Abstract:
A selectively released well packer is set between a pair of anchor shoe assemblies. Each assembly comprises a tubular setting sleeve having finger projections meshed with an anchor shoe cage. Wicker shoes are confined by the shoe cage. The packer seal and shoes are set by an axial translation of one shoe cage toward the other driven by a hydraulic sleeve piston. The packer is released by cutting the mandrel and pulling up on the tubing string. The uphole shoe cage is secured to the mandrel with limited axial freedom. Upward translation of the uphole portion of the severed mandrel therefore disengages the uphole anchor shoes and the packer seal. A buttress thread section of the mandrel engages a corresponding thread on the downhole setting sleeve to sequentially release the downhole anchor shoe.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and apparatus for producing valuable minerals from the earth. More particularly, the invention relates to an apparatus and method for setting pipe anchors to secure the position of downhole well tools such as annulus packers and subsequently releasing the tool for removal from the well. 
     2. Description of Related Art 
     Downhole well tools most commonly used to secure pipe or another tool such as an annulus packer to the inside wall of a wellbore casing are frequently characterized as “slips”. Characteristically, a slip comprises a plurality of radially expansible elements known to the art as a “wickers.” Traditionally, a plurality of wickers are distributed circumferentially around a cylindrical mandrel. By some means, the wickers are longitudinally secured to the mandrel, but radially free to at least limited expansion from the mandrel outside diameter. The inside wall engagement surfaces of a wicker are serrated with numerous penetrating tooth points or parallel rows of cutting edges. The wicker teeth or edges are of extremely hard material and are cut sharply for penetration into the steel casing wall surface. The wicker underside is ramped to cooperate with a conical slip face. The conical slip face is a circumferential surface on a tubular sleeve. By one of various means, the tubular sleeve is displaced axially along the mandrel surface relative to the longitudinally fixed wicker to wedge the conical slip face under the wicker and against the underside ramp. As the conical slip face advances axially along the mandrel, the wicker body is forced radially outward to press the serrated tooth edges into the inside wall of the casing thereby clamping the wickers and mandrel to the casing, for example. The mandrel is frequently secured to a tubular workstring such as production tubing or drill pipe but may also be wireline deployed. 
     Slips used in conjunction with annulus packers are frequently arranged in pairs. One or more slip sets are above the packer and one or more are below the packer. Distinctively, the wickers of the respective slips are biased in opposite directions. For example, the bottom wickers may be biased to cut more deeply into the casing wall if uploaded. Cooperatively, the upper slips may be biased to cut more deeply into the casing wall if downloaded. Hence, longitudinal movement of the packer along the casing bore, for example, is resisted in both directions. However, utility of this nature requires that the several tools be deployed sequentially. For example, a packer unit may comprise four distinct tools: (1) a debris barrier, (2) an upper slip set, (3) a lower slip set, and (4) a packer sleeve. When the packer unit is located at the desired setting position, a predetermined deployment sequence may require that the debris barrier is first deployed. Next, the procedure may specify engagement of the upper slip set to anchor the unit to the casing wall in support of the workstring weight. Third, the packer sleeve is inflated/expanded radially outward to pressure seal the annulus between the inside casing wall and the outer tool string wall. Finally, the lower slip is set to oppose any possible downhole pressure lifting of the work or production string. 
     Should, by error or accident, either or both slips be set prematurely, the location of the packer may be incorrect or the integrity of the packer seal may be compromised. To mechanically order the deployment sequence of slips and other well tools, mechanisms such a shear pins, shear rings, keys and J-slots have been used with limited success. However, these devices require that a channel of one form or another be cut into the tool mandrel to such depth as to encroach upon the ultimate tool strength. For example, a shear ring groove turned into the tubular wall of a slip mandrel may reduce the cross-sectional diameter by as much as 0.200 in. When translated to the loss of mandrel tensile strength, this 0.200 in. is significant. 
     In some cases, it is necessary to recover the tools set by a multiple step sequence. In those cases, recovery requires that the sequence be substantially repeated in the same order as that required by the setting. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is a slip setting system that may be sequenced into and out of engagement with a well wall or pipe. 
     Another object of the invention is a slip system that may be selectively programmed for the order of tool engagement and disengagement. 
     An additional object of the invention is a method and apparatus for releasing a downhole pipe anchor. 
     A further object of the invention is a method and apparatus for rectifying movement of a packer slip element along the packer mandrel. 
     These and other objects of the invention as will become evident from the following description of the preferred invention embodiments are served and accomplished by a well wall anchor having a reversible deployment mechanism. The well anchor comprises a tubular wicker shoe cage having a sliding fit over a tubular tool mandrel. The shoe cage has plurality of shoe retaining slots around the cage circumference for retaining a plurality of wicker shoes. A conical slip face is carried by an anchor actuating sleeve having collet fingers projecting axially from the slip face. The collet fingers are secured to the cage by calibrated shear pins that fail within a relatively narrow but predetermined load range. The anchor wicker shoes include retainer blocks that mesh with the shoe retaining slots in the shoe cage. An inside surface of the wicker shoes, opposite from the wicker teeth, is ramped to serve as a slip face. The wicker shoe slip face is aligned in juxtaposition with the conical slip face. The shear pins fail upon sufficient axial compression between the collet sleeve and the wicker shoe cage. The wicker expansion cone may advance against the wicker ramps to expand the wicker shoes radially for engagement of the wicker teeth with the well casing wall. 
     The combination packer and anchor is assembled over a tubular mandrel having two fixed reference structures. The upper reference structure is the mounting collar for a debris barrier. The second reference structure is a ring piston that is structurally secured to the mandrel. The radially expansible elements comprising a debris barrier, the packer sealing sleeve and upper and lower slip anchors are operatively slidable over the mandrel between the two reference structures. 
     The ring piston cooperates with a double acting cylinder to axially compress the radially expandable elements of the packer. Work string bore pressure applied through a mandrel orifice into a cylinder having the ring piston as one head and a mandrel slide ring as the other head drives the cylinder against the expandable packer elements. The expandable elements are consequently compressed against the upper reference structure and expanded. These elements expand sequentially in a predetermined order as determined by calibrated shear fasteners and the relative dimensions of axial shift channels. First, the debris barrier expands to shield the lower tools from additional debris interference. Next, the upper anchor is expanded when the calibrated shear fastener between the wicker shoe cage and the actuating sleeve fails. As the wicker shoes expand and the wicker points penetrate the well wall, the compressive load along the mandrel is transferred to the well wall. Subsequently, the expandable seal sleeves of the packer are extended against the well walls. Finally, the calibrated shear fastener between the wicker shoe cage and the actuating sleeve for the lower anchor fails resulting in the lower anchor set. 
     For collapse of the expandable elements and removal of the packer from the well, the mandrel is cut by any of well known means. Initially, following the cut of the mandrel, tension is drawn on the workstring from the surface to the effect of sliding the uphole portion of the cut mandrel under the anchors and packer. However, the anchor collar of the debris barrier is secured to the mandrel surface and does not slide. Hence, the upper end of the debris barrier sleeve is retracted from the well wall as the anchor collar is displaced axially from the downhole compression collar. 
     At the location where the debris barrier sleeve is completely retracted, the compression collar engages and abutment surface of the limit ring that is secured to the mandrel. The compression collar is rigidly secured to the upper caging ring and therefore draws the caging ring with it. In turn, limit walls on the wicker shoe retaining slots engage the wicker shoe blocks. Further uphole movement of the mandrel draws the uphole wicker shoes off the conical slip face thereby permitting the shoes to withdraw from engagement with the well wall. 
     The caging ring also engages the retaining blocks on the collet fingers to pull the collet sleeve and attached compression cup away from the packer seal assembly thereby decompressing the packer seal. 
     Further uphole displacement of the mandrel brings a section of buttress threads along the mandrel surface into engagement with meshing buttress threads on the collet cone sleeve for the lower anchor. Such meshing provides a positive engagement pickup on the sleeve thereby pulling the conical slip face away from the lower wicker shoe slip face. Hence, the lower anchor disengages from the well wall. The packer and anchor assembly may now be removed from the well or repositioned to a different depth. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
     FIGS. 1A through 1D illustrate, in axial quarter section, the invention in operative assembly as it is initially lowered into a wellbore and before actuation of any elements. 
     FIGS. 2A through 2D illustrate, in axial quarter section, the invention in operative assembly as it is actuated to set the packer sealing sleeve and the anchor wickers. 
     FIGS. 3A through 3D illustrate, in axial quarter section, the invention in operative assembly as it is actuated to remove the assembly from sealing sleeve and anchor wickers from the well. 
     FIG. 4 is an exploded pictorial of the present well tool anchor. 
     FIG. 5 is an enlarged, quarter section detail of the present well tool upper anchor in the run-in assembly state. 
     FIG. 6 is an enlarged, quarter section detail of the present well tool upper anchor in the set assembly state. 
     FIG. 7 is an enlarged, quarter section detail of the present well tool lower anchor in the run-in assembly state. 
     FIG. 8 is an enlarged, quarter section detail of the present well tool lower anchor in the set assembly state. 
     FIG. 9 is an elevation view of the well tool anchor setting sleeve. 
     FIG. 10 is an end elevation view of the well tool anchor setting sleeve. 
     FIG. 11 is an axial section view of the lower well tool anchor setting sleeve along cutting plane  11 — 11  of FIG.  10 . 
     FIG. 12 is an end elevation view of the body lock ring element of the lower well tool setting sleeve. 
     FIG. 13 is an axial section of the body lock ring element of the lower well tool setting sleeve along cutting plane  13 — 13  of FIG.  12 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is disclosed and described herein in the preferred embodiment context of a combined wellbore packer and workstring anchor. In this embodiment, both tools are activated hydraulically and deactivated mechanically. FIGS. 1 through 3 illustrate the invention in axial quarter section. Since the tool is long and slender, it is illustrated in four axially broken segments. For the present purposes, the left edge of the drawing frame is taken as the uphole reference direction. Accordingly, FIG. 1D illustrates the bottom-hole interface between the present tool mandrel  12  and the well work string of pipe  10  below the mandrel  12 . FIGS. 1A through 1D illustrate the assembly in the “run-in” state with the wellbore anchors and packer sleeve retracted. FIGS. 2A through 2D illustrate the “set” status of the anchors and packer. FIGS. 3A through 3D illustrate the deactivated status of the tool elements as they would be when the tools are withdrawn from the well. 
     With initial reference to the tool bottom and the work string  10  interface as best illustrated by FIG. 1D, the tool mandrel  12  is assembled by threads  13  to the work string box sleeve  11 . Also secured to the work string box sleeve  11  by assembly threads  21  is a lower cylinder wall  20 . The cylinder wall  20  extends upwardly from the box sleeve  11  and concentrically around the lower end of the mandrel  12  to confine a smooth wall, annular space  24  between the inside surface of the wall  20  and the outside surface of the mandrel  12 . Near the box sleeve  11 , the mandrel is perforated by one or more fluid flow orifices  22  for transfer of fluid pressure from within the mandrel center bore into the annular space  24 . 
     Additional features of the mandrel  12  include an external ring piston  16  secured to the mandrel O.D. by assembly threads  17 . On the uphole side of the ring piston  16 , the mandrel wall is again perforated by fluid flow orifices  14 . At the upper end of the mandrel  12  is a debris barrier  80  secured to the mandrel O.D. by assembly threads  86  between the mandrel  12  and an anchor collar  84 . At carefully selected position between the anchor collar  84  and the ring piston  16 , is a circumferential band of buttress thread  19  having a thread length T along the mandrel length. The buttress thread  19  depth is preferably as shallow as the specific application will allow for intrusion of annulus section thickness. Those of skill in the art know that in many cases, the ultimate tensile strength of the tool is determined by the undisturbed section thickness of the mandrel at this point. As a representative example, therefore, the buttress threads may only be about 0.017 in. deep into the outer surface of the mandrel. A retainer ring slot to accomplish the same purpose would need a minimum radial depth of about 0.100 in. and provide only a single engagement face. Hence, the buttress threads require only 0.034 in. material strength loss on the diameter whereas a C-ring slot may require 0.200 in.: a 0.166 in. advantage. 
     In sliding assembly along the mandrel outside surface are, for example, a debris barrier, packer seal elements and position anchors. These sliding elements are preferably displaced by an axial force actuator such as hydraulic piston elements. There are numerous design options for fluid power applications. The particular arrangement selected for the present invention, however, compresses the sliding elements between a sleeve ram  40  and the lower abutment ridge  47  on the mandrel. With respect to FIGS. 1B,  1 C and  1 D, a sleeve ram  40 , having a close sliding fit around the mandrel O.D. above the mandrel piston  16 , is in fixed, threaded assembly by threads  41  with an upper cylinder wall  30 . The inside diameter surface of the upper cylinder wall  30  has a sliding seal fit with the O.D. of the mandrel piston  16 . At its lower end, the upper cylinder wall  30  has a threaded assembly by threads  31  with a lower piston  26 . The lower end of the upper cylinder wall  30  is also secured to the upper end of the lower cylinder wall  20  by means of a calibrated shear fastener  33 . The lower piston  26  has a sliding seal fit relationship within the annular space  24  to provide a power cylinder displacement force against the end of the piston  26  by fluid pressure admitted from the mandrel bore through the orifice  22 . 
     With respect to FIGS. 1B and 8, the sleeve ram  40  abuts the lower anchor mechanism  50 . The lap sleeve  42  of the ram  40  overlays the lap sleeve  143  of a slip shoe retainer cage  52 . The lapping sleeves  42  and  143  are secured together structurally by calibrated shear pins  43 . 
     The lower tubular anchor mechanism  50  is illustrated in detail by FIGS. 7 through 11 as well as FIG.  1 B. Four basic components of the anchor mechanism include the slip shoe retainer cage  52 , the collet cone  54 , the wicker shoe  56  and the calibrated shear fasteners  43 . The lower slip shoe retainer cage  52  is substantially identical to the upper slip shoe retainer cage  72  illustrated pictorially by FIG.  4 . Correspondently, the lower cage  52  is a tubular element having a plurality of retainer slots  141  distributed around the perimeter: four slots, for example. Between the slots are collet bosses  142  having detent pockets defined within perimeter walls  146 . The ends of the collet bosses are rigidified by circumferential webs  140 . 
     The lower collet cone  54  includes a basic sleeve section  130  that tapers along a conical slip face  132  to the base of collet fingers  57  as clearly shown by FIGS. 9 and 11. The distal ends of the collet fingers have integral retainer blocks  134  that mesh with detents on the retainer cage. The retainer cage detents are defined by retainer walls  146  that circumscribe the detent area. For well run-in, the collet fingers are positioned to mesh the retainer blocks  134  with the detent areas of the retainer cage  52  and secured by calibrated shear fasteners  55 . The longitudinal dimension of the detent area is greater than that of the collet finger blocks for several reasons. First, sufficient finger block displacement clearance along the detent is necessary to accommodate a shear failure of the fastener  55 . Additionally, the geometry of the slip slope and the required radial displacement of the wicker shoes are essential design factors. Peripheral confinement of the retainer blocks  134  by the retainer walls  146  prevents complete disassembly. 
     The wicker shoes  56 , shown by FIGS. 1B,  7  and  8 , are meshed loosely between the collet fingers  57  with the slip face  122  juxtaposed against the collet cone slip face  132 . The wicker shoe retainer blocks are meshed loosely within the cage retainer slots  141  and the wicker shoe straps  126  extends between the mandrel  12  and the circumferential web  140  of the retainer cage. The wicker shoes are substantially immobile laterally but have free movement, to a limit, radially. 
     With respect to FIG. 11, the upper end of the collet cone sleeve  130  carries first, assembly threads  69  for assembly with the packer end cups  68 . Along a deeper counterbore from the sleeve end, internal buttress threads  131  are cut to mesh with cooperating external threads  135  on the body lock ring  58 . 
     The body lock ring  58 , shown by FIGS. 12 and 13, also includes internal buttress threads  137  for meshing with the buttress threads  19  around the mandrel  12 . The lock ring is also split as at  59  of FIG. 12 to facilitate radial collapse of the ring. Materially, the body lock ring  58  is resilient as needed to expand or contract circumferentially. When the collet sleeve  130  is sliding along the mandrel surface, the lock ring I.D. is less than when the lock ring buttress threads  137  are meshed with the mandrel buttress threads  19 . 
     The sealing elements of the packer  60  are rubber or elastomer sleeves that are dimensionally compressed to seal the annular space between the mandrel  12  and the internal wall surface  15  of the well which may be production casing or raw, wellbore walls. In this case, there are three rubber sleeves including a center sleeve  62  that is separated longitudinally from a flanking pair of end sleeves  64  by stabilizer rings  66 . 
     The collet cone  74  of the upper anchor  70  bears against the upper end cup  68  of the packer  60 . With respect to FIGS. 1A, and  4  through  6 , the collet cone  74  comprises a sleeve  100  having collet fingers  77  projecting longitudinally from the base of a conical slip face  102 . Retainer blocks  106  on the distal ends of the fingers  77  are meshed with the detents  94  in the bosses  92  of the upper cage ring  72 . The detents are defined by the perimeter wall  96 . The retainer blocks  106  are secured in meshed assembly with the cage detents  94  by shear fasteners  75 . The bosses  92  of the upper cage ring are laterally spaced by circumferential webs  90 . Approximately mid-length of the cage ring are four slots  91 , for example. Similar to the lower anchor  50 , the straps  116  of wicker shoes  76  mesh loosely under the cage web  90  with the shoe retainer block  114  meshed within the retainer slots  91  and the shoe slip face  112  juxtaposed with the conical slip face  102 . 
     The upper end of the upper cage ring  72  overlies the abutment ridge  47  that is a fixed reference point along the length of the mandrel. A compression collar element  88  of the debris barrier  80  is secured to the cage ring  72  by assembly threads  89 . The cage ring  72  is axially slidable over the limit ring  45  between upper and lower abutments  48  and  49 . 
     The anchor collar element  84  of the debris barrier  80  is secured to the mandrel  12  surface by assembly threads  86 . Secured between the anchor collar and the compression collar is an elastomer or rubber sleeve  82  that expands radially when the two collars are forced together. 
     The tool is lowered into a well in the mechanical status as described above with respect to FIGS. 1A through 1D. When located at the desired set position, the center bore of the mandrel  12  is pressurized from the surface with working fluid, which may, for example, be hydraulic oil or drilling fluid. Entering the expansion chambers  24  and  37  through the pressure orifices  22  and  14 , respectively, the lower piston  26  and sleeve ram  40  are displaced upwardly along the mandrel  12  by first shearing the fastener  33  between the lower cylinder wall  20  and the upper cylinder wall  30 . This initial movement is transferred along and through all of sliding elements of the tool to the compression collar  88  of the debris barrier  80  to first, extend the barrier sleeve  82  radially against the well wall. 
     When the abutment wall  49  engages the lower edge of the abutment ridge  47 , loading stress is focused upon the remaining shear fasteners. Fastener  75  between the upper anchor cage  72  and the collet finger  77  is calibrated as the second weakest fastener and fails next thereby allowing the upper anchor to collapse axially and the conical slip face  102  to be driven under the wicker shoe slip face  112 . Consequently, the wicker shoe  76  is displaced radially to drive the wickers  110  into the well wall  15 . 
     As the upper anchor  70  is set, the packer sealing elements  62  and  64  are compressed between the upper and lower collet sleeves and also expanded against the well wall  15 . The internal buttress threads  137  on the body lock ring  58  are not initially engaged with the corresponding threads  19  on the mandrel O.D. surface. Consequently, the lower collet cone  54  may be displaced along the mandrel surface to load compressively against the packer  60  until the calibrated shear force of fastener  55  is overcome. At that moment, the upper edge of the circumferential web  140  portion of the cage ring  52  engages the base of the wicker shoe to force the wicker shoe slip face upon the conical slip face  132  thereby expanding the wicker radially until the wicker teeth  120  penetrate the well wall  15 . Engagement of the buttress threads on the body lock ring  127  attached to the upper end of the lower cylinder wall  20  with the external buttress threads  129  on the lower piston  26  irreversibly secures the relative position. This completes the packer tool setting. 
     Removal of the tool from the well essentially requires the same sequence of that followed when setting the tool. Specifically, the debris barrier  80  and the upper anchor  70  is released followed by release of the packer seals  60 . Upon release of the packer seals, the lower anchor  50  is released. 
     The foregoing sequence is initiated by cutting the mandrel  12  in the approximate region of the cut line C—C illustrated by FIG.  2 D. This cut through the mandrel  12  tube into the lower cylinder space  24  between the upper end of the work string box sleeve  11  and the lower end of the lower piston  26  may be accomplished by any of several well known tools . 
     Following the mandrel  12  severance at C—C, tension is drawn on the mandrel  12  from the surface along the upper workstring to lift the mandrel relative to the packer and anchors. Predominantly, the mandrel slides under the packer and anchors. The anchor collar  84  for the debris barrier is secured to the mandrel  12  by threads  86 . Consequently, the anchor collar  84  moves with the mandrel  12  and pulls on the barrier sleeve  82  to retract it from the well wall. 
     As the barrier sleeve  82  reaches its extended limit, the upper abutment ridge  46  on the mandrel engages the abutment wall  48  on the compression collar  88 . Since the compression collar is assembled by threads  89  to the upper cage ring  72 , the connection with the upper cage ring draws the lower face of the retainer slot  91  against the upper wicker shoe retainer block  114 . This connection with the upper cage ring draws the lower face of the retainer slot  91  against the upper wicker shoe retainer block  114 . Additional pull of the mandrel after this engagement pulls the upper wicker shoe slip face  112  away from the conical slip face  102  of the upper collet cone  74  thereby disengaging the wickers  110  from the well wall  15 . The upper anchor  70  is now released. 
     At this point, retainer wall  96  on the upper cage ring has also engaged the retainer block  106  on the upper collet fingers  77 . Accordingly, after the wicker shoes are pulled away from the collet cone, the collet cone  74  and upper end cup  68  is pulled away from the packer  60  sealing sleeves. This removes the seal supporting compression on the sealing sleeves thereby withdrawing the packer. 
     Near the expanded limit of the foregoing train of connections, the buttress thread section T of the mandrel is pulled into engagement with the inner buttress threads  137  on the body lock ring  58 . This engagement pulls the conical slip face  132  on the lower collet sleeve  130  away from the lower wicker shoe slip face  122  thereby disengaging the lower wickers  120  from the well wall  15 . 
     When the lower anchor  50  is released, the entire weight of the lower work string is  10  is transferred to the lower anchor assembly via the upper cylinder wall  30 , the sleeve ram  40  to the cage ring  52 . Given the limited support surface of these components, prudence suggest that the lower workstring weight should be shifted to more substantial structure. To this end, the retainer wall  146  on the lower cage ring  52  engages the retainer block  134  on the lower collet finger  57 . This engagement provides a structural loading train between the buttress threads  19  on the mandrel to the calibrated shear fastener  43  sleeve ram  40  and the lap sleeve  143  on the cage ring  52 . If the lower workstring weight is sufficient to shear the calibrated fasteners  43 , the workstring weight load is shifted to mandrel piston  16 . 
     All elements of the tool assembly are now released from the well wall  15  thereby permitting the workstring  10  to be removed from the well or repositioned to a different depth. 
     Although our invention has been described in terms of specified embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.