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BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to releasable wellbore packers. In particular aspects, the invention relates to improved packer devices and methods for release of packer devices from a wellbore.  
         [0003]     2. Description of the Related Art  
         [0004]     Packers are set within a wellbore to form a fluid seal between the borehole wall and a tubing string. Non-retrievable, or permanent, packers are sometimes used where a permanent closure is desired. In order to remove a permanent packer, a milling tool is disposed into the wellbore above the packer and mill away the upper setting slips that hold the packer in its set position. This process is time consuming and requires an additional trip into the well. In other cases, retrievable packers are used, which allow the option to release the packer from its set position and removing it.  
         [0005]     A standard technique for removing retrievable packers involves pulling upwardly to shear a shear ring or other shearable member. U.S. Pat. No. 4,688,641 issued to Knierieman, for example, discloses a well packer that is releasable by use of a jarring tool that shears a threaded connection, there by releasing the packer from its set position. Shear members of a predetermined load are often used where the upward loading on the packer can be limited during normal production and standard well conditions. However, this is not always the case, and an alternative arrangement is needed.  
         [0006]     U.S. Pat. No. 3,990,510 describes a well anchor tool that uses a set of releasable collet fingers to set the packer element. A special retrieving tool, which is run into the wellbore separately, can engage the collet fingers and release them to unset the packer.  
         [0007]     Other retrievable packer designs are known, but these suffer from similar drawbacks. Retrievable packers generally do not provide for a means of hydraulically releasing the packer assembly from the wellbore.  
         [0008]     The present invention addresses the problems of the prior art.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention provides a releasable packer device and a method for releasing a packer from a set position in a wellbore. A packer assembly is described that incorporates a split body lock ring that is in ratcheting engagement with a central mandrel to secure the packer elements in a set position. In addition, there is a mechanical means for releasing the body lock ring from its locking position to an unlocked position. The body lock ring is released by radially expanding the ring by urging an axially-movable release sub with a releasing portion into contact with the body lock ring to unseat the ratcheting mechanism that retains the packer assembly in its set position.  
         [0010]     In a first preferred embodiment, the releasing portion of the axially-moveable release sub comprises at least one, and preferably a plurality of, thin and elongated fingers that are shaped and sized slip between the ratcheted surface of the body lock ring and the ratcheted surface of the central mandrel, thereby breaking the ratchet engagement. In a second embodiment, the releasing portion of the release sub comprises a wedge-shaped projection that will be inserted into the split ring gap of the body lock ring to radially expand it, thereby causing the ratchet engagement of the body lock ring with the central mandrel to become unseated.  
         [0011]     In operation, the packer assembly is set by moving a setting piston with respect to the central mandrel, thereby axially compressing the packer and slip elements of the packer assembly. A body lock ring provides a ratchet engagement that prevents unsetting of the packer and slip elements from occurring. Once the ratchet engagement of the body lock ring with the inner mandrel is broken, the setting piston will be released and permitted to move axially with respect to the central mandrel, and the packer elements will be unset from the wellbore wall. A further embodiment of the invention is described wherein a release sleeve, moveable by mechanical manipulation of a surface-run shifter tool, is used to unset the packer elements. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     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:  
         [0013]      FIGS. 1A, 1B , and IC present a partial side cross-sectional view of an exemplary releasable packer assembly constructed in accordance with the present invention.  
         [0014]      FIGS. 2A and 2B  are an enlarged side, cross-sectional view of an exemplary release mechanism for the releasable packer assembly constructed in accordance with the present invention, and in an unset, running-ill position.  
         [0015]      FIGS. 3A and 3B  are an enlarged side, cross-sectional view of an exemplary release mechanism for the releasable packer assembly constructed in accordance with the present invention, wherein the packer has been placed into a set position.  
         [0016]      FIGS. 4A and 4B  are an enlarged side, cross-sectional view of an exemplary release mechanism for the releasable packer assembly constructed in accordance with the present invention, during activation of the release mechanism.  
         [0017]      FIGS. 5A and 5B  are an enlarged side, cross-sectional view of an exemplary release mechanism for the releasable packer assembly constructed in accordance with the present invention, following release of the packer elements from their set position.  
         [0018]      FIG. 6  is an isometric view of an exemplary release sub.  
         [0019]      FIG. 7  is an end view of the exemplary release sub shown in  FIG. 6 .  
         [0020]      FIG. 8  is a cross-sectional view taken along lines  8 - 8  in  FIG. 7 .  
         [0021]      FIG. 9A  is an enlarged side, cross-sectional view of an alternative embodiment for a releasable packer assembly constructed in accordance with the present invention.  
         [0022]      FIG. 9B  is a cutaway view taken along lines  9 B- 9 B in  FIG. 9A .  
         [0023]      FIG. 10  is an isometric view of an alternative exemplary release sub.  
         [0024]      FIG. 11  is an end view of the release sub shown in  FIG. 10 .  
         [0025]      FIG. 12  is a cross-sectional cutaway taken along lines  12 - 12  in  FIG. 11 .  
         [0026]      FIG. 13  is an enlarged detail view of the body lock ring and surrounding components.  
         [0027]      FIGS. 14A-14B  are a side, cross-sectional view of a further alternative exemplary release mechanism in accordance with the present invention, prior to release of the packer assembly. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]      FIGS. 1A, 1B , and IC, as well as  2 A and  2 B, illustrate an exemplary hydraulically set, retrievable packer assembly  10 , constructed in accordance with the present invention. The packer assembly  10  includes a central mandrel  12  that defines an axial flowbore  14  along its length. The central axis of the flowbore  14  is illustrated at  16 . At the upper end of the packer assembly  10  is an upper sub  18 , which is secured by threaded connection  20  to the central mandrel  12 . The central mandrel  12  presents a radially reduced outer surface area  22  upon which compressible packer and slip elements are disposed. The central mandrel  12  also presents a downwardly-facing stop shoulder  24  proximate its upper end. A pair of slip-type packer elements  26 ,  28  and an elastomeric packer element  30  surround the central mandrel  12  upon the radially reduced outer surface area  22 . The slip and packer elements  26 ,  28 , and  30  are shown generally, but are of the type that is urged into a set position by axial compression. The slip-type packer elements  26 ,  28  are also known merely as “slips,” which are metallic toothed elements that are selectively urged radially outwardly to permit the teeth of the slip to engage the wall of a wellbore in a biting relation. The elastomeric packer element  30  is of the type that, when compressed axially, extrudes radially to form a fluid seal within a wellbore. A number of such elements are available commercially, and their structure and operation is, of course, well known to those of skill in the art.  
         [0029]     At the lower end of the slip element  28  is a setting piston  32  that is disposed in an axially moveable relation upon an outer radial surface  34  of the central mandrel  12 . Initially, the setting piston  32  is secured against axial movement with respect to the central mandrel  12  by a shear pin  36 . The shear pin  36  is a frangible member that is designed to break away, or fail, upon encountering a predetermined level of shear stress. A bridge sleeve  38  is secured to the lower end of the setting piston  32  by a threaded connection  40 . The lower end of the bridge sleeve  38  is secured by a second threaded connection  41  to a body lock ring housing  42 . An annular ring  44  radially surrounds the central mandrel  12  within the bridge sleeve  38  and is threaded at  46  to securely affix the annular ring  44  to the central mandrel  12 . An upper hydraulic fluid chamber  48  is defined radially between the central mandrel  12  and the bridge sleeve  38 . The upper end of the upper hydraulic fluid chamber  48  is defined by the setting piston  32 , while the lower end of the upper hydraulic fluid chamber  48  is defined by the annular ring  44 . A fluid communication port  50  (see  FIG. 1B ) is disposed through the central mandrel  12  to permit fluid communication between the flowbore  14  and the upper hydraulic chamber  48 .  
         [0030]     The lower end of the body lock ring housing  42  has a threaded connection  52  to an annular release sub housing  54 . The inner radial surface of the body lock ring housing  42  also presents a toothed ratchet surface  56  (see  FIG. 2A ) that is in locking engagement with a complimentary toothed outer ratchet surface  58  on body lock ring  60 . The body lock ring  60  is a split ring, or “C”-ring that radially surrounds the central mandrel  12  and has a split  61 , which is depicted in  FIG. 9B . The structure of the body lock ring  60  and associated ratchet surfaces and engagements is better understood with reference to the enlarged detail provided by  FIG. 13 . The body lock ring  60  includes a radially inner ratchet surface  62  that is less coarse (i.e., or finer pitch) than the outer ratchet surface  58 . The inner ratchet surface  62  engages the outer radial surface  64  of the central mandrel  12 . The outer radial surface  64  of the central mandrel  12  may be smooth, roughened, or contain a ratchet surface that is complimentary to the inner ratchet surface  62  of the body lock ring  60 .  
         [0031]     Referring again to  FIGS. 1C, 2A , and  3 A, it can be seen that the release sub housing  54  radially surrounds a release sub  66 . A plurality of frangible shear pins  57  (one shown) interconnects the release sub housing  54  to the release sub  66 . The release sub  66  is shown apart from other components in  FIGS. 6, 7 , and  8 , where it can be seen that the sub  66  includes a solid annular body  68  with a plurality of axially extending releasing portions  70 . The releasing portions  70  are fingers, each of which having a tapered end portion  72 , which is shaped and sized to slip between the body lock ring  60  and the central mandrel  12 . In the embodiment shown in  FIGS. 6, 7 , and  8 , there are eight such releasing portions  70  that are located in spaced relation from one another about the inner circumference of the body  68 . However, there may be more or fewer than eight releasing portions  70 .  
         [0032]     A release sleeve assembly  74  is shown in  FIG. 1C , as well as  FIGS. 2A-2B  and  3 A- 3 B. The release sleeve assembly  74  includes an annular release sleeve housing  76  that radially surrounds the central mandrel  12 . The lower end of the release sleeve housing  76  is secured to the central mandrel  12  by a threaded connection  78 . A lower hydraulic chamber  79  is defined radially within the piston housing  76 . A hydraulic fluid inlet port  80  for the chamber  79  is contained within the lower end of the release sleeve housing  76 . Release sleeve  82  is retained radially within the release sleeve housing  76 . The release sleeve  82  presents an upper ram end  84  and is initially secured to the central mandrel  12  by a frangible shear pin  86 .  
         [0033]      FIGS. 9A and 9B  depict an alternative construction for a packer assembly  10 ′ that features an alternate exemplary release sub mechanism. The exemplary packer assembly  10 ′ is identical to the exemplary packer assembly  10  in all respects, except where noted. A release sub  66 ′ is used in place of the release sub  66  described previously. The alternative release sub  66 ′ is illustrated apart from other components in  FIGS. 10, 11 , and  12 . The alternative release sub  66 ′ features an annular body  68 ′ with an axially-extending wedge-shaped expander as the releasing portion  70 ′.  FIG. 9B  illustrates the releasing portion  70 ′ proximate the body lock ring  60 . As illustrated in  FIGS. 9B and 10 , the releasing portion  70 ′ features converging side edge surfaces  90 ,  92 , which will adjoin diverging side edge surfaces  94 ,  96  of the split  61  on the body lock ring  60 . As the release sub  66 ′ is moved axially upwardly (in the direction of arrow  94  in  FIG. 9B ), the converging side surfaces  90 ,  92  will urge the split  61  to open wider, thereby increasing the diameter of the body lock ring  60 .  
         [0034]     In general, as is well known, the packer assembly  10  is disposed within a wellbore upon a production tubing string so that an annulus is defined between the packer assembly  10  and the wall of the surrounding wellbore. The packer assembly  10  may be releasably set against the borehole wall, as will be described. Initially, the packer assembly  10  is run into the wellbore in the position shown in  FIGS. 2A and 2B . A plug or ball (not shown) of a type known in the art, is dropped into the flowbore  14  and becomes seated upon a ball seat (not shown) within the production string at some point below the packer assembly  10 , thus closing off the flowbore  14  to fluid flow. Fluid pressure within the flowbore  14  is increased at the surface of the well, and pressurized fluid enters the upper hydraulic chamber  48  via the fluid communication port  50  in the central mandrel  12 . Upon application of a sufficiently high amount of fluid pressure within chamber  48 , the shear pin  36  will break, and the setting piston  32  will be moved upwardly with respect to the central mandrel  12 . Due to the interconnection of the bridge sleeve  38  to the setting piston  32  and body lock ring housing  42 , the body lock ring housing  42  and body lock ring  60  are moved upwardly with respect to the central mandrel as well. The ratchet engagement of the inner ratchet surface  62  with the outer surface  64  of the central mandrel  12  secures the body lock ring  60  in an axially upper position, as shown in  FIGS. 3A and 3B . At this point, the packer element  30  and slip elements  26 ,  28  are set within the wellbore. Fluid pressure within the flowbore  14  and upper hydraulic chamber  48  may be reduced at this point, since the packer  30  and slip elements  26 ,  28  will be retained in their set positions by the ratcheted engagement of the body lock ring  60  with the central mandrel  12 .  
         [0035]     When it is desired to unset the packer element  30  and slip elements  26 ,  28 , hydraulic fluid is flowed through the inlet port  80  and into the lower hydraulic chamber  79 . This is typically accomplished using a wireline-run device known as a punch tool, or punch communication tool. The punch tool (not shown) is run into the flowbore  14  on wireline and seated into a punch nipple (also not shown) that is incorporated into the tubing string, in a manner that is known in the art. The punch tool includes a radially outwardly-directed penetrator, and jarring force on the wireline will cause the penetrator to move radially outwardly and penetrate the central mandrel  12  proximate the inlet port  80 . When this occurs, a flowpath is created into the lower hydraulic chamber  79 , allowing hydraulic fluid to be flowed from the surface into the chamber  79  via the punch tool. Other means known in the art for transmitting hydraulic fluid from the surface into the chamber  79  may also be used to pressurize the chamber  79 .  
         [0036]     As the lower hydraulic chamber  79  is pressurized, the release sleeve assembly  74  is actuated. The shear pin  86  is broken, and the release sleeve  82  is moved axially upwardly with respect to the central mandrel  12 . The ram end  84  of the release sleeve  82  then abuts the lower end of the release sub  66  (or  66 ′). The shear pin  57  that secures the release sub  66  (or  66 ′) to the release sub housing  54  is then broken, and the release sub  66  (or  66 ′) is moved axially upwardly with respect to the central mandrel  12 . The release portions  70  (or  70 ′) of the release sub  66  (or  66 ′) will then cause the ratchet connection between the body lock ring  60  and the central mandrel  12  to be disengaged. Ramped surfaces  72  of release portions  70  will slide beneath the inner surface  62  of the body lock ring  60  and thereby release the ratcheted engagement with the outer surface  64  of the central mandrel  12 . The body lock ring  60  will also be expanded radially, permitting it to slip axially with respect to the central mandrel  12 . If, alternatively, the release sub  66 ′ is used, the side edge surfaces  90 ,  92  of the releasing portion  70 ′ will contact and engage the side edge surfaces  94 ,  96  of the body lock ring  60  and, in the manner of a wedge, will expand the gap  61  of the body lock ring  60 . The body lock ring  60  will be expanded radially, and the ratcheted engagement between the inner surface  62  of the body lock ring  60  with the outer surface  64  of the central mandrel will be disengaged. In both cases, the body lock ring  60  will be released from engagement with the central mandrel  12 , as depicted in  FIG. 4A  (for release sub  66 ).  
         [0037]     Following mechanical release of the body lock ring  60  from the central mandrel  12 , the packer  30  and slip elements  26 ,  28  are then released from their set position by reducing fluid pressure within the lower hydraulic chamber  79 . This is accomplished from the surface of the well. When fluid pressure within the lower hydraulic chamber  79  is reduced, the components that are axially compressing the picker  30  and slip elements  26 ,  28  are moved axially downwardly with respect to the central mandrel  12 . The setting piston  32 , bridge sleeve  38 , body lock ring housing  42 , body lock ring  60 , release sub housing  54 , release sub  66  (or  66 ′), and release sleeve  82  are all shifted downwardly to the position illustrated in  FIGS. 5A and 5B . The tubing string may then be withdrawn from the wellbore to remove the packer assembly  10 .  
         [0038]     Turning now to  FIGS. 14A and 14B , there is illustrated the lower portions of a packer assembly  10 ″ having an alternative mechanism for releasing the body lock ring  60 . Except where indicated otherwise, the structure and function of the packer assembly  10 ″ is the same as that of packer assemblies  10  and  10 ′ described earlier. In the packer assembly  10 ″, however, release sleeve  82  is moved upwardly to release the body lock ring  60  by mechanical, rather than hydraulic actuation. The inner mandrel  12 ′ is made up of two tubular portions  12 ′A and  12 ′B, which are interconnected by threading 12° C. The inner mandrel  12 ′ contains a radially enlarged sleeve housing  100  within which annular shifting sleeve  102  is reciprocally disposed. The mandrel  12 ′ also has at least one axially elongated slot  104  disposed therein. A plate  106  is disposed through the slot  104  and is fixedly secured to the outer radial surface  108  of the shifting sleeve  102  as well as to sliding release sleeve  110 , which lies radially outside of the mandrel  12 ′. It is noted that the plate  106  is capable of axial movement within the slot  104  between a lower end  104 A and an upper end  104 B. The shifting sleeve  102  presents a radially interior engagement profile  112 . The release sleeve  110  is secured by a shear pin  114  to the inner mandrel  12 ′, and the upper end of the release sleeve  110  is in fixedly engaged contact with the release sub  66 ″ via a locking ring  116  that has inner and outer toothed engagement surfaces  118 ,  120 , respectively. The inner toothed engagement surface  118  fixedly interlocks with a complimentary outer toothed surface  122  on the release sub  66 ″. The outer toothed engagement surface  120  interlocks with a complimentary toothed surface  124  on the release sleeve  110 . As a result of these interlocking engagements, upward movement of the release sleeve  110  will result in upward movement of the release sub  66 ″.  
         [0039]     In this embodiment, the release sub  66 ″ is slightly modified from the designs previously described. As illustrated in  FIG. 14A , the release sub  66 ″ includes an extended tubular lower extension  126 , which carries the toothed surface  124 . The release sub  66 ″ may carry either of the engagement portions  70  or  70 ′ described earlier in order to release the body lock ring  66 .  
         [0040]     In order to release the body lock ring  60  from engagement with the inner mandrel  12 ′, a shifting tool, shown schematically at  130  in  FIG. 14B , is lowered into the flowbore  14 . The shifting tool  130  has an engagement profile  132  that is complimentary to the engagement profile  112  of the shifting sleeve  102 . Typically, the engagement profile  132  of the shifting tool  130  is formed into a colleted end of the shifting tool  130  so that the two profiles  132 ,  112  may snap together into an interlocking engagement when the shifting tool  130  is brought into contact with the shifting sleeve  102 . Once the two profiles  132 ,  112  are brought into engagement, the shifting tool  130  can be moved upwardly, thereby sliding the shifting sleeve  102  upwardly as well. As the shifting sleeve  102  is moved upwardly, the plate  106  moves upwardly within the slot  14 , in the direction of arrow  134 . Due to the fixed connection of the plate  106  with the release sleeve  110 , the release sleeve  110  is also moved upwardly, along with the release sub  66 ″, which, in the manners described previously, will engage and release the body lock ring  60 .  
         [0041]     It can be seen that the invention provides a novel method of releasably setting and then unsetting a packer assembly within a wellbore. The invention also provides a novel packer assembly and system.  
         [0042]     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.

Summary:
A releasable packer device and a method for selectively releasing a packer assembly from a set position in a wellbore. A packer assembly is described that incorporates a split body lock ring that is in ratcheting engagement with a central mandrel to secure the packer elements in a set position. In addition, there is a mechanical means for releasing the body lock ring from its locking position to an unlocked position. The body lock ring is released by radially expanding the ring by urging an axially-movable release sub with a releasing portion into contact with the body lock ring to unseat the ratcheting mechanism that retains the packer assembly in its set position.