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TECHNICAL FIELD OF THE INVENTION 
     This invention relates, in general, to tools and equipment for completing a subterranean well that traverses a hydrocarbon bearing formation and, in particular, to a retrievable well packer for releasably sealing the annulus between a tubing string and the well casing using a collet member to positively operate a support ring. 
     BACKGROUND OF THE INVENTION 
     In the course of treating and preparing a subterranean well for production, a well packer is run into the well on a conveyance such as a work string, a production tubing, a wireline or the like. The purpose of the packer is to support production tubing and other completion equipment, such as a sand control screen adjacent to a producing formation, and to seal the annulus between the outside of the production tubing and the inside of the well casing to block movement of fluids through the annulus past the packer location. 
     Typically, the packer is provided with an upper and a lower set of anchor slips having opposed camming surfaces which cooperate with complementary opposed wedging surfaces, whereby the anchor slips are outwardly radially extendable into gripping engagement against the well casing bore in response to relative axial movement of the wedging surfaces. The packer also carries annular seal elements which are expandable radially into sealing engagement against the bore of the well casing in response to axial compression forces. The longitudinal movement of the packer components which set the anchor slips and the sealing elements may be produced, for example, hydraulically or mechanically. 
     After the packer has been set within the well casing, it should maintain its sealing and griping engagement upon removal of the hydraulic or mechanical setting force. Additionally, it is essential that the packer remain locked in its set configuration while withstanding hydraulic pressures applied externally or internally from the formation and/or manipulation of the tubing string and service tools without unsetting the packer or interrupting the seal. This is made more difficult in deep wells in which the packer and its components are subjected to high downhole temperatures and high downhole pressures. 
     Moreover, the packer should be able to withstand variation of externally applied hydraulic pressures at levels such as 10,000 psi in both directions, and still be retrievable after such exposure for long periods of time such as 10 to 15 years or more. After such long periods of extended service under extreme pressure and temperature conditions, it is desirable that the packer be retrievable from the well by appropriate manipulation of the tubing string, such as a quarter turn of rotation, to cause the packer to be released and unsealed from the well casing, with the anchor slips and seal elements being retracted sufficiently to avoid becoming stuck within wellbore restrictions. 
     It has been found, however, that in certain packer deployments, the deviation of the wellbore may cause the packer to rest on the inside of the well casing. In these deployments, it is difficult to properly set the upper anchor slips due to a lack of cooperation of the opposed camming surfaces of the upper anchor slips with the complementary opposed wedging surfaces as the force of gravity cannot fully act on the support ring. Therefore, a need has arisen for a retrievable packer that is capable of being properly deployed in a well wherein the packer rests on the inside of the well casing. A need has also arisen for such a retrievable packer that is capable of withstanding the extreme downhole pressures and temperatures without unsetting the packer or interrupting the seal. Further, a need has arisen for such a retrievable packer that is capable of being set, unset and reset in the well casing and remaining in the well for long periods of extended service then be retrieved from the well. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein comprises a retrievable packer that is capable of being properly deployed in a well wherein the packer rests on the inside of the well casing. The retrievable packer of the present invention is also capable of withstanding the extreme downhole pressures and temperatures without unsetting the packer or interrupting the seal. In addition, the retrievable packer of the present invention is capable of being set, unset and reset in the well casing and remaining in the well for long periods of extended service and later being retrieved from the well. 
     The retrievable packer of the present invention comprises a packer mandrel that is adapted for connection to a tubing string. A seal assembly is disposed about the packer mandrel. The seal assembly has a running position, wherein the seal assembly is not in sealing engagement with the well casing, and a sealing position, wherein the seal assembly is in sealing engagement with the well casing. A first slip wedge is slidably disposed about the packer mandrel. The first slip wedge is operably associated with the slip assembly and may include plurality of wedge sections. 
     The retrievable packer of the present invention also includes a support ring that is slidably disposed about the packer mandrel. The support ring is operably positionable at least partially between the first slip wedge and the packer mandrel to prevent radially inward travel of the first slip wedge and to apply an axial force on the first slip wedge to operate the seal assembly from the running position to the sealing position. A slip assembly is slidably disposed about the support ring. The slip assembly is operably associated with the first slip wedge and has a running position, wherein the slip assembly is not in gripping engagement with the well casing, and a gripping position, wherein the slip assembly is radially outwardly extended by contact with the first slip wedge into gripping engagement with the well casing. 
     In addition, the retrievable packer of the present invention includes a collet member that is slidably disposed about the packer mandrel. The collet member has a first operating position, wherein the collet member applies an axial force on the support ring to positively position the support ring at least partially between the first slip wedge and the packer mandrel, and a second operating position, wherein the collet member applies an axial force on the slip assembly to operate the slip assembly from the running position to the gripping position. 
     The seal assembly of the retrievable packer of the present invention may include a mandrel element slidably disposed about the packer mandrel, a second slip wedge slidably disposed about the mandrel element and at least one seal element disposed about the mandrel element such that a compressive force between the mandrel element and the second slip wedge radially expands the seal element. Likewise, the slip assembly of the retrievable packer of the present invention may include a slip carrier and a plurality of slips that are radially outwardly extendable, by contact with the first slip wedge, into gripping engagement with the well casing. 
     The collet member may include a plurality of collet fingers that are radially retracted when the collet member is in the first operating position and radially expanded when the collet member is in the second operating position. In addition, the collet member may comprise a spring cover. 
     It should be noted that the retrievable packer of the present invention may be set, unset and reset any number of times. Specifically, the seal assembly of the retrievable packer of the present invention can be repetitively operated between its running position and its sealing position without removing the packer from the well casing. Likewise, the slip assembly of the retrievable packer of the present invention can be repetitively operated between its running position and its gripping position without removing the packer from the well casing. 
     In another aspect, the present invention comprises a method of setting a retrievable packer to establish a sealing and gripping engagement with a well casing. This method includes lowering the packer into the well casing to a selected location, axially shifting a packer mandrel within the packer, positively positioning a support ring at least partially between a first slip wedge and the packer mandrel by applying an axial force on the support ring with a collet member, operating a seal assembly from a running position wherein the seal assembly is not in sealing engagement with the well casing to a sealing position wherein the seal assembly is in sealing engagement with the well casing, repositioning the collet member to apply the axial force on a slip assembly and operating the slip assembly from a running position wherein the slip assembly is not in gripping engagement with the well casing to a gripping position wherein the slip assembly is radially outwardly extended by contact with the first slip wedge into gripping engagement with the well casing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
     FIG. 1 is a schematic illustration of an offshore oil and gas platform operating a pair of retrievable packers of the present invention; 
     FIGS. 2A-2C are successive axial views in quarter section of a retrievable packer of the present invention; and 
     FIGS. 3A-3C are quarter sectional views of a retrievable packer of the present invention in its various positions. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention. 
     Referring initially to FIG. 1, a pair of retrievable packers operating from an offshore oil and gas platform are schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over a submerged oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to wellhead installation  22  including blowout preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as work string  30 . 
     A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is cemented within wellbore  32  by cement  36 . Work string  30  includes various tools including sand control screens  38 ,  40 ,  42  positioned in an interval of wellbore  32  adjacent to formation  14  between retrievable packers  44 ,  46  of the present invention. 
     Importantly, even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the retrievable packers of the present invention are equally well-suited for use in deviated wells, inclined wells or horizontal wells. Also, even though FIG. 1 depicts an offshore operation, it should be noted by one skilled in the art that the retrievable packers of the present invention are equally well-suited for use in onshore operations. 
     Referring now to FIG. 2, including FIGS. 2A-2C, therein is depicted a retrievable packer of the present invention that is generally designated  50 . Packer  50  includes a substantially tubular, longitudinally extending mandrel  52  having a substantially cylindrical bore  54  defining a longitudinal production flow passageway. Mandrel  52  is coupled to a substantially tubular, longitudinally extending section of tubing  56  by a coupling  58 . Coupling  58  includes a radially outwardly extending shoulder  60 . Positioned around mandrel  52  is a spiral wound compression spring  62  that is operated against shoulder  60  of coupling  58 . 
     Slidably positioned around mandrel  52  is a collet member  64 . In the illustrated embodiment, collet member  64  includes eight collet fingers  66 . As should be apparent to those skilled in the art, collet member  64  may have a variety of configurations including configurations having other numbers of collet fingers  66 , such configurations being considered within the scope of the present invention. In the illustrated embodiment, collet member  64  also includes a spring cover  68  that extends upwardly to cover a portion of spring  62 . It should be understood by those skilled in the art that collet member  64  could alternatively have a spring cover that entirely covers spring  62  or could have no spring cover associated therewith. Collet member  64  has an upper shoulder  70  that is in contact with the lower end of spring  62  such that spring  62  downwardly biases collet member  64 . 
     While packer  50  is being described using directional terms such as above, below, upper, lower, upward, downward and the like, it should be apparent to those skilled in the art that the use of such terms is in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. 
     Positioned around mandrel  52  in a groove  72  is a snap ring  74  that initially prevents collet member  64  from moving downwardly relative to mandrel  52 . A support ring  76  is slidably disposed around mandrel  52  below collet fingers  66  of collet member  64 . Support ring  76  has radially expanded end portion  78 . Slidably positioned around support ring  76  is a slip assembly  80 . Slip assembly  80  includes a slip carrier  82  and, in the illustrated embodiment, four radially extendable slips  84 . As should be apparent to those skilled in the art, slip assembly  80  may have a variety of configurations including configurations having other numbers of slips  84 , such configurations being considered within the scope of the present invention. Slips  84  each have a gripping outer surface for engaging and gripping the interior of the well casing in which packer  50  is disposed. Positioned around mandrel  52  in groove  86  is a snap ring  88  that initially prevents support ring  76  and slip assembly  80  from moving downwardly relative to mandrel  52 . 
     Slidably positioned around mandrel  52  at a preselected distance below support ring  76  and slip assembly  80  is a slip wedge  90 . In the illustrated embodiment, slip wedge  90  includes six wedge sections  92 . As should be apparent to those skilled in the art, slip wedge  90  may have a variety of configurations including configurations having other numbers of wedge sections  92 , such configurations being considered within the scope of the present invention. Wedge sections  92  each have a camming outer surface that will engage the inner surface of slips  84 , as explained in greater detail below. The interior surface of wedge sections  92  has a mating profile that matches the mating profile on the outer surface of support ring  76  such that support ring  76  can be received in the recess between wedges sections  92  and mandrel  52 , as explained in greater detail below. 
     Securably attached to slip wedge  90  and slidably positioned around mandrel  52  is a mandrel element  94 . In the illustrated embodiment, three compressible seal elements  96 ,  98 ,  100  are positioned around mandrel element  94 . Slidably and sealing positioned around mandrel element  94  below seal element  100  is a slip wedge  102  that has a camming outer surface. Collectively, mandrel element  94 , seal elements  96 ,  98 ,  100  and slip wedge  102  may be considered a seal assembly. As explained in greater detail below, when a compressive force is generated between mandrel element  94  and slip wedge  102 , seal elements  96 ,  98 ,  100  are radially expanded into contact with the well casing. Coupled to the lower end of mandrel element  94  and slidably positioned around mandrel  52  is a mandrel element extension  104 . 
     Slidably positioned around mandrel element extension  104  at a preselected distance below slip wedge  102  is a slip assembly  106 . Slip assembly  106  includes a slip carrier  108  and, in the illustrated embodiment, four radially extendable slips  110 . As should be apparent to those skilled in the art, slip assembly  106  may have a variety of configurations including configurations having other numbers of slips  110 , such configurations being considered within the scope of the present invention. Slips  110  have gripping outer surfaces for engaging and gripping the interior of the well casing in which packer  50  is disposed. Slips  110  each have an inner surface that engages the camming surface of slip wedge  102  as explained in greater detail below. 
     Positioned around mandrel  52  below slip assembly  106  is a drag block assembly  112 . Drag block assembly  112  includes a drag block mandrel  114 , a retainer  116  and four spring mounted drag blocks  118 . As should be apparent to those skilled in the art, drag block assembly  112  may have a variety of configurations including configurations having other numbers of drag blocks  118 , such configurations being considered within the scope of the present invention. Partially disposed within retainer  116  and slidably disposed around mandrel  52  is sleeve  120 . Sleeve  120  has a housing  122  positioned around its lower end with a spring  124  positioned therebetween. 
     The operation of packer  50  is now described. Once packer  50  is attached within a work string, including for example tubing section  56 , packer  50  is run downhole and located in the desired position with the well casing. A gripping and sealing relationship is established between the packer  50  and the well casing by mechanically shifting packer  50 . Specifically, mandrel  52  of packer  50  is moved downwardly relative to slip assembly  106 . Initially, slip wedge  102  travels with mandrel  52  until the camming surface of slip wedge  102  engage the inner surface of slips  110 , which causes slips  110  to move radially outwardly into gripping engagement with well casing  34 . 
     Referring in addition now to FIGS. 3A-3C, once slips  110  are set, mandrel  52  continues its downward travel which is now relative to not only slip assembly  106  but also to slip wedge  90 , mandrel element  94 , seal elements  96 ,  98 ,  100  and slip wedge  102 . At this time, collet member  64 , support ring  76  and slip assembly  80  continue to travel with mandrel  52  until the radially expanded end portion  78  of support ring  76  engages the inner surface of wedges sections  92  of slip wedge  90 . Specifically, as the bias force of spring  62  is acting downwardly on collet member  64 , collet fingers  66  positively operate against support ring  76  such that the radially expanded end portion  78  of support ring  76  slides between slip wedge  90  and mandrel  52 , as best seen in FIG.  3 B. 
     Continued downward travel of mandrel  52  now compresses seal elements  96 ,  98 ,  100  between mandrel element  94  and slip wedge  102  into a sealing engagement with well casing  34  due to the transmission of the spring force via collet member  64 , support ring  76  and slip wedge  90 . When the spring force reaches a sufficient level, for example, 50 to 75 percent of the maximum spring force, collet fingers  66  radially outwardly expand over the upper end of support ring  76  and come in contact with slip carrier  82 . As best seen in FIG. 3C, once collet fingers  66  contact slip carrier  82 , the spring force now downwardly operates on slip carrier  82  causing the inner surfaces of slips  84  to engage the camming surfaces of wedge sections  92  of slip wedge  90 , which causes slips  84  to move radially outwardly into gripping engagement with well casing  34 . In addition, the upper end of support ring  76  is contacted by snap ring  74 . This configuration of packer  50  represents the set position in which packer  50  has a sealing and gripping relationship with well casing  34 . 
     Importantly, it can be seen that due to the dual function of collet member  64  wherein the spring force of spring  62  is applied first to support ring  76  then to slip carrier  82 , support ring  76  is properly positioned between slip wedge  90  and mandrel  52  before slips  84  engage slip wedge  90 . This result is achieved regardless of the directional orientation of packer  50  as it does not rely on gravitational forces to position support ring  76  within slip wedge  90  but rather utilizes positive operation to assure proper positioning. 
     Once packer  50  is set within the well casing, packer  50  will provide its sealing and gripping functionality until it is desired to remove packer  50  from the well or reposition packer  50  within the well. The retrieval operation is initiated by rotating mandrel  52  a quarter turn which allows mandrel  52  to be moved upwardly. Specifically, this upward travel retracts collet member  64  which releases slips  84  from their gripping relationship with well casing  34 . Next, snap ring  74  contacts collet member  64  and snap ring  88  contacts support ring  76  causing collet fingers  66  to return to their radially contracted configuration and causing support ring  76  to retract from between slip wedge  90  and mandrel  52 . 
     This allows seal elements  96 ,  98 ,  100  to release from their sealing engagement with well casing  34 . Further upward travel of mandrel  52  allows slip wedge  102  to retract from slips  100 , which releases slips  110  from their gripping relationship with the well casing. Additional upward travel of mandrel  52  returns mandrel  52  to it initial configuration such that mandrel  52  may be retrieved to the surface or redeployed within the well following the setting procedure described above. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Summary:
A retrievable packer ( 50 ) for establishing a sealing and gripping engagement between a tubing string and a well casing ( 34 ) disposed in a wellbore is disclosed. The retrievable packer ( 50 ) comprises a collet member ( 64 ) that is slidably disposed about a packer mandrel ( 52 ). The collet member ( 64 ) has a first operating position wherein the collet member ( 64 ) applies an axial force on a support ring ( 76 ) to positively position the support ring ( 76 ) at least partially between a first slip wedge ( 90 ) and the packer mandrel ( 52 ) to set a seal assembly ( 96, 98, 100 ). In addition, the collet member ( 64 ) has a second operating position wherein the collet member ( 64 ) applies an axial force on a slip assembly ( 80 ) to set the slip assembly ( 80 ).