the inner bore of the casing  160 . Examples of suitable materials include but are not limited to rubber, foam, plastics, or combinations thereof. 
     In an embodiment, the bottom plug body  270  may be configured to engage a collar disposed within the casing  160 , for example, a baffle adapter or landing collar such as landing collar  170 , as will be discussed herein. For example, in the embodiment of  FIG. 2A , the bottom plug body  270  comprises a nose portion having an angled face such as a chamfer  272 . Chamfer  272  may be configured to sealably engage a seat comprising a complementary bevel or chamfer within the collar  170 , as will be discussed herein. 
     In an embodiment, the bottom plug body  270  may be configured to receive and engage the top plug body  280 , as will be discussed herein. For example, in the embodiment of  FIG. 2A  the bottom plug body  270  comprises an upper chamfer  274  configured to receive and engage a complementary chamfer of the top plug body  280 . 
     In an embodiment, the top plug body  280  generally comprises a tubular body defining a bore extending longitudinally therethrough. As shown in  FIG. 2A , the top plug body  280  may be configured to receive the top plug mandrel portion  240 , which may be positioned within the bore defined by the top plug body  280 . In the embodiment of  FIG. 2A , the top plug body  280  may be secured to top plug mandrel portion  240 . For example, the top plug body  280  may comprise a series of shoulders or bevels, a series of threads, a groove or channel configured to receive a snap-ring, a bore configured to receive a pin, or combinations thereof (or vice versa). In the embodiment of  FIG. 2A , the top plug body  280  comprises a threaded interface  286  along the inner surface thereof configured to engage the complementary threaded interface  246  of the top plug mandrel portion  280  and restrict movement of the top plug body  280  with respect to the top plug mandrel portion  240 , as will be discussed herein. 
     In an embodiment, the top plug body  280  may be configured to sealably engage an inner wall of a casing string, for example, casing  160 . For example, in the embodiment of  FIG. 2A , the top plug body  280  further comprises one or more wipers  285 . In an embodiment, the wipers  285  may generally be configured to substantially remove, separate, or clean fluids from the inner bore surface of the casing  160 . The wipers  285  may be provided in a suitable number and configuration, as will be appreciated by one of skill in the art viewing this disclosure. For example, the embodiment of  FIG. 2A  illustrates the top plug body  280  with four wipers, however more or fewer may be provided. The wipers  285  may extend radially outward from the top plug body  280 . As will be appreciated by one of skill in the art viewing this disclosure, the wipers  285  may be sized to sealably and slidably engage the inner bore of a casing string such as casing  160  of a particular size. The wipers  285  may extend outward from the bottom plug body at a suitable angle from the top plug body  280 . For example, in the embodiment of the  FIG. 2A , each of the four wipers  285  is angled, thereby forming a conical, cross-section. In an embodiment, the wipers  285  may be formed from a suitable material. Such a suitable material may be characterized as conformable or pliable, for example, such that the wipers  285  may be able to conform to inconsistencies in the inner bore of the casing  160 . Examples of suitable materials include but are not limited to rubber, foam, plastics, or combinations thereof. 
     In an embodiment, the top plug body  280  may be configured to engage the bottom plug, as will be discussed herein. For example, in the embodiment of  FIG. 2A , the top plug body  280  comprises a chamfer  282  configured to engage chamfer  274  of the bottom plug body  270 . 
     Referring again to  FIG. 1 , an embodiment of a SRP system  100  is illustrated. In the embodiment of  FIG. 1 , the SRP system  100  generally comprises the SRP release apparatus  200 , a bottom plug launching member  310 , a top plug launching member  320 , and a landing collar  170 . In an embodiment, the SRP system  100  optionally comprises a one-way valve  180  and/or a shoe  190 , which may or may not contain a float valve as well. In the embodiment of  FIG. 1 , the bottom plug launching member  310 , the top plug launching member  320 , or both, may be deployed from a dart-launching apparatus  300  located at the surface  104 , as will be appreciated by one of skill in the art viewing this disclosure. 
     Referring to  FIG. 4A , an embodiment of a bottom plug launching member  310  is illustrated. In an embodiment, the bottom plug launching member  310  may be generally configured to sealably engage a seat or landing within the bottom plug mandrel portion  220  and thereby restrict, block, or substantially restrict the passage of fluid. In the embodiment of FIG.  4 A, the bottom plug launching member  310  comprises a dart. The bottom plug launching member  310  generally comprises a longitudinal body  312  and one or more wipers  315 . 
     In an embodiment, the longitudinal body  312  may be characterized as a shaft or mandrel. The longitudinal body  312  may be any suitable size, as will be appreciated by one of skill in the art viewing this disclosure. The longitudinal body  312  may be formed from a single piece, alternatively, the longitudinal body  312  may be formed from multiple operably-connected components (e.g., a plurality of body portions or segments connected by a threaded connection or the like). 
     In an embodiment, the wipers  315  may be configured to sealably engage an inner wall of the work string  150  and/or the inner walls of the mandrel  210  of the SRP release apparatus  200 . The wipers  315  may be provided in a suitable number and configuration, as will be appreciated by one of skill in the art viewing this disclosure. For example, the embodiment of  FIG. 4A  illustrates the bottom plug launching member  310  with three wipers, however, more or fewer may be provided. The wipers  315  may extend radially outward from the bottom plug launching member  310 . As will be appreciated by one of skill in the art viewing this disclosure, the wipers  315  may be sized to sealably and slidably engage the inner bore of a work string such as work string  150  of a particular size. The wipers  315  may extend outward from the longitudinal body  312  at a suitable angle. For example, in the embodiment of the  FIG. 4A , each of the three wipers  315  is angled, thereby forming a conical, cross-section. In an embodiment, the wipers  315  may be formed form a suitable material. Such a suitable material may be characterized as conformable or pliable, for example, such that the wipers  315  may be able to conform to inconsistencies in the inner bore of the work string  150 . Examples of suitable materials include but are not limited to rubber, foam, plastics, or combinations thereof. 
     In an embodiment, the bottom plug launching member  310  may be configured to engage and be retained within the bottom plug mandrel portion  220 . For example, in the embodiment of  FIG. 4A , the bottom plug launching member  310  comprises one or more surfaces (e.g., chamfers  314 ) configured to engage one or more of the complementary surfaces (e.g., chamfers  222 ) within the bottom plug mandrel portion  220  and thereby be retained within the bottom plug mandrel portion  220 . 
     Referring to  FIG. 4B , an embodiment of a top plug launching member  320  is illustrated. In an embodiment, the top plug launching member  320  may be generally configured to sealably engage a seat or landing within the top plug mandrel portion  240  and thereby restrict, block, or substantially restrict the passage of fluid. In the embodiment of  FIG. 4B , the top plug launching member  320  comprises a dart. The top plug launching member  320  generally comprises a longitudinal body  322 , one or more wipers  325 , and an expandable ring  324 . 
     In an embodiment, the longitudinal body  322  may be characterized as a shaft or mandrel. The longitudinal body  322  may be any suitable size, as will be appreciated by one of skill in the art viewing this disclosure. The longitudinal body  322  may be formed from a single piece, alternatively, the longitudinal body  322  may be formed from multiple operably-connected components (e.g., a plurality of body portions or segments connected by a threaded connection or the like). 
     In an embodiment, the wipers  325  may be configured to sealably engage an inner wall of the work string  150  and/or the inner walls of the mandrel  210  of the SRP release apparatus  200 . The wipers  325  may be provided in a suitable number and configuration, as will be appreciated by one of skill in the art viewing this disclosure. For example, the embodiment of  FIG. 4B  illustrates the top plug launching member  320  with three wipers, however, more or fewer may be provided. The wipers  325  may extend radially outward from the bottom plug launching member  320 . As will be appreciated by one of skill in the art viewing this disclosure, the wipers  325  may be sized to sealably and slidably engage the inner bore of a work string such as work string  150  of a particular size. The wipers  325  may extend outward from the longitudinal body  322  at a suitable angle. For example, in the embodiment of the  FIG. 4B , each of the three wipers  325  is angled, thereby forming a conical, cross-section. In an embodiment, the wipers  325  may be formed form a suitable material. Such a suitable material may be characterized as conformable or pliable, for example, such that the wipers  325  may be able to conform to inconsistencies in the inner bore of the work string  150 . Examples of suitable materials include but are not limited to rubber, foam, plastics, or combinations thereof. 
     In an embodiment, the top plug launching member  320  may be configured to engage and be retained within the top plug mandrel portion  240 . For example, in the embodiment of  FIG. 4B , the top plug launching member  320  comprises one or more surfaces (e.g., chamfers  326 ) configured to engage one or more of the complementary surfaces (e.g., chamfers  242 ) within the top plug mandrel portion  240  and thereby be retained within the top plug mandrel portion  240 . 
     In an embodiment, the top plug launching member  320  may be configured to lock within the top plug mandrel portion  240 . For example, in the embodiment of  FIG. 4B , the top plug launching member  320  comprises an expandable ring  324  configured to expand into a complementary recess, slot, or groove within the top plug mandrel portion  240 . The expandable ring  324  may be configured to expand into recess  248 . in the top plug mandrel portion  240  and, when expanded, to interact with shoulder  244  to thereby prohibit the top plug launching member  320  from moving upward relative to the top plug mandrel portion  240  after the top plug launching member has engaged with the top plug mandrel portion  240 , for example, engaging a seat surface or landing such as chamfers  242 . 
     In the embodiment of  FIG. 1 , the collar  170  may be configured to engage and retain the bottom plug body  270 . Suitable examples of such a collar include a baffle adapter and/or a landing collar, as will be discussed in greater detail herein. Referring to  FIG. 5 , an embodiment of the collar  170  is illustrated. In the embodiment of  FIG. 5 , the collar  170  comprises a seat  175  comprising a surface (e.g., a chamfer) at a reduction in the diameter of the inner bore surface that will receive and engage, and thereby retain, the bottom plug body  270  (e.g., a complementary chamfer thereof). The collar  170  may be integrated within the casing  160  and positioned upward from the one-way valve  180  a desired distance (e.g., a shoe track). 
     In the embodiment of  FIG. 1 , the casing  160  comprises a one-way valve  180 , for example, a float valve, check valve, and/or flapper valve configured to allow fluid movement downward through the casing and restrict fluid movement upward through the casing. The one-way valve  180  may be integrated within the casing  160  and positioned upward from the shoe  190 . In an additional embodiment, the casing  160  may further comprise a bypass baffle above the one-way valve. A suitable bypass baffle is disclosed in U.S. Pat. No. 7,182,135, which is incorporated by reference herein in its entirety. 
     In the embodiment of  FIG. 1 , the casing  160  may comprise a shoe  190 , for example, a guide shoe or float shoe, as will be appreciated by one of skill in the art viewing this disclosure. The shoe  190  may be integrated within the casing  160  and positioned at the downhole terminal end of the casing  160 . 
     Also disclosed herein are one or more wellbore servicing methods employing an SRP release apparatus like SRP release apparatus  200  or  400  disclosed herein and/or an SRP system like SRP system  100  disclosed herein. In an embodiment, the SRP release apparatus  200  or  400  and/or the SRP system  100  may be employed in the performance of a cementing operation. 
     In an embodiment, a wellbore servicing method employing the SRP release apparatus and/or the SRP system may generally include the steps of positioning the SRP release apparatus within a casing string within a wellbore, releasing the bottom plug, circulating a cementitious slurry, releasing the top plug, displacing the at least a portion of the cementitious slurry into an annualar space, and allowing the cementitious slurry to set. In an embodiment, a wellbore servicing method may additionally and optionally include the step of removing the top plug and/or the bottom plug from the casing string. 
     In an embodiment, positioning the SRP release apparatus  200 ,  400  within a casing string within a wellbore may comprise positioning a casing string such as casing  160  within the wellbore  114  while attached to the downhole terminal end of a work string such as work string  150 . For example, as disclosed above, the casing  160  may be attached to the work string  150  via a liner hanger. The SRP release apparatus  200  may be attached to the work string  150  within a generally upper portion of the casing  160  and, as such, may be lowered into the wellbore  114  with the casing  160 . 
     In an embodiment, releasing the bottom plug may generally comprise causing structural failure of the first controlled strength segment  230 . In an embodiment, causing structural failure of the first controlled strength segment  230  may comprise deploying the bottom plug launching member  310  (e.g., via the operation of the dart-launching apparatus  300  located at the surface  104 ) and pumping the bottom plug launching member  310  downhole via the interior of the work string  150  to engage the seat within the bottom plug mandrel portion  220 , as illustrated in  FIG. 6 . In the embodiment of  FIG. 6 , the chamfers  314  of the bottom plug launching member  310  engage the chamfers  222  within the bottom plug mandrel portion  220 , thereby prohibiting the bottom plug launching member  310  from moving further downhole. 
     In an embodiment, after the bottom plug launching member  310  has been deployed from the surface  104 , a cementitious slurry may be forward-circulated via the interior of the work string  150  directly behind the bottom plug launching member  310  (or, optionally, with a small volume of a spacer fluid between the cementitious slurry and the bottom plug launching member  310 ). Because the wipers  315  of the bottom plug launching member  310  sealably or substantially sealably engage the inner walls of the work string  150 , the cementitious slurry is not intermingled or intermixed with (and, therefore, is not contaminated by) any fluid which may have been previously pumped via the work string  150 . 
     In an embodiment, once the bottom plug launching member  310  reaches and engages the bottom plug mandrel portion  220  (thereby sealing the interior flow path), continued pumping will increase the force applied to the mandrel  210 . Referring to  FIG. 6 , when the threshold at which the first controlled strength segment  230  will fail structurally is reached, the first controlled strength segment  230  will break, sever, separate, or otherwise fail structurally, causing the bottom plug mandrel portion  220  and the attached bottom plug body  270  (cumulatively referred to as the bottom plug  600 ) to separate from the SRP release apparatus  200  and move downhole within the casing  160 . In an embodiment, application of such a force may cause the first controlled strength segment  230  to structurally fail completely and/or uniformly. Alternatively, the first controlled strength segment  230  may structurally fail in part. Where the first controlled strength segment  230  only partially structurally fails, fluid (e.g., the cementitious slurry) may flow into the interior bore of the casing  160  and exert a force against the bottom plug body  270  via the wipers  275 , thereby bringing the first controlled strength segment  230  complete failure. 
     In an embodiment, port(s)  224  may prevent a pressure build-up (e.g., resulting from trapped pressure) between the top body  280  and bottom plug body  270  due to abrupt pressure changes that may occur while circulating and/or flowing a fluid prior to releasing the bottom plug. The port(s)  224  are bridged and sealed off on both sides of the port(s) when the bottom plug launching member  310  lands in the bottom plug mandrel portion  220  as illustrated in  FIG. 6 . 
     In an embodiment, the cementitious slurry continues to be pumped downhole until a desired volume of the cementitious slurry (e.g., a volume necessary to cement the casing  160  in place) has been pumped. The cementitious slurry will flow downward within the work string  150  through the SRP release apparatus and into the casing  160  behind the bottom plug  600 . Because the wipers  275  of the bottom plug  600  sealably or substantially sealably engage the inner walls of the casing  160 , the cementitious slurry is not intermingled or intermixed with (and, therefore, is not contaminated by) any fluid which may have been previously pumped via the casing  160 . 
     Referring to  FIG. 7 , in an embodiment, as the cementitious slurry is pumped downhole, the bottom plug  600  continues to moves downward within the casing  160  until the bottom plug  600  reaches the collar  170 . In the embodiment of  FIG. 7 , upon reaching the collar  170 , the chamfer  272  of the bottom plug engages the complementary seat  175  within the collar  170 , thereby prohibiting the bottom plug  600  from moving further downhole. 
     Referring to  FIG. 8 , in an embodiment, once the bottom plug  600  engages the collar  170 , continued pumping will increase the force applied to the bottom plug mandrel portion  220 . When the threshold at which the frangible member (shear pin  206 , illustrated in  FIG. 7 ) will fail (which may be greater than the force necessary to cause structural failure of the first controlled strength segment  230 ) is reached, the shear pin  206  will break or otherwise fail structurally, causing the bottom plug mandrel portion  220  with the bottom plug launching member  310  engaged therein to move downward through the bottom plug body  270  while the bottom plug body is retained within the collar  170 . In the embodiment of  FIG. 8 , the bottom plug mandrel portion  220  and bottom plug launching member  310  which is disposed within the bottom plug mandrel portion  220  separate from the bottom plug body  270  and collar  170  and move further downhole within the casing  160 , followed by the cementitious slurry. The cementitious slurry continues to flow downward within the casing  160 , through the open bore of the bottom plug body  270  until the cementitious slurry reaches the shoe  190  at the downhole terminal end of the casing  160  and then flows into the wellbore  114 . In an embodiment, where the casing  160  comprises a bypass baffle above the one-way valve  180 , the bypass baffle may catch the bottom plug mandrel portion  220  and/or the bottom plug launching member  310  while still allowing flow of the cementitious slurry into and through the shoe track without obstructing and/or damaging the one-way valve  180 . The cementitious slurry may be allowed to flow into an annular space between the casing  160  and a wall of the wellbore  114 , where the cementitious slurry may be allowed to set. 
     In an embodiment, releasing the top plug may generally comprise causing structural failure of the second controlled strength segment  250 . In an embodiment, causing structural failure of the second controlled strength segment  250  may comprise deploying the top plug launching member  320  (e.g., via the operation of the dart-launching apparatus  300  located at the surface  104 ) and pumping the top plug launching member  320  downhole via interior of the work string  150  to engage the seat within the top plug mandrel portion  240 , as illustrated in  FIG. 9 . In the embodiment of  FIG. 9 , the chamfers  326  of the top plug launching member  320  engage the chamfers  242  within the top plug mandrel portion  240 , thereby prohibiting the top plug launching member  320  from moving further downhole. Also in the embodiment of  FIG. 9 , when the top plug launching member  320  engages the top plug mandrel portion  240 , the expandable ring  324  expands into recess  248  and interacts with shoulder  244 , thereby prohibiting the top plug launching member  320  from moving upward relative to the top plug mandrel portion  240  after the top plug launching member has engaged a seat within the top plug mandrel portion  240 , such as chamfers  242 . 
     In an embodiment, after the top plug launching member  320  has been deployed from the surface  104 , a servicing fluid may be forward-circulated via the work string  150  directly behind the top plug launching member  320 , thereby displacing at least a portion of the cementitious slurry into the annular space between the casing  160  and a wall of the wellbore  114 . Because the wipers  325  of the top plug launching member  320  sealably or substantially sealably engage the inner walls of the work string  150 , the cementitious slurry is not intermingled or intermixed with (and, therefore, is not contaminated by) the servicing fluid which follows the top plug launching member within the work string  150 . 
     In an embodiment, once the top plug launching member  320  engages the top plug mandrel portion  240  (thereby sealing the interior flow path), continued pumping will increase the force applied to the mandrel  210 . Referring to  FIG. 9 , when the threshold at which the second controlled strength segment  250  will fail structurally is reached, the second controlled strength segment  250  will break, sever, separate, or otherwise fail structurally, causing the top plug mandrel portion  240  and the attached top plug body  280  (cumulatively referred to as the top plug  700 ) to separate from the SRP release apparatus  200  and move downhole within the casing  160 . In an embodiment, application of such a force may cause the second controlled strength segment  250  to structurally fail completely and/or uniformly. Alternatively, the second controlled strength segment  250  may structurally fail in part. Where the second controlled strength segment  250  only partially structurally fails, fluid (e.g., the cementitious slurry) may flow into the interior bore of the casing  160  and exert a force against the top plug body  280  via the wipers  285 , thereby bringing the second controlled strength segment  250  complete failure. 
     In an alternative embodiment where an SRP apparatus  400  is configured as disclosed with respect to  FIG. 2B , when the force applied to the mandrel  410  via the top plug launching member  320  reaches a threshold (which may be greater than the force necessary to cause structural failure of the first controlled strength segment  430 ), a frangible member retaining the collet releasing sleeve  465  in the first, upper position will break, allowing the collet releasing sleeve  465  to slide forward to the second, lower position. When the collet releasing sleeve  465  slides to the second, lower position, the collet fingers  463  are allowed to flex inward into the radially-contracted, collapsed conformation and disengage the shoulder  448  of the collet retainer sleeve  447 , and thereby releasing the top plug mandrel portion  440  and the attached top plug body, which cumulatively form the top plug. In other words, an embodiment where the SRP release apparatus is configured as SRP release apparatus  400 , the collet  465  serves the function of the second controlled strength segment  250  in an embodiment where the SRP release apparatus is configured as SRP release apparatus  200 . 
     Referring to  FIG. 10 , in an embodiment, as the servicing fluid is pumped downhole, the top plug  700  continues to moves downward within the casing  160  until the top plug  700  reaches the bottom plug body  270 , which remains engaged with the landing collar  170  within the casing  160 . In the embodiment of  FIG. 10 , upon reaching the bottom plug body  270 , the chamfer  282  of the top plug  700  engages the complementary chamfer  274  of the bottom plug body  270 , thereby prohibiting the top plug  700  from moving further downhole. In an embodiment, when the top plug  700  reaches the bottom plug body  270 , the cementitious slurry may be substantially displaced from the casing  160  (with exception to the cementitious slurry remaining within the shoe track, below the landing collar  170 ) and positioned within the annular space between the casing  160  and a wall of the wellbore  114 . 
     In an embodiment, it may be desirable to remove the top plug  700 , the bottom plug body  270 , and/or the collar  170  from the casing  160 . In an embodiment where these components are formed from drillable materials, removal may comprise “drilling out” these components. In alternative embodiments, one or more of these components may removable by degradation, consumption, or other means known to one of skill in the art viewing this disclosure. 
     In an embodiment, the SRP release apparatus  200 ,  400  the SRP system  100 , and/or the wellbore servicing methods employing the same as disclosed herein may be advantageously employed where prior art systems could not have been employed. For example, in an embodiment the SRP release apparatus  200 ,  400  and/or the SRP system  100  may be disposed within a relatively small-diameter casing string, whereas prior art subsurface release cementing plugs, which were released from collets, were too restrictive (as to fluid flow) as to be applied to the design on small diameter plug sets. The SRP release apparatus  200 ,  400  and/or the SRP system  100  as disclosed herein may be employed within a casing sized about 4.5 inches through about 7 inches. For example, the SRP release apparatus  200 ,  400  and/or SRP system  100  may be utilized in conjunction with a casing comprising an inner diameter of about 3.83 inches, alternatively, an inner diameter of less than about 6.54 inches. 
     It is noted that although some of the figures may exemplify a given operating environment, the principles of the devices, systems, and methods disclosed may be similarly applicable in other operational environments, such as offshore and/or subsea wellbore applications. 
     Additional Disclosure 
     The following are nonlimiting, specific embodiments in accordance with the present disclosure: 
     Embodiment A 
     A subsurface release plug release apparatus comprising: 
     a mandrel comprising:
         a bottom plug portion;   a top plug portion;   a work string attachment portion;   a first release portion between the bottom plug portion and the top plug portion, wherein the first release portion comprises a controlled strength segment configured to fail structurally and thereby release the bottom plug portion at a first fluid pressure; and   a second release portion between the top plug portion and the work string attachment portion, wherein the second release portion is configured to release the bottom plug portion at a second fluid pressure, wherein the first fluid pressure is less than the second fluid pressure;       

     a bottom plug body disposed about the bottom plug portion of the mandrel; and 
     a top plug body disposed about the top plug portion of the mandrel. 
     Embodiment B 
     The subsurface release plug release apparatus of Embodiment A, wherein the mandrel is manufactured by a process comprising winding a plurality of fibers around a mandrel template. 
     Embodiment C 
     The subsurface release plug release apparatus of one of Embodiments A or B, wherein the bottom plug body is releasably secured to the bottom plug portion of the mandrel via a frangible member. 
     Embodiment D 
     The subsurface release plug release apparatus of one of Embodiments A through C, wherein the bottom plug body is configured to engage and be retained by a landing collar integrated within a casing string. 
     Embodiment E 
     The subsurface release plug release apparatus of one of Embodiments A through D, wherein the second release portion comprises a controlled strength segment configured to fail structurally and thereby release the top plug portion. 
     Embodiment F 
     The subsurface release plug release apparatus of one of Embodiments A through D, wherein the second release portion comprises a collet configured to contract and thereby release the top plug portion. 
     Embodiment G 
     The subsurface release plug release apparatus of one of Embodiments A through F, wherein the bottom plug portion is configured to sealably receive and retain a bottom plug launching member. 
     Embodiment H 
     The subsurface release plug release apparatus of one of Embodiments A through G, wherein the top plug portion is configured to sealably receive and retain a top plug launching member. 
     Embodiment I 
     The subsurface release plug release apparatus of one of Embodiments A through H, wherein the bottom plug mandrel portion further comprises a port, wherein the port is configured to equalize pressure between flowbore substantially defined by the mandrel and an exterior of the mandrel. 
     Embodiment J 
     A wellbore servicing method comprising: 
     positioning a casing defining a flowbore within a wellbore with a subsurface release plug release apparatus disposed within a portion of the casing, the subsurface release plug release apparatus comprising:
         a mandrel comprising:
           a bottom plug portion;   a top plug portion;   a work string attachment portion;   a first release portion between the bottom plug portion and the top plug portion, wherein the first release portion comprises a controlled strength segment configured to fail structurally and thereby release the bottom plug portion at a first fluid pressure; and   a second release portion between the top plug portion and the work string attachment portion, wherein the second release portion is configured to release the bottom plug portion at a second fluid pressure, wherein the first fluid pressure is less than the second fluid pressure;   
           a bottom plug body disposed about the bottom plug portion of the mandrel; and   a top plug body disposed about the top plug portion of the mandrel;       

     causing the first release portion to release the bottom plug portion by causing structural failure of the controlled strength segment; 
     pumping a cementitious slurry via the flowbore of the casing; 
     causing the second release portion to release the top plug portion; 
     displacing the cementitious slurry from the flowbore of the casing into an annular space between the casing and a wellbore wall; and 
     allowing the cementitious slurry to set. 
     Embodiment K 
     The wellbore servicing method of Embodiment J, wherein the mandrel is manufactured by a process comprising winding a plurality of fibers around a mandrel template. 
     Embodiment L 
     The wellbore servicing method of one of Embodiments J or K, wherein the bottom plug body is releasably secured to the bottom plug portion of the mandrel via a frangible member. 
     Embodiment M 
     The wellbore servicing method of one of Embodiments J through L, further comprising pumping the bottom plug body and the bottom plug portion of the mandrel downward through the flowbore of the casing to engage a collar integrated within the casing, wherein engaging the collar retains the bottom plug body. 
     Embodiment N 
     The wellbore servicing method of one of Embodiments L or M, further comprising causing structural failure of the shear pin. 
     Embodiment O 
     The wellbore servicing method of Embodiment N, further comprising pumping the bottom plug portion of the mandrel downward through the collar while the bottom plug body is retained by the collar. 
     Embodiment P 
     The wellbore servicing method of Embodiment O, further comprising pumping the top plug body and the top plug portion of the mandrel downward through the flowbore of the casing to engage the bottom plug body. 
     Embodiment Q 
     The wellbore servicing method of one of Embodiments J through P, wherein the second release portion comprises a controlled strength segment configured to fail structurally and thereby release the top plug portion, and wherein causing the second release portion to release the top plug portion comprises causing structural failure of the controlled strength segment. 
     Embodiment R 
     The wellbore servicing method of one of Embodiments J through P, wherein the second release portion comprises a collet configured to contract radially and thereby release the top plug portion, and wherein causing the second release portion to release the top plug portion comprises causing the collet to expand radially. 
     Embodiment S 
     A wellbore servicing method comprising:
         positioning a casing defining a flowbore within a wellbore with a subsurface release plug release apparatus disposed within a portion of the casing, the subsurface release plug release apparatus comprising:
           a mandrel comprising:   a bottom plug portion;   a top plug portion;   a work string attachment portion;   a first release portion between the bottom plug portion and the top plug portion, wherein the first release portion comprises a controlled strength segment configured to fail structurally and thereby release the bottom plug portion at a first fluid pressure; and   a second release portion between the top plug portion and the work string attachment portion, wherein the second release portion is configured to release the top plug portion at a second fluid pressure, wherein the first fluid pressure is less than the second fluid pressure;   
           a bottom plug body disposed about the bottom plug portion of the mandrel; and   a top plug body disposed about the top plug portion of the mandrel; pumping a first obturating member to pass through the top plug portion of the mandrel and engage a first seat within the bottom plug portion of the mandrel; applying a fluid pressure to cause the first release portion to release the bottom plug portion by causing structural failure of the first controlled strength segment;   pumping a second obturating member to engage a second seat within the top plug portion of the mandrel; and   applying a fluid pressure to cause the second release portion to release the top plug portion.       

     Embodiment T 
     The method of Embodiment S, wherein the mandrel is manufactured by a process comprising winding a plurality of fibers around a mandrel template. 
     Embodiment U 
     The method of one of Embodiments S or T, wherein the bottom plug body is releasably secured to the bottom plug portion of the mandrel via a frangible member. 
     Embodiment V 
     The method of one of Embodiments S through U, further comprising pumping the bottom plug body and the bottom plug portion of the mandrel downward through the flowbore of the casing to engage a collar integrated within the casing, wherein engaging the collar retains the bottom plug body. 
     Embodiment W 
     The wellbore servicing method of one of Embodiments U or V, further comprising causing structural failure of the frangible member. 
     Embodiment X 
     The wellbore servicing method of Embodiment W, further comprising pumping the bottom plug body and the portion of the mandrel downward to engage a collar integrated within the casing, wherein the collar retains the bottom plug body. 
     Embodiment Y 
     The wellbore servicing method of Embodiment X, further comprising pumping the top plug body and the top plug portion of the mandrel downward through the flowbore of the casing to engage the bottom plug body. 
     Embodiment Z 
     The wellbore servicing method of one of Embodiments S through Y, wherein the second release portion comprises a controlled strength segment configured to fail structurally and thereby release the top plug portion, and wherein causing the second release portion to release the top plug portion comprises causing structural failure of the controlled strength segment. 
     Embodiment AA 
     The wellbore servicing method of one of Embodiments S through Y, wherein the second release portion comprises a collet configured to contract radially and thereby release the top plug portion, and wherein causing the second release portion to release the top plug portion comprises causing the collet to expand radially. 
     Embodiment AB 
     The wellbore servicing method of one of Embodiments S through AA, wherein the bottom plug portion of the mandrel comprises a port, and wherein the port provides fluid communication between an interior bore defined by the mandrel and an exterior portion of the mandrel between the bottom plug body and the top plug body prior to causing the bottom plug portion to be released. 
     While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, Rl, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R═Rl+k*(Ru−Rl), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc. 
     Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the embodiments of the present invention. The discussion of a reference in the Detailed Description of the Embodiments is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.