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PRIORITY CLAIM 
       [0001]    This application claims the benefit of Great Britain patent application no. GB 0906934.5 filed Apr. 23, 2009, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a fishing tool for milling and retrieving a packer from a casing in an oil or gas well and in particular to a fishing tool which combines milling, retrieval and debris management in a single tool. 
         [0003]    A packer is used to provide a seal within a casing of a well bore. When the seal is no longer required a milling and retrieval tool is typically used to remove the packer. These tools usually have an upper milling portion for milling or cutting through the slips which anchor the packer to the casing wall, and a lower attachment portion for picking up the remaining packer for transportation to the surface of the well. 
         [0004]    The milled cuttings from the packer are circulated out of the well bore by the standard circulation of fluid down through the work string and up the annulus between the tool and the casing wall. Mud or pills of high viscosity fluid are typically used to assist in this debris removal. 
         [0005]    As the debris is flushed up the outside of the tool, the packer can stick in the casing as the debris becomes trapped between the packer and the casing wall. When this occurs the packer can become disengaged from the retrieval tool and a further recovery procedure is required. 
         [0006]    It is object of the present invention to provide a packer milling and retrieval tool which collects the milled cuttings from a packer being retrieved. 
         [0007]    It is a further object of at least one embodiment of the present invention to provide a packer milling and retrieval tool that converts the flow from inside the work string to the outside of the work string and around the outside of the tool, so that milling cuttings are circulated up into the tool. 
       SUMMARY OF THE INVENTION 
       [0008]    According to a first aspect of the invention there is provided a packer tool comprising an upper milling portion, a lower attachment portion at least partially located within the upper milling portion, and a debris retainer for capturing milled cuttings within the tool. 
         [0009]    The upper milling portion may comprise:
       a sleeve which at least partially encloses the lower attachment portion such that an annular chamber is defined between the sleeve and the lower attachment portion; and   a mill provided on an open end of the sleeve.       
 
         [0012]    The sleeve may have a closed end remote from the open end, and the debris retainer may comprise a filter portion which permits fluid flow from the annular chamber to the exterior of the tool. 
         [0013]    The tool may further comprise one or more return flow ports which permit additional fluid flow from the annular chamber to the exterior of the tool. 
         [0014]    The debris retainer may further comprise a strainer or filter located in the or each return flow port. 
         [0015]    The debris retainer may further comprise a basket portion located within the annular chamber, the basket portion preventing any debris in the annular chamber from passing out of the open end of the sleeve. The debris retainer may further comprise a diverter plate located in the annular chamber and adapted to divert fluid flow in the chamber towards the basket portion. The basket portion may be formed from a plurality of biased finger members, the finger members being biased towards a closed position in which debris is prevented from passing out of the open end of the sleeve. 
         [0016]    The debris retainer may further comprise one or more magnets located in the annular chamber. 
         [0017]    The tool may further comprise:
       a central bore extending axially through the tool; and   one or more flow diversion ports providing fluid communication from the central bore to the exterior of the tool are located in the tool to provide fluid flow from the central bore to the outer surface of the tool.       
 
         [0020]    The or each flow diversion port may include a nozzle to direct a jet of fluid out of the port. 
         [0021]    The central bore may include a ball seat located downstream of the flow diversion ports. The ball seat may be shearable from the central bore. 
         [0022]    According to a second aspect of the invention there is provided a method of retrieving a packer from a well bore, the method comprising the steps of:
       (a) running a tool according to the first aspect of the invention on a work string;   (b) engaging the lower attachment portion to the packer;   (c) milling the packer with the upper milling portion to free the packer; and   (d) removing the work string from the well bore while retaining milled cuttings in the debris retainer.       
 
         [0027]    The method may further comprise the step of dropping a ball onto a ball seat in the tool so as to divert fluid flow from the work string through one or more flow diversion ports to the exterior of the tool. 
         [0028]    The ball seat may be shearable and the method may further comprise increasing the pressure in the tool until the ball seat shears, thereby resuming fluid flow through the tool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompany drawings of which: 
           [0030]      FIG. 1  is a cross-sectional view of a packer milling and retrieval tool according to a first embodiment of the present invention; 
           [0031]      FIG. 2  is a cross-sectional view of a debris catching chamber of a packer milling and retrieval tool according to a second embodiment of the present invention; 
           [0032]      FIG. 3  is a cross-sectional view of a debris catching chamber of a packer milling and retrieval tool according to a third embodiment of the present invention; 
           [0033]      FIG. 4  is a cross-sectional view of a packer milling and retrieval tool according to the third embodiment, retrieving a packer from a casing; 
           [0034]      FIG. 5  is a schematic representation of a packer milling and retrieval tool according to the present invention being deployed in a well bore; and 
           [0035]      FIGS. 6  ( a ) and (b) are cross-sectional views and end view respectively of the tool of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Reference is initially made to  FIG. 1  of the drawings which illustrates a packer milling and retrieval tool, generally indicated by reference numeral  10 , according to a first embodiment of the present invention. Tool  10  comprises a mandrel  12  having an upper milling portion  14  and a lower attachment portion  16 . Additionally, the tool has a chamber  18 . 
         [0037]    Tool  10  is shown in a casing  20  in a preferred orientation. Throughout the specification the terms upper and lower are used to refer to ends of the tool  10 . It will be understood that the tool could equally find application in inclined or horizontal wells where the referencing is then used as appropriate. 
         [0038]    Mandrel  12  has an upper end  22  including a threaded portion  24  for connection to a work string or drill string (not shown). Mandrel  12  includes a central bore  26  running axially through the centre of the tool  10 . A sleeve  28  is arranged from a face  30  of the mandrel  12  around a slimmer portion  32  of the mandrel. As the face  30  is perpendicular to the bore  26 , a chamber  18  is created by the annulus between the sleeve  28  and the slimmer portion  32  of the mandrel  12 . At a lower end  34  of the sleeve  28  is arranged a mill  14 . Mill  14  provides a cutting surface to anything arranged below it and around it. Such mills  14  are known to those skilled in the art. At a lower end  36  of the slimmer portion  32  of mandrel  12  is located retrieval means  16  which can attach to and pick up a packer (not shown). Retrieval means  16  are generally referred to as a stinger which includes a grapple or a collet arrangement which prevents the packer from falling off as it is retrieved. Such stingers are known in the art. 
         [0039]    On the face  30  are arranged ports  38  connecting the chamber  18  to an outer surface  40  of the tool  10 . Though the port  38  runs from the face  30  it may equally be positioned to run through the sleeve  28 . Additionally sleeve  28  is formed of a cylindrical portion which is punctuated to provide a strainer or filter. Alternatively the sleeve  28  is a slotted tube. Thus fluid can pass from the chamber  18  to be filtered through the sleeve  28  or pass through the ports  38 . Second ports  42  provide a passage for fluid from the central bore  26  to the outer surface  40  above the chamber  18 . Preferably there are three ports  42  arranged equidistantly around the circumference of the tool  10 . Each port  42  includes a jet nozzle  44  to provide in additional cleaning action when fluid exits the tool at the port  42 . 
         [0040]    A ball seat  55  is provided in the central bore at the top of the chamber  18 . The ball seat  55  is best illustrated in  FIG. 6 . Like parts to those of  FIG. 1  have been given the same reference numeral to aid clarity. Central bore  26  has a diameter  21  at the upper end  22 . A ledge  27  is then provided to reduce the diameter. Further the bore is again narrowed gradually over length  25  and ends in a narrowed bore  23  through the slimmer portion  32 . This arrangement ensures that drop ball  56 , when inserted in bore  26  falls into the length  25  where it is secured and effectively blocks fluid flow through the bore  26 . Fluid flow is then redirected through the three ports  42  which are located on ledge  27 . 
         [0041]    In use, tool  10  is connected to a work string and run into a casing  20 . Reference is now made to  FIG. 5  of the drawings which illustrates the tool  10  mounted on a work string  46  being run into the casing  20 . Like parts to those of  FIG. 1  have been given the same reference numeral to assist in clarity. During deployment fluid may be circulated through the tool through the central bore  26  around the base of the tool  36  and back up a annulus  48  created between the outer surface  40  of the tool  10  and the casing  20 . 
         [0042]    The tool  10  reaches a packer  50  which is set in the casing  20 . The stinger  16  will insert into an aperture  52  centrally located in the packer  50 . The tool  10  will further be run in until the mill  14  contacts packer  50  and by rotation of the tool  10 , the packer is milled to release it from the casing  20 . In particular, the slips  54  are milled through. As the packer  50  is milled, it is drawn into the chamber  18  so that the cuttings produced are released into the chamber  18 . 
         [0043]    As fluid flows through the central bore  26 , this is difficult to maintain and a ball  56  is dropped through the central bore  26  while  56  comes to rest in the ball seat  55  and thus blocks the passage of fluid axially through the tool  10 . 
         [0044]    Fluid is now diverted in the direction shown in arrow A of  FIG. 1  through the ports  42  and jetted out of the tool  10  by virtue of the nozzles  44 . Fluid travels down hole in the annulus  48  and circulates back up into the chamber  18  shown in the direction of the arrows B in  FIG. 1 . Fluid now circulating in the direction of arrow B is laden with millings and other cuttings. These millings and cuttings are trapped on the sleeve  28  while filtered fluid can travel in the direction of arrow C in  FIG. 1  and also through the port  38  in the direction of arrow D back to the outside of the tool. In this way only filtered well fluid passes back up the annulus  48  above the tool  10 . 
         [0045]    As the packer  50  is located within the chamber  18 , it prevents cuttings or millings falling back down the well and into well fluid below the packer  50 . While fluid circulation is maintained, the debris remains captured in the chamber  18  and can be brought to the surface. If, for some reason, the packer  50  becomes stuck during retrieval and the tool  10  has to be disengaged from the packer  50 , the cuttings and millings remain in the tool by virtue of the circulation of the fluid and also by the assistance in the retention of the cuttings to magnets  58  arranged in the chamber  18 . 
         [0046]    Reference is now made to  FIG. 2  of the drawings which illustrates a chamber  118  of a packer milling and retrieval tool in accordance with a second embodiment of the present invention. Like parts to those of  FIG. 1  have been given the same reference numeral with the addition of 100. Tool  110  includes a milling portion and retrieval portion as detailed with reference to  FIG. 1 . However, for the tool  110  the chamber  118  now includes a diverter plate  60  and an internal basket  62 . Diverter plate  60  is arranged at an upper end  62  of the chamber  118 . Diverter plate  60  comprises a conical section arranged around the slimmer portion  132  of the mandrel  112 . Basket  62  is arranged on an inner wall  64  of sleeve  128 . Basket  62  comprises a strain or filter or may be a slotted liner. 
         [0047]    In use, fluid travelling in direction B which is laden with millings or cuttings travels between the slimmer portion  132  and the basket  62 . Fluid is redirected at the diverter  60  around the diverter in a torturous path shown in arrow E. In making the torturous path, the cuttings and millings fall out of the flow due to the reduction in pressure in taking a longer path. Cuttings and millings then fall back in the direction of arrow F into the basket  62 . Well fluid free of the cuttings can then travel out of the tool  110  via the ports  138  in an identical manner to the tool of  FIG. 1 . 
         [0048]    This embodiment has the advantage that if the packer becomes detached at any point and fluid flow and circulation is stopped, collected cuttings will remain in the basket  62  within the chamber  118  for retrieval to the surface. 
         [0049]    Reference is now made to  FIGS. 3 and 4  of the drawings which illustrates a third embodiment of a packer milling and retrieval tool, generally indicated by reference numeral  210 . Like parts to those of  FIG. 1  have been given the same reference numeral but with the addition of 200. Tool  210  includes a packer retrieval portion  216  and a milling portion  214  as described with reference to the first embodiment. In this embodiment, chamber  218  now includes fingers  66  at a lower end  68  and a strainer  70  at the upper end  262 . 
         [0050]    As shown in  FIG. 4 , in use, the tool  210  mills the packer  250  using the milling elements  214  while the retrieval means  216  engages the packer  250 . The packer  250  is swallowed into an annulus  72  between the sleeve  228  and the slimmer portion  232 . Referring back to  FIG. 3 , the well fluid laden with cuttings is forced up in the direction of arrows B into the chamber  218 . To enter the chamber the well fluid forces the fingers  66  upwards by virtue of springs  74  arranged on the sleeve  228 . The fingers  66  will remain in an upright and open position while fluid flows into the chamber  218 . Fluid exits the chamber by passing through the strainer  70  and out of the port  238 . Millings and cuttings are prevented from taking this path by the strainer  70 . Strainer  70  is a conical strainer covering the upper end  262  of the chamber  218 . 
         [0051]    When the tool  210  is pulled from the well, the cuttings and millings  76  will fall from the strainer  70  back down the chamber  218 . As fluid flow is now no longer in the direction of arrow B, the fingers  66  will drop closing the lower end  68  of the chamber  218 . This will provide a basket  78  at the lower end  68  of the chamber to retain the cuttings  76  as the tool is brought to the surface. 
         [0052]    The principal advantage of the present invention is that it provides a tool which captures cuttings and millings in a packer milling and retrieval tool. As the tool converts the flow from inside the work string to the outside of the work string and around the outer diameter of the tool, millings and cuttings are circulated up into the tool instead of around the outside of the tool and thus the cuttings are captured and retained in the tool. 
         [0053]    A further advantage of the tool is that if the packer is lost for some reason i.e. if the packer becomes stuck in the hole and the tool needs to be disengaged from the packer, then the cuttings are retained in the tool rather than dumped. 
         [0054]    A yet further advantage of the present invention is that by dropping a ball into the central bore, fluid flow can be selectively diverted from the tool to the annulus between the tool and the casing. This provides a cross-over tool and allows reverse circulation through the tool in the casing. Flow can be re-routed back down the central bore if the ball seat is shearable as is known in the art. 
         [0055]    Various modifications may be made to the invention herein described without departing from the scope thereof. For example, whilst each of the preferred embodiments described herein includes a central bore for axial fluid flow through the tool the bore is a preferable, rather than essential, feature. The tool can be provided without a central bore and diversion ports if preferred.

Summary:
A packer tool ( 10 ) for milling and retrieving a packer from the casing of a well bore is provided. The tool ( 10 ) comprises an upper milling portion ( 14 ), a lower attachment portion ( 16 ) at least partially located within the upper milling portion ( 14 ), and a debris retainer ( 28,128,228 ) for capturing milled cuttings within the tool ( 10 ). A method of milling and retrieving a packer using the tool is also provided.