Abstract:
Releasing slips for use with a downhole tool, a tool for deploying downhole in a well utilizing the releasing slips and a well in which a downhole tool is deployed utilizing the releasing slips of the invention is described herein. The tool has a plurality of slips for selective engagement with a wall of a wellbore. The slips include releasing slips and biting slips. The releasing slips have a low friction surface, e.g., a substantially smooth surface for engaging the wall of the wellbore. The smooth wall engaging face of the releasing slips facilitate easy release of the slips, thereby facilitating easy removal of the downhole tool. The slips may include a plurality of hardened members that protrude from the wall engaging face of the releasing slips to reduce wear on the face of the releasing slip.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an improved releasing slip for use with a hold down tool/bridge plug/packer for lowering into a wellbore. In particular, the releasing slip of the invention has a low friction face to facilitate ease of release. 
       BACKGROUND OF THE INVENTION 
       [0002]    A production packer is a standard component of completion hardware in oil and gas wells. Production packers are used to provide a seal between the outside of production tubing and the inside of a casing, liner, or wellbore wall. When recovering oil and gas from a well, in many geological formations it is necessary to isolate the zone containing the oil and gas producing formation from the remainder of the underground structure so as to prevent contamination of the oil and gas producing zone from salt water or other undesirable contaminants. 
         [0003]    Packers may be lowered into the well and expanded to isolate the oil and gas producing zone. Packers may be placed above and below the producing zone, or, if the producing zone is near the bottom of the well, a single packer may be placed above the producing zone. Packers are typically provided with slips for providing gripping engagement with the wall of a wellbore. Once a packer is set, the packer may experience forces that could displace the packer in the casing. One example of such a force is pressure from the formation. 
         [0004]    In some circumstances, it may be desirable to utilize a hold down tool or bridge plug in the well to assist in keeping a packer in position. A hold down tool/bridge plug typically includes a plurality of slips that may be selectively forced into tight engagement with a wall of the well bore. 
         [0005]    One difficulty associated with the use of conventional slips or gripping members is that the slips that are engaged with the wellbore can be extremely difficult to release when it is desired to release the tool. 
         [0006]    An innovative oil well hold down tool is taught in U.S. Pat. No. 3,356,141 to Albert K. Kline (the &#39;141 patent). The system taught in the &#39;141 patent provided for one or more slips to be released prior to release of all the loaded slips, depending on the circumference of the tool used. The early releasing slips have become known as “releasing slips”. When the releasing slip or slips are released, normally by pulling up against them or their mounting device, the tool as a whole is then free to move laterally in the well slightly. The lateral movement of the tool is enough to lessen or remove entirely the bite of the remaining slips. The tool can then be moved up the well, or relatched and then moved further down the well and reset, or removed entirely. 
         [0007]    There are numerous uses of the releasing slip principle taught by the &#39;141 patent. Applicant&#39;s company manufactures several tools utilizing the teachings of the &#39;141 patent. For example, one tool addressed improvements to the invention of the &#39;141 patent related to the releasing slips. The device was used to assist in the release of hold down tools that have mechanically, as opposed to hydraulically, loaded slips above the pack-off portion of the tool. 
         [0008]    One drawback of hold down tools utilizing prior art designs is that, when engaged, the slips bite into the casing wall while the hold down tool is performing its functions. Therefore, during release, even the releasing slips provide resistance, which causes problems including that the biting surfaces of the releasing slips become worn fairly quickly, requiring their replacement. An additional difficulty is that during higher pressure operations, the releasing slips can provide sufficient resistance that release becomes difficult and may also cause other problems. These problems may include overstressing the pulling unit topside, parting of the tubing that is used to transfer the tension from the pulling unit to the tool, rupture or permanent deformation of the mounting device for the slips, and ultimately, an inability to remove the tool at all. 
       SUMMARY OF THE INVENTION 
       [0009]    This present invention replaces the releasing slips with a part or parts that have no biting effect on the casing. In one embodiment, the surface of the releasing slip of the present invention is entirely smooth. When pulled upwards, the releasing slips of the present invention move up much more easily, allowing the tool to move laterally, thereby partially unloading the remaining slips, and thus allowing the remaining slips to more easily release. The releasing slips in this case are, in practice, used as a wedge, which allow the remaining slips to function normally. The releasing slips of the invention are not required to provide biting capability for the hold down tool to perform its function. The releasing slips of the invention allow the tool to release much more easily, especially in severe applications. 
         [0010]    A second embodiment of the present invention utilizes one or more hardened carbide pieces or other suitable material on the contacting face of the releasing slip of the invention. The smooth surface of the hardened piece or pieces are preferably configured such that the piece or pieces lay flat against a wall, thereby providing greatly reduced resistance to release. The carbide pieces are harder than any standard grade of casing, which greatly reduces wear on the part. 
         [0011]    In the case of larger diameter tools, more than one releasing slip may be used in the circumferential arrangement of the upper slips. Preferably, the releasing slips cover somewhat less than half the circumference of the tool so that the tool can move laterally in the wellbore when the releasing slips are released or disengaged from the wellbore wall. The biting slips preferably also encompass less than half the circumference. As an example, a hold down tool of the present invention may use two releasing slips and four biting slips, although other numbers of slips and ratios of releasing slips to biting slips may be functional. In a preferred embodiment, the releasing slips are wider than the biting slips and the biting slips encompass less than 180 degrees of tool circumference. 
         [0012]    There are several advantages of the present invention. Most importantly, a tool utilizing the inventive slips significantly reduces the problems described above with respect to removal of the tool. The monetary benefit associated with the tool includes the relatively smaller benefits associated with improved service life of the releasing slips and also the substantially larger benefits associated with avoiding an inability to release the tool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a partially sectioned elevation view of a packer being placed in a hole, attached to a hold down tool, in which the invention is embodied. 
           [0014]      FIG. 2  is the structure of  FIG. 1  attached at a desired position within a well bore. 
           [0015]      FIG. 3  is an isometric view of a slip housing base of the hold down tool of  FIG. 1 . 
           [0016]      FIG. 4  is an isometric view of the slip housing of  FIG. 3  shown with slips installed therein. 
           [0017]      FIG. 5  is an isometric view of a biting slip for installation into the slip housing of  FIG. 4 , 
           [0018]      FIG. 6  is an isometric view of a releasing slip for installation into the slip housing of  FIG. 4 . 
           [0019]      FIG. 7  is an isometric view of a releasing slip of  FIG. 4  with carbide pieces on a wall engaging face of the releasing slip. 
           [0020]      FIG. 8  is a partial cut-away view of a retrievable bridge plug in which the invention is embodied. 
           [0021]      FIG. 9  is a partial cut-away view of a packer in which the invention is embodied. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring first primarily to  FIGS. 1 and 2 , shown is well bore  10  having a wall  12 . A packer  14  is shown lowered into well bore  10 . Packer  14  includes an expansible element such as packer slips  15  for selectively engaging wall  12 . A hold down tool  16  is connected to packer  14 . Hold down tool  16  includes a cone assembly  18 . Cone assembly  18  has an upwardly facing cone  20  and an outer casing  22 . Outer casing  22  defines a j-slot  24  having a long vertical section  26  and a short horizontal section  28 . Cone assembly  18  further defines an internal abutment  30 . 
         [0023]    A coupling member  32  is attached to an upper end of hold down tool  16 . A tubing string  34  is connected to coupling member  32  for supporting hold down tool  16  and packer  14  within well bore  10 . 
         [0024]    A spring  36  is located above hold down tool  16 . Spring  36  has an upper end in abutment with coupling member  32 . A cylindrical mandrel  38  extends downwardly inside cone assembly  18 . Mandrel  38  defines a protuberance  40  and has a lower end  42 . Mandrel  38  further has a pin  44  protruding from an outer surface. Pin  44  is provided for extending into j-slot  24 . 
         [0025]    Mandrel  38  and cone assembly  18  are releasably connected together via pin  44  and j-slot  24 . When pin  44  is positioned in long vertical section  26  of j-slot  24 , mandrel  38  may be moved downwardly (as shown in  FIG. 2 ) until lower end  42  of mandrel  38  seats on internal abutment  30  of cone assembly  18 . 
         [0026]    Slip housing  46  is located above cone assembly  18 . Slip housing  46  is made up of a slip housing cover  48  ( FIGS. 1 ,  2 ,  4 ) and a slip housing base  50  ( FIGS. 3 ,  4 ). Slip housing base  50  is slidably mounted on mandrel  38 . Slip housing cover  48  and slip housing base  50  define an annular space therebetween. Slip housing base  50  has an upper end in engagement with a lower end of spring  36 . Spring  36  urges slip housing base  50  against protuberance  40  on mandrel  38 . Slip housing base  50  has a lower end defining a flange portion  52 . Flange portion  52  defines a plurality of downwardly facing openings  54  ( FIG. 3 ). 
         [0027]    A plurality of slips  56  are carried within slip housing  46  and are sized to be received within openings  54  of slip housing base  50 . Slips  56  each have an extension  58  ( FIGS. 4-7 ) on an upper end for locating in the annular space between the slip housing cover  48  and the slip housing base  50 . Slips also have a wall engaging face  60  ( FIGS. 4-7 ). Slips  56  further define a slip neck  61  ( FIGS. 5-7 ). Slips  56  are loosely received within openings  54  of slip housing base  50  wherein flange portions  52  of slip housing base  50  that are located between openings  54  provide supportive engagement with slip necks  61 . 
         [0028]    Slips  56  are comprised of biting slips  62  ( FIGS. 4 ,  5 ) and releasing slips  66  ( FIGS. 4 ,  6 ,  7 ). Faces  60  of biting slips  62  have a plurality of wickers or teeth  64  to facilitate gripping engagement with wall  12  of bore  10 . Faces  60  of releasing slips  66  have smooth surface  68  to facilitate ease of release. In an alternative embodiment, smooth surface  68  of releasing slip  66  may be impregnated with one or more hardened carbide pieces  70  to reduce wear on face  60  of releasing slips  66 . 
         [0029]    Slip housing base  50  functions to selectively urge slips  56  downwardly when mandrel  38  is moved downwardly. Slips  56  are oriented vertically and are positioned circumferentially above upwardly facing cone  20  of hold down tool  16 . Therefore, when slips  56  are moved downwardly with mandrel  38 , slips  56  engage the upwardly facing cone  20 . Upwardly facing cone  20  then forces engagement faces  60  proximate the lower ends of slips  56  outwardly into engagement with wall  12  of well bore  10 . 
         [0030]    When it is desired to release the slips  56 , mandrel  38  is moved upwards. The force of the mandrel moving upward is first transmitted through slip housing base  50 . Flange portion  52  of slip housing base  50  lifts slips  56  upwards. Slip necks  61  may be of different lengths, so that flange portion  52  does not engage slips simultaneously. 
         [0031]    Referring now to  FIG. 8 , a bridge plug  100  is shown utilizing the slips of the invention. Bridge plug  100  includes a tubular housing  102 . Tubular housing  102  is made up of lower mandrel  104 , connecting rod  106  that is threadably received on an upper rod of lower mandrel  104 , and an upper mandrel  108  that is threadably received on an upper end of connecting rod  106 . A pulling head cap  110  is threadably received on an upper end of upper mandrel  108 . 
         [0032]    A control body  112  surrounds lower mandrel  104 . A plurality of drag blocks  114  are supported by control body  112 . Drag blocks  114  are biased outwardly by drag block springs  116 . 
         [0033]    A lower cone member  118  surrounds lower mandrel  104 . Lower cone member  118  has a cone section  120  and a lower cylindrical section  122 . A plurality of lower slips  124  surround lower cylindrical section  122  of lower cone member  118 . Plurality of lower slips  124  are located below cone section  120  of lower cone member  118 . 
         [0034]    An element retainer  126  is threadably received on an upper end of lower cone member  118 . Packing and seal sleeve  128  and attached packing element  130  are adjacent to connecting rod  106  in an abutment with element retainer  126 . An upper cone member  132  is threadably received on an upper end of packing and seal sleeve  128 . 
         [0035]    A slip sleeve  134  is provided above upper cone member  132 . A plurality of upper slips  136  surrounds slip sleeve  134 . Upper slips  136  are made up of releasing slips  138  and biting slips  140 . A thrust spring  142  is provided having a lower end in engagement with slip sleeve  134 . A spring ring  144  is affixed to upper mandrel  108 . Spring ring  144  is in engagement with an upper end of thrust spring  142 . 
         [0036]    In practice, when packing element  130  engages a wall of a wellbore, packing element  130  moves upwardly with regard to tubular housing  102  with attached upper cone member  132 . Upper cone member  132  contacts upper slips  136  and forces slips  136  into engagement with a wall of the wellbore. 
         [0037]    Referring now to  FIG. 9 , shown is a packer  200  utilizing the releasing slips of the invention. Packer  200  includes a mandrel  202 . A top sub  204  is threadably attached to an upper end of mandrel  202 . A control body  206  surrounds mandrel  202 . A plurality of drag blocks  208  are supported by control body  206 . Drag blocks  208  are biased outwardly by drag block springs  210 . 
         [0038]    A lower slip sleeve  212  is threadably attached to an upper end of control body  206 . A lower cone member  214  surrounds lower slip sleeve  212 . A plurality of lower slips  216  surround lower slip sleeve  212 . The plurality of lower slips  216  are located below lower cone member  214 . 
         [0039]    An element retainer  218  is threadably received on an upper end of lower cone member  214 . A packing and seal sleeve  220  as well as a packing element  222  are in threaded communication with element retainer  218 . 
         [0040]    An upper cone member  224  is threadably received on an upper end of packing and seal sleeve  220 . An upper slip support  226  is located above upper cone member  224 . A plurality of upper slips  228  surround upper slip support  226 . Upper slips  228  are made up of releasing slips  230  and biting slips  232 . A slip spring  234  is provided for biasing each of upper slips  228  outwardly. An upper slip housing assembly  236  is located above upper slips  228 . 
         [0041]    In practice, when packing element  222  engages a wall of the wellbore, packing element  222  moves upwardly with regard to mandrel  202 . Attached upper cone member  224  moves upwards as well. Upper cone member  224  contacts upper slips  228  and forces slips  228  into engagement with a wall of the wellbore. 
         [0042]    When pulled against for release, as described above, releasing slips  66  ( FIGS. 4 ,  6 ,  7 ),  138  ( FIG. 8 ),  230  ( FIG. 9 ) are easily lifted and disengaged from wall  12  since releasing slips  66 ,  138 ,  230  have a low friction wall engaging face, as can best be seen in  FIGS. 6 and 7 . Once releasing slips  66 ,  138 ,  230  are lifted, tool  16 ,  100 ,  200  is able to move laterally, thereby partially unloading the remaining biting slips  62  ( FIGS. 4 ,  5 ),  140  (FIG,  8 ),  232  ( FIG. 9 ), which allows biting slips  62 ,  140 ,  232  to more easily release. Therefore, releasing slips  66 ,  138 ,  230  function as a wedge to force biting slips  62 ,  140 ,  232  to securely engage wall  12 . Releasing slips  66 ,  138 ,  230  are not required to provide biting capability for tool  16 ,  100 ,  200  to perform its function. Releasing slips  66 ,  138 ,  230  of the invention allow tool  16  ( FIGS. 1 ,  2 ),  100  ( FIG. 8 ),  200  ( FIG. 9 ) to release much more easily, especially in severe applications. 
         [0043]    In one embodiment, hardened pieces  70  ( FIG. 7 ), such as hardened carbide disks or pieces of other suitable material protrude from contacting face  60  of releasing slip  66 , or from a contact face of releasing slips  138 ,  230 . Smooth surface  68  of a hardened piece  70  or pieces  70  are preferably configured such that the piece or pieces  70  lay flat against wall  12 , thereby providing greatly reduced resistance to release. The carbide pieces  70  are harder than any standard grade of casing, which greatly reduces wear on releasing slip or slips  66 ,  138 ,  230 . 
         [0044]    In the case of larger diameter tools  16 ,  100 ,  200 , more than one releasing slip  66 ,  138 ,  230  may be used in the circumferential arrangement of the slips  56 . Preferably, releasing slips  66 ,  138 ,  230  cover somewhat less than half the circumference of tool  16 ,  100 ,  200 , so that tool  16 ,  100 ,  200  can move laterally in wellbore  10  when releasing slips  66 ,  138 ,  230  are released or disengaged from wall  12 . Consequently, biting slips  62 ,  140 ,  232  preferably encompass more than half the circumference of tool  16 ,  100 ,  200 . 
         [0045]    Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.