Patent Publication Number: US-10760372-B2

Title: High expansion well tool and associated methods

Description:
BACKGROUND 
     This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an example described below, more particularly provides a high expansion well tool and associated methods. 
     A well plug may be used to isolate one section of a wellbore from another section, either permanently or temporarily. If temporary isolation is desired, the well plug may be retrievable from the wellbore. Typically, a well plug includes an annular seal for sealing off an annulus between the wellbore and a body of the plug, and an anchoring device (such as one or more slips) for securing the plug against displacement in the wellbore. 
     A well packer is typically similar to a well plug, in that a well packer can include an annular seal and an anchoring device. However, a well packer is typically provided with an interior longitudinal flow passage that permits flow through the packer and any tubular string connected to the packer. Note that the terms “plug” and “packer” are not mutually exclusive, since some plugs provide for selective flow therethrough, and some packers have provisions for selectively blocking flow therethrough. 
     It will, therefore, be appreciated that improvements are continually needed in the arts of designing, constructing and utilizing plugs and packers for subterranean wells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a representative partially cross-sectional view of an example of a well system and associated method which can embody principles of this disclosure. 
         FIGS. 2A-F  are representative cross-sectional views of an example of a well tool embodying the principles of this disclosure, and which may be used in the system and method of  FIG. 1 , the well tool being depicted in a run-in configuration. 
         FIGS. 3A-D  are representative cross-sectional views of the well tool in a set configuration. 
         FIGS. 4A  &amp; B are representative perspective views of an example of a radial expansion device in respective radially retracted and radially expanded configurations. 
         FIG. 5  is a representative perspective view of an example of a slip assembly that may be used with the well tool. 
         FIGS. 6A-D  are representative cross-sectional views of the well tool in a communicated configuration. 
         FIGS. 7A-D  are representative cross-sectional views of the well tool in an unset retrieval configuration. 
         FIG. 8  is a representative cross-sectional view of a portion of the well tool with an example of an annular seal having a reinforcement therein. 
     
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in  FIG. 1  is a well system  10  for use with a subterranean well, and an associated method, which can embody principles of this disclosure. However, it should be clearly understood that the system  10  and method are merely one example of an application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited at all to the details of the system  10  and method described herein and/or depicted in the drawings. 
     In the  FIG. 1  example, a wellbore  12  is lined with casing  14  and cement  16 . In other examples, a portion of the wellbore  12  in which the principles of this disclosure are practiced may be uncased, unlined or “open hole.” 
     As depicted in  FIG. 1 , there is a restriction  18  in the wellbore  12 . In this example, the restriction  18  is a reduced inner diameter, that is, an inner diameter less than an inner diameter of the casing  14  on either side of the restriction. For example, the restriction  18  could comprise a nipple or reduced diameter seat, an interior portion of a casing valve or other well tool, a casing patch, etc. In other examples, the restriction  18  could comprise an obstruction other than a reduced inner diameter (such as, a partial casing collapse or other casing damage, etc.). 
     Thus, the scope of this disclosure is not limited to any particular type of restriction, or to the presence of a restriction at all. 
     It is desired in the  FIG. 1  example to isolate a lower portion of the wellbore  12  from an upper portion of the wellbore. This isolation is to be accomplished at a location below or further downhole from the restriction  18 . For this purpose, a bottom hole assembly  20  is introduced into the wellbore  12 . 
     In the  FIG. 1  example, the bottom hole assembly  20  includes a setting tool  22  and a well tool  24 . The bottom hole assembly  20  is conveyed into the wellbore  12  by a wireline, slickline, electric line, coiled tubing or other type of conveyance  26 . In other examples, the bottom hole assembly  20  could include other or different tools (such as, a casing collar locator, etc.), and a conveyance may not be used for positioning the bottom hole assembly in the wellbore  12  (for example, fluid flow could be used to convey the bottom hole assembly to a desired location). 
     The well tool  24  in the  FIG. 1  example is of the type referred to by those skilled in the art as a “bridge plug.” After setting the well tool  24  in the wellbore  12 , a portion of the wellbore downhole from the well tool will be fluid- and pressure-isolated from a portion of the wellbore uphole from the well tool. However, in other examples, the well tool  24  could be of the type referred to by those skilled in the art as a “packer.” Thus, the scope of this disclosure is not limited to use of any particular type or configuration of well tool. 
     As depicted in  FIG. 1 , the well tool  24  includes an annular seal  28  and an anchor mechanism  30 . The annular seal  28  is radially extendable from the well tool  24  downhole to thereby sealingly engage an inner surface of the wellbore  12 . In this manner, the annular seal  28  prevents fluid flow through an annulus  31  formed radially between the well tool  24  and the wellbore  12 . 
     The anchor mechanism  30  is outwardly extendable from the well tool  24  downhole to thereby grippingly engage the inner surface of the wellbore  12 . In this manner, the anchor mechanism  30  secures the well tool  24  against longitudinal displacement relative to the wellbore  12 . 
     Note that it is not necessary for the well tool  24  to include the anchor mechanism  30 , or for the anchor mechanism to be separate from the annular seal  28 . For example, the sealing engagement between the annular seal  28  and the wellbore  12  could also provide sufficient gripping engagement to secure the well tool  24  against longitudinal displacement, or the anchor mechanism  30  could be integral with the annular seal. Thus, the scope of this disclosure is not limited to any particular components, combination of components or configuration of the well tool  24 . 
     In the  FIG. 1  example, the well tool  24  must pass through the restriction  18 , in order to be positioned at the desired location for setting the well tool. The annular seal  28  and the anchor mechanism  30  cannot extend too far outward from the well tool  24 , so that they prevent the well tool from passing through the restriction  18 , but the annular seal and the anchor mechanism must be capable of extending sufficiently far outward from the well tool when it is desired for the annular seal to sealingly engage the wellbore  12 , and for the anchor mechanism to grippingly engage the wellbore. 
     If there is a relatively large inner dimensional difference between the wellbore  12  and the restriction  18 , this means that the annular seal  28  and the anchor mechanism  30  must be capable of a corresponding relatively large outward extension from the well tool  24  after the well tool has passed through the restriction  18 . In addition, if the well tool  24  is to be subsequently retrieved from the wellbore  12 , the annular seal  28  and the anchor mechanism  30  must be capable of a corresponding relatively large inward retraction when desired, so that the well tool can pass back through the restriction. 
     Referring additionally now to  FIGS. 2A-F , cross-sectional views of an example of the well tool  24  that may be used in the system  10  and method of  FIG. 1  are representatively illustrated. For convenience and clarity of description, the well tool  24  is described below as it may be used in the  FIG. 1  system  10  and method, however, it should be clearly understood that the well tool may be used in other systems and methods, in keeping with the principles of this disclosure. 
     In  FIGS. 2A-D , successive longitudinal sections of the well tool  24  are depicted. In  FIG. 2E , a lateral cross-section is depicted, taken along line  2 E- 2 E of  FIG. 2C . In  FIG. 2F , a longitudinal cross-section is depicted, taken along line  2 F- 2 F of  FIG. 2E . Accordingly, the longitudinal cross-section depicted in  FIG. 2F  is orthogonal to the longitudinal cross-section depicted in  FIG. 2C . 
     The well tool  24  is in a run-in configuration as illustrated in  FIGS. 2A-F . In this configuration, the well tool  24  can be conveyed to a desired location in the wellbore  12 , and then set using the setting tool  22 , for example. If necessary, the well tool  24  can be displaced through the restriction  18  prior to being set. In addition, the well tool  24  is capable of being retrieved through the restriction  18  after having been set in the wellbore  12 . 
     Note that the setting tool  22  is not depicted in  FIGS. 2A-F . The setting tool  22  may be any type of mechanically, electrically, hydraulically or otherwise actuated setting tool capable of applying a longitudinally directed force to an outer setting sleeve  32  of the well tool  24 , and an oppositely directed force to a connector  34  of the well tool, to thereby produce relative longitudinal displacement between the setting sleeve and the connector. The longitudinal force applied to the setting sleeve  32  is in a downward direction as viewed in  FIGS. 2A-D , and the force applied to the connector  34  is in an upward direction as viewed in  FIGS. 2A-D . Such setting tools are well known to those skilled in the art, and so the setting tool  22  is not described further herein. 
     As viewed in  FIGS. 2A-F , the connector  34  is connected at an upper end of an inner mandrel assembly  36  that extends longitudinally through most of the well tool  24 . A significant portion of the mandrel assembly  36  is tubular, so that a flow passage  38  is provided through the mandrel assembly between upper ports  40  and lower ports  42  formed through a wall of the mandrel assembly. Note, however, that flow through the upper ports  40  is blocked by a valve sleeve  44  in the  FIGS. 2A-F  run-in configuration. The valve sleeve  44  is releasably secured in this flow blocking position relative to the inner mandrel assembly  36  by release members  46  (such as, shear pins, shear screws, a snap ring, etc.). 
     The setting sleeve  32  comprises an uppermost portion of an outer housing assembly  48  of the well tool  24 . A body lock ring  50  is initially inwardly retained in engagement with an outer surface of the inner mandrel assembly  36  by a retainer sleeve  52 , so that the body lock ring permits upward displacement of the inner mandrel assembly  36  relative to the outer housing assembly  48 , but prevents downward displacement of the inner mandrel assembly relative to the outer housing assembly. 
     A similar body lock ring  54  is contained in a collar  56  secured to the outer housing assembly  48 . However, the body lock ring  54  does not engage the inner mandrel assembly  36  in the run-in configuration. 
     An upper section  48   a  of the outer housing assembly  48  is initially releasably secured against upward longitudinal displacement relative to a lower section  48   b  of the outer housing assembly by release members  60  (such as, shear pins, shear screws, a snap ring, etc.). A downwardly directed force can be applied by the setting tool  22  to the outer housing assembly  48  (and transmitted from the upper section  48   a  to the lower section  48   b ) to set the well tool  24 , but the release members  60  ensure that only a predetermined upwardly directed force can be applied to the upper section  48   a , prior to permitting limited upward displacement of the upper section  48   a  relative to the lower section  48   b  during retrieval of the well tool  24 , as described more fully below. A stop ring  62  (such as, a C-ring or snap ring, etc.) permits only limited upward displacement of the upper section  48   a  relative to the lower section  48   b , after the release members  60  are sheared or otherwise released. 
     In the  FIGS. 2A-F  example, the well tool  24  includes two annular seals  28 , an upper annular seal  28   a  and a lower annular seal  28   b . The upper and lower annular seals  28   a,b  are configured the same in this example, although they face in opposite longitudinal directions. In other examples, only a single annular seal may be used, or other numbers of annular seals may be used. 
     As may be seen in  FIG. 2B , the lower section  48   b  of the outer housing assembly  48  is connected to an upper end of the upper annular seal  28   a . An upper anti-extrusion back-up or barrier  64   a  is also connected to the lower section  48   a  and outwardly overlies most of the upper annular seal  28   a . A lower anti-extrusion barrier  64   b  outwardly overlies most of the lower annular seal  28   b . The upper and lower anti-extrusion barriers  64   a,b  are configured the same in this example, although they face in opposite longitudinal directions. 
     The upper and lower annular seals  28   a,b  in this example are in the form of deformable sleeves. The deformable sleeves may be made of a resilient material (such as, an elastomer) capable of sealingly engaging the inner surface of the wellbore  12 . In other examples, the deformable sleeves could be made of a substantially non-resilient material (such as, a plastic, metal or composite material). The scope of this disclosure is not limited to use of any particular material or configuration for the upper or lower annular seals  28   a,b.    
     The upper and lower anti-extrusion barriers  64   a,b  in this example are in the form of deformable sleeves that have a substantially increased rigidity and/or strength as compared to the annular seals  28   a,b . The anti-extrusion barriers  64   a,b  serve to prevent extrusion of the annular seals  28   a,b  when the annular seals sealingly engage the inner surface of the wellbore  12  and a pressure differential is experienced across the annular seals in the annulus  31  (see  FIG. 1 ). 
     Thus, in this example, the anti-extrusion barriers  64   a,b  are outwardly extendable with the respective annular seals  28   a,b , but are significantly more resistant to extrusion than are the annular seals. For example, the anti-extrusion barriers  64   a,b  may be made of a relatively high-strength material (such as, KEVLAR™, a metal or composite material). However, use of the anti-extrusion barriers  64   a,b  is not necessary, since the annular seals  28   a,b  may be sufficiently extrusion resistant in some cases to resist extrusion due to an expected pressure differential in the annulus  31 . 
     In some examples, the anti-extrusion barriers  64   a,b  could be integrated with the annular seals  28   a,b  as “reinforcements” in the seals. One example of this is representatively illustrated in  FIG. 8  for the upper annular seal  28   a.    
     As depicted in  FIG. 2C , a radial expansion mechanism  66  is positioned on the inner mandrel assembly  36  between the upper and lower annular seals  28   a,b . The radial expansion mechanism  66  serves to radially outwardly extend the annular seals  28   a,b  downhole when the well tool  24  is set. For this purpose, the radial expansion mechanism  66  includes an upper set of circumferentially distributed segments  66   a  cooperatively engaged with a lower set of circumferentially distributed segments  66   b.    
     In the  FIGS. 2A-F  run-in configuration, the radial expansion mechanism  66  is radially retracted and the annular seals  28   a,b  are longitudinally spaced apart from the segments  66   a,b  so that the annular seals and the segments can pass through the restriction  18 , in this example. When the well tool  24  is set, the annular seals  28   a,b  are longitudinally displaced relative to the radial expansion mechanism  66 , so that the annular seals then radially overlie and encircle the segments  66   a,b , and the radial expansion mechanism can then radially outwardly extend the annular seals into sealing engagement with the inner surface of the wellbore  12 , as described more fully below. 
     Longitudinal compression of the segments  66   a,b  is initially prevented by an inner sleeve assembly  68  including an upper sleeve  68   a , a middle sleeve  68   b  and a lower sleeve  68   c . The sleeves  68   a - c  abut each other, a release member  70  (such as, a shear ring) initially prevents upward displacement of the middle sleeve  68   b  relative to the upper sleeve  68   a , and release members  72  (such as, shear pins, shear screws, a snap ring, etc.) initially prevent downward displacement of the lower sleeve  68   c  relative to an outer housing  74 . 
     The outer housing  74  is initially releasably secured against longitudinal displacement relative to the inner mandrel assembly  36  by release members  76  (which are more clearly visible in  FIG. 2E ). The lower ports  42  in the inner mandrel assembly  36  are rotationally aligned with ports  78  in the outer housing  74 . This alignment is maintained by bolts or lugs  80  (which are more clearly visible in  FIG. 2F ) extending through the outer housing  74  and into slots  82  formed on the inner mandrel assembly  36 . 
     The anchor mechanism  30  includes a set of multiple slips  84  positioned longitudinally between a lower conical wedge  86  connected at a lower end of the inner mandrel assembly  36 , and an upper wedge  88  connected to the outer housing  74 . In the run-in configuration of  FIGS. 2A-F , the slips  84  are inwardly retracted, so that they can pass through the restriction  18  (see  FIG. 1 ). 
     Extension springs  90  radially inwardly bias the slips  84  toward the inner mandrel assembly  36 . When the well tool  24  is set, as described more fully below, a longitudinal distance between the lower and upper wedges  86 ,  88  will decrease, thereby outwardly extending the slips  84  into gripping engagement with the inner surface of the wellbore  12 . 
     Release members  92  (such as, shear pins, shear screws, a snap ring, etc.) initially prevent upward longitudinal displacement of the outer housing  74  relative to the upper wedge  88 . A body lock ring  94  is initially retained in engagement with an outer surface of the inner mandrel assembly  36  by a lower retainer sleeve extension  96  of the outer housing  74 . The body lock ring  94  prevents upward displacement of the outer housing  74  and upper wedge  88  relative to the inner mandrel assembly  36  when the well tool  24  is set, as described more fully below. 
     Referring additionally now to  FIGS. 3A-D , the well tool  24  is representatively illustrated in a set configuration. The annular seals  28   a,b  have been extended radially outward, so that they can sealingly contact the inner surface of the wellbore  12  (see  FIG. 1 ). The slips  84  have been extended outward, so that they can grippingly engage the inner surface of the wellbore  12 . 
     To achieve this set configuration of the well tool  24  from the run-in configuration depicted in  FIGS. 2A-F , a downwardly directed (as viewed in  FIGS. 3A-D ) force is applied by the setting tool  22  to the setting sleeve  32  while an upwardly directed (as viewed in  FIGS. 3A-D ) force is applied by the setting tool to the connector  34 . When sufficient force has been applied, the inner mandrel assembly  36  displaces upward relative to the outer housing assembly  48 . 
     At this point, the release members  76  prevent relative longitudinal displacement between the inner mandrel assembly  36  and the outer housing  74 , and so the outer housing  74  displaces upward with the inner mandrel assembly relative to the outer housing assembly  48  (which is biased downward by the force exerted by the setting tool  22  on the setting sleeve  32 ). This results in a decrease in the longitudinal separation between the outer housing  74  and the outer housing assembly  48 . 
     The upper annular seal  28   a  and upper anti-extrusion barrier  64   a  are radially outwardly deformed by passing downwardly over an upper expansion cone  98  secured to the upper inner sleeve  68   a . In this manner, the upper annular seal  28   a  and the upper anti-extrusion barrier  64   a  are expanded radially over the radial expansion mechanism  66 , so that they outwardly overlie and encircle an upper portion of the radial expansion mechanism. 
     When a further sufficient force has been applied, the release members  72  shear or otherwise release, thereby permitting the outer housing  74  to displace upwardly relative to the outer housing assembly  48 , and further decreasing the longitudinal separation between the outer housing  74  and the outer housing assembly  48 . The lower annular seal  28   b  and lower anti-extrusion barrier  64   b  are radially outwardly deformed by passing upwardly over a lower expansion cone  100  connected to the lower inner sleeve  68   c . In this manner, the lower annular seal  28   b  and the lower anti-extrusion barrier  64   b  are expanded radially over the radial expansion mechanism  66 , so that they outwardly overlie and encircle a lower portion of the radial expansion mechanism. 
     When a further sufficient force has been applied, the release members  76  shear or otherwise release, thereby permitting the inner mandrel assembly  36  and the lower wedge  86  to displace upward relative to the outer housing  74  and the upper wedge  88 . In this manner, the longitudinal separation between the upper and lower wedges  88 ,  86  decreases, thereby forcing the slips  84  to displace outward. In this manner, the slips  84  are displaced into gripping engagement with the inner surface of the wellbore  12  (see  FIG. 1 ). The body lock ring  94  prevents the inner mandrel assembly  36  from displacing downward relative to the upper wedge  88 , thereby maintaining the gripping engagement between the slips  84  and the inner surface of the wellbore  12 . 
     When a further sufficient force has been applied, the release member  70  shears or otherwise releases, thereby permitting an upper end of the middle inner sleeve  68   b  to telescope into a lower end of the upper inner sleeve  68   a . This also allows the radial expansion mechanism  66  to longitudinally compress and thereby radially outwardly expand the upper and lower annular seals  28   a,b  into sealing engagement with the inner surface of the wellbore  12  (see  FIG. 1 ). The upper and lower anti-extrusion barriers  64   a,b  are also outwardly expanded by the longitudinal compression of the radial expansion mechanism  66 , so that the anti-extrusion barriers can prevent extrusion of the annular seals due to a pressure differential across them in the annulus  31  (see  FIG. 1 ). 
     Note that an externally ridged or toothed surface  114  at an upper end of the upper inner sleeve  68   a  engages a series of internally ridged or toothed flexible collets  116  in the lower section  48   b  of the outer housing assembly  48  in the set configuration. As described more fully below, this engagement between the surface  114  and the collets  116  ensures that the upper inner sleeve  68   a  will displace upward with the lower section  48   b  of the outer housing assembly  48  in initial stages of unsetting the well tool  24 . Initially, the collets  116  are releasably secured against displacement relative to the outer housing assembly  48  by release members  118  (such as, shear screws, shear pins, a shear or snap ring, etc.). 
     Referring additionally now to  FIGS. 4A  &amp; B, an example of the radial expansion mechanism  66  is representatively illustrated in respective radially retracted and radially expanded configurations. Note that, in the radially retracted configuration, the radial expansion mechanism  66  is longitudinally extended, and in the radially expanded configuration, the radial expansion mechanism is longitudinally compressed. 
     The  FIG. 4A  radially retracted configuration of the radial expansion mechanism  66  corresponds to the run-in configuration of the well tool  24  (e.g., as depicted in  FIGS. 2A-F ). The  FIG. 4B  radially expanded configuration of the radial expansion mechanism  66  corresponds to the set configuration of the well tool  24  (e.g., as depicted in  FIGS. 3A-D ). 
     As the segments  66   a,b  are displaced longitudinally toward each other from the  FIG. 4A  configuration to the  FIG. 4B  configuration, the segments are cooperatively engaged, so that they deflect each other in a radially outward direction. Conversely, if the segments  66   a,b  are displaced longitudinally away from each other from the  FIG. 4B  configuration to the  FIG. 4A  configuration, as described more fully below for unsetting of the well tool  24 , the segments are also cooperatively engaged, so that they deflect each other in a radially inward direction. 
     Referring additionally now to  FIG. 5 , an example of a slip assembly  102  of the anchor mechanism  30  is representatively illustrated. The slip assembly  102  in this example includes the slips  84  and the springs  90  described above. In addition, the slip assembly  102  includes spacers  104  for maintaining appropriate circumferential spacing between the slips  84 , and a retainer  106  for retaining the slip assembly  102  in its configuration about the inner mandrel assembly  36  (see  FIG. 3E ). 
     In addition, lower ends of longitudinally extending positioning rods or bars  108  extend into the retainer  106 , and upper ends of the positioning bars extend into a recess in the upper wedge  88  (see  FIG. 3D ). The positioning bars  108  maintain the slips  84  approximately “centered” between the lower and upper wedges  86 ,  88  as the well tool  24  is being conveyed into the wellbore  12  (see  FIG. 2D ), and as the well tool is being retrieved from the wellbore (see  FIG. 7D ). 
     Referring additionally now to  FIGS. 6A-D , the well tool  24  is representatively illustrated in a communicated configuration, prior to retrieval of the well tool. If the well tool  24  is not to be retrieved, the communicated configuration of  FIGS. 6A-D  may not be used. 
     The communicated configuration provides for equalizing pressure across the well tool  24  prior to retrieving the well tool. To achieve this communicated configuration, a downwardly directed force is applied to a retrieval sleeve  110 . In this example, the retrieval sleeve  110  has a tubular fishing neck  112  connected at an upper end thereof for convenient engagement by an appropriate fishing/jarring tool or other type of retrieval tool well known to those skilled in the art. 
     When a sufficient downwardly directed force is applied to the retrieval sleeve  110 , the release members  46  shear or otherwise release, thereby permitting the valve sleeve  44  to displace downward with the retrieval sleeve relative to the inner mandrel assembly  36 . The inner mandrel assembly  36  is still prevented from displacing downwardly by the body lock ring  94 , and the slips  84  remain grippingly engaged with the inner surface of the wellbore  12 , when the downwardly directed force is applied to the retrieval sleeve  110 . 
     In this manner, the upper ports  40  in the inner mandrel assembly  36  are unblocked and fluid flow is permitted between the annulus  31  (see  FIG. 1 ) above the annular seals  28   a,b  and the annulus below the annular seals via the flow passage  38 . This allows any pressure differential across the well tool  24  to be relieved prior to unsetting the well tool and retrieving it from the wellbore  12 . 
     Referring additionally now to  FIGS. 7A-D , the well tool  24  is representatively illustrated in an unset retrieval configuration, in which the well tool may be retrieved from the wellbore  12 . Note that the annular seals  28   a,b  and the anti-extrusion barriers  64   a,b  are radially inwardly retracted out of engagement with the wellbore  12 , and the slips  84  are inwardly retracted out of engagement with the wellbore. The well tool  24  can now be displaced uphole and through the restriction  18  (see  FIG. 1 ), if necessary. 
     To achieve the  FIGS. 7A-D  unset retrieval configuration of the well tool  24 , a sufficient upwardly directed force is applied to the retrieval sleeve  110 . This upwardly directed force may be applied by the same fishing/jarring tool engaged with the fishing neck  112  as was previously used to apply the downwardly directed force to the retrieval sleeve to achieve the communicated configuration of  FIGS. 6A-D . 
     When the sufficient upwardly directed force is applied to the retrieval sleeve  110 , the release members  60  shear or otherwise release, thereby permitting the upper section  48   a  of the outer housing assembly  48  to displace upward relative to the lower section  48   b . This longitudinally separates the retainer  52  from the body lock ring  50 , thereby permitting the outer housing assembly  48  to displace upward relative to the inner mandrel assembly  36 . 
     As the outer housing assembly  48  displaces upward relative to the inner mandrel assembly  36 , the body lock ring  54  eventually engages a radially enlarged collar  112  secured on the inner mandrel assembly. This engagement prevents subsequent downward displacement of the outer housing assembly  48  relative to the inner mandrel assembly  36 . 
     Due to the upward displacement of the outer housing assembly  48  relative to the inner mandrel assembly  36 , the radial expansion mechanism  66  is longitudinally extended to its  FIG. 4A  radially retracted configuration. This allows the annular seals  28   a,b  and the anti-extrusion barriers  64   a,b  to retract radially inward with the segments  66   a,b  of the radial expansion mechanism  66 . 
     Note that, due to the engagement between the externally toothed surface  114  and the collets  116 , the upper inner sleeve  68   a  initially displaces upward with the lower section  48   b  of the outer housing assembly  48 . The upper expansion cone  98  displaces upward with the upper inner sleeve  68   a , thereby also upwardly displacing the upper segments  66   a  and longitudinally extending the radial expansion mechanism  66  to its  FIG. 4A  radially retracted configuration. When a sufficient upward force is applied due to full longitudinal extension of the radial expansion mechanism  66 , the release members  118  shear or otherwise release, thereby permitting the outer housing assembly  48  to displace upward relative to the collets  116 , and permitting further upward displacement of the outer housing assembly  48  relative to the radial expansion mechanism. 
     The upper annular seal  28   a  and the upper anti-extrusion barrier  64   a  displace upward with the outer housing assembly  48 , so that they no longer outwardly overlie the radial expansion mechanism  66 . Similarly, the lower annular seal  28   b  and the lower anti-extrusion barrier  64   b  no longer outwardly overlie the radial expansion mechanism  66  as it is longitudinally extended and displaced upward with the outer housing assembly  48 . 
     After the radial expansion mechanism  66  is radially retracted and the annular seals  28   a,b  and the anti-extrusion barriers  64   a,b  no longer encircle the radial expansion mechanism, a sufficient upwardly directed force applied to the outer housing  74  (via the retrieval sleeve  110 , the outer housing assembly  48  and the radial expansion mechanism  66 ) causes the release members  92  to shear or otherwise release, thereby permitting the outer housing  74  to displace upward relative to the upper wedge  88 . This longitudinally separates the retainer sleeve extension  96  from the body lock ring  94 , and thereby permits the upper wedge  88  to displace upward relative to the inner mandrel assembly  36 . 
     As a result, a longitudinal distance between the upper and lower wedges  88 ,  86  increases, thereby permitting the springs  90  to retract the slips  84  out of engagement with the inner surface of the wellbore  12 . At this point, the well tool  24  is completely unset and it can be retrieved from the wellbore  12 . 
     In the event that any of the annular seals  28   a,b  or anti-extrusion barriers  64   a,b  do not fully retract after having been radially extended, these components can be forced back to their retracted configurations as the well tool  24  is retrieved upwardly through the restriction  18 . This is possible because the annular seals  28   a,b  and the anti-extrusion barriers  64   a,b  are no longer radially outwardly overlying the radial expansion mechanism  66 , but are instead longitudinally spaced apart from the radial expansion mechanism in the unset retrieval configuration of the well tool  24 . 
     In some examples, it may be desirable to not include the lower annular seal  28   b  or the lower anti-extrusion barrier  64   b  in the well tool  24 , if it is determined that they are not needed for the expected pressure differential across the well tool and their upwardly facing configuration would possibly present a problem with retrieving the well tool upward through a tight restriction. Thus, the scope of this disclosure is not limited to use of both of the upper and lower annular seals  28   a,b  or both of the upper and lower anti-extrusion barriers  64   a,b . In one example, the lower annular seal  28   b  could be used without the lower anti-extrusion barrier  64   b , even though the upper anti-extrusion barrier  64   a  is used with the upper annular seal  28   a.    
     In some situations, retrieval of the well tool  24  may be prevented for any of a variety of reasons. For such situations, the well tool  24  includes provisions whereby at least an upper portion of the well tool can be retrieved, separate from a lower portion of the well tool. 
     Specifically, upper and lower portions of the outer housing assembly lower section  48   a  are releasably connected by means of release members  120  (such as, shear pins or screws, a shear ring, etc.). In addition, a weakened area  58  (such as, a recess or reduced wall thickness area) is provided in the inner mandrel assembly  36 . If sufficient tensile forces are applied to the outer housing assembly  48  and the inner mandrel assembly  36  (such as, via a fishing tool), the release members  120  will shear or otherwise release, and the weakened area  58  will part, thereby allowing retrieval of an upper portion of the well tool  24  from the well. 
     It may now be fully appreciated that the above disclosure provides significant advancements to the arts of designing, constructing and utilizing well tools (such as, plugs and packers) for subterranean wells. In examples described above, the well tool  24  can achieve relatively high radial expansion of the annular seals  28   a,b  when set, while still permitting the well tool to be conveyed through a relatively small restriction  18  in the wellbore  12 . The well tool  24  can subsequently be unset and retrieved through the restriction  18 , if necessary. 
     A well tool  24  for use in a subterranean well is provided to the art by the above disclosure. In one example, the well tool  24  can comprise an annular seal  28   a,b  and a radial expansion mechanism  66  having radially retracted and radially expanded configurations. The annular seal  28   a,b  is longitudinally displaceable relative to the radial expansion mechanism  66  in the radially retracted configuration of the radial expansion mechanism  66 . 
     In any of the examples described herein, the radial expansion mechanism  66  may be displaceable to the radially expanded configuration only after the annular seal  28   a,b  radially outwardly encircles the radial expansion mechanism  66 . 
     In any of the examples described herein, the annular seal  28   a,b  may be longitudinally displaceable from a first position in which the annular seal  28   a,b  is longitudinally spaced apart from the radial expansion mechanism  66  to a second position in which the annular seal  28   a,b  overlies the radial expansion mechanism  66 . 
     In any of the examples described herein, the annular seal  28   a,b  may displace from the first position to the second position in response to relative displacement between an inner mandrel assembly  36  and a setting sleeve  32  of the well tool  24 . 
     In any of the examples described herein, the well tool  24  may include an anti-extrusion barrier  64   a,b  which is longitudinally displaceable with the annular seal  28   a,b.    
     In any of the examples described herein, the anti-extrusion barrier  64   a,b  may expand radially outward in response to displacement of the annular seal  28   a,b  and the anti-extrusion barrier  64   a,b  relative to the radial expansion mechanism  66 . 
     In any of the examples described herein, the radial expansion mechanism  66  may comprise multiple circumferentially distributed segments  66   a,b , and the radial expansion mechanism  66  may translate between the radially retracted and radially expanded configurations in response to relative longitudinal displacement between first and second sets of the segments  66   a,b.    
     A method of setting a well tool  24  in a subterranean well is also provided to the art by the above disclosure. In one example, the method can comprise: positioning the well tool  24  in the subterranean well, the well tool  24  comprising an annular seal  28   a,b  and a radial expansion mechanism  66 , and then longitudinally displacing the annular seal  28   a,b  to a radially outward position relative to the radial expansion mechanism  66 . 
     In any of the examples described herein, the method may include, after the longitudinally displacing step, radially expanding the radial expansion mechanism  66 , thereby radially outwardly displacing the annular seal  28   a,b  into sealing contact with a wellbore  12 . 
     In any of the examples described herein, the radially outwardly displacing step may include longitudinally displacing a first set of segments  66   a  of the radial expansion mechanism  66  relative to a second set of segments  66   b  of the radial expansion mechanism  66 . 
     In any of the examples described herein, the method may include grippingly engaging an anchor mechanism  30  of the well tool  24  with the wellbore  12  prior to the radially expanding step. 
     In any of the examples described herein, the method may include radially outwardly displacing an anti-extrusion barrier  64   a,b  prior to the radially expanding step and after the longitudinally displacing step. 
     In any of the examples described herein, the method may include longitudinally displacing an anti-extrusion barrier  64   a,b  with the annular seal  28   a,b  relative to the radial expansion mechanism  66 . 
     In any of the examples described herein, the longitudinally displacing step may include longitudinally displacing the annular seal  28   a,b  from a first position in which the annular seal  28   a,b  is longitudinally spaced apart from the radial expansion mechanism  66  to a second position in which the annular seal  28   a,b  at least partially overlies the radial expansion mechanism  66 . 
     Also described above is a well system  10  for use with a subterranean well. In one example, the well system  10  can comprise a well tool  24  positioned in a wellbore  12  of the subterranean well, the well tool  24  comprising an annular seal  28   a,b , a radial expansion mechanism  66 , an inner mandrel assembly  36  and a setting sleeve  32 . A setting tool  22  produces a relative longitudinal displacement between the setting sleeve  32  and the inner mandrel assembly  36 . The annular seal  28   a,b  radially outwardly overlies the radial expansion mechanism  66  in response to the relative longitudinal displacement. 
     In any of the examples described herein, the radial expansion mechanism  66  may have radially retracted and radially expanded configurations, and the annular seal  28   a,b  may be longitudinally displaceable relative to the radial expansion mechanism  66  in the radially retracted configuration. 
     In any of the examples described herein, the radial expansion mechanism  66  may be displaceable to the radially expanded configuration only after the annular seal  28   a,b  radially outwardly overlies the radial expansion mechanism  66 . 
     In any of the examples described herein, the annular seal  28   a,b  may be longitudinally displaceable by the setting tool  22  from a first position in which the annular seal  28   a,b  is longitudinally spaced apart from the radial expansion mechanism  66  to a second position in which the annular seal  28   a,b  radially overlies the radial expansion mechanism  66 . 
     In any of the examples described herein, the well tool  24  may include an anti-extrusion barrier  64   a,b  which is longitudinally displaceable with the annular seal  28   a,b.    
     In any of the examples described herein, the anti-extrusion barrier  64   a,b  may expand radially outward in response to displacement of the annular seal  28   a,b  and the anti-extrusion barrier  64   a,b  relative to the radial expansion mechanism  66 . 
     Although various examples have been described above, with each example having certain features, it should be understood that it is not necessary for a particular feature of one example to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example&#39;s features are not mutually exclusive to another example&#39;s features. Instead, the scope of this disclosure encompasses any combination of any of the features. 
     Although each example described above includes a certain combination of features, it should be understood that it is not necessary for all features of an example to be used. Instead, any of the features described above can be used, without any other particular feature or features also being used. 
     It should be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of this disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments. 
     In the above description of the representative examples, directional terms (such as “above,” “below,” “upper,” “lower,” “upward,” “downward,” etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein. 
     The terms “including,” “includes,” “comprising,” “comprises,” and similar terms are used in a non-limiting sense in this specification. For example, if a system, method, apparatus, device, etc., is described as “including” a certain feature or element, the system, method, apparatus, device, etc., can include that feature or element, and can also include other features or elements. Similarly, the term “comprises” is considered to mean “comprises, but is not limited to.” 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of this disclosure. For example, structures disclosed as being separately formed can, in other examples, be integrally formed and vice versa. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the invention being limited solely by the appended claims and their equivalents.