Patent Publication Number: US-9835007-B2

Title: Control interface for seal back-up/slip

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the design of downhole slip assemblies and plug devices. 
     2. Description of the Related Art 
     Slips are used in packer devices and other downhole devices to create an anchoring engagement with a surrounding casing or other tubular member. Slip assemblies typically present an outer radial surface having teeth formed thereupon to bite into the interior surfaced of the surrounding tubular member. Slips are often formed of a rigid metal or other rigid material that is intended to break apart into arcuate slip segments when the slip element is set. 
     SUMMARY OF THE INVENTION 
     The present invention provides slip assembles and methods for setting a slip assembly. Downhole tools are described which incorporate a slip assembly in accordance with the present invention. In described embodiments, a plug device is described which includes a rupturable slip element, an expander swage element and a pusher sub. The expander swage element features a tapered outer surface. 
     In described embodiments, the slip element includes a cylindrical body having an unslotted, solid slip portion which is intended to be placed into contact with the surrounding tubular when set. A plurality of generally axial rupture slots are formed within slotted portions of the slip element. The rupture slots may take a number of forms or shapes, including straight and tortuous. The slots provide lines of predetermined weakness along which the solid portion of the slip element will fracture when the slip element is set. In embodiments, the plug device also includes an elastomeric packer element that will seal against the surrounding tubular when the plug is set. In instances where the rupture slots have a tortuous shape, the tortuous shape also helps prevent axial extrusion of the elastomeric packer element within the surrounding tubular past the slip element. 
     Preferably, the slip element is formed of a degradable, dissolving metal material, such as a controlled electrolytic metallic (“CEM”) nanostructured material. This material is degradable or dissolvable over time in response to contact by brine. In some embodiments, the CEM material is covered by a polymeric or other coating which is not prone to dissolution or degradation in response to brine or similar fluids. 
     In described embodiments, the plug device includes a control interface, typically formed between the slip element and the pusher sub, which controls radial expansion of the separate slip element segments after the slip element has been ruptured. The control interface helps to ensure that the slip segments are guided radially outwardly into contact and engagement with the surrounding tubular. The control interface also helps ensure regular spacing between the slip segments, which in turn, helps prevent axial extrusion of the packer element past the slip element. In described embodiments, the pusher sub has a cylindrical body with an opening that receives an end portion of the slip element. In particular embodiments, the opening presents axially-extending control protrusions that are shaped and sized to reside within complementary recesses in the slip element. 
     To set the plug devices, the swage element and pusher sub are urged axially toward one another, typically with the assistance of a setting tool. The tapered outer surface of the swage element ruptures the slip element into separate slip segments and urges the ruptured slip segments into engagement with the surrounding tubular. 
     The inventors have determined that, when the slip assembly is located adjacent an elastomeric packer element, the regular spacing and substantially uniform loading of the slip segments is useful for preventing axial extrusion of the packer element after it is set. Irregular gaps between the slip segments are prevented, and rotation of the pusher sub with respect to the slip segments is prevented. The use of control protrusions and slotting in accordance with the present invention allows the slip assembly to load more evenly, thereby reducing the risk of subsequent failure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein: 
         FIG. 1  is a side, cross-sectional view of a wellbore having a plug device and setting tool disposed therein. 
         FIG. 2  is an external side view of an exemplary plug device constructed in accordance with the present invention. 
         FIG. 3  is a side, partial cross-sectional view of the plug device of  FIG. 2 , now shown adjacent wellbore casing. 
         FIG. 4  is an external side view of the plug device shown in  FIGS. 2-3  now having been set against the casing. 
         FIG. 5  is a side, partial cross-sectional view of the set plug device of  FIG. 4 . 
         FIG. 6  is an external side view of an alternative plug device in accordance with the present invention. 
         FIG. 7  is an external side view of the plug device shown in  FIG. 6 , now having been set. 
         FIG. 8  is an external side view of a further alternative plug device in accordance with the present invention. 
         FIG. 9  is an external side view of the plug device shown in  FIG. 8 , now having been set. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an exemplary wellbore  10  that has been drilled through the earth  12  from the surface  14 . The wellbore  10  has been lined with metallic casing  16  of a type well known in the art. A running string  18  is disposed within the wellbore  10  from the surface  14 . In the depicted embodiment, the running string  18  is a wireline. In alternative embodiments, however, the running string  18  may be coiled tubing or be made up of interconnected section of tubing sections, as is known. A setting tool  20  is secured to the lower end of the running string  18 . A plug device  22 , which is set by the setting tool  20  is affixed to the setting tool  20 . The setting tool  20  functions to transmit axial setting forces to the plug device  22 . In a currently preferred embodiment, the setting tool  20  is an explosive-based setting tool, such as the Baker E-4 Wireline Setting Tool which is available commercially from Baker Hughes Incorporated of Houston, Tex. In general operation, electrical current is transmitted from surface  14  along the wireline  18  to the setting tool  20 . The electrical current sets off an explosive charge in the setting tool  20  which generates the forces for setting the plug device  22 . 
     Where otherwise not described, the plug device  22  generally is constructed and operates in the same manner as a Baker Hughes Model D packer. The plug device  22  may be set using a wireline setting tool of a type known in the art for setting devices such as the Model D packer within a wellbore. However, other setting mechanisms and techniques may also be used. 
     An exemplary plug device  22  is depicted in greater detail in  FIGS. 2-4 . The plug device  22  is generally made up of three major components: an expander swage element  24 , a slip element  26  and a pusher sub  28 . The expander swage element  24  has a cylindrical body  30  with tapered distal portion  32 . An axial fluid flowbore  34  is formed within the expander swage element  24 . 
     The slip element  26  has a cylindrical body  35  that is formed of a rigid, rupturable material. In preferred embodiments, the body  35  is formed of metal that is disintegrated or dissolves in response to contact by an appropriate fluid. In particular embodiments, the slip element  26  is made up of one or more decomposable metals such as that used in fabrication of IN-TALLIC® brand decomposable metallic components which are available commercially from Baker Hughes Incorporated of Houston, Tex. These metals are controlled electrolytic metallic (“CEM”) nanostructured material. Disintegration of CEM materials works through electrochemical reactions that are controlled by nanoscale coatings within a composite grain structure. In certain embodiments, a slip element  26  formed of CEM material will disintegrate, dissolve or degrade over time during exposure to brine fluids. However, the actual degradation rate will depend upon the temperature and concentration of the brine. Also, acids will degrade the slip element  26  at a much higher rate. In particular embodiments, the slip element  26  has a protective coating that covers the degradable metal material of the slip element  26 . When the slip element  26  is composed of degradable material, the plug device  22  is intended to function as a plug or packer device for a limited period of time and then degrade away. The ability to speed up the degradation process by adding acid to the wellbore  10  proximate the plug device  22  allows an operator to alter the time during which the plug device  22  is operative. 
     In particular embodiments, the degradable material making up the slip element  26  has a covering that is substantially non-degradable. In particular embodiments, the covering comprises a polymer that is not degradable in brine. In other embodiments, the slip element  26  is coated with a degradable polymer, such as TDI-Ester polyurethane. The degradable polymer will allow the slip element  26  to also seal against the casing  16  and subsequently degrade along with the remainder of the slip element  26 . 
     In the embodiment shown in  FIGS. 2-3 , the slip element  26  does not have outer wickers for biting into the surrounding casing  16 . It should be understood, however, that such wickers might be formed upon the outer radial surface of the slip element  26 . The lower axial end  36  of the slip element  26  has a plurality of axially disposed recesses  38  formed therein. In addition, lower axial rupture slots  40  are preferably also formed within the lower axial end  36 . An elastomeric sealing element or packer  41  is located adjacent the slip element  26 . 
     Upper rupture slots  42  are formed in an upper portion  44  of the slip element  26 . Preferably, the rupture slots  42  extend from the axial upper end  46  of the slip element  26 . In the depicted embodiment, the upper rupture slots  42  are shaped in a tortuous fashion. The inventors have determined that the tortuous shape for the rupture slots  42  provides an advantage with respect to inhibiting potential extrusion of an elastomeric seal (such as sealing element  41 ) by providing a tortuous path through which the seal material must traverse in order to extrude axially along the wellbore casing  16 . The body  35  of the slip element  26  also features a solid, unslotted portion  47 . The slip element  26  also presents a central opening  48  which is tapered in a manner complementary to the tapered portion  32  of the expander swage element  24 . 
     The pusher sub  28  includes a cylindrical body  50  having a rounded end nose  52 . An interior diameter  54  is formed within the body  50 . A plurality of control protrusions  56  project axially outwardly from the upper axial end  58  of the body  50 . The control protrusions  56  are shaped and sized to reside within the recesses  38  of the slip element  26 . The control protrusions  56  reside within the recesses  38  and each protrusion  56  is moveable radially inwardly and outwardly within its recess  38 . A lateral fluid port  59  is disposed through the pusher sub  28  which allows for fluid bypass during setting of the plug device  22 . 
     In order to set the plug device  22 , the setting tool  20  applies axial setting forces to the swage element  24  and the pusher sub  28 . The axial setting forces are illustrated by arrows  60  in  FIG. 2 . When the setting forces are applied, the swage element  24  causes the slip element  26  to be ruptured.  FIGS. 4-5  illustrate the plug device  22  in a set position wherein the slip element  26  has been ruptured so that the slip element  26  and sealing element  41  are set against the casing  16 . The solid portion  47  of the body  35  of the slip element  26  is ruptured so that the ruptured segments  35   a ,  35   b ,  35   c ,  35   d  are separated along lines that are in alignment with the rupture slots  40 ,  42 . As the slip segments  35   a ,  35   b ,  35   c ,  35   d  are urged radially outwardly by the expander swage  24 , the aligned control protrusions  56  and recesses  38  act as guides to ensure that the slip segments  35   a - 35   d  are loaded against the casing  16  evenly and in a uniformly spaced manner. As a result, the control protrusions  56  and recesses  38  control the gaps between the slip segments  35   a - 35   d . It is noted that the control protrusions  56  and recesses  38  are preferably located about the circumference of the plug device  22  in a uniform spaced configuration. 
       FIGS. 6-7  illustrate an alternative embodiment for a plug device  62  that is constructed in accordance with the present invention. The plug device  62  is similar in many respects to the plug device  22  described previously. Where not otherwise described, the plug device  62  is constructed and operates in the same manner as the plug device  22 . In this embodiment, the upper rupture slots  42 ′ in the slip element  26  have a straight linear configuration rather than a tortuous shape. A set of arcuate support segments  64  is disposed radially within the upper end  46  of the slip element  26 . The support segments  64  also preferably underlie a portion of the seal element  41 . It is noted that the separations  66  between adjacent support segments  64  are radially offset from the rupture slots  42 ′ of the slip element body  35 . Preferably also, raised ridges  68  on the support segments  64  reside within the upper rupture slots  42 ′. The ridges  68  function to keep the support segments  64  in alignment with the slip element  26 . The ridges  68  also ensure that the support segments  64  will block the sealing element  41  from extruding into the rupture slots  42 ′ of the slip element  26 . 
       FIG. 6  depicts the plug device  62  in a run-in condition, prior to it having been set.  FIG. 7  depicts the plug device  62  after setting. When the expander swage element  24  is moved axially to rupture the slip element  26 , the support segments  64  help to ensure that the sealing element  41  does not extrude axially through the now enlarged rupture slots  42 ′ and thereby serve basically the same purpose as the tortuous shape of the slots  42  described previously. 
       FIGS. 8-9  illustrate a further alternative plug device  70  wherein certain components, including the slip element  26 ′, are constructed differently in a number of respects. There is no elastomeric seal element, such as seal element  41 . The slip element  26 ′ presents a radially outer surface with wickers  72  that are intended to bite into the surrounding tubular (i.e., casing  16 ) when the plug device  70  is set. The slip element  26 ′ could be embedded with a hard material, such as carbide, to form the wickers  72 . It is noted that wickers such as  72  could be formed upon any of the slip elements described herein. 
     The inventors have determined that, when the slip element ( 26 ,  26 ′) is located adjacent an elastomeric packer element  41 , the regular spacing and substantially uniform loading of the slip segments is useful for preventing axial extrusion of the packer element  41  after it is set. Irregular gaps between the slip segments ( 35   a - 35   d ) are prevented. The use of control protrusions  56  and slotting  38  in accordance with the present invention allows the slip assembly to load more evenly, thereby reducing the risk of subsequent failure. 
     After a slip element  26  or  26 ′ formed of degradable material is set so that the slip element body  35  is separated into slip segments  35   a - 35   d , the segments  35   a - 35   d  will degrade over time in response to brine within the wellbore  10 . In instances where the slip element  26 ,  26 ′ has a non-degradable coating, breaking up of the slip element  26  or  26 ′ into slip segments  35   a - 35   d  would expose the degradable material of the slip element  26 ,  26 ′ to the brine. The coating is then useful for protecting the slip element  26 ,  26 ′ from dissolving or degrading prematurely. 
     It is noted that plug devices of the present invention may have various alternative constructions. For example, control protrusions ( 56 ) might be formed on the slip element ( 26 ) while recesses ( 38 ) are formed on the pusher sub ( 28 ). Also, while the control protrusions  56  that are depicted in the drawings have a generally elongated rectangular shape, they may have a curved arcuate profile which interfits with a complementary arcuate profile on the pusher sub  28 , thereby providing a curved wave interface. Other interlocking profiles which function to prevent relative rotation of the pusher sub  28  and respect to the slip element  26  might be used as well. Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.