Patent Publication Number: US-9845651-B2

Title: Retrievable downhole tool system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/954,238, which was filed on Mar. 17, 2014, and is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     In the oilfield industry, various downhole tools (e.g., packers, bridge plugs, frac plugs) may be used to isolate sections of a wellbore. Such downhole tools may include a sealing element, which is generally made of rubber, and slips configured to bite into a surrounding tubular and maintain a position of the tubular in the wellbore. The sealing element and slips may initially be in a contracted configuration, allowing the downhole tool to be run into the wellbore without engaging the wellbore or any other surrounding tubular. 
     Upon reaching a desired location, such as an interface between two formation zones, the tool may be set. As part of the setting process, the slips and the sealing element may be expanded so as to engage the surrounding tubular (e.g., casing, liner, wellbore wall), which may provide the desired zonal isolation. 
     Such downhole tools may be retrievable or non-retrievable. In the latter case, the tools are generally removed by drilling them out. With retrievable tools, on the other hand, a retrieval tool may be provided that attaches to the wireline (or another suitable line), which may engage with the downhole tool. Using the retrieval tool, the sealing element and the slips may be disengaged from the surrounding tubular and pulled out of the wellbore. 
     In use, a large pressure differential may develop across the downhole tool. At some point, this pressure differential may cause the downhole tool to fail. Such failure may be caused by the slips applying an insufficient holding force, the sealing elements failing to provide a seal, or by shearable elements of the downhole tool&#39;s setting assembly failing under this pressure. 
     SUMMARY 
     Embodiments of the disclosure may provide a downhole tool including a release mandrel, a plurality of slips disposed at least partially around the release mandrel, an upper cone disposed at least partially around the release mandrel and on a first axial side of the plurality of slips, and a lower cone disposed at least partially around the release mandrel and on a second axial side of the plurality of slips. The downhole tool may also include a collet positioned axially and radially between the release mandrel and the lower cone. The collet is configured to prevent downward movement of the lower cone relative to the release mandrel at least when the downhole tool is in a run-in configuration and when the downhole tool is in a set configuration. 
     Embodiments of the disclosure may also provide a retrievable bridge plug system. The system includes a bride plug including a release mandrel including an upper connection, an outer mandrel coupled to the release mandrel by one or more shear devices, a plurality of slips disposed at least partially around the release mandrel, an upper cone disposed at least partially around the release mandrel and on a first axial side of the plurality of slips, a lower cone disposed at least partially around the release mandrel and on a second axial side of the plurality of slips, and a collet coupled with the outer mandrel and positioned axially and radially between the release mandrel and the lower cone. The collet is configured to prevent downward movement of the lower cone relative to the release mandrel at least when the bridge plug is in a set configuration. The system may also include a retrieval tool having an upper end and a lower end, with the retrieval tool being configured to receive the upper connection of the release mandrel though the lower end, and to shear the one or more shear devices, so as to move the bridge plug from a set configuration to a retrieval configuration. 
     Embodiments of the present disclosure may also provide a method for running and retrieving a downhole tool into a surrounding tubular. The method includes coupling an adapter to the downhole tool. The downhole tool includes a release mandrel including an upper connection coupled with the adapter, a plurality of slips disposed at least partially around the release mandrel, an upper cone disposed at least partially around the release mandrel and on a first axial side of the plurality of slips, a lower cone disposed at least partially around the release mandrel and on a second axial side of the plurality of slips, and a collet positioned axially and radially between the release mandrel and the lower cone. The collet is configured to prevent downward movement of the lower cone relative to the release mandrel, when the downhole tool is in a run-in configuration. The method further includes running the downhole tool into the surrounding tubular using the adapter, setting the downhole tool into a set configuration in the surrounding tubular using the adapter, and releasing the downhole tool from the adapter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may best be understood by referring to the following description and accompanying drawings that are used to illustrate one or more embodiments. In the drawings: 
         FIG. 1A  illustrates a side, quarter-sectional view of a downhole tool, according to an embodiment. 
         FIG. 1B  illustrates an enlarged, side, quarter-sectional view of a portion of the downhole tool of  FIG. 1A , according to an embodiment. 
         FIG. 2  illustrates a side, quarter-sectional view of a setting tool for use with the downhole tool, according to an embodiment. 
         FIG. 3  illustrate a side, quarter-sectional view of a retrieval tool for use with the downhole tool, according to an embodiment. 
         FIGS. 4A and 4B  illustrate side, quarter-sectional views of a downhole tool system including the downhole tool and the setting tool, with the downhole tool in a run-in configuration and a set configuration, respectively, according to an embodiment. 
         FIG. 5  illustrates a side, quarter-sectional view of the downhole tool system including the downhole tool and the retrieval tool, with the downhole tool in in a retrieval configuration, according to an embodiment. 
         FIG. 6  illustrates a flowchart of a method for running and retrieving a downhole tool, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure may provide a downhole tool, e.g., a bridge plug, that may be capable of withstanding high pressure, e.g., 10 kpsi or greater, in a wellbore. The tool may include slips that engage a surrounding tubular, as well as a setting assembly that includes upper and lower cones. The tool may also include sealing elements to seal with the surrounding tubular. Further, the tool may include a collet that is wedged between a central release mandrel of the tool and the lower cone, which prevents the lower cone from moving away from the slips, such that, as the upper cone is driven downwards during setting, the lower cone maintains its position. With such configuration, pressure on the cones may tend to further expand the slips into engagement with the surrounding tubular, as will be described in greater detail below. 
     The present disclosure may also provide embodiments of an adapter for a setting tool that may be employed with the downhole tool, as well as a retrieval tool that may be employed therewith. In particular, the tool may include a rupture disk, e.g., proximal to an upper end thereof, which may prevent fluid communication through a bore defined through the tool. In combination with the sealing elements, this may result in a fluid-tight seal provided by the tool. The retrieval tool may include a probe that fractures this rupture disk, thereby providing fluid communication through the bore of the tool, and relieving the pressure that, as mentioned above, may drive the slips further into engagement with the wellbore. 
     These are but a few aspects of the presently disclosed device and methods. Additional aspects will become apparent from the description of embodiments below, with reference to the figures. 
     Before turning to the specific embodiments, however, it will be noted that the following disclosure describes several embodiments for implementing different features, structures, or functions of the invention. Embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference characters (e.g., numerals) and/or letters in the various embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed in the Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the embodiments presented below may be combined in any combination of ways, e.g., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. 
     Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. In addition, unless otherwise provided herein, “or” statements are intended to be non-exclusive; for example, the statement “A or B” should be considered to mean “A, B, or both A and B.” 
     In some contexts, “downhole” (e.g., “downhole tool”) may refer to a component that is configured to be disposed in the wellbore. Directional terms such as “up,” “upper,” “down,” “lower,” “above,” “below,” “upward,” “downward,” etc. may be used for the sake of convenience to refer to the illustrated embodiments; however, these terms are intended to refer to the positioning of the elements relative to one another, and not to limit the embodiments to any particular frame of reference or perspective. Accordingly, for example, “upper” and “lower” may mean “closer to the surface” and “farther into a wellbore,” respectively, when used in the context of an apparatus disposed in a wellbore, acknowledging that wellbores may be non-vertical, e.g., deviated or horizontal. 
       FIG. 1A  illustrates a side, quarter-sectional view of a downhole tool  100 , e.g., in a run-in configuration, according to an embodiment. The downhole tool  100  may be, for example, a bridge plug, which may prevent fluid communication from the top end to the bottom end, at least prior to retrieval, as will be described below. In other embodiments, the tool  100  may be a frac plug, another type of plug, a packer, or another tool configured to be disposed in a wellbore. 
     The tool  100  may include a release mandrel  102  which may be a single piece that extends from one end of the tool  100  to the other, but in other embodiments, may include an intermediate inner mandrel  104  and a lower mandrel  106 , as shown. It will be appreciated that the term “mandrel” may include a single, unitary piece or two or more pieces coupled together. The release mandrel  102  may provide an upper connection  108 , which may be configured to engage with an adapter and/or retrieval tool, as will be described below. In an embodiment, the upper connection  108  may include external threads  110  which may provide for such engagement, but in other embodiments, internal threads, or other engaging members may be provided. 
     The tool  100  may also include an outer mandrel, which may be provided as a single piece, or may, as shown, include an upper, outer mandrel  112  and a lower, outer mandrel  114 . The upper, outer mandrel  112  may be disposed at least partially around the release mandrel  102 , and may be connected thereto by one or more shear devices, such as a shear screw  116 . In other embodiments, other types of shear devices may be used, such as adhesives, welds, shear pins, shear rings, etc. The upper, outer mandrel  112  may include a recess  111 , positioned proximal to the upper connection  108 , which may provide for engagement with a collet of a setting tool, as will be described in greater detail below. The lower, outer mandrel  114  may be disposed at least partially around the intermediate mandrel  104 , and may be coupled on an upper axial end with a lower axial end of the upper, outer mandrel  114 . Further, the lower, outer mandrel  114  may define a shoulder  118 , proximal to an axial upper end thereof. 
     A lock-ring housing  120  may be disposed at least partially around the upper, outer mandrel  114 , e.g., engaging threads formed in the upper, outer mandrel  114 . The lock-ring housing  120  may be movable downward, but, through the engagement with threads on the upper, outer mandrel  114 , may be prevented from moving upwards, e.g., providing a ratcheting mechanism. Moreover, a shear screw (or another shearable structure)  122  may be received through the lock-ring housing  120  and prevent the lock ring disposed with the lock-ring housing  120  from rotating with respect thereto. 
     A gage ring  124  may be positioned below the lock-ring housing  120 . Further, the tool  100  may include one or more sealing elements, e.g., a first sealing element  126 , a second sealing element  128 , and a third sealing element  130 . The first, second, and third sealing elements  126 ,  128 ,  130  may be separated from one another by spacers  132 ,  134 , as shown. Further, the gage ring  124  may be positioned between the first sealing element  126  and the lock-ring housing  122 , e.g., to control the deformation of the first sealing element  126  during the setting process. The sealing elements  126 ,  128 ,  130  may be formed from rubber of any suitable hardness or may be formed from other materials. 
     The tool  100  may also include an upper cone  135  and a follower spring  136 . The upper cone  135  and the follower spring  136  may be disposed at least partially around one or both of the upper, outer mandrel  112  and the lower, outer mandrel  114 . The follower spring  136  may bear against a retainer  138  and may engage the third sealing element  130 , similarly to the gage ring  124  engaging the first sealing element  126 . The first, second, and third sealing elements  126 ,  128 ,  130  may be axially compressed, and thereby radially expanded, between the gage ring  124  and the retainer  138  during the setting process, as will be described below. 
     The tool  100  may also include slips  140 , which may be disposed at least partially around, e.g., at circumferential intervals, the intermediate mandrel  104  and the lower, outer mandrel  114 . The slips  140  may be biased radially inwards by a slip spring  142 , which may be received in a groove  144  formed in the slips  140 . The groove  144  may, in a specific example, be formed proximal an axial middle of the slips  140 , as shown, but in other embodiments, may be formed elsewhere, e.g., proximal the axial ends thereof. 
     A slip cage  146  may be disposed around the slips  140 , and may provide openings  148 . The slips  140  may extend radially outwards through the openings  148 , e.g., when the slips  140  are expanded outwards during setting, as will be described below. Further, the slip cage  146  may be coupled with a slip cage cap  147  on a lower end thereof and may be coupled with the upper cone  135  via a shear screw  149  (or another shearable structure). 
     Furthermore, the tool  100  may include a lower cone  150 . The upper cone  135  and the lower cone  150  may be disposed on opposite axial sides of the slips  140 . The slip cage cap  147  may be connected with the lower cone  150  via a shear screw  151  (or another shearable structure). Further, the upper cone  135  and the lower cone  150  may be generally wedge-shaped or tapered in cross-section (e.g., conical or frustoconical), and may be configured to bear on reverse-tapered surfaces  152 ,  154  on either axial side of the slips  140 . Accordingly, when the upper cone  135  and the lower cone  150  are driven axially toward one another, the upper cone  135  and lower cone  150  may drive the slips  140  radially outwards. It will be appreciated that either or both of the upper and lower cones  135 ,  150 , may individually be provided as a single, elongated piece with a tapered end to engage the plurality of slips  140 , or may be provided as two or more pieces to provide this functionality 
     The tool  100  may further include a lower collet  156 , which may be attached to the lower, outer mandrel  114 , e.g., via threads. The lower collet  156  may include a plurality of circumferentially separated fingers  158 , which may terminate with protrusions  160  on the lower ends thereof. The protrusions  160  may extend axially downwards from a lower end  162  of the lower cone  150 . The lower end  162  of the lower cone  150  may define a radially-inward protrusion  164 , which may engage with the protrusion  160  of the lower collet  156 . 
     The lower mandrel  106  may be tapered, extending to a larger diameter as proceeding upwards. Further, the lower mandrel  106  may be sized to retain the lower collet  156  in engagement with the lower cone  150 , e.g., by preventing the fingers  158  from deflecting inwards such that the protrusions  160  may disengage from the protrusion  164  of the lower end  162  of the lower cone  150 . Thus, the lower collet  156  may be held both radially and axially between the lower mandrel  106  (e.g., part of the release mandrel  102 ) and the lower cone  150 , thereby preventing downward movement of the lower cone  135  by transmitting forces to the lower mandrel  106 . Also, optionally toward the bottom of the tool  100 , the lower mandrel  106  may also include a lower connection  163  which may be, in a specific example, externally threaded as shown. 
     The tool  100  may also include a rupture disk  166 , e.g., toward the top of the tool  100 . Moreover, the release mandrel  102  and the lower mandrel  106  may be hollow, defining a generally continuous bore  168  therethrough. The rupture disk  166  may obstruct the bore  168 , thereby preventing the communication therethrough, and permitting the tool  100  to maintain a pressure differential from above the tool  100  to below the tool  100 , e.g., to permit zonal isolation. The rupture disk  166  may be held in place with respect to the release mandrel  102  by a keeper  170 , which may be threaded or otherwise attached to the release mandrel  102 . The rupture disk  166  may be connected to the keeper  170  or may be pressed against a shoulder of the release mandrel  102  by the keeper  170 . In other embodiments, any suitable assembly for maintaining the rupture disk  166  in position may be employed. 
       FIG. 1B  illustrates an enlarged view of a portion of the downhole tool  100  of  FIG. 1A , according to an embodiment. As shown, the downhole tool  100  may include a pressure port  172 , which may be positioned such that it is above the sealing elements  126 ,  128 ,  130  when the downhole tool  100  is in a set configuration (the pre-set, run-in configuration is shown in  FIG. 1B ). In the illustrated, run-in configuration, the pressure port  172  may be generally aligned with the gage ring  124 , or positioned elsewhere, e.g., near the top of the first sealing element  126 , so as to result in the pressure port  172  being located above the first sealing element  126  when the tool  100  is set. A pressure channel  174  may be defined radially between the release mandrel  102  and the upper, outer mandrel  112 , and may extend axially, inward of the follower spring  136 , until turning radially outwards at the shoulder  118  of the lower, outer mandrel  114  and meeting the upper cone  135 . The pressure channel  174  may terminate at fluid-tight seals provided by O-rings (or any other suitable sealing members), such as an O-ring  176  between the upper cone  135  and the upper, outer mandrel  112 , an O-ring  178  between the upper cone  135  and the lower, outer mandrel  114 , and an O-ring  180  between the release mandrel  102  and the lower, outer mandrel  114 . Accordingly, the pathway established from above the first sealing element  126  to the upper cone  135  may communicate the pressure above the tool  100 , past the sealing elements  126 ,  128 ,  130 , and to the upper cone  135 . When the pressure above the tool  100  is the higher pressure, this pressure may drive the upper cone  135  into engagement with the slips  140 . 
     A second pathway for pressure communication with the upper cone  135  may be also be established, e.g., from the pressure below tool  100  to an axial top side of the upper cone  135 . The second pathway may be established between the non-sealing connection between the retainer  138  and the upper end of the upper cone  135 . Fluid may migrate past this non-sealing connection, and into a radial space  182  between the upper cone  135  and the upper, outer mandrel  112 . The radial space  182  may be sealed by the O-ring  176 , for example. Accordingly, when the bottom side of the tool  100  is the high-pressure side, the pressure on both the top and the bottom of the upper cone  135  may be equalized, i.e., the pressure above may tend to drive the upper cone  135  into the slips  140  with equal force as the pressure below drives the upper cone  135  away from the slips  140 , such that additional strain on shearable members or the like is avoided. 
       FIG. 2  illustrates a side, quarter-sectional view of an adapter  200  for use with the downhole tool  100 , according to an embodiment. The adapter  200  may be a wireline or electric line adapter, or any other suitable adapter. The adapter  200  may include a release collet  202 , which may include deflectable fingers  204  and protrusions  206 . The protrusions  206  may be configured to seat into the recess  111  ( FIG. 1 ) of the upper connection  108  of the release mandrel  102 . 
     The adapter  200  also includes a setting sleeve  208 , which is disposed around the release collet  202  and is configured to bear against the lock-ring housing  120  when the adapter  200  engages the downhole tool  100 . The adapter  200  further includes an outer adapter  210 . Set screws  211 A may be used to attach the outer adapter  210  to the setting sleeve  208 , and set screws  211 B may be provided to attach the outer adapter  210  to a setting tool. 
     The adapter  200  may further include a mandrel  212 , an adjuster sub  214 , a sleeve  216 , and a torque nut  218 , A pin  219  may be positioned within the torque nut  218 , The release collet  202  may be coupled with the mandrel  212  and the sleeve  216 , and a shear ring  220  may be disposed between the sleeve  216  and the release collet  202 , A cap  228  may be positioned over the mandrel  212 . The adjuster sub  214  may be coupled, e.g., threaded, to the mandrel  212 , and may extend upward to form a connector  222 . Set screws  224  may be received through the connector  222 , such that the connector  222  connects with and may be held by a setting tool. 
     In operation, the setting sleeve  208  and the outer adapter  210  may engage a setting tool, which may push down on the setting sleeve  208  and the outer adapter  210 . The setting sleeve  208  and the release collet  202  may be axially movable relative to one another. As such, the adapter  200  may transmit an axial downward force via the setting sleeve  208  onto the lock-ring housing  120 , and an axial upward force via the release collet  202  onto the release mandrel  102 . 
       FIG. 3  illustrates a side, quarter-sectional view of a retrieval tool  300 , which may be used in combination with the downhole tool  100  ( FIG. 1A ), according to an embodiment. The retrieval tool  300  may include an upper sub  302 , a lower sub (or “shoe”)  304 , and an intermediate sub  306  connecting together the upper and lower subs  302 ,  304 . The upper and lower subs  302 ,  304  and the intermediate sub  306  may collectively define an inner bore  305  through the retrieval tool  300 . 
     In an embodiment, a rubber stop  307  may be disposed between the upper sub  302  and the intermediate sub  306 . For example, at a lower end  308 , the upper sub  302  may define a smaller inner diameter than a shoulder  310  of the intermediate sub  306 . The rubber stop  307  may be disposed between the shoulder  310  and the lower end  308 . At least a portion of the rubber stop  307  may overhang the shoulder  310 . For example, the rubber stop  307  may define a tapered inner surface  312  that may face downward and overhang the shoulder  310 . 
     A probe  314  may be connected with a radial inside of the upper sub  302 . The probe  314  may include a body  315  that defines a connection  316  extending upwards from the upper sub  302 . The connection  316  may be configured to engage a wireline, e-line, or another type of tool, etc. Further, the connection  316  may be configured to engage with the lower connection  163  of the lower mandrel  106  of the downhole tool  100  ( FIG. 1A ). In an embodiment, the connection  316  may be internally threaded, as shown, but in others, may be externally threaded, or be connected with the wireline, e-line, or lower connection  163  via another type of connection. The body  315  may be connected to the upper sub  302 , e.g., via meshing threads provided on the bore of the upper sub  302  and the outer surface of the body  315 . 
     The probe  314  may also include a probe tip  318 , which may extend downwards from the body  315  and past the rubber stop  307 . In an embodiment, the probe tip  318  may be coupled with the body  315  via a set screw  320 . The probe tip  318  may be angled, in some embodiments, to establish a point of contact. Further, the probe tip  318  may be configured to break the rupture disk  166  of the tool  100  ( FIG. 1A ). 
     The retrieval tool  300  may also include a lock ring  322 , which may be coupled with and disposed radially inside of the intermediate sub  306 . For example, the lock ring  322  may be disposed below the shoulder  310 . The lock ring  322  may define threads  324 , which may be configured to engage the threads  110  of the downhole tool  100  ( FIG. 1A ). Accordingly, the lock ring  322  may act as a ratchet by interaction with the threads  110 , allowing the retrieval tool  300  to be set down on the downhole tool  100 , but preventing the retrieval tool  300  from then being pulled away from the downhole tool  100 . In an embodiment, the lock ring  322  may be coupled with the intermediate sub  306  by adjuster screws  326 ,  328 . 
     The lower sub  304  may extend downward from the intermediate sub  306  and form a lower end  330  of the retrieval tool  300 . At the lower end  330 , the lower sub  304  may provide cut-aways  332 , which may assist in the retrieval tool  300  moving through sand, debris, etc. of the downhole environment. 
       FIG. 4A  illustrates a side, quarter-sectional view of a downhole tool system in which the downhole tool  100  is coupled with the adapter  200 , e.g., with the downhole tool still in a run-in configuration, according to an embodiment. As shown, the release collet  202  of the adapter  200  may engage the recess  111  formed in the upper, outer mandrel  112 , proximal to the upper connection  108  (in some embodiments, the recess  111  may be considered part of the upper connection  108 , despite being formed in the upper, outer mandrel  112 ). Further, the setting sleeve  205  may engage the lock-ring housing  120 . In this configuration, a wireline  400 , for example, may be used to deploy the tool  100  into the wellbore. As shown, in the run-in configuration, the sealing elements  126 ,  128 ,  130  are in a radially-contracted configuration, and axially-relaxed configuration. Similarly, the slips  140  are held at a radially-contracted position by the slips spring  142 . As such, in the run-in configuration, the sealing elements  126 ,  128 ,  130  and the slips  140  may generally not engage with a surrounding tubular  402  (e.g., casing), or at least may not prevent run-in of the tool  100 . 
     Upon reaching a desired depth in the wellbore, the adapter  200  may be employed to set the tool  100 , e.g., move the tool  100  from the run-in configuration to the set-configuration. To set the tool  100 , a hydraulic or explosive setting tool above the adapter  200  may be employed. The setting sleeve  208  of the adapter  200  may thus be forced downward relative to the tool  100 , while the release collet  202  holds the upper, outer mandrel  112  (and thus the release mandrel  102 ) in place. 
       FIG. 4B  illustrates a side, quarter-sectional view of the downhole tool system with the downhole tool  100  de-coupled from the adapter  200 , e.g., with the downhole tool  100  in a set configuration, according to an embodiment. Once the downhole tool  100  is moved into the set configuration, the release collet  202  may release from and be pulled away from the upper connection  108  of the tool  100 , as shown in  FIG. 4B . Comparing  FIGS. 4A and 4B , illustrates that the release mandrel  102  of the tool  100  may generally remain stationary relative to the surrounding tubular  402  (and/or the adapter  200 ) during setting. Further, the lower mandrel  106  and the upper and lower, outer mandrels  112 ,  114  may similarly remain stationary. 
     In contrast, the setting sleeve  208  bearing on the lock-ring housing  120  causes shear screws  122 ,  149 , and  151  to shear (but not necessarily in that order). The continued force by the setting sleeve  205  pushes the lock-ring housing  120  downwards, relative to the release mandrel  102 , thereby axially squeezing and radially expanding the sealing elements  126 ,  128 ,  130 . Further, the follower spring  136  is compressed against the retainer  138 , applying a force against the upper cone  135 . Since the lower mandrel  104  and the lower, outer mandrel  114  are stationary, the lower collet  156  remains entrained between the lower cone  150  and the lower, outer mandrel  114 . Thus, the lower cone  150  is prevented from moving downward by interaction with the lower collet  156 . Accordingly, as the upper cone  135  is driven downward, the lower cone  150  may remain stationary, and thus the distance between the upper and lower cones  135 ,  150  may be reduced, causing the upper and lower cones  135 ,  150  to push the slips  140  radially outwards, through the openings  148  and into engagement with the surrounding tubular  402 . 
     The bore  168  of the tool  100  may be blocked by the rupture disk  166 . Further, the annulus between the tool  100  and the surrounding tubular  402  may be sealed by the sealing elements  126 ,  128 ,  130 . Accordingly, the tool  100  may support the production of a pressure differential above and below the first and third sealing elements  126 ,  128 . As mentioned above, however, regardless of whether the higher-pressure side is above or below the sealing elements  126 ,  128 , the high pressure may be communicated with the upper cone  135 . Moreover, since the lower cone  150  rests on the lower collet  156 , which is directly connected with the lower mandrel  114 , the lower cone  150  may not require any shearable members or set screws to maintain the set configuration. Further, any pressure below the tool  100  may tend to push the lower cone  150  upwards, further into engagement with the slips  140 , thus increasing the holding force of the tool  100 . 
       FIG. 5  illustrates a side, quarter-sectional view of the retrieval tool  300  engaging the release mandrel  102  of the downhole tool  100 , with the downhole tool  100  moved into a retrieval configuration, according to an embodiment. The retrieval tool  300  may be lowered onto the release mandrel  102  via a wireline or e-line attached to the connection  316  of the retrieval tool  300 , such that the upper connection  108  is received through the lower end of the retrieval tool  300 . In other embodiments, another downhole tool, similar or identical to the illustrated downhole tool  100  may be positioned above (i.e., superposed) with respect to the illustrated downhole tool  100 , and the lower connection (corresponding to the lower connection  163  of the illustrated downhole tool  100 ) of the superposed tool may be connected with the connection  316  of the retrieval tool  300 . Similarly, a second retrieval tool may be coupled with the lower connection  163 , for engagement with another, subjacent retrievable tool. 
     Accordingly, for example, several downhole tools  100  may be employed in a single wellbore and retrieved as a single unit. For example, a retrieval tool  300  may be coupled with the lower connection  163  of each of the downhole tools  100 . When it is desired to retrieve the downhole tools  100 , a retrieval tool  300  may be coupled with the upper connection  108  of the top-most downhole tool  100 , so as to release that downhole tool  100 . The downhole tool  100 , with the retrieval tools  300  coupled to both the upper and lower connections  108 ,  163  thereof may then be moved lower in the wellbore, until the retrieval tool  300  connected with the lower connection  163  then engages the upper connection  108  of the next-lower downhole tool  100 . The next-lower downhole tool  100  may then release, with the forces discussed above being applied through the top-most downhole tool  100  and the retrieval tool  300  disposed between the two downhole tools  100 . This second downhole tool  100  may thus be released from the wellbore, and may drop down such that the retrieval tool  300  connected to its lower connection  163  engages another downhole tool  100 . This process may repeat as many times as desired. 
     The retrieval tool  300  may receive the external threads  110  (see  FIG. 1A ) of the upper connection  108  into the lock ring  322 . The lock ring  322  may provide a ratcheting function, as described above, and may thus prevent the retrieval tool  300 , once engaging the external threads  110 , from separating from the release mandrel  102 . As the retrieval tool  300  is set down onto the upper connection  108 , the connection  108  may seal with the rubber stop  307 , so as to prevent fluid communication out of the bore  305  (see  FIG. 3 ) of the retrieval tool  300 . 
     As the retrieval tool  300  is set down on the release mandrel  102 , the probe tip  318  may engage and break through the rupture disk  166  (see  FIG. 1A ). Since the retrieval tool  300  may have the through-going bore  305 , and the downhole tool  100  may also have the through-going bore  168 , rupturing the rupture disk  166  may restore fluidic communication between previously-isolated locations above and below the first and third sealing elements  126 ,  130 . 
     The inner components of the retrieval tool  300 , described above with reference to  FIG. 3 , may then cooperate to transmit an upward pulling force to the release mandrel  102  via upper connection  108 . Eventually, this force may shear the shear screw  116  between the release mandrel  102  and the upper, outer mandrel  114  (see  FIG. 1A ). The release mandrel  102  and, thus, the lower mandrel  106  may then be pulled upwards with respect to the surrounding tubular  402  and the other components of the downhole tool  100 . With the tapered, lower mandrel  106  moved upward, the lower collet  156  may be released from engagement with the lower cone  150 . The release of the lower collet  156  may free the lower cone  150  to move downward, away from the slips  140 . Further, this may free the upper cone  135 , engaging the shoulder  118  of the lower, outer mandrel  114 , which is attached to the collet  156 , to move upwards, away from the slips  140 . During this transition, pressure may equalize on both sides of the tool  100 , removing the above-described holding effects relying on pressure differential in the wellbore. 
     At this point, the tool  100  is in a relaxed state, and the previously axially compressed sealing elements  126 ,  128 ,  130 , e.g. as pushed by the follower spring  136 , may move axially upward, and may expand axially and contract radially away from the surrounding tubular  402 . Further, the upper and lower cones  135 ,  150  may fail to overcome the inward biasing force on the slips  140  applied by the slip spring  142 , thus allowing the slips  140  to retract radially inwards. At this point, the tool  100  may be in a retrievable configuration, in which the tool  100  may be removed from the wellbore. 
       FIG. 6  illustrates a flowchart of a method  600  for running and retrieving a downhole tool into a surrounding tubular. The method  600  may be best understood with reference to the foregoing description of the downhole tool  100 , adapter  200 , and/or retrieval tool  300 . However, at least some embodiments may operate by use of other structures and thus may not be limited specifically to the foregoing apparatus. 
     The method  600  may include coupling an adapter to the downhole tool, as at  602 . In an embodiment, the downhole tool may include a release mandrel comprising an upper connection coupled with the adapter, and a plurality of slips disposed at least partially around the release mandrel. The downhole tool may also include an upper cone disposed at least partially around the release mandrel and on a first axial side of the plurality of slips, and a lower cone disposed at least partially around the release mandrel and on a second axial side of the plurality of slips. The downhole tool may further include a collet positioned axially and radially between the release mandrel and the lower cone. The collet may be configured to prevent downward movement of the lower cone relative to the release mandrel, when the downhole tool is in a run-in configuration. The method  600  may also include running the downhole tool into the surrounding tubular using the adapter, as at  604 . 
     The method  600  may also include setting the downhole tool into a set configuration in the surrounding tubular, using the adapter, as at  606 . In an embodiment, setting the downhole tool may include moving at least the upper cone and the plurality of slips downward with respect to the release mandrel and the lower cone. Further, the release mandrel may be held substantially stationary (e.g., the release mandrel may move to a limited degree, but such movement is not used to effect the setting) with respect to the surrounding tubular. Furthermore, moving the upper cone and the plurality of slips downward may include bringing the upper cone and the lower cone closer together and expanding the plurality of slips outward to engage the surrounding tubular. The collet may prevent the lower cone from moving away from the plurality of slips. 
     The method  600  may also include releasing the downhole tool from the adapter, as at  608 . The method  600  may also include retrieving the downhole tool using a retrieval tool, as at  610 . For example, the downhole tool may include an outer mandrel coupled with the release mandrel by one or more shear devices, and coupled with the collet so as to be constrained to move therewith. Retrieving at  610  may thus include shearing the one or more shear devices and moving the release mandrel relative to the outer mandrel and the collet. 
     In an embodiment, the downhole tool may further include one or more sealing elements. For example, setting the downhole tool at  606  may include engaging the surrounding tubular using the one or more sealing elements by axially compressing and radially expanding the one or more sealing elements. Further, retrieving the downhole tool at  610  may include allowing the one or more sealing elements to axially expand and radially contract. The downhole tool may also include a first fluid passage extending from a first axial side of the one or more sealing elements to the upper cone, with the upper cone being positioned on a second axial side of the one or more sealing elements. The downhole tool may further include a second fluid passage configured to communicate pressure to the upper cone. The pressure communicated to the upper cone may tend to push the upper cone toward the plurality of slips. 
     The downhole tool may also include a rupture disk positioned in a bore extending through the release mandrel, to prevent fluid communication through the release mandrel. Accordingly, the retrieving at  610  may also include rupturing the rupture disk using a probe tip of the retrieval tool, such that pressure above and below the one or more sealing elements is substantially equalized. 
     In an embodiment, the release mandrel may further include an upper connection that is coupled with the adapter when running the downhole tool into the surrounding tubular, and a lower connection that is coupled with a second retrieval tool when running the downhole tool into the wellbore. Accordingly, retrieving at  610  may further include engaging a second upper connection of a second downhole tool using the second retrieval tool, while the second retrieval tool is connected with the lower connection. 
     The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.