Patent Publication Number: US-11396786-B1

Title: Wiper plug

Description:
BACKGROUND 
     Field 
     Embodiments of the present disclosure generally relate to plugs that are used during the cementing of liners, such as those used in oil, gas, and water wells. 
     Description of the Related Art 
     A wellbore is formed by using a drill bit on a drill string to drill through a geological formation. A drilling fluid, known as mud, is circulated to lubricate the drill bit, remove rock cuttings from the wellbore, and provide a hydrostatic pressure to counteract the in situ pressure of the geological formation. After drilling through the geological formation to a predetermined depth, the drill string and drill bit are removed, and the wellbore is lined by inserting a string of casing into the wellbore. At least a portion of the annulus between the inner surface of the wellbore and casing is filled with cement using a cementing operation. Typically, a cementing operation involves the pumping of a cement slurry through the casing, out of the bottom of the casing, and up the annulus. 
     A casing string is hung off from a wellhead located at the top of the wellbore. An equivalent string of tubulars that is hung off from a location within the wellbore below the wellhead is typically referred to as a liner. A liner is deployed to a desired depth in the wellbore using a workstring, and suspended from a previously-installed casing by using a liner hanger. A setting tool is then operated to set a liner hanger against the previously installed casing. The liner hanger may include slips riding outwardly on cones in order to engage the surrounding casing. The setting tool is typically operated by pumping a ball through the workstring to a seat located below the setting tool. Pressure is exerted on the seated ball to operate the setting tool. Thereafter, pressure is increased to release the ball and the ball seat. Usually, after actuating the liner hanger, the liner is cemented in place by pumping a cement slurry down the workstring, into the liner, out of the bottom of the liner, and into the annulus between the liner and the inner surface of the wellbore. 
     Wiper plugs are used to segregate the cement slurry from the drilling fluid while the cement slurry travels down the casing or liner. In a liner cementation operation, darts may be used to segregate the cement slurry from other fluids while the cement slurry travels down the workstring. Each dart picks up a corresponding wiper plug that is installed in an upper portion of the liner below the liner hanger to ensure the fluids remain segregated while the cement travels down through the liner. Sometimes, only one dart and a corresponding wiper plug is used; the dart and corresponding wiper plug operate to segregate the cement from fluid, such as drilling fluid, that is pumped after the cement to move the cement out of the bottom of the liner and into the annulus between the liner and the inner surface of the wellbore. 
     A wiper plug typically has an elastomeric body mounted on a mandrel and elastomeric external fins that bear against the inner wall of the casing. The fins wipe mud solids and other accumulated debris off the inner wall of the casing. The effectiveness of a wiper plug relies on at least one fin creating a seal against the surrounding casing or liner, and the body sealing against the mandrel. The elastomer material usually has a hardness that provides for structural robustness, such as for wiping of the casing or liner, and resistance to abrasion, yet is sufficiently malleable to be deformed so as to provide the necessary seals. However, the hardness decreases with increasing temperature, and thus at elevated temperatures within wellbores, the elastomeric body and the fins become susceptible to extrusion, which compromises their sealing capability. 
     Therefore, there is a need for an improved wiper plug design. 
     SUMMARY 
     The present disclosure generally relates to a wiper plug for use in a wellbore or other conduit, such as a pipeline. 
     In one embodiment, a wiper plug includes a mandrel having a nose portion at a leading end thereof. A seal unit, including a body and one or more fins extending outwardly from the body, is disposed about the mandrel. An anti-extrusion assembly is disposed about the mandrel at a leading end of the seal unit. The anti-extrusion assembly is arranged to transition between a first configuration, in which the anti-extrusion assembly is not energized, and a second configuration, in which the anti-extrusion assembly is energized. The nose portion protrudes beyond the anti-extrusion assembly. 
     In another embodiment, a wiper plug includes a mandrel and a seal unit disposed about the mandrel, the seal unit having a body and one or more fins extending outwardly from the body. An anti-extrusion assembly is disposed about the mandrel at a leading end of the seal unit. The anti-extrusion assembly is arranged to transition between a first configuration, in which the anti-extrusion assembly is not energized, and a second configuration, in which the anti-extrusion assembly is energized, in response to a pressure applied to an obturating object landed in the wiper plug. 
     In another embodiment, a wiper plug includes a mandrel and a seal unit disposed around the mandrel. The seal unit includes a body having an inner surface, a leading end, and a trailing end, and one or more fins extending outwardly from the body. The inner surface includes a first, generally cylindrical, portion and a second portion. The second portion includes an inwardly extending shoulder located between the first portion and the leading end and facing toward the trailing end. The shoulder is substantially perpendicular to a longitudinal axis of the mandrel. The second portion further includes a first taper between the shoulder and the leading end. The seal unit body has a first inner diameter at a first location on the first taper proximal to the leading end and a second inner diameter at a second location on the first taper distal from the leading end. The first inner diameter is greater than the second inner diameter. 
     In another embodiment, a method includes suspending a wiper plug from a support disposed in a tubular, and energizing an anti-extrusion assembly of the wiper plug while the wiper plug remains suspended from the support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, as the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a longitudinal cross-sectional view of a wiper plug. 
         FIG. 2  is a longitudinal cross-sectional view of the wiper plug of  FIG. 1 , but with some components omitted. 
         FIG. 3  is a longitudinal cross-sectional view of a component of the wiper plug of  FIG. 1 . 
         FIG. 4  is a longitudinal cross-sectional view of some components of the wiper plug of  FIG. 1 . 
         FIG. 5A  is a longitudinal cross-sectional view of the wiper plug of  FIG. 1  during an exemplary phase of operation. 
         FIG. 5B  is a longitudinal cross-sectional view of an embodiment of the wiper plug of  FIG. 1  during the exemplary phase of operation of  FIG. 5A . 
         FIG. 6A  is a longitudinal cross-sectional view of the wiper plug of  FIG. 1  during an exemplary phase of operation. 
         FIG. 6B  is a longitudinal cross-sectional view of an embodiment of the wiper plug of  FIG. 1  during the exemplary phase of operation of  FIG. 6A . 
         FIG. 7A  is a longitudinal cross-sectional view of the wiper plug of  FIG. 1  during an exemplary phase of operation. 
         FIG. 7B  is a longitudinal cross-sectional view of an embodiment of the wiper plug of  FIG. 1  during the exemplary phase of operation of  FIG. 7A . 
         FIG. 8A  is a longitudinal cross-sectional view of the wiper plug of  FIG. 1  during an exemplary phase of operation. 
         FIG. 8B  is a longitudinal cross-sectional view of an embodiment of the wiper plug of  FIG. 1  during the exemplary phase of operation of  FIG. 8A . 
         FIG. 9  is a longitudinal cross-sectional view of the wiper plug of  FIG. 1  during an exemplary phase of operation. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     The present disclosure concerns wiper plug designs in which extrusion of a resilient component is inhibited. During use, a tendency of a resilient component of a wiper plug to deform detrimentally with a consequential loss of sealing integrity is thereby mitigated. Wiper plugs of the present disclosure provide robust wiping of the inner surface of a casing or liner, and sealing against the casing or liner that is effective at elevated temperatures that exist in a wellbore. 
       FIG. 1  is a longitudinal cross-sectional view of a wiper plug  100 .  FIG. 2  is a longitudinal cross-sectional view of the wiper plug  100  of  FIG. 1 , but with some components omitted for clarity. The wiper plug  100  has a longitudinal axis  102 , a leading end  104 , and a trailing end  106 . For the purpose of orientation, the leading end  104  and trailing end  106  define opposite ends of the wiper plug  100  along the longitudinal axis  102  according to a direction of travel ( 418 ,  FIGS. 8A, 8B ) through a tubular for which the wiper plug  100  is configured. The wiper plug  100  has a mandrel  110  that, as illustrated, includes a lower mandrel segment  112 , a center mandrel segment  160 , and an upper mandrel segment  170 . In some embodiments, it is envisaged that the mandrel  110  may include greater than three segments. In some embodiments, it is envisaged that the mandrel  110  may include fewer than three segments. In some embodiments, it is envisaged that the mandrel  110  may be configured as a single component. For the purpose of orientation, the leading end  104  of the wiper plug  100  is also the leading end of the mandrel  110 , and the trailing end  106  of the wiper plug  100  is also the trailing end of the mandrel  110 . 
     The lower mandrel segment  112  has a longitudinal bore  114  therethrough. An outer surface  116  of the lower mandrel segment  112  includes a first portion  117  that is generally cylindrical and substantially aligned with the longitudinal axis  102 . The outer surface  116  also includes a slope  118  describing a generally frustoconical profile extending at an acute angle  118   a  to the longitudinal axis  102 . A first outer diameter of the lower mandrel segment  112  at a first end  118   b  of the slope  118  proximal to the leading end  104  is greater than a second outer diameter of the lower mandrel segment  112  at a second end  118   c  of the slope  118  distal from the leading end  104 . 
     The outer surface  116  of the lower mandrel segment  112  includes a second portion  152  that is generally cylindrical and substantially aligned with the longitudinal axis  102 . The slope  118  is located between the first  117  and second  152  generally cylindrical portions. The outer surface  116  of the lower mandrel segment  112  includes a ridge  154 . The second generally cylindrical portion  152  is located between the ridge  154  and the slope  118 . 
     The lower mandrel segment  112  includes a nose portion  120  located at the leading end  104 . The nose portion  120  has a bore  122  with a diameter that is greater than a diameter of the bore  114  of the lower mandrel segment  112  at a location distal from the leading end  104 . In some embodiments, it is envisaged that the nose portion  120  may have a bore  122  diameter that is less than or equal to the diameter of the bore  114  of the lower mandrel segment  112  at a location distal from the leading end  104 . The nose portion  120  includes one or more seals  124  (two are illustrated) on an outer surface. The nose portion  120  includes a lock ring  126  on the outer surface. In some embodiments, it is envisaged that the one or more seals  124  and/or the lock ring  126  may be omitted. 
     The lower mandrel segment  112  includes a lower seat assembly  130 . The lower seat assembly  130  includes a catcher  132  that extends into the bore  122  of the nose portion  120 . The catcher  132  is generally tubular, having an end port  134  and one or more side ports  138 . The catcher  132  includes a ledge  136  around the end port  134 . A lower seat sleeve  140  is at least partially disposed in the catcher  132 , and has a profile  142  configured to interact with an obturating object, such as a dart or a ball. The lower seat sleeve  140  is held in place by a releasable fastener  144 , such as a shear ring, shear pin, collet, latch, or the like. In some embodiments, it is contemplated that the lower seat assembly  130  may be omitted. 
     The center mandrel segment  160  is coupled to the lower mandrel segment  112 , and has an outer surface  162  including a portion  163  that is generally cylindrical and substantially aligned with the longitudinal axis  102 . The center mandrel segment  160  also has a bore  164  that includes a taper  166  from a first bore diameter at a first location  166   a  distal from the lower mandrel segment  112  to a second smaller diameter at a second location  166   b  proximal to the lower mandrel segment  112 . The center mandrel segment  160  is coupled to the upper mandrel segment  170 . The upper mandrel segment  170  includes one or more retainers  172 , such as locking dogs, collets, latches, and the like. As illustrated in  FIG. 1 , each retainer  172  is disposed in a corresponding opening  174  in the upper mandrel segment  170 . The one or more retainers  172  secure the wiper plug  100  to a support ( 410 , shown in  FIG. 5A ) for deployment. 
     An upper seat sleeve  180  having a profile  182  is at least partially disposed in the upper mandrel segment  170  and at least partially disposed in the center mandrel segment  160 . The profile  182  is configured to interact with an obturating object, such as a dart or a ball. The upper seat sleeve  180  extends across each opening  174  in the connector, and therefore maintains each retainer  172  in a radially extended position. The upper seat sleeve  180  is held in place by a releasable fastener  184 , such as a shear ring, shear pin, collet, latch, or the like. An o-ring  186  provides a seal between the upper seat sleeve  180  and the center mandrel segment  160 . A lock ring  188  in the center mandrel segment  160  is configured to engage a recess  192  in the upper seat sleeve  180 , as described below. The upper seat sleeve  180  has an external taper  194  such that an outer diameter of the upper seat sleeve  180  at a location distal from a lower end  196  of the upper seat sleeve  180  is greater than an outer diameter of the upper seat sleeve  180  at a location proximal to the lower end  196  of the upper seat sleeve  180 . 
     The mandrel  110 —including at least one or more of the components of the lower mandrel segment  112 , the center mandrel segment  160 , or the upper mandrel segment  170 —is made of a material that provides structural rigidity, such as a metal, a plastic, or a composite material, such as fiberglass. In some embodiments, it is contemplated that the mandrel  110  may be made of a material that may be readily disintegrated upon being drilled through by a standard oilfield drill bit or mill. For example, material may include aluminum. In some embodiments, it is contemplated that the mandrel  110  may be made of a material that may be readily dissolved by a suitable solvent. For example, the material may include polylactic acid, and the solvent may include water. 
     A seal unit  200  is disposed around the mandrel  110 . The seal unit  200  is illustrated in  FIG. 3 . The seal unit  200  has a longitudinal axis  202 . When assembled on the mandrel  110 , the longitudinal axis  202  of the seal unit  200  is substantially coincident with the longitudinal axis  102  of the wiper plug  100 . For example, the longitudinal axis  202  of the seal unit  200  may intersect the longitudinal axis  102  of the wiper plug  100  at an angle of from zero degrees to two degrees. For the purpose of orientation with the description, the seal unit  200  has a leading end  204  consistent with the leading end  104  of the wiper plug  100 , and a trailing end  206  consistent with the trailing end  106  of the wiper plug  100 . 
     The seal unit  200  has a body  210  from which a plurality of fins project outwardly. As illustrated, the seal unit  200  has a leading fin  212  located proximate to the leading end  204 , a trailing fin  218  located proximate to the trailing end  206 , and two intermediate fins  214 ,  216  located between the leading fin  212  and the trailing fin  218 . As illustrated, the leading fin  212  is configured to perform both a sealing function against a surrounding surface and a wiping function of the surrounding surface when in operation. As illustrated, one intermediate fin  214  is configured to perform primarily a wiping function of a surrounding surface and secondarily a sealing function against the surrounding surface when in operation. As illustrated, the trailing fin  218  and one intermediate fin  216  are configured to perform primarily a sealing function against a surrounding surface and secondarily a wiping function of the surrounding surface when in operation. As illustrated, the body  210  and the fins  212 ,  214 ,  216 ,  218  form a unitary structure of the seal unit  200 . However, it is also contemplated that the seal unit  200  may include individual segments. For example, each segment may include a body portion and a fin. 
     The seal unit  200  is made of a resilient material, such as an elastomer, that provides resistance to deformation, yet is sufficiently flexible to yield elastically when under load. It is contemplated that the elastomer may have properties tailored for different parts or sections of the seal unit  200 . For example, one or more fins  212 / 214 / 216 / 218  may include an elastomer possessing a greater stiffness than one or more other fins  212 / 214 / 216 / 218  and/or the body  210 . In some embodiments, it is contemplated that the seal unit  200  may not include additional materials. However, in some embodiments, it is contemplated that the seal unit  200  may include additional materials. For example, the seal unit  200  may include one or more support members in the body  210  and/or in one or more fins  212 / 214 / 216 / 218 . The one or more support members may provide enhanced stiffness to one or more sections of the seal unit  200 . The one or more support members may be made of metal, such as aluminum, or a composite, such as fiberglass. 
     Although four fins  212 ,  214 ,  216 ,  218  are illustrated, it is contemplated that the seal unit  200  may have any suitable number of fins, such as one fin, two fins, three fins, four fins, five fins, six fins, seven fins, or more than seven fins. Additionally, it is contemplated that any suitable number of the fins of the seal unit  200  (such as no fins, one fin, two fins, three fins, or more than three fins) may be configured to perform primarily a wiping function of a surrounding surface and secondarily a sealing function against the surrounding surface when in operation. Additionally, it is contemplated that any suitable number of the fins of the seal unit  200  (such as no fins, one fin, two fins, three fins, or more than three fins) may be configured to primarily a sealing function against a surrounding surface and secondarily a wiping function of the surrounding surface when in operation. 
     The body  210  has an inner surface  220  that includes a portion  222  extending from the trailing end  206  toward the leading end  204  that is generally cylindrical and substantially aligned with the longitudinal axis  202 . In some embodiments, it is contemplated that the portion  222  of the inner surface  220  extending from the trailing end  206  toward the leading end  204  may be undulating. In some embodiments, it is contemplated that the portion  222  of the inner surface  220  extending from the trailing end  206  toward the leading end  204  may not be generally cylindrical. For example, the portion  222  of the inner surface  220  extending from the trailing end  206  toward the leading end  204  may describe a generally frustoconical profile. 
     The inner surface  220  of the body  210  includes an inwardly extending shoulder  224  located between the leading end  204  and the portion of the inner surface  220  that extends from the trailing end  206  toward the leading end  204 . The shoulder  224  faces toward the trailing end  206  and extends substantially perpendicular to the longitudinal axis  202 . For example, the shoulder  224  may extend at angle of from eighty-five to ninety degrees to the longitudinal axis  202 . In some embodiments, it is contemplated that the shoulder  224  may extend at an acute angle to the longitudinal axis  202 . For example, the shoulder  224  may extend at an acute angle toward the trailing end  206  and toward the longitudinal axis  202 . Alternatively, or additionally, the shoulder  224  may include a profile, such as a “V” shaped profile. 
     The inner surface  220  of the body  210  includes a first taper  226  between the shoulder  224  and the leading end  204 . As illustrated, the first taper  226  describes a generally frustoconical profile, although one or more alternative profiles, such as a curve, are contemplated in some embodiments. The first taper  226  is shown having an angle  226   a  with respect to the longitudinal axis  202 . The first taper  226  is oriented such that an inner diameter of the body  210  at a first location  232  on the first taper  226  proximal to the leading end  204  is greater than an inner diameter of the body  210  at a second location  234  distal from the leading end  204 . 
     The inner surface  220  of the body  210  includes a second taper  228  between the shoulder  224  and the first taper  226 . The second taper  228  describes a generally frustoconical profile, although one or more alternative profiles, such as a curve or other polygonal profile, are contemplated in some embodiments. The second taper  228  is shown having an angle  228   a  with respect to the longitudinal axis  202 . The second taper  228  is oriented such that an inner diameter of the body  210  at the second location  234  is greater than an inner diameter of the body  210  at a third location  236  on the second taper  228 , the third location  236  being proximal to the shoulder  224 . In this embodiment, the angle  228   a  is different from the angle  226   a . However, it is contemplated the first and second tapers  226 ,  228  may have the same or different angles  226   a ,  228   a  or alternative profiles. 
     The first location  232  is on the first taper  226  at the leading end  204 , the second location  234  is at a meeting point of the first taper  226  and the second taper  228 , and the third location  236  is at the shoulder  224 . In some embodiments, it is contemplated that the first location  232  may be at any location between the leading end  204  and the shoulder  224 . In some embodiments, it is contemplated that the second location  234  may be at any location between the first location  232  and the shoulder  224 . In some embodiments, it is contemplated that the third location  236  may be at any location between the second location  234  and the shoulder  224 . In some embodiments, it is contemplated that the second taper  228  may not meet with the first taper  226 . For example, the inner surface  220  may include a generally cylindrical section and/or an enlarged section between the first taper  226  and the second taper  228 . 
     In some embodiments, it is contemplated that the second taper  228  may be omitted. For example, the inner surface  220  may include a generally cylindrical section and/or an enlarged section between the first taper  226  and the shoulder  224 . Alternatively, the first taper  226  may extend up to the shoulder  224 . 
     Returning to  FIG. 1 , the seal unit  200  is at least partially disposed around the lower mandrel segment  112  and at least partially disposed around the center mandrel segment  160 . As illustrated, the generally cylindrical portion  222  of the inner surface  220  of the seal unit  200  that extends from the trailing end  206  of the seal unit  200  is disposed around the generally cylindrical portion  163  of the outer surface  162  of the center mandrel segment  160 . Additionally, the first taper  226  of the inner surface  220  of the seal unit  200  is disposed around the slope  118  of the outer surface  116  of the lower mandrel segment  112 . As illustrated, the angle of the first taper  226  is substantially equal (such as differing by zero degrees to two degrees) to the angle  118   a  of the slope  118 . In some embodiments, it is contemplated that the angle of the first taper  226  may be greater than the angle  118   a  of the slope  118 . In some embodiments, it is contemplated that the angle of the first taper  226  may be less than the angle  118   a  of the slope  118 . 
     In the configuration illustrated in  FIG. 1 , and with reference to  FIGS. 1, 2, and 3 , the second taper  228  of the inner surface  220  of the seal unit  200  is disposed around the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . It is contemplated that the second taper  228  of the inner surface  220  of the seal unit  200  may be dimensioned such that the second taper  228  provides an interference fit around the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . For example, the inner diameter of the body  210  of the seal unit  200  at the third location  236  (proximal to the shoulder  224 ) on the second taper  228  may be less than an outer diameter of the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . In such an example, the second taper  228  provides an interference fit around the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112  even if the inner diameter of the body  210  of the seal unit  200  at the second location  234  is greater than or equal to the outer diameter of the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . 
     In embodiments in which the second taper  228  of the inner surface  220  of the seal unit  200  is omitted, and there exists a portion of the seal unit  200  body  210  between the first taper  226  of the inner surface  220  and the shoulder  224 , it is contemplated that the portion of the seal unit  200  between the first taper  226  of the inner surface  220  and the shoulder  224  may be disposed around the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . 
     In embodiments in which the first taper  226  of the inner surface  220  of the seal unit  200  extends to the shoulder  224  of the inner surface  220  of the seal unit  200 , it is contemplated that at least a portion of the first taper  226  may be disposed around the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . Additionally, in such embodiments, it is contemplated the first taper  226  of the inner surface  220  of the seal unit  200  may be dimensioned such that the first taper  226  provides an interference fit around the first generally cylindrical portion  117  of the outer surface  116  of the lower mandrel segment  112 . 
     Continuing with  FIG. 1 , an anti-extrusion assembly  300  is disposed around the lower mandrel segment  112  between the seal unit  200  and the leading end  104  of the wiper plug  100 . The anti-extrusion assembly  300  is disposed around the second generally cylindrical portion  152  of the outer surface  116  of the lower mandrel segment  112 . The anti-extrusion assembly  300  is illustrated in detail in an exploded cross-sectional view in  FIG. 4 . The anti-extrusion assembly  300  has a longitudinal axis  302  that, in use, is substantially coincident with the longitudinal axis  102  of the wiper plug  100 . For example, the longitudinal axis  302  of the anti-extrusion assembly  300  may intersect the longitudinal axis  102  of the wiper plug  100  at an angle of from zero degrees to two degrees. The anti-extrusion assembly  300  includes a setting ring  310 , a retaining ring  330 , and a ductile ring  350  located between the setting ring  310  and the retaining ring  330 . 
     The setting ring  310  has a base  312  and an annular projection  316  extending outwardly from the base  312 . The base  312  extends longitudinally from the projection  316 . The projection  316  has a first surface  322  that, in use, faces the trailing end  106  of the wiper plug  100 . The first surface  322  is illustrated as being substantially perpendicular to the longitudinal axis  302 . For example, the first surface  322  may extend at angle of from eighty-five to ninety degrees to the longitudinal axis  202 . However, in some embodiments, the first surface  322  may include a portion that is frustoconical, and thus may be at an acute angle to the longitudinal axis  302 . For example, the first surface  322  may include a portion that extends outwardly from the base  312  and toward the trailing end  106  of the wiper plug  100 . The projection  316  has a second surface  324  that, in use, faces the leading end  104  of the wiper plug  100 . The second surface  324  is frustoconical, and is at an acute angle  324   a  to datum line  302 ′ which is parallel to the longitudinal axis  302 . 
     The retaining ring  330  has a first recess  332  configured to accommodate at least a portion of the base  312  of the setting ring  310 . The first recess  332  is at least partially defined by a first shoulder  334  that, in use, faces the trailing end  106  of the wiper plug  100 . The retaining ring  330  has a second recess  336  configured to accommodate at least a portion of the ridge  154  of the lower mandrel segment  112 . The second recess  336  is at least partially defined by a second shoulder  338  that, in use, faces the ridge  154  of the lower mandrel segment  112 . The retaining ring  330  has a surface  342  that, in use, faces the trailing end  106  of the wiper plug  100 . The surface is frustoconical, and is at an acute angle  342   a  to datum line  302 ′ which is parallel to the longitudinal axis  302 . 
     The ductile ring  350  is made from a material, such as polytetrafluoroethylene, that possesses flexural strength and is resistant to tearing. The ductile ring  350  has a first surface  352  that, in use, faces the trailing end  106  of the wiper plug  100 . The first surface  352  is frustoconical, and is at an acute angle  352   a  to datum line  302 ′ which is parallel to the longitudinal axis  302 . The ductile ring  350  has a second surface  354  that, in use, faces the leading end  104  of the wiper plug  100 . The second surface  354  is frustoconical, and is at an acute angle  354   a  to datum line  302 ′ which is parallel to the longitudinal axis  302 . 
     In some embodiments, it is contemplated that the angle  324   a  of the second surface  324  of the projection  316  of the setting ring  310  may be substantially equal to the angle  352   a  of the first surface  352  of the ductile ring  350 . For example, the angle  324   a  may differ from the angle  352   a  by zero to two degrees. In some embodiments, it is contemplated that the angle  324   a  of the second surface  324  of the projection  316  of the setting ring  310  may be less than the angle  352   a  of the first surface  352  of the ductile ring  350 . In some embodiments, it is contemplated that the angle  324   a  of the second surface  324  of the projection  316  of the setting ring  310  may be greater than the angle  352   a  of the first surface  352  of the ductile ring  350 . 
     In some embodiments, it is contemplated that the angle  354   a  of the second surface  354  of the ductile ring  350  may be substantially equal to the angle  352   a  of the first surface  352  of the ductile ring  350 . For example, the angle  354   a  may differ from the angle  352   a  by zero to two degrees. In some embodiments, it is contemplated that the angle  354   a  of the second surface  354  of the ductile ring  350  may be less than the angle  352   a  of the first surface  352  of the ductile ring  350 . In some embodiments, it is contemplated that the angle  354   a  of the second surface  354  of the ductile ring  350  may be greater than the angle  352   a  of the first surface  352  of the ductile ring  350 . 
     In some embodiments, it is contemplated that the angle  354   a  of the second surface  354  of the ductile ring  350  may be substantially equal to the angle  342   a  of the surface  342  of the retaining ring  330 . For example, the angle  354   a  may differ from the angle  342   a  by zero to two degrees. In some embodiments, it is contemplated that the angle  354   a  of the second surface  354  of the ductile ring  350  may be less than the angle  342   a  of the surface  342  of the retaining ring  330 . In some embodiments, it is contemplated that the angle  354   a  of the second surface  354  of the ductile ring  350  may be greater than the angle  342   a  of the surface  342  of the retaining ring  330 . 
     As illustrated in  FIG. 1 , when the anti-extrusion assembly  300  is mounted on the lower mandrel segment  112 , the nose portion  120  protrudes beyond the anti-extrusion assembly  300 . In some embodiments, it is contemplated that the nose portion  120  may not protrude beyond the anti-extrusion assembly  300 . In some embodiments, it is contemplated that the nose portion  120  may be omitted. 
     As illustrated in  FIG. 1 , when the anti-extrusion assembly  300  is mounted on the lower mandrel segment  112 , the second recess  336  of the retaining ring  330  accommodates at least a portion of the ridge  154  of the lower mandrel segment  112 . The second shoulder  338  of the second recess  336  of the retaining ring  330  is illustrated as abutting the ridge  154  of the lower mandrel segment  112 . However, in some embodiments, it is contemplated that second shoulder  338  of the second recess  336  of the retaining ring  330  may not abut the ridge  154  of the lower mandrel segment  112 . 
     The setting ring  310  is located between the retaining ring  330  and the seal unit  200 , and the ductile ring  350  is located between the projection  316  of the setting ring  310  and the frustoconical surface of the retaining ring  330 . The second surface  324  of the projection  316  of the setting ring  310  abuts the first surface  352  of the ductile ring  350 . The second surface  354  of the ductile ring  350  abuts the frustoconical surface of the retaining ring  330 . 
     The anti-extrusion assembly  300  is configured such that movement of the setting ring  310  toward the retaining ring  330  compresses the ductile ring  350 , resulting in deformation of the ductile ring  350 . The deformation of the ductile ring  350  transitions the ductile ring  350  from a radially retracted condition to a radially extended condition. The base  312  of the setting ring  310  extends into the first recess  332  of the retaining ring  330 . A gap  358  exists between the first shoulder  334  of the first recess  332  of the retaining ring  330  and the end  314  of the base  312  that extends from the projection  316  into the first recess  332  of the retaining ring  330 . An interaction between the first shoulder  334  of the first recess  332  of the retaining ring  330  and an end  314  of the base  312  of the setting ring  310  limits the extent to which the setting ring  310  may move toward the retaining ring  330 , and therefore limits the extent to which the ductile ring  350  may be deformed. 
     Upon mounting the anti-extrusion assembly  300  onto the lower mandrel segment  112 , the ductile ring  350  is disposed around, and in contact with, a portion of the base  312  of the setting ring  310  that does not extend into the first recess  332  of the retaining ring  330 . In some embodiments, it is contemplated that the base  312  of the setting ring  310  may not extend into the first recess  332  of the retaining ring  330  upon mounting the anti-extrusion assembly  300  onto the lower mandrel segment  112 . In some embodiments, it is contemplated that the ductile ring  350  may not be disposed around the base  312  of the setting ring  310 . For example, the ductile ring  350  may be disposed around, and in contact with, the second cylindrical portion  152  of the outer surface  116  of the lower mandrel segment  112 . 
       FIG. 1  illustrates that the leading end  204  of the seal unit  200  abuts the anti-extrusion assembly  300  at the first surface  322  of the projection  316  of the setting ring  310 . However, in some embodiments, it is contemplated that upon assembly of the wiper plug  100 , the leading end  204  of the seal unit  200  may not abut the anti-extrusion assembly  300 . Additionally, the shoulder  224  of the body  210  of the seal unit  200  is disposed proximal to, and facing, an end  168  of the center mandrel segment  160 . In some embodiments, it is contemplated that upon assembly of the wiper plug  100 , the shoulder  224  of the body  210  of the seal unit  200  abuts the end  168  of the center mandrel segment  160 . In some embodiments, it is contemplated that upon assembly of the wiper plug  100 , the shoulder  224  of the body  210  of the seal unit  200  bears against the end  168  of the center mandrel segment  160 . 
     In embodiments in which upon assembly of the wiper plug  100 , the shoulder  224  of the body  210  of the seal unit  200  bears against the end  168  of the center mandrel segment  160  and the leading end  204  of the seal unit  200  abuts the anti-extrusion assembly  300 , it is contemplated that the seal unit  200  may apply a preload to the anti-extrusion assembly  300 . In some embodiments, it is contemplated that the preload may cause the setting ring  310  to apply sufficient force on the ductile ring  350  to deform the ductile ring  350 . For example, an outer diameter of the ductile ring  350  may become enlarged. In some embodiments, it is contemplated that the preload may not cause the setting ring  310  to apply sufficient force on the ductile ring  350  to deform the ductile ring  350 . 
     In some embodiments, a wiper plug includes a mandrel and a seal unit disposed around the mandrel. The seal unit includes a body having an inner surface, a leading end, and a trailing end, and one or more fins extending outwardly from the body. The inner surface includes a first, generally cylindrical, portion and a second portion. The second portion includes an inwardly extending shoulder located between the first portion and the leading end and facing toward the trailing end. The shoulder is substantially perpendicular to a longitudinal axis of the mandrel. The second portion further includes a first taper between the shoulder and the leading end. The seal unit body has a first inner diameter at a first location on the first taper proximal to the leading end and a second inner diameter at a second location on the first taper distal from the leading end. The first inner diameter is greater than the second inner diameter. 
     In some embodiments, an outer surface of the mandrel includes a slope, and the first taper is disposed adjacent the slope. In some embodiments, the inner surface of the seal unit further includes a second taper between the shoulder and the first taper. In some embodiments, the body of the seal unit has a third inner diameter at a third location on the second taper proximal to the shoulder, the third inner diameter less than the second inner diameter. In some embodiments, the wiper plug includes an anti-extrusion assembly disposed about the mandrel at the leading end of the seal unit. 
       FIGS. 5A to 9  illustrate the wiper plug  100  during several stages of operation. The wiper plug  100  is inserted into a bore, such as a wellbore or other bore, such as a pipeline. In  FIG. 5A , the wiper plug  100  is illustrated disposed within a tubular  405 . It is contemplated that the tubular  405  may be a liner or a casing of a wellbore. The wiper plug  100  is suspended from a support  410 , such as a portion of a liner hanger running/setting tool. Each retainer of the wiper plug  100  projects radially outward into a recess  412  of the support  410 . In some embodiments, it is contemplated that the recess  412  may extend around an entire inner circumference of the support  410 . The upper seat sleeve  180  in the position shown in  FIG. 5A  prevents each retainer from moving radially inwardly. 
     A first obturating object, shown in  FIG. 5A  as a ball  414 , is dropped into the wellbore, and conveyed by gravity and/or by pumping a fluid through a work string (not shown) to the wiper plug  100 . In  FIG. 5A , the ball  414  is illustrated as having landed on the profile  142  of the lower seat sleeve  140 . The ball  414  landed on the profile  142  of the lower seat sleeve  140  blocks fluid communication through the wiper plug  100 . Pressure is exerted against the ball  414 , and upon reaching a first threshold, triggers activation of one or more tools in the wellbore. For example, the pressure may cause a liner hanger to become anchored in the wellbore. 
       FIG. 5B  illustrates a variation of  FIG. 5A  in the deployment of the wiper plug  100 . In  FIG. 5B , wiper plug  100 ′ represents at least one embodiment of the wiper plug  100  in which the anti-extrusion assembly  300  is at least partially energized when pressure is exerted against the ball  414 . In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly  300  may result from a preload applied by the seal unit  200 , such as described above. Alternatively, or additionally, in some embodiments it is contemplated that the energizing of the anti-extrusion assembly  300  may result from the pressure exerted against the ball  414  also being exerted against the seal unit  200  in the annular space  408  between the mandrel  110  and the tubular  405 . For example, pressure exerted against the ball  414  may be communicated to the annular space  408  via a port in the support  410  and/or around the one or more retainers  172 . It is contemplated that the preload and/or pressure exerted on the seal unit  200  may result in a force being transferred from the seal unit  200  to the first surface  322  of the projection  316  of the setting ring  310  of the anti-extrusion assembly  300 . 
     As illustrated in  FIG. 5B , a force of sufficient magnitude applied via the seal unit  200  to the setting ring  310  of the anti-extrusion assembly  300  causes the setting ring  310  to move toward the retaining ring  330 . Because the second shoulder  338  of the second recess  336  of the retaining ring  330  abuts the ridge  154  of the lower mandrel segment  112 , the retaining ring  330  is prevented from moving away from the setting ring  310 . Therefore, movement of the setting ring  310  toward the retaining ring  330  compresses the ductile ring  350 , resulting in deformation of the ductile ring  350 . 
     The configuration of the second surface  324  of the projection  316  of the setting ring  310 , the first  352  and second  354  surfaces of the ductile ring  350 , and the corresponding surface  342  of the retaining ring  330  promote deformation of the ductile ring  350  radially outward such that an outer diameter of the ductile ring  350  becomes enlarged, as illustrated in  FIG. 5B . In some embodiments, it is contemplated that the outer diameter of the ductile ring  350  may become enlarged to the extent that the ductile ring  350  contacts the tubular  405 . In some embodiments, it is contemplated that the ductile ring  350  makes a 360 degree contact with the tubular  405 . In other embodiments, it is contemplated that the ductile ring  350  may not contact the tubular  405 . In some embodiments, it is contemplated that the extent to which the ductile ring  350  may be deformed outwardly from between the projection  316  of the setting ring  310  and the retaining ring  330  is limited at least in part by the end  314  of the base  312  of the setting ring contacting the first shoulder  334  of the first recess  332  of the retaining ring  330 . 
     Additionally, the force imparted on the seal unit  200  by the pressure applied on the displacement fluid may cause at least a portion  240  of the seal unit  200  to become extruded, as exemplified in  FIG. 5B . It is contemplated that a susceptibility of the seal unit  200  to extrusion may be exacerbated by exposure to the elevated temperatures that typically exist in wellbores. Extrusion of a fin  212 / 214 / 216 / 218  of the seal unit  200  may compromise the integrity of the seals between the fin  212 / 214 / 216 / 218  and the surrounding tubular  405 . However for the wiper plug  100 ′ of the present disclosure, as shown in  FIG. 5B , extrusion of the seal unit  200  at the leading end  204  of the seal unit  200  is limited by the anti-extrusion assembly  300 . Thus, extrusion of the leading end  204  is restricted, and extrusion of the seal unit at the leading fin  212  is inhibited. Hence, sealing integrity of at least the leading fin  212  against the surrounding tubular  405  is maintained. 
     Further application of pressure against the ball  414  to a second threshold that is higher than the first threshold causes the release of the lower seat sleeve  140 . For example, the force on the lower seat sleeve  140  resulting from the pressure may cause the releasable fastener  144  to fail.  FIG. 6A  illustrates a continuation of the operation depicted in  FIG. 5A , and shows the wiper plug  100  after the release of the lower seat sleeve  140 . The lower seat sleeve  140  and the ball  414  move into the catcher  132 ; the lower seat sleeve  140  rests against the ledge  136  around the end port  134  of the catcher  132 . Fluid communication through the wiper plug  100  is now reestablished since fluid may travel through the one or more side ports  138  of the catcher  132 . 
       FIG. 6B  illustrates a continuation of the operation depicted in  FIG. 5B , and shows the wiper plug  100 ′ after the release of the lower seat sleeve  140 . The lower seat sleeve  140  and the ball  414  move into the catcher  132 ; the lower seat sleeve  140  rests against the ledge  136  around the end port  134  of the catcher  132 . Fluid communication through the wiper plug  100 ′ is now reestablished since fluid may travel through the one or more side ports  138  of the catcher  132 . 
       FIG. 6B  illustrates the ductile ring  350  remaining radially outwardly deformed to an extent similar to that depicted in  FIG. 5B . However, in some embodiments, it is contemplated that the ductile ring  350  may become at least partially radially retracted. For example, the reestablishment of fluid communication through the wiper plug  100 ′ results in a reduction of the pressure exerted on the seal unit  200 . Because of the resilient nature of the material of the seal unit  200 , the seal unit  200  may return back towards the shape and positioning shown in  FIG. 1 . Such a return may reduce the force exerted by the seal unit  200  on the setting ring  310 . In embodiments in which the ductile ring  350  retains at least some resiliency, the ductile ring  350  may at least partially retract back towards the shape and positioning shown in  FIG. 1 . 
     In some embodiments, it is contemplated that the operations illustrated in  FIGS. 5A to 6B  of landing the first obturating object in the lower seat sleeve  140  and releasing the lower seat sleeve  140  may be omitted.  FIG. 7A  illustrates not only a continuation of the operation depicted in  FIG. 6A , but also relevant operations for embodiments in which landing the first obturating object in the lower seat sleeve  140  and releasing the lower seat sleeve  140  are omitted. A cement slurry is pumped into the wellbore and through the wiper plug  100 . A second obturating object, shown in  FIG. 7A  as a dart  416 , is dropped into the wellbore, and conveyed by gravity and/or by pumping a displacement fluid, such as a drilling fluid, through a work string (not shown) to the wiper plug  100 . In  FIG. 7A , the dart  416  is illustrated as having landed on the profile  182  of the upper seat sleeve  180 . The dart  416  landed on the profile  182  of the upper seat sleeve  180  blocks fluid communication through the wiper plug  100 . 
       FIG. 7B  illustrates a continuation of the operation depicted in  FIG. 6B .  FIG. 7B  also illustrates relevant operations for embodiments of wiper plug  100 ′ in which landing the first obturating object in the lower seat sleeve  140  and releasing the lower seat sleeve  140  are omitted. A cement slurry is pumped into the wellbore and through the wiper plug  100 ′. As described with respect to  FIG. 7A , the second obturating object, shown in  FIG. 7B  as dart  416 , is dropped into the wellbore, and conveyed by gravity and/or by pumping a displacement fluid, such as a drilling fluid, through a work string (not shown) to the wiper plug  100 ′. In  FIG. 7B , the dart  416  is illustrated as having landed on the profile  182  of the upper seat sleeve  180 . The dart  416  landed on the profile  182  of the upper seat sleeve  180  blocks fluid communication through the wiper plug  100 ′. 
       FIG. 7B  shows the anti-extrusion assembly  300  of wiper plug  100 ′ is at least partially energized when pressure is exerted against the dart  416 . In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly  300  may result from a preload applied by the seal unit  200 , such as described above. Alternatively, or additionally, in some embodiments it is contemplated that the energizing of the anti-extrusion assembly  300  may result from the pressure exerted against the dart  416  also being exerted against the seal unit  200  in the annular space  408  between the mandrel  110  and the tubular  405 . For example, pressure exerted against the dart  416  may be communicated to the annular space  408  via a port in the support  410  and/or around the one or more retainers  172 . It is contemplated that the preload and/or pressure exerted on the seal unit  200  may result in a force being transferred from the seal unit  200  to the first surface  322  of the projection  316  of the setting ring  310  of the anti-extrusion assembly  300 . 
       FIG. 8A  illustrates a continuation of the operation depicted in  FIG. 7A , and shows the wiper plug  100  after the release of the upper seat sleeve  180 . The application of pressure against the dart  416  to a third threshold causes the release of the upper seat sleeve  180 . For example, the force on the upper seat sleeve  180  resulting from the pressure may cause the releasable fastener  184  to fail. The upper seat sleeve  180  and the dart  416  move down until the external taper  194  of the upper seat sleeve  180  engages the taper  166  of the bore  164  of the center mandrel segment  160  and the lock ring  188  in the center mandrel segment  160  engages the recess  192  in the upper seat sleeve  180 . In some embodiments, it is contemplated that the external taper  194  of the upper seat sleeve  180  and/or the taper  166  of the bore  164  of the center mandrel segment  160  may be omitted. In some embodiments, it is contemplated that the upper seat sleeve  180  and the dart  416  move down until the engagement between the lock ring  188  in the center mandrel segment  160  and the recess  192  in the upper seat sleeve  180  prevents further downward movement of the upper seat sleeve  180 . In some embodiments, it is contemplated that the upper seat sleeve  180  and the dart  416  move down until the lower end  196  of the upper seat sleeve  180  engages a portion of the lower mandrel segment  112 . 
     When the upper seat sleeve  180  moves down past each opening  174  in the upper mandrel segment  170 , each corresponding retainer  172  is no longer prevented from moving radially inward. Continued application of pressure to the dart  416  results in a downward force on the wiper plug  100  which promotes the radial inward movement of each retainer  172  due to the interaction between each retainer and the corresponding recess  412  of the support  410 . The radial inward movement of each retainer  172  thus releases the wiper plug  100  from the support  410 . Because at least one of the fins  212 ,  214 ,  216 ,  218  of the seal unit  200  provides a seal against the tubular  405 , pressure applied to the displacement fluid results in a corresponding force imparted onto the wiper plug  100 . Thus, continued pumping of the displacement fluid moves the wiper plug  100  through the tubular  405  in the direction shown by arrow  418 . Hence, the leading end  104  of the wiper plug  100  faces in the direction of travel  418 , and the trailing end  106  of the wiper plug  100  faces against the direction of travel  418 . 
       FIG. 8B  illustrates a continuation of the operation depicted in  FIG. 7B , and shows the wiper plug  100 ′ after the release of the upper seat sleeve  180 . The application of pressure against the dart  416  to a third threshold causes the release of the upper seat sleeve  180 . For example, the force on the upper seat sleeve  180  resulting from the pressure may cause the releasable fastener  184  to fail. The upper seat sleeve  180  and the dart  416  move down until the external taper  194  of the upper seat sleeve  180  engages the taper  166  of the bore  164  of the center mandrel segment  160  and the lock ring  188  in the center mandrel segment  160  engages the recess  192  in the upper seat sleeve  180 . In some embodiments, it is contemplated that the external taper  194  of the upper seat sleeve  180  and/or the taper  166  of the bore  164  of the center mandrel segment  160  may be omitted. In some embodiments, it is contemplated that the upper seat sleeve  180  and the dart  416  move down until the engagement between the lock ring  188  in the center mandrel segment  160  and the recess  192  in the upper seat sleeve  180  prevents further downward movement of the upper seat sleeve  180 . In some embodiments, it is contemplated that the upper seat sleeve  180  and the dart  416  move down until the lower end  196  of the upper seat sleeve  180  engages a portion of the lower mandrel segment  112 . 
     When the upper seat sleeve  180  moves down past each opening  174  in the upper mandrel segment  170 , each corresponding retainer  172  is no longer prevented from moving radially inward. Continued application of pressure to the dart  416  results in a downward force on the wiper plug  100 ′ which promotes the radial inward movement of each retainer  172  due to the interaction between each retainer and the corresponding recess  412  of the support  410 . The radial inward movement of each retainer  172  thus releases the wiper plug  100 ′ from the support  410 . Because at least one of the fins  212 ,  214 ,  216 ,  218  of the seal unit  200  provides a seal against the tubular  405 , pressure applied to the displacement fluid results in a corresponding force imparted onto the wiper plug  100 ′. Thus, continued pumping of the displacement fluid moves the wiper plug  100 ′ through the tubular  405  in the direction shown by arrow  418 . Hence, the leading end  104  of the wiper plug  100 ′ faces in the direction of travel  418 , and the trailing end  106  of the wiper plug  100 ′ faces against the direction of travel  418 . 
       FIG. 8B  illustrates the ductile ring  350  remaining radially outwardly deformed to an extent similar to that depicted in  FIG. 7B . However, in some embodiments, it is contemplated that the ductile ring  350  may become at least partially radially retracted. For example, the release of the wiper plug  100 ′ from the support  410  may result in pressures above and below the seal unit  200  becoming substantially balanced, such as within 50 psi (3.45 bar). Because of the resilient nature of the material of the seal unit  200 , the seal unit  200  may return back towards the shape and positioning shown in  FIG. 1 . Such a return may reduce the force exerted by the seal unit  200  on the setting ring  310 . In embodiments in which the ductile ring  350  retains at least some resiliency, the ductile ring  350  may at least partially retract back towards the shape and positioning shown in  FIG. 1 . 
     Displacement of the wiper plug  100 ,  100 ′ through the tubular  405  causes the cement slurry to be moved through the tubular  405  and into an annulus surrounding the tubular  405 .  FIG. 9  illustrates a continuation of the operations depicted in  FIGS. 8A and 8B , and depicts a termination of the travel of the wiper plug  100 ,  100 ′ through the tubular  405 . The wiper plug  100 ,  100 ′ is engaged with a collar  420  in the tubular  405 . The collar  420  has a bore  425  configured to receive at least part of the nose portion  120  of the mandrel  110  of the wiper plug  100 ,  100 ′.  FIG. 9  illustrates the bore  425  receiving the one or more seals  124  and the lock ring  126  of the nose portion  120  of the mandrel  110  of the wiper plug  100 ,  100 ′. 
       FIG. 9  illustrates the anti-extrusion assembly  300  in an energized condition. In some embodiments, it is contemplated that the anti-extrusion assembly  300  is not in an energized condition after the wiper plug  100 ,  100 ′ has landed in the collar  420 . In some embodiments, it is contemplated that the anti-extrusion assembly  300  is in an energized condition after the wiper plug  100 ,  100 ′ has landed in the collar  420 . In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly  300  may occur prior to the wiper plug  100 ′ landing in the collar  420 , such as in any one or more of the operations depicted in  FIGS. 5B, 6B, 7B , and/or  8 B, and that the anti-extrusion assembly  300  remains at least partially energized after the wiper plug  100 ′ has landed in the collar  420 . 
     In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly  300  may result from a preload applied by the seal unit  200 , such as described above. Alternatively, or additionally, in some embodiments it is contemplated that the energizing of the anti-extrusion assembly  300  may result from a continued application of pressure applied to the displacement fluid after the wiper plug  100 ,  100 ′ has landed in the collar  420 . For example, in conducting a pressure test following the landing of the wiper plug  100 ,  100 ′ in the collar  420 , pressure applied to the displacement fluid may result in a force being transferred from the seal unit  200  to the first surface  322  of the projection  316  of the setting ring  310  of the anti-extrusion assembly  300 . 
     As illustrated in  FIG. 9 , a force of sufficient magnitude applied via the seal unit  200  to the setting ring  310  of the anti-extrusion assembly  300  causes the setting ring  310  to move toward the retaining ring  330 . As described above, the retaining ring  330  is prevented from moving away from the setting ring  310 , and therefore movement of the setting ring  310  toward the retaining ring  330  compresses the ductile ring  350 , resulting in deformation of the ductile ring  350 . 
     The configuration of the second surface  324  of the projection  316  of the setting ring  310 , the first  352  and second  354  surfaces of the ductile ring  350 , and the corresponding surface  342  of the retaining ring  330  promote deformation of the ductile ring  350  radially outward such that an outer diameter of the ductile ring  350  becomes enlarged, as illustrated in  FIG. 9 . In some embodiments, it is contemplated that the outer diameter of the ductile ring  350  may become enlarged to the extent that the ductile ring  350  contacts the tubular  405 . In some embodiments, it is contemplated that the ductile ring  350  makes a 360 degree contact with the tubular  405 . In other embodiments, it is contemplated that the ductile ring  350  may not contact the tubular  405 . In some embodiments, it is contemplated that the extent to which the ductile ring  350  may be deformed outwardly from between the projection  316  of the setting ring  310  and the retaining ring  330  is limited at least in part by the end  314  of the base  312  of the setting ring contacting the first shoulder  334  of the first recess  332  of the retaining ring  330 . 
     Additionally, the force imparted on the seal unit  200  by the pressure applied on the displacement fluid may cause at least a portion  240  of the seal unit  200  to become extruded, as exemplified in  FIG. 9 . It is contemplated that a susceptibility of the seal unit  200  to extrusion may be exacerbated by exposure to the elevated temperatures that typically exist in wellbores. Extrusion of a fin  212 / 214 / 216 / 218  of the seal unit  200  may compromise the integrity of the seals between the fin  212 / 214 / 216 / 218  and the surrounding tubular  405 . However for the wiper plug  100 ,  100 ′ of the present disclosure, as shown in  FIG. 9 , extrusion of the seal unit  200  at the leading end  204  of the seal unit  200  is limited by the anti-extrusion assembly  300 . Thus, extrusion of the leading end  204  is restricted, and extrusion of the seal unit at the leading fin  212  is inhibited. Hence, sealing integrity of at least the leading fin  212  against the surrounding tubular  405  is maintained. 
     In the operations described above with respect to  FIGS. 5A to 9 , extrusion of the body  210  of the seal unit  200  may compromise the integrity of the seal between the seal unit  200  and the mandrel  110  of the wiper plug  100 ,  100 ′. However, the interaction between the seal unit  200  and the slope  118  of the lower mandrel segment  112  limits extrusion of the body  210  of the seal unit  200 , and limits the degree to which sealing contact between the seal unit  200  and the lower mandrel segment  112  may be compromised. Additionally, in embodiments in which the mounting of the seal unit  200  around the mandrel  110  is configured to be an interference fit, it is contemplated that the interference fit may assist in maintaining the integrity of the seal between the seal unit  200  and the lower mandrel segment  112 . 
     Hence, wiper plugs  100 ,  100 ′ of the present disclosure provide for at least a portion of the seal unit  200  to be maintained in sealing contact with the mandrel  110  and at least a portion of the seal unit  200  to be maintained in sealing contact with the surrounding tubular  405 , and integrity of the seals is preserved. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.