Patent Description:
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.

<CIT> describes a plug and ball seat assembly for releasing a plug. The assembly is selectively maintained in a housing using a mounting system. The plug and ball seat assembly includes a ball seat selectively connected to the plug. The mounting system is designed such that disengaging the ball seat from the plug also disengages the plug from the housing, thereby releasing the plug. In another aspect, a method of releasing a plug includes selectively connecting a ball seat to the plug and disposing the plug and ball seat assembly within a tubular. When the plug is ready for release, the ball seat is disconnected from the plug and allowed to move axially relative to the plug. In turn, the plug and ball seat assembly disconnects from the tubular and releases downhole.

<CIT> describes a single-direction plug for use with cementing applications and with drilling with casing applications, for example a cement plug for installation in a wellbore casing. The plug includes a body and gripping members for preventing movement of the body in a first axial direction relative to the casing. The plug further comprises a sealing member for sealing a fluid path between the body and the casing. The plug is movable in a second axial direction with fluid pressure but is not movable in the first direction due to fluid pressure.

<CIT> describes a cementing system using a tubular member coupled to a string of tubing where upper and lower tubular liner wiper plugs are independently attached to and separately releasable from the tubular member. The upper tubular liner wiper plug has outer liner wiper seal members, an outer latching mechanism and an inner latching mechanism. A fluid bypass is located in the liner wiper plug below the wiper seal members with a check valve structure for bypassing fluid from below the seal members to the bore of the tubular member in response to a pressure differential. A second check valve structure is provided in the tubular member to provide a fluid bypass from the exterior of the tubular member above the seal members to the interior of the tubular member in response to a pressure differential. The lower tubular liner wiper plug is provided with upper, internal spring latch fingers for releasable attachment to the tubular member and an internal, releasable valve sleeve in a bore and a valve opening in a tubular depending section of the wiper plug. A pump down plug member locks into the releasable valve sleeve above the valve opening to form a lower plug assembly. When the lower plug assembly reaches a lower landing collar, the releasable valve sleeve is released by pressure and moves to open the valve opening to permit cement slurry to pass through the valve opening to the float shoe and through to the annulus of the well bore and the liner.

The present invention is defined herein in accordance with the appended claims. 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. The anti-extrusion assembly further comprises: a setting ring disposed adjacent the seal unit; a retaining ring; and a ductile ring disposed between the setting ring and the retaining ring.

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. The anti-extrusion assembly further comprises: a setting ring disposed adjacent the seal unit; a retaining ring; and a ductile ring disposed between the setting ring and the retaining ring.

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, the energizing comprising: landing an obturating object in the wiper plug; and applying a pressure to the landed obturating object.

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.

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> is a longitudinal cross-sectional view of a wiper plug <NUM>. <FIG> is a longitudinal cross-sectional view of the wiper plug <NUM> of <FIG>, but with some components omitted for clarity. The wiper plug <NUM> has a longitudinal axis <NUM>, a leading end <NUM>, and a trailing end <NUM>. For the purpose of orientation, the leading end <NUM> and trailing end <NUM> define opposite ends of the wiper plug <NUM> along the longitudinal axis <NUM> according to a direction of travel (<NUM>, <FIG>, <FIG>) through a tubular for which the wiper plug <NUM> is configured. The wiper plug <NUM> has a mandrel <NUM> that, as illustrated, includes a lower mandrel segment <NUM>, a center mandrel segment <NUM>, and an upper mandrel segment <NUM>. In some embodiments, it is envisaged that the mandrel <NUM> may include greater than three segments. In some embodiments, it is envisaged that the mandrel <NUM> may include fewer than three segments. In some embodiments, it is envisaged that the mandrel <NUM> may be configured as a single component. For the purpose of orientation, the leading end <NUM> of the wiper plug <NUM> is also the leading end of the mandrel <NUM>, and the trailing end <NUM> of the wiper plug <NUM> is also the trailing end of the mandrel <NUM>.

The lower mandrel segment <NUM> has a longitudinal bore <NUM> therethrough. An outer surface <NUM> of the lower mandrel segment <NUM> includes a first portion <NUM> that is generally cylindrical and substantially aligned with the longitudinal axis <NUM>. The outer surface <NUM> also includes a slope <NUM> describing a generally frustoconical profile extending at an acute angle 118a to the longitudinal axis <NUM>. A first outer diameter of the lower mandrel segment <NUM> at a first end 118b of the slope <NUM> proximal to the leading end <NUM> is greater than a second outer diameter of the lower mandrel segment <NUM> at a second end 118c of the slope <NUM> distal from the leading end <NUM>.

The outer surface <NUM> of the lower mandrel segment <NUM> includes a second portion <NUM> that is generally cylindrical and substantially aligned with the longitudinal axis <NUM>. The slope <NUM> is located between the first <NUM> and second <NUM> generally cylindrical portions. The outer surface <NUM> of the lower mandrel segment <NUM> includes a ridge <NUM>. The second generally cylindrical portion <NUM> is located between the ridge <NUM> and the slope <NUM>.

The lower mandrel segment <NUM> includes a nose portion <NUM> located at the leading end <NUM>. The nose portion <NUM> has a bore <NUM> with a diameter that is greater than a diameter of the bore <NUM> of the lower mandrel segment <NUM> at a location distal from the leading end <NUM>. In some embodiments, it is envisaged that the nose portion <NUM> may have a bore <NUM> diameter that is less than or equal to the diameter of the bore <NUM> of the lower mandrel segment <NUM> at a location distal from the leading end <NUM>. The nose portion <NUM> includes one or more seals <NUM> (two are illustrated) on an outer surface. The nose portion <NUM> includes a lock ring <NUM> on the outer surface. In some embodiments, it is envisaged that the one or more seals <NUM> and/or the lock ring <NUM> may be omitted.

The lower mandrel segment <NUM> includes a lower seat assembly <NUM>. The lower seat assembly <NUM> includes a catcher <NUM> that extends into the bore <NUM> of the nose portion <NUM>. The catcher <NUM> is generally tubular, having an end port <NUM> and one or more side ports <NUM>. The catcher <NUM> includes a ledge <NUM> around the end port <NUM>. A lower seat sleeve <NUM> is at least partially disposed in the catcher <NUM>, and has a profile <NUM> configured to interact with an obturating object, such as a dart or a ball. The lower seat sleeve <NUM> is held in place by a releasable fastener <NUM>, such as a shear ring, shear pin, collet, latch, or the like. In some embodiments, it is contemplated that the lower seat assembly <NUM> may be omitted.

The center mandrel segment <NUM> is coupled to the lower mandrel segment <NUM>, and has an outer surface <NUM> including a portion <NUM> that is generally cylindrical and substantially aligned with the longitudinal axis <NUM>. The center mandrel segment <NUM> also has a bore <NUM> that includes a taper <NUM> from a first bore diameter at a first location 166a distal from the lower mandrel segment <NUM> to a second smaller diameter at a second location 166b proximal to the lower mandrel segment <NUM>. The center mandrel segment <NUM> is coupled to the upper mandrel segment <NUM>. The upper mandrel segment <NUM> includes one or more retainers <NUM>, such as locking dogs, collets, latches, and the like. As illustrated in <FIG>, each retainer <NUM> is disposed in a corresponding opening <NUM> in the upper mandrel segment <NUM>. The one or more retainers <NUM> secure the wiper plug <NUM> to a support (<NUM>, shown in <FIG>) for deployment.

An upper seat sleeve <NUM> having a profile <NUM> is at least partially disposed in the upper mandrel segment <NUM> and at least partially disposed in the center mandrel segment <NUM>. The profile <NUM> is configured to interact with an obturating object, such as a dart or a ball. The upper seat sleeve <NUM> extends across each opening <NUM> in the connector, and therefore maintains each retainer <NUM> in a radially extended position. The upper seat sleeve <NUM> is held in place by a releasable fastener <NUM>, such as a shear ring, shear pin, collet, latch, or the like. An o-ring <NUM> provides a seal between the upper seat sleeve <NUM> and the center mandrel segment <NUM>. A lock ring <NUM> in the center mandrel segment <NUM> is configured to engage a recess <NUM> in the upper seat sleeve <NUM>, as described below. The upper seat sleeve <NUM> has an external taper <NUM> such that an outer diameter of the upper seat sleeve <NUM> at a location distal from a lower end <NUM> of the upper seat sleeve <NUM> is greater than an outer diameter of the upper seat sleeve <NUM> at a location proximal to the lower end <NUM> of the upper seat sleeve <NUM>.

The mandrel <NUM>-including at least one or more of the components of the lower mandrel segment <NUM>, the center mandrel segment <NUM>, or the upper mandrel segment <NUM>-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 <NUM> 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 <NUM> 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 <NUM> is disposed around the mandrel <NUM>. The seal unit <NUM> is illustrated in <FIG>. The seal unit <NUM> has a longitudinal axis <NUM>. When assembled on the mandrel <NUM>, the longitudinal axis <NUM> of the seal unit <NUM> is substantially coincident with the longitudinal axis <NUM> of the wiper plug <NUM>. For example, the longitudinal axis <NUM> of the seal unit <NUM> may intersect the longitudinal axis <NUM> of the wiper plug <NUM> at an angle of from zero degrees to two degrees. For the purpose of orientation with the description, the seal unit <NUM> has a leading end <NUM> consistent with the leading end <NUM> of the wiper plug <NUM>, and a trailing end <NUM> consistent with the trailing end <NUM> of the wiper plug <NUM>.

The seal unit <NUM> has a body <NUM> from which a plurality of fins project outwardly. As illustrated, the seal unit <NUM> has a leading fin <NUM> located proximate to the leading end <NUM>, a trailing fin <NUM> located proximate to the trailing end <NUM>, and two intermediate fins <NUM>, <NUM> located between the leading fin <NUM> and the trailing fin <NUM>. As illustrated, the leading fin <NUM> 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 <NUM> 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 <NUM> and one intermediate fin <NUM> 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 <NUM> and the fins <NUM>, <NUM>, <NUM>, <NUM> form a unitary structure of the seal unit <NUM>. However, it is also contemplated that the seal unit <NUM> may include individual segments. For example, each segment may include a body portion and a fin.

The seal unit <NUM> 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 <NUM>. For example, one or more fins <NUM>/<NUM>/<NUM>/<NUM> may include an elastomer possessing a greater stiffness than one or more other fins <NUM>/<NUM>/<NUM>/<NUM> and/or the body <NUM>. In some embodiments, it is contemplated that the seal unit <NUM> may not include additional materials. However, in some embodiments, it is contemplated that the seal unit <NUM> may include additional materials. For example, the seal unit <NUM> may include one or more support members in the body <NUM> and/or in one or more fins <NUM>/<NUM>/<NUM>/<NUM>. The one or more support members may provide enhanced stiffness to one or more sections of the seal unit <NUM>. The one or more support members may be made of metal, such as aluminum, or a composite, such as fiberglass.

Although four fins <NUM>, <NUM>, <NUM>, <NUM> are illustrated, it is contemplated that the seal unit <NUM> 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 <NUM> (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 <NUM> (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 <NUM> has an inner surface <NUM> that includes a portion <NUM> extending from the trailing end <NUM> toward the leading end <NUM> that is generally cylindrical and substantially aligned with the longitudinal axis <NUM>. In some embodiments, it is contemplated that the portion <NUM> of the inner surface <NUM> extending from the trailing end <NUM> toward the leading end <NUM> may be undulating. In some embodiments, it is contemplated that the portion <NUM> of the inner surface <NUM> extending from the trailing end <NUM> toward the leading end <NUM> may not be generally cylindrical. For example, the portion <NUM> of the inner surface <NUM> extending from the trailing end <NUM> toward the leading end <NUM> may describe a generally frustoconical profile.

The inner surface <NUM> of the body <NUM> includes an inwardly extending shoulder <NUM> located between the leading end <NUM> and the portion of the inner surface <NUM> that extends from the trailing end <NUM> toward the leading end <NUM>. The shoulder <NUM> faces toward the trailing end <NUM> and extends substantially perpendicular to the longitudinal axis <NUM>. For example, the shoulder <NUM> may extend at angle of from eighty-five to ninety degrees to the longitudinal axis <NUM>. In some embodiments, it is contemplated that the shoulder <NUM> may extend at an acute angle to the longitudinal axis <NUM>. For example, the shoulder <NUM> may extend at an acute angle toward the trailing end <NUM> and toward the longitudinal axis <NUM>. Alternatively, or additionally, the shoulder <NUM> may include a profile, such as a "V" shaped profile.

The inner surface <NUM> of the body <NUM> includes a first taper <NUM> between the shoulder <NUM> and the leading end <NUM>. As illustrated, the first taper <NUM> describes a generally frustoconical profile, although one or more alternative profiles, such as a curve, are contemplated in some embodiments. The first taper <NUM> is shown having an angle 226a with respect to the longitudinal axis <NUM>. The first taper <NUM> is oriented such that an inner diameter of the body <NUM> at a first location <NUM> on the first taper <NUM> proximal to the leading end <NUM> is greater than an inner diameter of the body <NUM> at a second location <NUM> distal from the leading end <NUM>.

The inner surface <NUM> of the body <NUM> includes a second taper <NUM> between the shoulder <NUM> and the first taper <NUM>. The second taper <NUM> 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 <NUM> is shown having an angle 228a with respect to the longitudinal axis <NUM>. The second taper <NUM> is oriented such that an inner diameter of the body <NUM> at the second location <NUM> is greater than an inner diameter of the body <NUM> at a third location <NUM> on the second taper <NUM>, the third location <NUM> being proximal to the shoulder <NUM>. In this embodiment, the angle 228a is different from the angle 226a. However, it is contemplated the first and second tapers <NUM>, <NUM> may have the same or different angles 226a, 228a or alternative profiles.

The first location <NUM> is on the first taper <NUM> at the leading end <NUM>, the second location <NUM> is at a meeting point of the first taper <NUM> and the second taper <NUM>, and the third location <NUM> is at the shoulder <NUM>. In some embodiments, it is contemplated that the first location <NUM> may be at any location between the leading end <NUM> and the shoulder <NUM>. In some embodiments, it is contemplated that the second location <NUM> may be at any location between the first location <NUM> and the shoulder <NUM>. In some embodiments, it is contemplated that the third location <NUM> may be at any location between the second location <NUM> and the shoulder <NUM>. In some embodiments, it is contemplated that the second taper <NUM> may not meet with the first taper <NUM>. For example, the inner surface <NUM> may include a generally cylindrical section and/or an enlarged section between the first taper <NUM> and the second taper <NUM>.

In some embodiments, it is contemplated that the second taper <NUM> may be omitted. For example, the inner surface <NUM> may include a generally cylindrical section and/or an enlarged section between the first taper <NUM> and the shoulder <NUM>. Alternatively, the first taper <NUM> may extend up to the shoulder <NUM>.

Returning to <FIG>, the seal unit <NUM> is at least partially disposed around the lower mandrel segment <NUM> and at least partially disposed around the center mandrel segment <NUM>. As illustrated, the generally cylindrical portion <NUM> of the inner surface <NUM> of the seal unit <NUM> that extends from the trailing end <NUM> of the seal unit <NUM> is disposed around the generally cylindrical portion <NUM> of the outer surface <NUM> of the center mandrel segment <NUM>. Additionally, the first taper <NUM> of the inner surface <NUM> of the seal unit <NUM> is disposed around the slope <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>. As illustrated, the angle of the first taper <NUM> is substantially equal (such as differing by zero degrees to two degrees) to the angle 118a of the slope <NUM>. In some embodiments, it is contemplated that the angle of the first taper <NUM> may be greater than the angle 118a of the slope <NUM>. In some embodiments, it is contemplated that the angle of the first taper <NUM> may be less than the angle 118a of the slope <NUM>.

In the configuration illustrated in <FIG>, and with reference to <FIG>, <FIG>, and <FIG>, the second taper <NUM> of the inner surface <NUM> of the seal unit <NUM> is disposed around the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>. It is contemplated that the second taper <NUM> of the inner surface <NUM> of the seal unit <NUM> may be dimensioned such that the second taper <NUM> provides an interference fit around the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>. For example, the inner diameter of the body <NUM> of the seal unit <NUM> at the third location <NUM> (proximal to the shoulder <NUM>) on the second taper <NUM> may be less than an outer diameter of the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>. In such an example, the second taper <NUM> provides an interference fit around the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM> even if the inner diameter of the body <NUM> of the seal unit <NUM> at the second location <NUM> is greater than or equal to the outer diameter of the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>.

In embodiments in which the second taper <NUM> of the inner surface <NUM> of the seal unit <NUM> is omitted, and there exists a portion of the seal unit <NUM> body <NUM> between the first taper <NUM> of the inner surface <NUM> and the shoulder <NUM>, it is contemplated that the portion of the seal unit <NUM> between the first taper <NUM> of the inner surface <NUM> and the shoulder <NUM> may be disposed around the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>.

In embodiments in which the first taper <NUM> of the inner surface <NUM> of the seal unit <NUM> extends to the shoulder <NUM> of the inner surface <NUM> of the seal unit <NUM>, it is contemplated that at least a portion of the first taper <NUM> may be disposed around the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>. Additionally, in such embodiments, it is contemplated the first taper <NUM> of the inner surface <NUM> of the seal unit <NUM> may be dimensioned such that the first taper <NUM> provides an interference fit around the first generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>.

Continuing with <FIG>, an anti-extrusion assembly <NUM> is disposed around the lower mandrel segment <NUM> between the seal unit <NUM> and the leading end <NUM> of the wiper plug <NUM>. The anti-extrusion assembly <NUM> is disposed around the second generally cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>. The anti-extrusion assembly <NUM> is illustrated in detail in an exploded cross-sectional view in <FIG>. The anti-extrusion assembly <NUM> has a longitudinal axis <NUM> that, in use, is substantially coincident with the longitudinal axis <NUM> of the wiper plug <NUM>. For example, the longitudinal axis <NUM> of the anti-extrusion assembly <NUM> may intersect the longitudinal axis <NUM> of the wiper plug <NUM> at an angle of from zero degrees to two degrees. The anti-extrusion assembly <NUM> includes a setting ring <NUM>, a retaining ring <NUM>, and a ductile ring <NUM> located between the setting ring <NUM> and the retaining ring <NUM>.

The setting ring <NUM> has a base <NUM> and an annular projection <NUM> extending outwardly from the base <NUM>. The base <NUM> extends longitudinally from the projection <NUM>. The projection <NUM> has a first surface <NUM> that, in use, faces the trailing end <NUM> of the wiper plug <NUM>. The first surface <NUM> is illustrated as being substantially perpendicular to the longitudinal axis <NUM>. For example, the first surface <NUM> may extend at angle of from eighty-five to ninety degrees to the longitudinal axis <NUM>. However, in some embodiments, the first surface <NUM> may include a portion that is frustoconical, and thus may be at an acute angle to the longitudinal axis <NUM>. For example, the first surface <NUM> may include a portion that extends outwardly from the base <NUM> and toward the trailing end <NUM> of the wiper plug <NUM>. The projection <NUM> has a second surface <NUM> that, in use, faces the leading end <NUM> of the wiper plug <NUM>. The second surface <NUM> is frustoconical, and is at an acute angle 324a to datum line <NUM>' which is parallel to the longitudinal axis <NUM>.

The retaining ring <NUM> has a first recess <NUM> configured to accommodate at least a portion of the base <NUM> of the setting ring <NUM>. The first recess <NUM> is at least partially defined by a first shoulder <NUM> that, in use, faces the trailing end <NUM> of the wiper plug <NUM>. The retaining ring <NUM> has a second recess <NUM> configured to accommodate at least a portion of the ridge <NUM> of the lower mandrel segment <NUM>. The second recess <NUM> is at least partially defined by a second shoulder <NUM> that, in use, faces the ridge <NUM> of the lower mandrel segment <NUM>. The retaining ring <NUM> has a surface <NUM> that, in use, faces the trailing end <NUM> of the wiper plug <NUM>. The surface is frustoconical, and is at an acute angle 342a to datum line <NUM>' which is parallel to the longitudinal axis <NUM>.

The ductile ring <NUM> is made from a material, such as polytetrafluoroethylene, that possesses flexural strength and is resistant to tearing. The ductile ring <NUM> has a first surface <NUM> that, in use, faces the trailing end <NUM> of the wiper plug <NUM>. The first surface <NUM> is frustoconical, and is at an acute angle 352a to datum line <NUM>' which is parallel to the longitudinal axis <NUM>. The ductile ring <NUM> has a second surface <NUM> that, in use, faces the leading end <NUM> of the wiper plug <NUM>. The second surface <NUM> is frustoconical, and is at an acute angle 354a to datum line <NUM>' which is parallel to the longitudinal axis <NUM>.

In some embodiments, it is contemplated that the angle 324a of the second surface <NUM> of the projection <NUM> of the setting ring <NUM> may be substantially equal to the angle 352a of the first surface <NUM> of the ductile ring <NUM>. For example, the angle 324a may differ from the angle 352a by zero to two degrees. In some embodiments, it is contemplated that the angle 324a of the second surface <NUM> of the projection <NUM> of the setting ring <NUM> may be less than the angle 352a of the first surface <NUM> of the ductile ring <NUM>. In some embodiments, it is contemplated that the angle 324a of the second surface <NUM> of the projection <NUM> of the setting ring <NUM> may be greater than the angle 352a of the first surface <NUM> of the ductile ring <NUM>.

In some embodiments, it is contemplated that the angle 354a of the second surface <NUM> of the ductile ring <NUM> may be substantially equal to the angle 352a of the first surface <NUM> of the ductile ring <NUM>. For example, the angle 354a may differ from the angle 352a by zero to two degrees. In some embodiments, it is contemplated that the angle 354a of the second surface <NUM> of the ductile ring <NUM> may be less than the angle 352a of the first surface <NUM> of the ductile ring <NUM>. In some embodiments, it is contemplated that the angle 354a of the second surface <NUM> of the ductile ring <NUM> may be greater than the angle 352a of the first surface <NUM> of the ductile ring <NUM>.

In some embodiments, it is contemplated that the angle 354a of the second surface <NUM> of the ductile ring <NUM> may be substantially equal to the angle 342a of the surface <NUM> of the retaining ring <NUM>. For example, the angle 354a may differ from the angle 342a by zero to two degrees. In some embodiments, it is contemplated that the angle 354a of the second surface <NUM> of the ductile ring <NUM> may be less than the angle 342a of the surface <NUM> of the retaining ring <NUM>. In some embodiments, it is contemplated that the angle 354a of the second surface <NUM> of the ductile ring <NUM> may be greater than the angle 342a of the surface <NUM> of the retaining ring <NUM>.

As illustrated in <FIG>, when the anti-extrusion assembly <NUM> is mounted on the lower mandrel segment <NUM>, the nose portion <NUM> protrudes beyond the anti-extrusion assembly <NUM>. In some embodiments, it is contemplated that the nose portion <NUM> may not protrude beyond the anti-extrusion assembly <NUM>. In some embodiments, it is contemplated that the nose portion <NUM> may be omitted.

As illustrated in <FIG>, when the anti-extrusion assembly <NUM> is mounted on the lower mandrel segment <NUM>, the second recess <NUM> of the retaining ring <NUM> accommodates at least a portion of the ridge <NUM> of the lower mandrel segment <NUM>. The second shoulder <NUM> of the second recess <NUM> of the retaining ring <NUM> is illustrated as abutting the ridge <NUM> of the lower mandrel segment <NUM>. However, in some embodiments, it is contemplated that second shoulder <NUM> of the second recess <NUM> of the retaining ring <NUM> may not abut the ridge <NUM> of the lower mandrel segment <NUM>.

The setting ring <NUM> is located between the retaining ring <NUM> and the seal unit <NUM>, and the ductile ring <NUM> is located between the projection <NUM> of the setting ring <NUM> and the frustoconical surface of the retaining ring <NUM>. The second surface <NUM> of the projection <NUM> of the setting ring <NUM> abuts the first surface <NUM> of the ductile ring <NUM>. The second surface <NUM> of the ductile ring <NUM> abuts the frustoconical surface of the retaining ring <NUM>.

The anti-extrusion assembly <NUM> is configured such that movement of the setting ring <NUM> toward the retaining ring <NUM> compresses the ductile ring <NUM>, resulting in deformation of the ductile ring <NUM>. The deformation of the ductile ring <NUM> transitions the ductile ring <NUM> from a radially retracted condition to a radially extended condition. The base <NUM> of the setting ring <NUM> extends into the first recess <NUM> of the retaining ring <NUM>. A gap <NUM> exists between the first shoulder <NUM> of the first recess <NUM> of the retaining ring <NUM> and the end <NUM> of the base <NUM> that extends from the projection <NUM> into the first recess <NUM> of the retaining ring <NUM>. An interaction between the first shoulder <NUM> of the first recess <NUM> of the retaining ring <NUM> and an end <NUM> of the base <NUM> of the setting ring <NUM> limits the extent to which the setting ring <NUM> may move toward the retaining ring <NUM>, and therefore limits the extent to which the ductile ring <NUM> may be deformed.

Upon mounting the anti-extrusion assembly <NUM> onto the lower mandrel segment <NUM>, the ductile ring <NUM> is disposed around, and in contact with, a portion of the base <NUM> of the setting ring <NUM> that does not extend into the first recess <NUM> of the retaining ring <NUM>. In some embodiments, it is contemplated that the base <NUM> of the setting ring <NUM> may not extend into the first recess <NUM> of the retaining ring <NUM> upon mounting the anti-extrusion assembly <NUM> onto the lower mandrel segment <NUM>. In some embodiments, it is contemplated that the ductile ring <NUM> may not be disposed around the base <NUM> of the setting ring <NUM>. For example, the ductile ring <NUM> may be disposed around, and in contact with, the second cylindrical portion <NUM> of the outer surface <NUM> of the lower mandrel segment <NUM>.

<FIG> illustrates that the leading end <NUM> of the seal unit <NUM> abuts the anti-extrusion assembly <NUM> at the first surface <NUM> of the projection <NUM> of the setting ring <NUM>. However, in some embodiments, it is contemplated that upon assembly of the wiper plug <NUM>, the leading end <NUM> of the seal unit <NUM> may not abut the anti-extrusion assembly <NUM>. Additionally, the shoulder <NUM> of the body <NUM> of the seal unit <NUM> is disposed proximal to, and facing, an end <NUM> of the center mandrel segment <NUM>. In some embodiments, it is contemplated that upon assembly of the wiper plug <NUM>, the shoulder <NUM> of the body <NUM> of the seal unit <NUM> abuts the end <NUM> of the center mandrel segment <NUM>. In some embodiments, it is contemplated that upon assembly of the wiper plug <NUM>, the shoulder <NUM> of the body <NUM> of the seal unit <NUM> bears against the end <NUM> of the center mandrel segment <NUM>.

In embodiments in which upon assembly of the wiper plug <NUM>, the shoulder <NUM> of the body <NUM> of the seal unit <NUM> bears against the end <NUM> of the center mandrel segment <NUM> and the leading end <NUM> of the seal unit <NUM> abuts the anti-extrusion assembly <NUM>, it is contemplated that the seal unit <NUM> may apply a preload to the anti-extrusion assembly <NUM>. In some embodiments, it is contemplated that the preload may cause the setting ring <NUM> to apply sufficient force on the ductile ring <NUM> to deform the ductile ring <NUM>. For example, an outer diameter of the ductile ring <NUM> may become enlarged. In some embodiments, it is contemplated that the preload may not cause the setting ring <NUM> to apply sufficient force on the ductile ring <NUM> to deform the ductile ring <NUM>.

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.

<FIG> illustrate the wiper plug <NUM> during several stages of operation. The wiper plug <NUM> is inserted into a bore, such as a wellbore or other bore, such as a pipeline. In <FIG>, the wiper plug <NUM> is illustrated disposed within a tubular <NUM>. It is contemplated that the tubular <NUM> may be a liner or a casing of a wellbore. The wiper plug <NUM> is suspended from a support <NUM>, such as a portion of a liner hanger running/setting tool. Each retainer of the wiper plug <NUM> projects radially outward into a recess <NUM> of the support <NUM>. In some embodiments, it is contemplated that the recess <NUM> may extend around an entire inner circumference of the support <NUM>. The upper seat sleeve <NUM> in the position shown in <FIG> prevents each retainer from moving radially inwardly.

A first obturating object, shown in <FIG> as a ball <NUM>, 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 <NUM>. In <FIG>, the ball <NUM> is illustrated as having landed on the profile <NUM> of the lower seat sleeve <NUM>. The ball <NUM> landed on the profile <NUM> of the lower seat sleeve <NUM> blocks fluid communication through the wiper plug <NUM>. Pressure is exerted against the ball <NUM>, 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> illustrates a variation of <FIG> in the deployment of the wiper plug <NUM>. In <FIG>, wiper plug <NUM>' represents at least one embodiment of the wiper plug <NUM> in which the anti-extrusion assembly <NUM> is at least partially energized when pressure is exerted against the ball <NUM>. In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly <NUM> may result from a preload applied by the seal unit <NUM>, such as described above. Alternatively, or additionally, in some embodiments it is contemplated that the energizing of the anti-extrusion assembly <NUM> may result from the pressure exerted against the ball <NUM> also being exerted against the seal unit <NUM> in the annular space <NUM> between the mandrel <NUM> and the tubular <NUM>. For example, pressure exerted against the ball <NUM> may be communicated to the annular space <NUM> via a port in the support <NUM> and/or around the one or more retainers <NUM>. It is contemplated that the preload and/or pressure exerted on the seal unit <NUM> may result in a force being transferred from the seal unit <NUM> to the first surface <NUM> of the projection <NUM> of the setting ring <NUM> of the anti-extrusion assembly <NUM>.

As illustrated in <FIG>, a force of sufficient magnitude applied via the seal unit <NUM> to the setting ring <NUM> of the anti-extrusion assembly <NUM> causes the setting ring <NUM> to move toward the retaining ring <NUM>. Because the second shoulder <NUM> of the second recess <NUM> of the retaining ring <NUM> abuts the ridge <NUM> of the lower mandrel segment <NUM>, the retaining ring <NUM> is prevented from moving away from the setting ring <NUM>. Therefore, movement of the setting ring <NUM> toward the retaining ring <NUM> compresses the ductile ring <NUM>, resulting in deformation of the ductile ring <NUM>.

The configuration of the second surface <NUM> of the projection <NUM> of the setting ring <NUM>, the first <NUM> and second <NUM> surfaces of the ductile ring <NUM>, and the corresponding surface <NUM> of the retaining ring <NUM> promote deformation of the ductile ring <NUM> radially outward such that an outer diameter of the ductile ring <NUM> becomes enlarged, as illustrated in <FIG>. In some embodiments, it is contemplated that the outer diameter of the ductile ring <NUM> may become enlarged to the extent that the ductile ring <NUM> contacts the tubular <NUM>. In some embodiments, it is contemplated that the ductile ring <NUM> makes a <NUM> degree contact with the tubular <NUM>. In other embodiments, it is contemplated that the ductile ring <NUM> may not contact the tubular <NUM>. In some embodiments, it is contemplated that the extent to which the ductile ring <NUM> may be deformed outwardly from between the projection <NUM> of the setting ring <NUM> and the retaining ring <NUM> is limited at least in part by the end <NUM> of the base <NUM> of the setting ring contacting the first shoulder <NUM> of the first recess <NUM> of the retaining ring <NUM>.

Additionally, the force imparted on the seal unit <NUM> by the pressure applied on the displacement fluid may cause at least a portion <NUM> of the seal unit <NUM> to become extruded, as exemplified in <FIG>. It is contemplated that a susceptibility of the seal unit <NUM> to extrusion may be exacerbated by exposure to the elevated temperatures that typically exist in wellbores. Extrusion of a fin <NUM>/<NUM>/<NUM>/<NUM> of the seal unit <NUM> may compromise the integrity of the seals between the fin <NUM>/<NUM>/<NUM>/<NUM> and the surrounding tubular <NUM>. However for the wiper plug <NUM>' of the present disclosure, as shown in <FIG>, extrusion of the seal unit <NUM> at the leading end <NUM> of the seal unit <NUM> is limited by the anti-extrusion assembly <NUM>. Thus, extrusion of the leading end <NUM> is restricted, and extrusion of the seal unit at the leading fin <NUM> is inhibited. Hence, sealing integrity of at least the leading fin <NUM> against the surrounding tubular <NUM> is maintained.

Further application of pressure against the ball <NUM> to a second threshold that is higher than the first threshold causes the release of the lower seat sleeve <NUM>. For example, the force on the lower seat sleeve <NUM> resulting from the pressure may cause the releasable fastener <NUM> to fail. <FIG> illustrates a continuation of the operation depicted in <FIG>, and shows the wiper plug <NUM> after the release of the lower seat sleeve <NUM>. The lower seat sleeve <NUM> and the ball <NUM> move into the catcher <NUM>; the lower seat sleeve <NUM> rests against the ledge <NUM> around the end port <NUM> of the catcher <NUM>. Fluid communication through the wiper plug <NUM> is now reestablished since fluid may travel through the one or more side ports <NUM> of the catcher <NUM>.

<FIG> illustrates a continuation of the operation depicted in <FIG>, and shows the wiper plug <NUM>' after the release of the lower seat sleeve <NUM>. The lower seat sleeve <NUM> and the ball <NUM> move into the catcher <NUM>; the lower seat sleeve <NUM> rests against the ledge <NUM> around the end port <NUM> of the catcher <NUM>. Fluid communication through the wiper plug <NUM>' is now reestablished since fluid may travel through the one or more side ports <NUM> of the catcher <NUM>.

<FIG> illustrates the ductile ring <NUM> remaining radially outwardly deformed to an extent similar to that depicted in <FIG>. However, in some embodiments, it is contemplated that the ductile ring <NUM> may become at least partially radially retracted. For example, the reestablishment of fluid communication through the wiper plug <NUM>' results in a reduction of the pressure exerted on the seal unit <NUM>. Because of the resilient nature of the material of the seal unit <NUM>, the seal unit <NUM> may return back towards the shape and positioning shown in <FIG>. Such a return may reduce the force exerted by the seal unit <NUM> on the setting ring <NUM>. In embodiments in which the ductile ring <NUM> retains at least some resiliency, the ductile ring <NUM> may at least partially retract back towards the shape and positioning shown in <FIG>.

In some embodiments, it is contemplated that the operations illustrated in <FIG> of landing the first obturating object in the lower seat sleeve <NUM> and releasing the lower seat sleeve <NUM> may be omitted. <FIG> illustrates not only a continuation of the operation depicted in <FIG>, but also relevant operations for embodiments in which landing the first obturating object in the lower seat sleeve <NUM> and releasing the lower seat sleeve <NUM> are omitted. A cement slurry is pumped into the wellbore and through the wiper plug <NUM>. A second obturating object, shown in <FIG> as a dart <NUM>, 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 <NUM>. In <FIG>, the dart <NUM> is illustrated as having landed on the profile <NUM> of the upper seat sleeve <NUM>. The dart <NUM> landed on the profile <NUM> of the upper seat sleeve <NUM> blocks fluid communication through the wiper plug <NUM>.

<FIG> illustrates a continuation of the operation depicted in <FIG>. <FIG> also illustrates relevant operations for embodiments of wiper plug <NUM>' in which landing the first obturating object in the lower seat sleeve <NUM> and releasing the lower seat sleeve <NUM> are omitted. A cement slurry is pumped into the wellbore and through the wiper plug <NUM>'. As described with respect to <FIG>, the second obturating object, shown in <FIG> as dart <NUM>, 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 <NUM>'. In <FIG>, the dart <NUM> is illustrated as having landed on the profile <NUM> of the upper seat sleeve <NUM>. The dart <NUM> landed on the profile <NUM> of the upper seat sleeve <NUM> blocks fluid communication through the wiper plug <NUM>'.

<FIG> shows the anti-extrusion assembly <NUM> of wiper plug <NUM>' is at least partially energized when pressure is exerted against the dart <NUM>. In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly <NUM> may result from a preload applied by the seal unit <NUM>, such as described above. Alternatively, or additionally, in some embodiments it is contemplated that the energizing of the anti-extrusion assembly <NUM> may result from the pressure exerted against the dart <NUM> also being exerted against the seal unit <NUM> in the annular space <NUM> between the mandrel <NUM> and the tubular <NUM>. For example, pressure exerted against the dart <NUM> may be communicated to the annular space <NUM> via a port in the support <NUM> and/or around the one or more retainers <NUM>. It is contemplated that the preload and/or pressure exerted on the seal unit <NUM> may result in a force being transferred from the seal unit <NUM> to the first surface <NUM> of the projection <NUM> of the setting ring <NUM> of the anti-extrusion assembly <NUM>.

<FIG> illustrates a continuation of the operation depicted in <FIG>, and shows the wiper plug <NUM> after the release of the upper seat sleeve <NUM>. The application of pressure against the dart <NUM> to a third threshold causes the release of the upper seat sleeve <NUM>. For example, the force on the upper seat sleeve <NUM> resulting from the pressure may cause the releasable fastener <NUM> to fail. The upper seat sleeve <NUM> and the dart <NUM> move down until the external taper <NUM> of the upper seat sleeve <NUM> engages the taper <NUM> of the bore <NUM> of the center mandrel segment <NUM> and the lock ring <NUM> in the center mandrel segment <NUM> engages the recess <NUM> in the upper seat sleeve <NUM>. In some embodiments, it is contemplated that the external taper <NUM> of the upper seat sleeve <NUM> and/or the taper <NUM> of the bore <NUM> of the center mandrel segment <NUM> may be omitted. In some embodiments, it is contemplated that the upper seat sleeve <NUM> and the dart <NUM> move down until the engagement between the lock ring <NUM> in the center mandrel segment <NUM> and the recess <NUM> in the upper seat sleeve <NUM> prevents further downward movement of the upper seat sleeve <NUM>. In some embodiments, it is contemplated that the upper seat sleeve <NUM> and the dart <NUM> move down until the lower end <NUM> of the upper seat sleeve <NUM> engages a portion of the lower mandrel segment <NUM>.

When the upper seat sleeve <NUM> moves down past each opening <NUM> in the upper mandrel segment <NUM>, each corresponding retainer <NUM> is no longer prevented from moving radially inward. Continued application of pressure to the dart <NUM> results in a downward force on the wiper plug <NUM> which promotes the radial inward movement of each retainer <NUM> due to the interaction between each retainer and the corresponding recess <NUM> of the support <NUM>. The radial inward movement of each retainer <NUM> thus releases the wiper plug <NUM> from the support <NUM>. Because at least one of the fins <NUM>, <NUM>, <NUM>, <NUM> of the seal unit <NUM> provides a seal against the tubular <NUM>, pressure applied to the displacement fluid results in a corresponding force imparted onto the wiper plug <NUM>. Thus, continued pumping of the displacement fluid moves the wiper plug <NUM> through the tubular <NUM> in the direction shown by arrow <NUM>. Hence, the leading end <NUM> of the wiper plug <NUM> faces in the direction of travel <NUM>, and the trailing end <NUM> of the wiper plug <NUM> faces against the direction of travel <NUM>.

<FIG> illustrates a continuation of the operation depicted in <FIG>, and shows the wiper plug <NUM>' after the release of the upper seat sleeve <NUM>. The application of pressure against the dart <NUM> to a third threshold causes the release of the upper seat sleeve <NUM>. For example, the force on the upper seat sleeve <NUM> resulting from the pressure may cause the releasable fastener <NUM> to fail. The upper seat sleeve <NUM> and the dart <NUM> move down until the external taper <NUM> of the upper seat sleeve <NUM> engages the taper <NUM> of the bore <NUM> of the center mandrel segment <NUM> and the lock ring <NUM> in the center mandrel segment <NUM> engages the recess <NUM> in the upper seat sleeve <NUM>. In some embodiments, it is contemplated that the external taper <NUM> of the upper seat sleeve <NUM> and/or the taper <NUM> of the bore <NUM> of the center mandrel segment <NUM> may be omitted. In some embodiments, it is contemplated that the upper seat sleeve <NUM> and the dart <NUM> move down until the engagement between the lock ring <NUM> in the center mandrel segment <NUM> and the recess <NUM> in the upper seat sleeve <NUM> prevents further downward movement of the upper seat sleeve <NUM>. In some embodiments, it is contemplated that the upper seat sleeve <NUM> and the dart <NUM> move down until the lower end <NUM> of the upper seat sleeve <NUM> engages a portion of the lower mandrel segment <NUM>.

When the upper seat sleeve <NUM> moves down past each opening <NUM> in the upper mandrel segment <NUM>, each corresponding retainer <NUM> is no longer prevented from moving radially inward. Continued application of pressure to the dart <NUM> results in a downward force on the wiper plug <NUM>' which promotes the radial inward movement of each retainer <NUM> due to the interaction between each retainer and the corresponding recess <NUM> of the support <NUM>. The radial inward movement of each retainer <NUM> thus releases the wiper plug <NUM>' from the support <NUM>. Because at least one of the fins <NUM>, <NUM>, <NUM>, <NUM> of the seal unit <NUM> provides a seal against the tubular <NUM>, pressure applied to the displacement fluid results in a corresponding force imparted onto the wiper plug <NUM>'. Thus, continued pumping of the displacement fluid moves the wiper plug <NUM>' through the tubular <NUM> in the direction shown by arrow <NUM>. Hence, the leading end <NUM> of the wiper plug <NUM>' faces in the direction of travel <NUM>, and the trailing end <NUM> of the wiper plug <NUM>' faces against the direction of travel <NUM>.

<FIG> illustrates the ductile ring <NUM> remaining radially outwardly deformed to an extent similar to that depicted in <FIG>. However, in some embodiments, it is contemplated that the ductile ring <NUM> may become at least partially radially retracted. For example, the release of the wiper plug <NUM>' from the support <NUM> may result in pressures above and below the seal unit <NUM> becoming substantially balanced, such as within <NUM> psi (<NUM> bar). Because of the resilient nature of the material of the seal unit <NUM>, the seal unit <NUM> may return back towards the shape and positioning shown in <FIG>. Such a return may reduce the force exerted by the seal unit <NUM> on the setting ring <NUM>. In embodiments in which the ductile ring <NUM> retains at least some resiliency, the ductile ring <NUM> may at least partially retract back towards the shape and positioning shown in <FIG>.

Displacement of the wiper plug <NUM>, <NUM>' through the tubular <NUM> causes the cement slurry to be moved through the tubular <NUM> and into an annulus surrounding the tubular <NUM>. <FIG> illustrates a continuation of the operations depicted in <FIG> and <FIG>, and depicts a termination of the travel of the wiper plug <NUM>, <NUM>' through the tubular <NUM>. The wiper plug <NUM>, <NUM>' is engaged with a collar <NUM> in the tubular <NUM>. The collar <NUM> has a bore <NUM> configured to receive at least part of the nose portion <NUM> of the mandrel <NUM> of the wiper plug <NUM>, <NUM>'. <FIG> illustrates the bore <NUM> receiving the one or more seals <NUM> and the lock ring <NUM> of the nose portion <NUM> of the mandrel <NUM> of the wiper plug <NUM>, <NUM>'.

<FIG> illustrates the anti-extrusion assembly <NUM> in an energized condition. In some embodiments, it is contemplated that the anti-extrusion assembly <NUM> is not in an energized condition after the wiper plug <NUM>, <NUM>' has landed in the collar <NUM>. In some embodiments, it is contemplated that the anti-extrusion assembly <NUM> is in an energized condition after the wiper plug <NUM>, <NUM>' has landed in the collar <NUM>. In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly <NUM> may occur prior to the wiper plug <NUM>' landing in the collar <NUM>, such as in any one or more of the operations depicted in <FIG>, <FIG>, <FIG>, and/or 8B, and that the anti-extrusion assembly <NUM> remains at least partially energized after the wiper plug <NUM>' has landed in the collar <NUM>.

In some embodiments, it is contemplated that the energizing of the anti-extrusion assembly <NUM> may result from a preload applied by the seal unit <NUM>, such as described above. Alternatively, or additionally, in some embodiments it is contemplated that the energizing of the anti-extrusion assembly <NUM> may result from a continued application of pressure applied to the displacement fluid after the wiper plug <NUM>, <NUM>' has landed in the collar <NUM>. For example, in conducting a pressure test following the landing of the wiper plug <NUM>, <NUM>' in the collar <NUM>, pressure applied to the displacement fluid may result in a force being transferred from the seal unit <NUM> to the first surface <NUM> of the projection <NUM> of the setting ring <NUM> of the anti-extrusion assembly <NUM>.

As illustrated in <FIG>, a force of sufficient magnitude applied via the seal unit <NUM> to the setting ring <NUM> of the anti-extrusion assembly <NUM> causes the setting ring <NUM> to move toward the retaining ring <NUM>. As described above, the retaining ring <NUM> is prevented from moving away from the setting ring <NUM>, and therefore movement of the setting ring <NUM> toward the retaining ring <NUM> compresses the ductile ring <NUM>, resulting in deformation of the ductile ring <NUM>.

Additionally, the force imparted on the seal unit <NUM> by the pressure applied on the displacement fluid may cause at least a portion <NUM> of the seal unit <NUM> to become extruded, as exemplified in <FIG>. It is contemplated that a susceptibility of the seal unit <NUM> to extrusion may be exacerbated by exposure to the elevated temperatures that typically exist in wellbores. Extrusion of a fin <NUM>/<NUM>/<NUM>/<NUM> of the seal unit <NUM> may compromise the integrity of the seals between the fin <NUM>/<NUM>/<NUM>/<NUM> and the surrounding tubular <NUM>. However for the wiper plug <NUM>, <NUM>' of the present disclosure, as shown in <FIG>, extrusion of the seal unit <NUM> at the leading end <NUM> of the seal unit <NUM> is limited by the anti-extrusion assembly <NUM>. Thus, extrusion of the leading end <NUM> is restricted, and extrusion of the seal unit at the leading fin <NUM> is inhibited. Hence, sealing integrity of at least the leading fin <NUM> against the surrounding tubular <NUM> is maintained.

In the operations described above with respect to <FIG>, extrusion of the body <NUM> of the seal unit <NUM> may compromise the integrity of the seal between the seal unit <NUM> and the mandrel <NUM> of the wiper plug <NUM>, <NUM>'. However, the interaction between the seal unit <NUM> and the slope <NUM> of the lower mandrel segment <NUM> limits extrusion of the body <NUM> of the seal unit <NUM>, and limits the degree to which sealing contact between the seal unit <NUM> and the lower mandrel segment <NUM> may be compromised. Additionally, in embodiments in which the mounting of the seal unit <NUM> around the mandrel <NUM> 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 <NUM> and the lower mandrel segment <NUM>.

Hence, wiper plugs <NUM>, <NUM>' of the present disclosure provide for at least a portion of the seal unit <NUM> to be maintained in sealing contact with the mandrel <NUM> and at least a portion of the seal unit <NUM> to be maintained in sealing contact with the surrounding tubular <NUM>, and integrity of the seals is preserved.

Claim 1:
A wiper plug (<NUM>; <NUM>') comprising:
a mandrel (<NUM>) having a nose portion (<NUM>) at a leading end (<NUM>) thereof;
a seal unit (<NUM>) disposed about the mandrel (<NUM>), the seal unit (<NUM>) including a body (<NUM>) and one or more fins (<NUM>, <NUM>, <NUM>, <NUM>) extending outwardly from the body (<NUM>); and
an anti-extrusion assembly (<NUM>) disposed about the mandrel (<NUM>) at a leading end (<NUM>) of the seal unit (<NUM>), the anti-extrusion assembly (<NUM>) arranged to transition between a first configuration, in which the anti-extrusion assembly (<NUM>) is not energized, and a second configuration, in which the anti-extrusion assembly (<NUM>) is energized;
wherein the nose portion (<NUM>) protrudes beyond the anti-extrusion assembly; and
wherein the anti-extrusion assembly (<NUM>) further comprises:
a setting ring (<NUM>) disposed adjacent the seal unit (<NUM>);
a retaining ring (<NUM>); and
a ductile ring (<NUM>) disposed between the setting ring (<NUM>) and the retaining ring (<NUM>).