Abstract:
Apparatus and methods are provided for anchoring within tubular structures and releasing therefrom. In a described embodiment, a packer includes multiple debris barriers, which are deployed when slips of the packer are radially outwardly extended. The debris barriers prevent debris from settling about the slips, thereby enhancing convenient retrieval of the packer. Use of the debris barriers may also permit control over how the slips are extended.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation in part of Ser. No. 09/004,394, filed Jan. 8, 1998, now U.S. Pat. No. 6,112,811, issued Sep. 5, 2000, the disclosure of which is incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to anchoring apparatus utilized in subterranean wells and, in an embodiment described herein, more particularly provides a packer for use in extreme service conditions. 
     In a typical packer having a single slip, which may consist of a single slip member or multiple circumferentially distributed slip segments, forces applied to the packer are necessarily resisted by the same slip. Thus, when a downwardly directed tubing load and a downwardly directed differential pressure are applied to the packer, the single slip must resist both by its gripping engagement with a tubular structure (such as casing, tubing, other equipment, etc.) in which it is set. In extreme service conditions, the slip may need to be radially outwardly forced into contact with the tubular structure, in order to resist the forces applied to the packer, with enough force to cause damage to the tubular structure, the packer, or both. 
     If the gripping surface area on the slip is increased in an attempt to increase the gripping engagement between the slip and the tubular structure, it has been found that it is more difficult for the slip to initially bite into the tubular structure. This is due to the fact that more of the slip is required to deform more of the tubular structure. Consequently, more radially outwardly directed force must be applied to the slip, thereby causing damage to the tubular structure. 
     It would be advantageous to be able to use multiple axially spaced apart slips on an anchoring device, in order to distribute forces applied to the device among the slips. In addition, it would be advantageous for each of the multiple slips to be dual slips, so that each of the slips could resist forces applied thereto in both axial directions. Unfortunately, the use of multiple axially spaced apart slips presents additional problems, particularly when the slips are dual slips. 
     For example, it may be difficult to retrieve the anchoring device after the slips have been grippingly engaged with the tubular structure. This is due to the fact that slips generally have inclined teeth, serrations, etc. formed thereon which, when axially opposed with other slips, resist disengagement from the tubular structure. 
     As another example, mechanisms to extend and then retract multiple slips may be prohibitively complex, and therefore unreliable, uneconomical and/or too delicate for use in extreme service conditions. Thus, an extreme service anchoring apparatus utilizing multiple axially spaced apart slips should include appropriately robust, economical and reliable mechanisms for extending the slips and, where the apparatus is to be made retrievable, should include a retracting mechanism with similar qualities. 
     To further enable convenient retrieval of an anchoring apparatus, debris which accumulates about the apparatus should be minimized. Such accumulation of debris may be eliminated or lessened by providing an appropriately configured debris barrier. However, deployment of the debris barrier should not require complex mechanisms or procedures, and should not interfere with anchoring the apparatus. Additionally, deployment of the debris barrier or barriers may be useful in controlling anchoring of the apparatus. 
     From the foregoing, it can be seen that it would be quite desirable to provide an anchoring apparatus in which one or more debris barriers may be conveniently deployed. It is accordingly an object of the present invention to provide conveniently deployable debris barriers for an anchoring apparatus. It is another object of the present invention to provide debris barriers which may control or enhance setting of the apparatus. It is a still further object of the present invention to provide methods of producing a slip for an anchoring apparatus, the slip being configured for convenient use with a debris barrier. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a packer is provided which uses one or more debris barriers to reduce debris accumulation about the packer. The packer is reliable, retrievable, economical and convenient in operation. Associated methods are also provided. 
     In one aspect of the present invention, apparatus is provided which includes multiple debris barriers positioned relative to a slip, such that the slip is substantially between the debris barriers when the slip is radially outwardly extended. In one described embodiment, the slip pushes the debris barriers up sloped outer surfaces of wedge members, thereby radially outwardly extending the debris barriers. 
     In another aspect of the present invention, each debris barrier is disposed in a recess. The slip pushes the debris barriers out of the recesses when the slip is radially outwardly extended. In one described embodiment, the recesses are configured so that one of the debris barriers is pushed out of its recess before another one of the debris barriers. This enables the setting action of the slip to be controlled. 
     In another aspect of the present invention, radially extendable debris barriers are provided on the apparatus and disposed above and below the upper slip. The debris barriers are positioned on laterally inclined outer side surfaces of wedges associated with the upper slip. When the upper slip is radially outwardly extended by the wedges, axial displacement of the slip relative to the wedges causes the debris barriers to radially outwardly extend as well. At least the upper one of the debris barriers closes off an annular gap between the upper wedge and the tubular structure in which the apparatus is set, thereby excluding debris from accumulating about the apparatus and enhancing retrieval of the apparatus. 
     In yet another aspect of the present invention, methods of producing a slip are provided. The slip has relatively narrow slots, which enhance the slip&#39;s ability to support a debris barrier. In one embodiment, the slots are cut using an abrasive water jet. In another embodiment, the slots are cut with the slip immersed in a liquid. 
     The exemplary embodiment of the invention described below is in a packer specifically designed for use in extreme service conditions. However, the principles of the present invention may be readily utilized in other equipment, such as plugs, hangers, etc. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A-1F are quarter-sectional views of successive axial sections of a first apparatus embodying principles of the present invention, the apparatus being shown in a configuration in which it is run into a subterranean well; 
     FIGS. 2A-2F are quarter-sectional views of successive axial sections of the first apparatus, the apparatus being shown in a configuration in which it is set within a tubular structure in the well; 
     FIGS. 3A-3F are quarter-sectional views of successive axial sections of the first apparatus, the apparatus being shown in a configuration in which it is retrieved from the well; 
     FIGS. 4A&amp;B are quarter-sectional views of an axial section of a second apparatus embodying principles of the present invention, FIG. 4A showing the apparatus in a configuration in which it is run into a subterranean well, and FIG. 4B showing the apparatus in a configuration in which it is set within a tubular structure in the well; 
     FIGS. 5A&amp;B are quarter-sectional views of an axial section of a third apparatus embodying principles of the present invention, FIG. 5A showing the apparatus in a configuration in which it is run into a subterranean well, and FIG. 5B showing the apparatus in a configuration in which it is set within a tubular structure in the well; 
     FIG. 6 is an elevational view of a device embodying principles of the present invention; and 
     FIG. 7 is a schematic view of a method of producing a slip, the method embodying principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIGS. 1A-1F is a packer  10  which embodies principles of the present invention. In the following description of the packer  10  and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the embodiment of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. 
     The packer  10  includes an inner generally tubular mandrel  12 , which is internally threaded at its upper end for attachment to a tubular string (not shown in FIGS. 1A-1F) in a conventional manner. Loads may be transmitted to the mandrel  12  from the tubular string in each axial direction. For example, an axially downwardly directed load may be applied to the mandrel  12  by the weight of the tubular string. An axially upwardly directed load may be applied to the mandrel  12  by axial contraction of the tubular string, such as when relatively cool injection fluids are pumped through the tubular string. Many other situations may also result in loads being applied to the mandrel  12 . 
     For resisting these loads and other forces applied to the packer  10 , the packer includes an upper slip assembly  14  and a lower slip assembly  16 . The packer  10  also includes a seal assembly  18 , an axially compressible assembly or release device  20 , a hydraulic setting assembly  22 , an internal slip assembly  24 , and a retrieval mechanism  26 . 
     The upper slip assembly  14  includes a dual barrel slip  28 , an upper wedge  30 , a lower wedge  32 , a debris barrier  34 , and a generally C-shaped snap ring  36  disposed in an annular recess  66  formed on the mandrel  12 . The slip  28  is of the dual type, meaning that it is configured for resisting forces applied thereto in both axial directions. For this purpose, teeth or other gripping structures  38  on the slip  28  are oppositely oriented relative to other teeth or other gripping structures  40  on the slip. In the representatively illustrated slip  28 , the teeth  38 ,  40  are formed directly on the slip, which is a circumferentially continuous axially slotted barrel slip of the type well known to those of ordinary skill in the art. The lower slip assembly  16  includes a similar slip  42 . However, it is to be clearly understood that the slips  28 ,  42 , or either of them, may be differently configured without departing from the principles of the present invention. For example, the teeth  38 ,  40  or other gripping structures may be separately attached to the remainder of the slip, the slips  28 ,  42  may be C-shaped, or otherwise circumferentially discontinuous, the slips may be circumferentially divided into slip segments, etc. 
     The upper wedge  30  is releasably secured to the mandrel  12  with a pin  44  installed through the wedge and into the mandrel. Multiple generally conical downwardly facing outer side surfaces  46  formed on the wedge  30  engage complementarily shaped inner side surfaces  48  formed on the slip  28 , so that when the slip is displaced axially upward relative to the wedge, in a manner described more fully below, the slip is radially outwardly displaced relative to the mandrel  12 . The lower wedge  32  similarly has multiple generally conical upwardly facing outer side surfaces  50  formed thereon, and the slip  28  has complementarily shaped inner side surfaces  52  formed thereon, for radially outwardly displacing the slip. Additionally, the wedges  30 ,  32  and slip  28  have inclined surfaces  54 ,  56  formed thereon, respectively, to prevent axial separation therebetween, and to aid in radially inwardly retracting the slips when the packer  10  is retrieved, as described more fully below. 
     The lower slip assembly  16  is generally similar to the upper slip assembly  14 . The lower slip assembly  16  includes the slip  42 , an upper wedge  58  releasably secured against displacement relative to the mandrel  12  by a pin  60 , a lower wedge  62 , and a snap ring  64  disposed in an annular recess  68  formed on the mandrel  12 . The slip  42  and wedges  58 ,  62  have the corresponding surfaces  46 ,  48 ,  50 ,  52 ,  54 ,  56  formed thereon, albeit oppositely oriented as compared to the upper slip assembly  14 . 
     The seal assembly  18  includes multiple circumferential seal elements  70  of conventional design carried about the mandrel  12 . Of course, more or less of the seal elements  70  or differently configured seal elements may be utilized in a packer or other apparatus constructed in accordance with the principles of the present invention. The seal elements  70  are axially straddled by backup shoes  72 . The seal elements  70  are radially outwardly extendable relative to the mandrel  12  by axially compressing them between an upper generally tubular element retainer  74  and a lower generally tubular element retainer  76 . 
     The setting assembly  22  includes a lower portion of the lower element retainer  76  which carries internal seals  78  thereon for sealing engagement with the mandrel  12 , and which carries external seals  80  thereon and is threadedly attached to an outer tubular housing  82 . A difference in diameters between the seals  78 ,  80  forms an annular piston or differential piston area on the element retainer  76 . Another annular piston  84  is sealingly engaged radially between the housing  82  and the mandrel  12 , and is disposed axially between a snap ring  86  and an upper tubular portion of the wedge  58 . 
     An opening  88  formed radially through the mandrel  12  permits fluid communication between the interior of the mandrel and an annular chamber  90  formed radially between the mandrel and the housing  82 , and axially between the element retainer  76  and the annular piston  84 . A predetermined fluid pressure differential is applied to the interior of the mandrel  12  (e.g., via the tubular string connected thereto and extending to the earth&#39;s surface) and thus to the chamber  90  to set the packer  10 , as will be more fully described below. 
     The internal slip assembly  24  includes a slip member  92  disposed radially between the housing  82  and the upper tubular portion of the wedge  58 . The slip member  92  is engaged with the housing  82  by means of relatively coarse teeth or buttress-type threads  94 , and the slip member is engaged with the upper tubular portion of the wedge  58  by means of relatively fine teeth or buttress-type threads  96 . The teeth or threads  94 ,  96  are inclined, so that the slip member  92  permits the wedge  58  to displace axially downward relative to the housing  82 , but prevents axially upward displacement of the wedge  58  relative to the housing. 
     A shear screw  98  installed laterally through a generally tubular retainer  100  threadedly attached to the housing  82 , and into a recess  102  formed externally on the wedge  58  releasably secures the housing against displacement relative to the wedge  58 . A circumferential wave spring  104  compressed axially between the slip member  92  and the retainer  100  maintains an axially upwardly directed force on the slip member, so that the slip member is maintained in engagement with both the housing  82  and the wedge  58 . A pin  106  is installed through the housing  82  and into an axial slot formed through the slip member  92 , to prevent rotation of the slip member. 
     The release device  20  includes an upper portion of the element retainer  74 , which is axially telescopingly engaged with a lower portion of the wedge  32 . A generally C-shaped snap ring  108  engages a profile  110  formed internally on the element retainer  74 , and abuts the lower end of the wedge  32 . Thus, as shown in FIG. 1B, the ring  108  prevents axial compression of the release device  20 . However, when the mandrel  12  is axially upwardly displaced relative to the ring  108 , permitting the ring to radially inwardly retract into an annular recess  112  formed externally on the mandrel, the release device is permitted to axially compress, thereby relieving axial compression of the seal assembly  18  in a manner more fully described below. 
     A pin  114  is installed through an axially elongated slot  116  formed through the element retainer  74 , through the wedge  32 , and into a recess  118  formed on the mandrel  12 . The pin  114  releasably secures the wedge  32  relative to the mandrel  12 , and prevents axial separation of the element retainer  74  and wedge  32 , while still permitting the wedge and element retainer to displace axially toward each other. 
     The retrieval mechanism  26  permits the packer  10  to be conveniently retrieved from the tubular structure in which it is set. It includes a generally C-shaped snap ring  120  disposed radially between the mandrel  12  and a generally tubular support sleeve  122 . The support sleeve  122  maintains the ring  120  in engagement with a profile  124  formed externally on the mandrel  12 . A pin  126  installed through the sleeve  122  and into a recess  128  formed externally on the mandrel  12  releasably secures the sleeve against displacement relative to the mandrel, thereby securing the ring  120  against disengagement from the profile  124 . 
     An abutment member  130  is sealingly engaged radially between the mandrel  12  and a generally tubular lower housing  132  threadedly attached to a generally tubular intermediate housing  134 , which is threadedly attached to a lower end of the wedge  62 . The abutment member  130  is disposed axially between a lower end of the housing  134  and the ring  120 , thereby preventing axially upward displacement of the ring relative to the housing  134 . The lower housing  132  is provided with threads for attachment to a tubular string therebelow (not shown in FIG.  1 F). 
     When it is desired to retrieve the packer  10 , the sleeve  122  is shifted axially upward relative to the mandrel  12 , thereby shearing the pin  126  and permitting the ring  120  to radially outwardly expand into an annular recess  136  formed internally on the sleeve. The ring  120  thus disengages from the profile  124  and permits axial displacement of the mandrel  12  relative to the substantial remainder of the packer  10 . As described above, such axially upward displacement of the mandrel  12  also permits the release device  20  to axially contract. The sleeve  122  may be shifted relative to the mandrel  12  by any of a variety of conventional shifting tools (not shown) in a conventional manner. 
     As representatively illustrated in FIGS. 1A-1F, the packer  10  is in a configuration in which it may be run into a well and positioned within a tubular structure in the well. Specifically, both slips  28 ,  42  and the seal elements  70  are radially inwardly retracted. 
     Referring additionally now to FIGS. 2A-2F, the packer  10  is representatively illustrated set within a tubular structure (represented by inner side surface  138 ). The slips  28 ,  42  are radially outwardly extended into gripping engagement with the tubular structure  138 , and the seal assembly  18  is axially compressed and radially outwardly extended into sealing engagement with the tubular structure. Note that the seal assembly  18  is shown as a single seal element  70  for clarity of illustration, and to demonstrate that alternate configurations of the seal assembly may be utilized without departing from the principles of the present invention. 
     To set the packer  10 , a fluid pressure is applied to the interior of the mandrel  12 . This fluid pressure enters the opening  88  and urges the piston  84  downward while urging the lower element retainer  76  upward. When the fluid pressure reaches a predetermined level, the shear screw  98  shears, thereby permitting the wedge  58  to displace axially downward relative to the housing  82 . The wedge  58  is prevented from displacing axially upward relative to the housing  82  by the internal slip assembly  24 , as described above. 
     Shearing of the shear screw  98  also permits the housing  82  and element retainer  76  to displace axially upward relative to the mandrel  12 . The retainer  76  pushes axially upward on the seal assembly  18 , axially compressing and radially outwardly extending the seal element  70 . The seal assembly  18  pushes axially upward on the upper retainer  74 . The upper retainer  74  is prevented from displacing axially upward relative to the wedge  32  by the ring  108 , so the retainer  74  pushes axially upward on the wedge  32  via the ring  108 , shearing the pin  114  and permitting axially upward displacement of the wedge relative to the mandrel  12 . 
     Axially upward displacement of the wedge  32  causes the slip  28  to be radially outwardly displaced by cooperative engagement of the surfaces  50 ,  52 , and by cooperative engagement of the surfaces  46 ,  48 . The slip  28  is thus radially outwardly extended by axial displacement of the wedge  32  toward the wedge  30 . As the slip  28  is radially outwardly displaced, it also displaces somewhat axially upward relative to the upper wedge  30 . This axially upward displacement of the slip  28  causes the debris barrier  34  to be displaced axially upward relative to the inclined generally conical outer side surface  46 . 
     The debris barrier  34  has a generally triangular-shaped cross-section, such that it is complementarily positionable radially between the surface  46  on which it is disposed and the tubular structure  138 . In this manner, debris is prevented from falling and accumulating about the slip assembly  14  and seal assembly  18 . Such accumulation of debris could possibly prevent ready retraction of the slip  28  when it is desired to retrieve the packer  10 . To facilitate its radial expansion, the debris barrier  34  is formed of a suitable deformable material, such as TEFLON® or an elastomer. Of course, the debris barrier  34  may be differently shaped and may be formed of other materials without departing from the principles of the present invention. Note that the debris barrier  34  does not prevent fluid flow radially between the packer  10  and the tubular structure  138 , but does close off the annular gap therebetween to debris flow. 
     In a similar manner to that described above for the upper slip  28 , the lower slip  42  is radially outwardly displaced by axial displacement of the wedge  58  toward the wedge  62 . Note that the wedge  62  and housing  134  are prevented from displacing axially upward relative to the mandrel  12  by the ring  64  and by another snap ring  140  disposed in a recess  142  formed externally on the mandrel  12 . 
     At this point, it is instructive to examine the unique manner in which different types of forces applied to the packer  10  are distributed among the slips  28 ,  42 . An axially downwardly directed load applied to the mandrel  12  (for example, by the tubular string attached to the upper end of the mandrel, or by the tubular string attached to the lower end of the lower housing  132 ) is resisted by engagement of the teeth  38  on the upper portion of the upper slip  28  with the tubular structure  138 . Conversely, an axially upwardly directed load applied to the mandrel  12  is resisted by engagement of the teeth  38  on the lower portion of the lower slip  42  with the tubular structure  138 . 
     An axially downwardly directed pressure differential applied to the seal assembly  18  is resisted by engagement of the teeth  40  on the upper portion of the lower slip  42  with the tubular structure  138 . An axially upwardly directed pressure differential applied to the seal assembly  18  is resisted by engagement of the teeth  40  on the lower portion of the upper slip  28  with the tubular structure  138 . 
     The above described distribution of forces provides unique advantages to the packer  10  in extreme service conditions. Note that the teeth  40  on the lower portion of the upper slip  28  and on the upper portion of the lower slip  42  serve to resist forces resulting from pressure differentials across the seal assembly  18 . The teeth  38  on the upper portion of the upper slip  28  and on the lower portion of the lower slip  42  serve to resist forces resulting from loads transmitted to the mandrel  12 . Accordingly, the different types of forces are distributed on each slip  28 ,  42 . 
     Even more beneficial is the fact that, when the forces are combined, that is, when a load is applied to the mandrel  12  in the same direction as a pressure differential applied to the seal assembly  18 , these forces are resisted by different ones of the slips  28 ,  42 . For example, a downwardly directed load applied to the mandrel  12  is resisted by the upper slip  28 , and a downwardly directed pressure differential applied to the seal assembly  18  is resisted by the lower slip  42 . Conversely, an upwardly directed load transmitted to the mandrel  12  is resisted by the lower slip  42 , and an upwardly directed pressure differential applied to the seal assembly  18  is resisted by the upper slip  28 . Thus, concentrations of loading on the tubular structure  138  are avoided by distributing combined forces among the slips  28 ,  42 , thereby reducing the possibility of damage to the tubular structure and the packer  10 . 
     In the configuration of the packer  10  shown in FIGS. 2A-2F, a compressive force is stored in the seal assembly  18  even after the fluid pressure applied to the interior of the mandrel  12  is relieved, due to the internal slip assembly  24  preventing the wedge  58  and element retainer  76  from displacing axially toward each other. Since the slips  28 ,  42  are grippingly engaged with the tubular structure  138  axially straddling the seal assembly  18 , this stored compressive force corresponds to a tensile force applied to the tubular structure between the slips. It will be readily appreciated that the compressive force stored in the seal assembly  18  prevents disengagement of the slips  28 ,  42  from the tubular structure, since the seal assembly urges upwardly on the wedge  32  via the release device  20 , and urges downwardly on the wedge  58  via the retainer  76 , housing  82  and internal slip assembly  24 . Or, stated from a different perspective, the tensile force stored in the tubular structure between the slips  28 ,  42  urges the slips toward their respective wedges  32 ,  58 . 
     Therefore, in order to conveniently disengage the slips  28 ,  42  from the tubular structure, the packer  10  includes the retrieval mechanism  26  and the release device  20 . The retrieval mechanism  26 , when activated, permits axially upward displacement of the mandrel  12  relative to the substantial remainder of the packer  10 . The release device  20 , upon axially upward displacement of the mandrel  12 , releases the stored compressive force from the seal assembly  18  by permitting the seal assembly to axially elongate. 
     Referring additionally now to FIGS. 3A-3F, the packer  10  is representatively illustrated in a configuration in which it may be retrieved from the tubular structure  138 . The sleeve  122  has been shifted upwardly, thereby permitting the ring  120  to disengage from the profile  124 . The mandrel  12  has then been displaced axially upward by, for example picking up on the tubular string attached thereto. 
     Axially upward displacement of the mandrel  12  has permitted the ring  108  to radially inwardly retract into the recess  112 , thereby permitting the element retainer  74  to axially upwardly displace relative to the seal assembly  18 . As a result, the compressive force in the seal assembly  18  is released, the seal assembly is permitted to axially elongate, and the seal elements  70  are radially inwardly retracted out of engagement with the tubular structure  138  (not shown in FIGS.  3 A- 3 F). 
     When the compressive force is released from the seal assembly  18 , the corresponding tensile force in the tubular structure  138  between the slips  28 ,  42  is also released. The slips  28 ,  42  are thus permitted to radially inwardly retract. Note that at this point the inner wedges  32 ,  58  are not biased axially away from each other, and the slips  28 ,  42  are not biased axially toward each other. 
     Further axially upward displacement of the mandrel  12  causes the ring  36  to engage the wedge  30 , and the ring  64  to engage the wedge  58 . If the slips  28  have not already completely radially inwardly retracted due to their own resiliency, cooperative engagement of the surfaces  54 ,  56  will cause the slips to retract out of engagement with the tubular structure  138 . Such axially upward displacement of the mandrel  12  also causes the ring  86  to engage the element retainer  76 , and the ring  140  to engage the wedge  62 , ensuring that the remainder of the packer  10  is retrieved. 
     Note that, if it is not possible to shift the sleeve  122  as described above, the mandrel  12  may still be axially upwardly displaced to retrieve the packer  10  by severing the mandrel axially between the recess  142  and the profile  124 . The mandrel  12  may be severed by conventional methods, such as a linear shaped charge, a thermal cutter, or a chemical cutter, etc. 
     Thus has been described the packer  10  and methods of anchoring and retrieving apparatus within a tubular structure in a subterranean well. The packer  10  is uniquely configured for use in extreme service conditions, such as those in which very large combined forces may be applied to the packer, but it is also usable in other conditions. Additionally, the packer  10  has been described as incorporating, in a single embodiment, many advantageous features of the present invention. However, it is to be understood that these features may be separately incorporated into various embodiments of the present invention. 
     Referring additionally now to FIGS. 4A&amp;B, an axial portion of a packer  150  embodying principles of the present invention is representatively illustrated. The axial portion of the packer  150  shown in FIGS. 4A&amp;B includes an upper dual barrel slip  152  similar in many respects to the upper slip  28  of the packer  10  described above. The remainder of the packer  150  may be similar to the packer  10 , or it may be similar to a conventional packer. 
     In FIG. 4A, the packer  150  is depicted in a configuration in which it is run into a subterranean well. In FIG. 4B, the packer  150  is depicted as it is set within the well, the slip  152  grippingly engaging an inner side surface  154  of a tubular member, such as casing, tubing, a liner, etc. The slip  152  is radially outwardly extended from the configuration shown in FIG. 4A to the configuration shown in FIG. 4B by displacement of a lower wedge member  156  axially upward toward an upper wedge member  158 , similar to the manner in which the slip  28  is radially outwardly extended in the packer  10  described above. 
     However, note that a circumferential debris barrier  160  is positioned above the slip  152  and a circumferential debris barrier  162  is positioned below the slip. In FIG. 4A, the upper debris barrier  160  is disposed in a circumferential recess  164  formed externally on a sloped or inclined outer side surface  166  formed on the upper wedge  158 . Similarly, the lower debris barrier  162  is disposed in a circumferential recess  168  formed externally on a sloped or inclined outer side surface  170  formed on the lower wedge  156 . 
     When the lower wedge  156  is displaced upward relative to the upper wedge  158 , the slip  152  pushes each of the debris barriers  160 ,  162  out of its respective recess  164 ,  168 . Furthermore, the slip  152  pushes each of the debris barriers  160 ,  162  axially across its respective inclined surface  166 ,  170 , so that the debris barriers are radially outwardly extended as the slip is radially outwardly extended. In FIG. 4B, the debris barriers  160 ,  162  are shown engaged with the tubular member inner side surface  154 , thereby preventing debris accumulation about the slip  152 . 
     Multiple debris barriers  160 ,  162  may be utilized so that the slip  152  is uniformly extended, that is, with each opposite end of the slip radially outwardly extending at approximately the same time and at approximately the same rate. This ensures substantially uniform gripping engagement of each opposite end of the slip  152  as the packer  150  is set, thus avoiding any undesirable movement of the slip relative to the mandrel  172  as the packer is set. 
     Note that the debris barriers  160 ,  162  expand radially outward at a rate greater than the rate at which the slip  152  expands radially outward. This is due to the fact that the debris barriers  160 ,  162  are pushed out of the recesses  164 ,  168  by the slip  152 , thereby radially expanding the debris barriers, before the debris barriers are pushed across their respective inclined surfaces  166 ,  170  of the wedges  158 ,  156 . Thus, greater radial compression of the debris barriers  160 ,  162  against the inner side surface  154  is achieved as compared to the debris barrier  34  described above. 
     Although the debris barriers  160 ,  162  are depicted as having generally circular cross-sections, and the recesses  164 ,  168  are depicted as having generally circular cross-sections, it is to be clearly understood that the debris barriers and/or the recesses may be otherwise shaped without departing from the principles of the present invention. Additionally, the debris barriers  160 ,  162  may be made of elastomeric material, nonelastomeric material, plastic material, metal, or any other material, without departing from the principles of the present invention. 
     An alternate placement of the debris barriers  160 ,  162  may be in circumferential recesses  174 ,  176  formed externally on the slip  152  and shown in FIG. 4A in dashed lines. The debris barriers  160 ,  162  might also be positioned on axial extensions of the slip  152  above and below the gripping portion of the slip. It will be readily appreciated that the debris barriers  160 ,  162  may be otherwise positioned without departing from the principles of the present invention. However, it is preferred, but not required, that at least a substantial portion of the slip  152  be disposed between the debris barriers  160 ,  162 . 
     Referring additionally now to FIGS. 5A&amp;B, an axial portion of a packer  180  embodying principles of the present invention is representatively illustrated. The packer  180  is depicted in FIG. 5A in a configuration in which it is run into a subterranean well. The packer  180  is depicted in FIG. 5B in a configuration in which it is set in a tubular member in the well. The packer  180  is similar in many respects to the packer  150  described above and similar elements shown in FIGS. 5A&amp;B are indicated by their same reference numbers, with an added suffix “a”. 
     In the packer  180 , circumferential recesses  182 ,  184  formed externally on the upper and lower wedges  158   a ,  156   a , respectively, are configured so that one end of the slip  152   a  is radially outwardly extended into gripping engagement with the inner side surface  154   a  before the other end. Thus, the debris barrier configuration may be used to control setting of the slip  152   a.    
     An upper peripheral edge surface  186  of the upper recess  182  opposite the slip  152   a  is laterally angled or sloped at an angle A which is different from an angle B at which a lower peripheral edge surface  188  of the lower recess  184  opposite the slip is laterally angled or sloped. As representatively illustrated in FIGS. 5A&amp;B, angle A is greater than angle B, so that it is easier for the slip  152   a  to push the upper debris barrier  160   a  out of the upper recess  182  than it is for the slip to push the lower debris barrier  162   a  out of the lower recess  184 . Thus, the upper end of the slip  152   a  will push the upper debris barrier  160   a  out of the upper recess  182  and across the inclined surface  186  before the lower end of the slip will push the lower debris barrier  162   a  out of the lower recess  184  and across the inclined surface  188 , resulting in the upper end of the slip grippingly engaging the inner side surface  154   a  before the lower end of the slip. This situation, in which one end of the slip  152   a  engages the inner side surface  154   a  before the other end, may be desirable, for example, to ensure that the end of the slip opposite the displacing wedge  156   a  grips the inner side surface first. 
     Other methods of deploying one debris barrier before another, or of engaging one end of a slip before another, may be utilized without departing from the principles of the present invention. For example, one of the debris barriers  160   a ,  162   a  may have a strength or a resistance to being expanded which is different from that of the other debris barrier, one of the debris barriers may be positioned differently on its respective wedge  158   a ,  156   a  from the other debris barrier, one end of the slip  152   a  may be configured differently from the other end of the slip, one of the peripheral edge surfaces  186 ,  188  may have a radius, instead of a slope, different from the other, etc. 
     Referring additionally now to FIG. 6, a slip  190  embodying principles of the present invention is representatively illustrated. The slip  190  is a dual barrel slip and may be utilized for any of the slips  10 ,  152 ,  152   a  described above. The slip  190  is unique in at least one respect in that it has a series of circumferentially spaced apart slots  192  extending radially, but not completely axially, therethrough. The slots  192  alternate axial directions (i.e., the axial end of the slip from which they extend) circumferentially about the slip  190 . 
     The slots  192  are formed in the slip  190  sufficiently thin so support of debris barriers thereacross is enhanced. It is preferred that the slots  192  have a thickness or width of approximately 0.020 to 0.060 inch, and that the slots be formed by water jet cutting, although other slot widths and methods of cutting may be utilized without departing from the principles of the present invention. 
     To produce the slip  190 , it is preferred that the slip first be formed in a tubular shape, with gripping structures, teeth, or serrations  194  formed externally thereon. Openings  196  and/or other features, other than the slots  192 , may also be formed on the slip  190  at this time. The slip  190  is then heat treated as desired to produce, for example, a desired strength, hardness, etc. of the slip. Then, the slots  192  are formed using conventional water jet cutting techniques. Other methods of producing the slip  190  may be utilized without departing from the principles of the present invention. 
     The above described method of producing the slip  190  removes less material in forming the slots  192  than does conventional milling methods. As a result, the slip tensile strength is increased, more slots may be used for a given slip diameter, thereby increasing the flexibility of the slip (i.e., decreasing its resistance to radial expansion), enabling the slip to be shortened, and producing cost savings in other components of an anchoring device on which the slip is utilized. Note that the slip  152   a  shown in FIGS. 5A&amp;B is produced by the above described method of producing the slip  190 , resulting in a shorter slip, mandrel  172   a  and wedges  156   a ,  158   a  as compared to the slip  152  produced by conventional milling techniques and its associated mandrel  172  and wedges  156 ,  158  shown in FIGS. 4A&amp;B. 
     Referring additionally now to FIG. 7, a method  200  of producing a slip embodying principles of the present invention is representatively and schematically illustrated. The method  200  is depicted in FIG.  7  and described herein as being used in producing the slip  190 , however, it is to be clearly understood that other slips and other types of slips may be produced by the method, without departing from the principles of the present invention. 
     In the method  200 , it is preferred that the slip  190  first be formed in a tubular shape, with gripping structures, teeth, or serrations  194  formed  4 i externally thereon. Openings  196  and/or other features, other than the slots  192 , may also be formed on the slip  190  at this time. The slip  190  is then heat treated as desired to produce, for example, a desired strength, hardness, etc. of the slip. 
     The slip  190  is then immersed in a liquid  202 , such as water, the liquid being in intimate contact with the slip. In this manner, the liquid  202  forms a heat sink for the slip  190  so that, when the slots  192  are cut in the slip, minimal change in the metallurgical properties of the slip is experienced. Thus, the slots  192  may be cut in the slip  190  without appreciably affecting the strength, hardness, toughness, etc. of the slip. 
     The slots  192  are cut using a conventional flame or plasma jet cutting torch  204  which is displaced linearly by a conventional translational displacement device  206  of the type used in CNC machine tools. The displacement device  206  displaces the torch  204  both horizontally and vertically (although not necessarily at the same time) as representatively illustrated in FIG. 7, but it is to be clearly understood that separate displacement devices may be utilized for displacement in different directions, the torch may be otherwise displaced, for example, in other directions, by the displacement device, the slip  190  may be displaced instead of displacing the torch, etc., without departing from the principles of the present invention. 
     The slip  190  is engaged with a rotational displacement device  208 , which rotates the slip relative to the torch  204 . The slip  190  is engaged with the device  208 , for example, by use of a chuck which grips the slip, etc. In this manner, the torch  204  may be rotationally aligned with each of the series of slots  192 . For example, the torch  204  may be aligned with one desired slot  192 , the slot cut by the torch, and then the slip rotated by the device  208 , so that the torch may be aligned with another desired slot and cut the slot, etc., thereby incrementally progressing rotationally about the slip, until all of the slots have been cut in the slip. However, it is to be clearly understood that the slots  192  may be otherwise cut by the torch  204 , for example, by rotating the torch about the slip, etc., without departing from the principles of the present invention. 
     Displacement of the slip  190  and torch  204  relative to each other by the devices  206 ,  208  is controlled by a conventional controller  210 , which may be of the type used in conventional CNC machine tools. For example, the controller  210  may be programmed to cause the device  206  to displace the torch  204  relative to the slip  190  so that a first slot  192  is cut in the slip, cause the device  206  to displace the torch away from the slip, cause the device  208  to rotate the slip relative to the torch and thereby align the torch with a second desired slot, cause the device  206  to displace the torch into close proximity with the slip, cause the device  206  to displace the torch relative to the slip so that the second slot is cut in the slip, etc. However, it is not necessary for the controller  210  to be programmed in this manner, nor for the controller to be used at all, in the method  200 . For example, the displacement devices  206 ,  208  could be manually operated. 
     Note that the method described above for water jet cutting of the slots  192  in the slip  190  may be performed using the displacement devices  206 ,  208  and controller  210 , similar to the method  200 , except that immersion of the slip in the liquid  202  may not be utilized, and the torch  204  would instead be a water jet cutting device. Additionally, note that it is not necessary in the water jet, flame or plasma jet slot cutting methods described above for the slip  190  to be heat treated prior to cutting the slots  192 , since the slip may be heat treated after the slots are cut, or not at all. Other methods of cutting the slots  192  may be utilized as well, without departing from the principles of the present invention. 
     Of course, it would be obvious to a person of ordinary skill in the art to make modifications, substitutions, additions, deletions, substitutions, and other changes to the exemplary embodiment of the present invention described above, and such changes are contemplated by the principles of the present invention. For example, the slip  152 ,  152   a  or  190  may be other than a dual barrel slip, the debris barriers  160 ,  162  may be otherwise configured and/or positioned on the packer  150 , other mechanisms may be employed to deploy the debris barriers, etc. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.