Abstract:
An improved cage slip system is disclosed. The cage is constructed so that the cones which actuate the slips extend into the cage openings. The radial extension of the slips is limited so as to retain them if they are extended in an unsupported situation. The cones have a maximum outside dimension equal to the outside dimension of the cage so as to increase the rating of the slips by increasing the bearing area of the cones on the slips. The beneficial features of the cage design are retained while a greater degree of radial expansion of the slips is possible allowing minimization of tool inventory for situations where a lighter wall casing requires further slip extension. The release system allows the lower cones to be driven out from under the lower slips, thus facilitating release of the grip of the lower slips from the casing for extraction of the packer. The mechanical release is functional through the mandrel, whether tension or compression is placed on the mandrel. Alternative designs are presented for the capture of the lower cone by the cage.

Description:
This application claims benefit to Provisional application Ser. No. 60/104,833 filed Oct. 19, 1998. 
    
    
     FIELD OF THE INVENTION 
     The field of this invention relates to retention devices for downhole tools, particularly slip systems located in cages and release methods for such systems. 
     BACKGROUND OF THE INVENTION 
     Slips are used in downhole tools such as packers to retain the position of the tool. Slips can be provided in a cage where a sleeve has openings through which the slips extend, separated by structural components of the cage to give it the integrity needed to withstand forces applied during the operation of the tool. These conventional caged slip systems offer protection to the slips while running in the hole. Apart from protecting the slips during run-in, the cage itself typically serves as a pickup device when retrieving slips. One of the design drawbacks of existing caged slip systems is a limitation on the extendable diametrical range of the slips. The longitudinal elements which define the openings through which the slips extend also serve as travel stops. Since these longitudinal components require a predetermined structural strength, they cannot be thinned to allow additional slip extension. This concept is illustrated in FIG. 1 which shows the prior art. In FIG. 1 a prospective view of a slip  10  is shown. The cross-section of the slip  10  is U shaped and the longitudinal strip  12  extends within the U and acts as an outward travel stop for the caged slip  10 . The openings or windows  14  are defined between the longitudinal strips  12 . Accordingly, in the prior art, the requisite thickness of the longitudinal strips  12  limited the amount of outward travel of the slips  10 . Additionally, in the prior art designs, the cones which would force the slips outwardly were located inside the cage as represented graphically by arrow  16 . One such product is the Model SC-2P retrievable packer made by Baker Oil Tools. The placement of the cones within the cage defined by longitudinal members  12  reduced the available bearing area of the cones on the slips and therefore limited the capacity of the slips to resist differential forces which are present in the wellbore. Thus, these two significant limitations of prior caged slip designs amounted to lower performance ratings of the overall tool, as well as the need to have more tools available for varying sizes of casing. The reason for this was that depending on the casing weight per foot, its inside dimension would vary. Thus, different tools might be needed in the prior art to extend sufficiently far if lighter wall casing was in use. 
     Thus, some of the objectives of the present invention are to allow greater extension of the slips while retaining or expanding the ability of the slip system to withstand differential loads. Additionally, another objective is to allow within a given tool body size sufficient rangeability and slip extension so as to avoid stocking a large inventory of tools to handle a variety of situations. Another objective is to uniquely position the cone within the openings of the cage so that the cones extend outwardly as far as the outer extremity of the cage. All this is accomplished while at the same time retaining the beneficial qualities of a caged slip during run-in. Another objective, which is accomplished by putting the cones in the windows of the cage, allows the cage thickness to be increased to improve its tensile strength without reduction of the amount of slip extension. Finally, another objective is to be able to retain the slips to a predetermined extension diametrically outwardly. Thus, the slips are limited in radial extension to prevent them from escaping the cage if they are extended in an unsupported condition. Yet another objective of the present invention is to facilitate release of the slips by mechanically driving the lower cone out from the lowermost slips, as opposed to trying to pull and disengage slips off of a stationary cone. The objective of the release system is to be able to unsupport the slips, regardless of whether the mandrel of the packer is in tension or compression so that the slip is not pulled away from a cone when the cone forces the wickers of the slip against a casing or tubular. Those and other features of the present invention will become more apparent to those skilled in the art from a review of the preferred embodiment described below. 
     SUMMARY OF THE INVENTION 
     An improved caged slip system is disclosed. The cage is constructed so that the cones which actuate the slips extend into the cage openings. The radial extension of the slips is limited so as to retain them if they are extended in an unsupported situation. The cones have a maximum outside dimension equal to the outside dimension of the cage so as to increase the rating of the slips by increasing the bearing area of the cones on the slips. The beneficial features of the cage design are retained while a greater degree of radial expansion of the slips is possible allowing minimization of tool inventory for situations where a lighter wall casing requires further slip extension. The release system allows the lower cones to be driven out from under the lower slips, thus facilitating release of the grip of the lower slips from the casing for extraction of the packer. The mechanical release is functional through the mandrel, whether tension or compression is placed on the mandrel. Alternative designs are presented for the capture of the lower cone by the cage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art caged slip showing limitations of bearing load transmitted to the slips from the cones, as well as limitations of outer extension created by the design. 
     FIG. 2 is a perspective exploded view of the apparatus. 
     FIG. 3 is an assembled perspective view of the same apparatus. 
     FIG. 4 is a section along lines  4 — 4  of FIG.  3 . 
     FIGS. 5 a - 5   c  are a sectional view of a packer using the slips of the present invention in the run-in position. 
     FIGS. 6 a - 6   c  are the same views as shown in FIGS. 5 a-c  with the slips in the set position. 
     FIGS. 7 a-c  are the same views as FIGS. 6 a-c  with the slips now in the released position. 
     FIGS. 8 a-d  illustrate the preferred embodiment which facilitates mechanical displacement of the lower cone away from the lower slips, illustrating the assembly in the run-in position. 
     FIGS. 9 a-d  are the views of FIGS. 8 a-d,  showing the packer in the set position. 
     FIGS. 10 a-d  illustrate the fully released position after the lower cone has been moved downwardly from the lower slips and the mandrel picked up from the surface. 
     FIG. 11 is a side view of the preferred embodiment of the cage, indicating the lower end slots which capture the lower cone. 
     FIG. 12 is an end view of the cage shown in FIG.  11 . 
     FIG. 13 is an end view of the lower cone, indicating the dove-tailed passages which accept the lowermost portions of the cage shown in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 illustrates the slip area of a downhole tool which in the preferred embodiments shown in FIGS. 5-7 is a packer. FIG. 2 illustrates the Mandrel  18  which can also be seen in FIG. 5 b . The exploded view of FIG. 2 aids in understanding of how the assembly is put together and further aids in understanding of its operation. The cage  20  has a closed end  22  from which extend a series of longitudinal members  24  defining openings or windows  25 . At their lower end  26 , each of the longitudinal members  24  are threaded so as to accept a ring  28  in order to complete the assembly. Other mechanisms for attaching the ring  28  to the longitudinal members  24  are within the purview of the invention. To begin the assembly, cone  30  is initially inserted through lower end  26  so that the shoulder  32  is retained by member  34  which forms a part of the closed end  22 . As shown in FIG. 2, there are four discrete ramps  36 , each having an outer dimension  38  with shoulder  32  defined adjacent thereto. The outer dimension  38  of the cone  30  is, at most, equal to, but can be smaller than, the outer dimension of the members  34  which define the closed end  22  of the cage  20 . 
     With cone  30  inserted through the open end of cage  20  until shoulders  32  connect with members  34 , the slips  48  are pushed into place and the mandrel  18  can now be installed through cones  30  and  40  which are already in place with respect to cage  20 . Cone  40 , which is preferably identical to cone  30  but in opposed orientation, slides over the mandrel  18  past lower end  26 . Again, the tapers  42  extend in the gap between the longitudinal members  24  as shown in FIG.  3 . The outer dimension  44  of the cone  40  is equal to the outer dimension of the members  24 . FIG. 3 shows more clearly the extent of the outer dimension of cone  30  as being eqidistant with the outer surface  46  of the members  24  which define the cage  20 . It could be shorter if desired. 
     Once cone  40  is installed over mandrel  18 , ring  28  is threaded through lower end  26  and the assembly is complete as shown as FIG.  3 . 
     FIG. 11 illustrates the preferred embodiment for the cage  20 ′. Each of the longitudinal members  24 ′ has a slot  78 . Referring to the end view of FIG. 12, it can be seen that the longitudinal members  24 ′ have a trapezoidal cross-section designed to be slidably inserted into a conforming slot  80  in the cone  40 ′. A pin (not shown) extends into threaded opening  82  after extending through the slot  78 . Accordingly, the length of slot  78  defines a range of relative movement between the cage  20 ′ and the cone  40 ′. Each of the longitudinal members  24 ′ has a hole  84  to accept a shear screw  86  (see FIG. 8 d  to control the sequence of setting the sealing element assembly  88  after setting the slips  48 . Upon release of the slips  48  as will be described below for the preferred embodiment, the pin in opening  82  catches in the slot  78  to retain the lower cone  40 ′ to the cage  20 ′. This design of the preferred embodiment of the cage  20 ′ eliminates the use of the ring  28  which can be difficult to mount over slender longitudinal members  24  and which may require the elimination of some material to accommodate a thread which would accept the ring  28 . Instead, the longitudinal members  24 ′ are guided in a dove-tail type arrangement for relative longitudinal movement as between the lower cone  40 ′ and the cage  20 ′. In all other respects, the function of the components, including the lower cone  40 ′ and the cage  20 ′, is similar to the embodiment illustrated in FIGS. 2 and 3. 
     As part of the assembly after installation of cone  30 , the slips  48  (there being four shown in FIG. 2) are installed into the cage  20  prior to insertion of the mandrel  18 . In the preferred embodiment, the slips  48  are all identical and, therefore, only one will be described with the understanding that the description is equally applicable to the remaining slips. However, it should be noted that it is within the purview of the invention to use slips of differing design and that only the preferred embodiment is intended to include identical slips laid out at 90° spacing about the longitudinal axis of the tool with opposed wickers. The slip  48  has opposed wickers  50  and  52  extending from opposed T-shaped bodies  54  and  56 , respectively. A recess  58  is located on each side of each of the members  24  such that the extending tab sections  60  and  62  extend into recess  58  symmetrically on both sides of bodies  54  and  56 . The recesses  58  clearly do not retain the bodies  54  and  56  against outward movement. Instead, the function of recesses  58  is in the retrieval of the downhole tool for effecting release of the slips  20 . In essence, tabbed section  62  defines a pickup shoulder  64  which is engaged by a shoulder  66  (formed as part of recess  58 ) for release of the slips  20 , as will be described below. 
     Referring again to FIG. 2, the members  24  each have an undercut  68  extending from opposed edges thereof. “Undercut” is a term meant to include open slots as shown or closed slots such as a grove disposed completely in the middle of the edge of members  24 . This undercut engages a pair of opposed tabs  70  and this is the mechanism which limits the radial outward travel of the slips  48  as the tabs  70  come into contact with the end of the undercut  68 . The assembled view of FIG. 3 does not show the tabs  70  and undercut  68  but they can be more readily seen in FIG.  2 . 
     Thus, after cone  30  is inserted through the open end of cage  20  and all the slips  48  are inserted such that their tabs  70  are in undercut  68  and tabbed section  60  and  62  are within recess  58 , the mandrel  18  is pushed through the cone  30  as the cone  40  is installed over the mandrel and the entire assembly is secured by ring  28 . 
     The slips  48  are biased radially inwardly by band springs  72  which are more clearly shown in FIG.  4 . It should be noted that the band springs have been deliberately omitted from FIGS. 2 and 3 for clarity of the drawings but are shown in the section view of FIG.  4 . The band springs  72  span over a slip  48  generally in the area of recess  74  shown in FIG.  3 . The springs  72  extend below the members  24  through apertures  76  which even at full extension of the slips  48  still leaves clearance so that the spring  72  is not cut as the slips  48  are forced out by the cones  30  and  40 . 
     The operation of the caged slip assembly as depicted in FIGS. 2 and 3 is also shown in section in FIGS. 5 and 7. FIG. 5 is the run-in position which shows the slips  48  in a retracted position so that the wickers  50  do not extend beyond the outer dimension  46  of the cage  20 . FIG. 6 b  illustrates the slips  48  in the extended position which is also shown in the perspective view of FIG.  3 . Both cones move with respect to the slips. In order to accomplish this, in the known manner, by differential movement, the cone  40  is held stationary while the cone  30  is advanced toward it. This results in ramp  36  pushing out the slips  48  against tapers  42  of cone  40 . As a result, the slips  48  move radially outwardly until they engage the casing (not shown) or until the tabs  70  engage their travel limits within undercut  68 . The released position is shown in FIG.  7 (b). This is accomplished by an upward force directed to cone  30  which forces shoulder  32  against member  34 . The upward force applied to cone  30  pulls the tapered surface  36  out from under the slips  48  plus engages shoulder  32  to the cage  20  to impart an upward force on the cage  20 . This in turn is transmitted to the slip assembly by virtue of shoulder  66  contacting pickup shoulder  64 , which in turn pulls the slips  48  away from tapered surfaces  42  of cone  40 . 
     When setting the packer P as shown in FIGS. 5 and 6, relative movement occurs between a bottom sub  90  and a lock ring  92  which contains locking teeth  94 . Setting of the packer P as shown in FIG. 6 c  involves downward movement of lock ring  92  relative to sub  90 , with teeth  94  holding the set. Release is accomplished by a pickup force on the mandrel  96 . Mandrel  96  has a ring  98  which engages release ring  100  and carries it to shoulder  102 . The connection between the mating teeth  94  is now liberated as the release ring  100  moves away from teeth  94  to allow lock ring  92  to move past teeth  94  on the sub  90 . The packer P can then be extended for removal from the wellbore. During release, the sequence is such that the upper cone  30  is pulled away from the upper end of the slips  48 , as shown in FIG. 7 b . As previously described, the cage  20  is left to pull the teeth or wickers  52  out of the casing with cone  40  still wedging against slip  48 . This type of release can be problematic in the sense that the wickers  52  have already dug into the casing and pulling them off of a cone such as  40  may at times be difficult to accomplish. Thus, in a preferred embodiment of the present invention illustrated in FIGS. 8-10, the lower cone  40 ′ is actually mechanically driven out from under the lower wickers  52  prior to cage  20 ′ interacting with the slips  48  in an attempt to pull wickers  52  relative to the casing. This will be explained in more detail below. 
     Those skilled in the art will appreciate the advantageous features of the disclosed design. The cones  30  and  40  have tapers  36  and  42  which extend to outer dimensions such as  38  which are at least equal to the outer dimension  46  of the cage  20 . What this means is that the ramp surfaces  36  and  42  can bear over a greater area on the slips  48  and the amount of bearing area is not limited as in the prior art where the cone assembly in its entirety, including the ramp surfaces, was behind the openings  14  of the longitudinal members  12  which define the cage as shown in the prior art FIG.  1 . Additionally, the use of the tabs  70  regulates the radial outward movement of the slips  48  in case they are extended to their maximum limit without encountering a segment of the casing. 
     With the design shown in FIGS. 2 and 3, the thickness of members  24  can vary to allow the appropriate structural strength to the cage assembly  20 . However, varying the thickness of members  24  does not limit the outer travel available to the slips  48 . The definition of the outer travel of the slips  48  is given by the depth and/or location of the undercut  68  and the position of the tabs  70  on the slips  48  in relation with the wickers  50 . Since the members  24  already have larger recesses such as  58  to accommodate the slips  48 , the undercut  68  can be varied so that a relatively thick cross-section of the members  24  can be employed while in discrete small areas an undercut  68  can be provided to allow significant radial movement of the slips  48 . This versatility allows a single tool to be used in situations involving casings of different wall thicknesses as opposed to having on tap a variety of tools to be used depending on the particular casing size in which the slips  48  are to be set. Finally, the full advantages of protecting the slips  48  used in a caged design is retained while these other additional advantages are obtained. To further protect the slips  48  during run-in, the springs  72  hold them in a retracted position between the members  24 . Thus, with the cones in effect being disposed in the windows defined between members  24 , a greater load capacity of the slips  48  is achieved as the compact area on the slips  48  is increased. The cage  20  also serves as a transmission conduit for a pickup force which pulls the slips  48  off of tapers  42  on cone  40 . 
     Referring to FIGS. 9 a-d , the setting and releasing technique of the preferred embodiment will be described. The mandrel  96 ′ extends through the packer P. A setting sleeve  104  is used to push against upper gauge ring  106 , which in turn compresses the element assembly  88  against the lower cone  40 ′ which is held by the mandrel  96 ′ at threads  108 . The lower cone  40 ′ supports the body  18 ′. The upper cone  30 ′ is retained to the body  18 ′ by lock pin  110 . Accordingly, downward pressure on the setting sleeve  104  with a known setting tool breaks shear pin  86 , allowing wickers  52  to be ramped outwardly on lower cone  40 ′. Thereafter, lock pin  110  moves down with cone  30 ′ in a slot  116  in body  18 ′, allowing upper cone  30 ′ to move wickers  50  outwardly against the casing. Thereafter, the sealing element system  88  is compressed and the set position of the slips  48  is held by body lock ring  112 , while the set of the seal element system  88  is held by body lock ring  114 . The fully set position is shown in FIG.  9 . Here, the lock pin  110  has translated in slot  116  of body  18 ′, allowing the upper cone  30 ′ to be forced under wickers  50 , whereupon lock ring  112  holds the set of the slips  48 . The sealing element system  88  has been compressed against the casing and its position secured by lock ring  114 . 
     Referring to FIGS. 9 c  and  d,  the body  18 ′ has a lower end  118  with an internal pickup shoulder  120 . A split ring  122  sits in groove  124  on the mandrel  96 ′. At the lower end of the lower cone  40 ′ is a wedge member  126  biased with a garter spring  128  against an elongated groove  130  on the mandrel  96 ′. The wedge  126  is held to the lower cone  40 ′ by a ring  132  which is secured from drift ring  134 , which is itself connected to lower cage  20 ′ at thread  136 . 
     Release of the packer P involves rotating mandrel  96 ′ to the right under a setdown force. The mandrel  96 ′ bears against body  18 ′ at a shoulder  138  (see FIG. 9 a ). The thread  108  is left-hand so that rotating the mandrel  96  to the right, with mandrel  96 ′ bearing down on body  18 ′, forces the lower cone  40 ′ to rotate in the opposite direction and thus translate downhole away from wickers  52 . The pin (not shown) in groove  78  defines the lower range of movement of lower cone  40 ′. The bias of garter spring  128  on wedge  126  further facilitates the relative rotation and, thus, translation of the lower cone  40  with respect to the mandrel  96 ′. After a sufficient amount of rotation to the right which would have driven the lower cone  40  downwardly, a pickup force is applied to the mandrel  96 ′ and the body  18 ′ is engaged by mandrel  96 ′ as split ring  122  engages shoulder  120 . A pickup force thereafter results in pulling out the upper cone  30 ′, and with it cage  20 ′, from under wickers  50  in the manner previously described. However, due to the initial forcible movement of lower cone  40 ′ downwardly, the cage  20 ′ can pull the slips  48  back to a relaxed position shown in FIG. 10 c,  without having to pull the wickers  52  out of the casing since the downward extension of lower cone  40 ′ has undermined the wickers  52  at the time that the upper cone  30 ′ is pulled out from under wickers  50  and continues to pull the slip assembly  48  through cage  20 ′ upwardly in a situation where wickers  52  are no longer wedged into the casing by lower cone  40 ′. The slips  48  settle into the position shown in FIG. 10 c,  while the sealing element system  88  fully relaxes so that the packer P can be pulled out. 
     Situations could arise where it is not known at the surface if there is a downward force applied on mandrel  96  at thread  108 . If there is a residual tensile force while mandrel  96 ′ is turned to the right, mandrel  96 ′ will simply unthread at thread  108  and rise upwardly. The packer P can still be released in the manner just described if, after sufficient turning to the right to release thread  108 , weight is again set down. This setdown weight after undoing thread  108  will put a downward load on lower cone  40 ′ through the undone threads  108  to force it down and away from under wickers  52 . Thereafter, an upward force can be applied to mandrel  96  and the release procedure from that point is identical. 
     Those skilled in the art can see that one of the unique features of the packer P of the present invention is that the slips are not pulled off of the cones, which is generally a difficult way to release. Instead, whether the mandrel  96  is in compression or tension, a technique is illustrated to mechanically force the lower cone  40 ′ out from under wickers  52  of slips  48  a sufficient distance so that when an upward force is applied, the upper cone  30 ′ can be pulled out from under wickers  50 , which can then be followed by upward movement of the slips  48  where wickers  52  are already undermined due to previous downward forcing of lower cone  40 ′. The contrast in the release of the packer P between the preferred embodiment illustrated in FIGS. 8-10 can be more clearly seen by a comparison to the technique revealed in FIGS. 5-7. The significant difference in the two embodiments is that the lower cone  40 ′ is forcibly moved out from below the lower slip or lower wickers  52 . The technique shown in FIGS. 8-10 can be used for any kind of slip system and is not limited to the cage and slip design revealed in FIGS. 2 and 3. It can be used for slip systems oriented in one direction or combination slip systems oriented in opposed directions without departing from the spirit of the invention, and can be used with a variety of slip-retaining systems. Rather than using a thread such as  108 , other techniques to mechanically displace the lower cone  40  can be employed, such as a J-slot system. One of the features of the present invention is that it is simple to build and operate and, therefore, more reliable, particularly when compared to prior systems involving a multitude of pistons which are actuated hydraulically by dropping balls so as to cause setting and release hydraulically of a sealing system and slip system, such as previously used in dual-bore packers by Baker Oil Tools and offered under Model CT-ESP. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.