Abstract:
A slip system includes a set of drive slips having wickers thereon, substantially all of which being truncated in cross-section; a set of gripping slips operatively interengagable with the set of drive slips; a drive slip end ring in operable communication with the set of drive slips; and a gripping slip end ring in operable communication with the set of gripping slips, the end rings capable of transmitting a load applied in an axial direction of the system to the set of gripping slips and the set of drive slips to tangentially load the set of drive slips and the set of gripping slips against each other thereby increasing a radial dimension of the system and distributing stresses created in a target tubular and method.

Description:
BACKGROUND 
   In the hydrocarbon exploration and recovery industry, it is often necessary to anchor equipment within a tubular structure such as a casing or tubing string. A common and long used apparatus for such duty is a set of slips with attendant support structure. In some embodiments, slips are utilized with conical structures that impart radially outwardly directed impetus on each slip as the slip is axially moved along the cone, usually under a compressive load. While such configurations have been extensively used, it is also known that this type of configuration can become stuck in the tubular structure in which it has been set, thereby rendering retrieval thereof difficult. 
   In another embodiment of a slip configuration, the slips are tangentially loaded to avoid the need for the conical portion. Depending upon the configuration of these tangentially loaded systems, there has been difficulty in retrieval or difficulty in creating acceptable holding strength. 
   As the art to which this disclosure pertains is always interested in improved technology, the disclosure hereof is likely to be well received. 
   SUMMARY 
   A slip system includes a set of drive slips having wickers thereon, substantially all of which being truncated in cross-section; a set of gripping slips operatively interengagable with the set of drive slips; a drive slip end ring in operable communication with the set of drive slips; and a gripping slip end ring in operable communication with the set of gripping slips, the end rings capable of transmitting a load applied in an axial direction of the system to the set of gripping slips and the set of drive slips to tangentially load the set-of drive slips and the set of gripping slips against each other thereby increasing a radial dimension of the system and distributing stresses created in a target tubular. 
   A method for distributing stress in a target tubular imparted by a slip system includes embedding a plurality of sharp wickers of the slip system into the target tubular; and contacting an inside dimension of the target tubular with a plurality of truncated wickers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
       FIG. 1  is a perspective view of one embodiment of the slip system disclosed herein in a set position; 
       FIG. 2  is a perspective view of one embodiment of the slip system disclosed herein in a retracted position; 
       FIG. 3  is a perspective view of one of the slips from the illustration of  FIG. 1 ; 
       FIG. 4  is a perspective view of another of the slips illustrated in  FIG. 1  having a distinct wicker configuration; and 
       FIG. 5  is an illustration of an alternate slip ring configured to unset the slip system. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , the slip system  10  is illustrated in perspective view. Apparent in  FIG. 1  is the configuration of a set of drive slips  12  and a set of grip slips  14  that together cooperate in a way that promotes tangential loading of the slips against one another to radially expand. Radial expansion is necessary to set the system  10  by driving certain portions of the wicker threads (numerically introduced and discussed hereunder) into a receiving tubular structure (not shown). System  10  further includes a drive slip ring  16  and a grip slip ring  18 . Ring  16  is endowed with interengagement (for example, T-shaped) slots  20  about a perimeter thereof, each of the slots  20  being substantially the same shape and set of dimensions as each other. Ring  18  on the other hand, in one embodiment, includes a plurality of interengagement (for example, T-shaped) slots  22  disposed about a periphery thereof having a first set of dimensions and a plurality of interengagement (for example, T-shaped) slots  24  having another set of dimensions. In the illustrated embodiment of  FIG. 1 , slots  22  and  24  alternate (single alternating) around the perimeter of ring  18 . It is to be understood, however, that more of slot  22  or slot  24  could be grouped together in alternate embodiments such as, for example, two slot  22 &#39;s next to one another and two slot  24 &#39;s next to one another alternating with the  22 &#39;s (double alternating). Further, there is no requirement that there be any particular number of a certain type of slot  22  or  24 , for example, there may only be one slot  24  or two slots  24 , etc. or each slot could be unique as desired (random alternating). 
   In each of the rings  16  and  18 , the position of slots  20 ,  22  or  24  are such, relative to each other, that slips  12  and  14  are alternately positioned when engaged with adjacent T-shaped slots in each ring. The alternate positioning of slips  12  and  14  is easily seen in  FIGS. 1 and 2 . 
   Finally, of note in  FIGS. 1 and 2  is the trapezoidal shape of each of the slips  12  and  14 . The trapezoidal shape is important because it facilitates radial expansion of the slip system  10  upon axial compression of the system  10  into a shorter axial dimension. Growth in the radial direction is of course important to a slip system because it is such radial growth that allows the system itself to become anchored into the receiving tubular structure. Because of the trapezoidal shape and positioning of that shape, each slip acts as a wedge (perimetrically) against its two neighboring slips. When the axial length of system  10  is increased, the radial dimension of the system  10  will necessarily and naturally decrease. 
   It is to be noted that the radial expansion of system  10  is affected entirely by tangential application of force through the slips  12  and  14 ; this means that the ID of the slip system can remain completely open and that conical structures previously used to radially displace slips are not necessary. 
   Referring now to  FIG. 3 , one of the drive slips  12  is illustrated in perspective view and enlarged from the  FIGS. 1 and 2  views. In the  FIG. 3  view there is visible interlocking members provided in each of the slips in order to keep them engaged as a single unit while simultaneously allowing them to slide relative to each other. Each one of the slips includes a keyed flange  26 , which in the embodiment illustrated, is of L-shape but may be of any shape that allows sliding motion while inhibiting disassociation of each slip from its neighboring slip. On an opposite side of slip  12  is a complementary flange keyhole  28 , one end of which is visible. It will be understood that the flange keyhole  28  extends the length of slip  12  as does keyed flange  26 . If one were to obtain an opposing slip (i.e. slip  14 ) one would notice that the keyed flange  26  and the flange keyhole  28  can be engaged as the slips  12  and  14  slid axially relative to one another. Sliding movement is thus enabled while lateral disassociation is prevented or at least inhibited. 
   It should also be noted in passing that an angle of the mating surfaces  30 , on each slip  12  and  14 , is dictated by a radius extending from the axis of system  10 . This angle ensures smooth and distributed contact along each face  30  to improve overall efficiency and strength of system  10 . 
   Still referring to  FIG. 3 , drive slips  12  of the current disclosure possess a number of wickers  32 , a substantial number of which are truncated. In the illustrated embodiment, all of the wickers  32  are truncated, but it is to be appreciated that merely a substantial number of the wickers must be truncated to achieve the benefit of distribution of stresses in the receiving tubular structure. It is possible to add pointed wickers without departing from the scope of the invention. Truncation  34  removes what would otherwise be a sharper point of a slip gripping wicker. In one embodiment the truncation amount is of a dimension that is about the same as the amount of a sharp wicker that would be embedded in the material of the receiving tubular structure. Slips  12  are so configured to enhance retrieveability of the slip system  10  as well as assist in the distribution of stresses in the receiving tubular structure. 
   Each one of the wickers  32  that is truncated, is so truncated to an extent about equal to the amount of penetration into the receiving tubular structure that is anticipated for pointed wickers on the gripping slips  14 . The reason for this is so that when the pointed wickers are maximally embedded in the receiving tubular structure, the wickers  32  will be radially loaded against the receiving tubular structure without penetrating it into. This distributes the stresses of the receiving tubular structure more evenly about the tubular structure consistent with contact around the entirety of the slip system  10 . One further benefit of the configuration of slips  12  is realized in the case of paraffin or other debris lining the inside dimension of the receiving tubular structure. Because wickers  32  are still above the surface of slips  12 , those wickers are able to penetrate debris at the inside dimension of the receiving tubular structure and still ensure contact of truncation  34  with the inside dimension surface of the receiving tubular structure forming a frictional engagement therewith. 
   Each wicker  32 , of course, possesses a pair of flanks  36 , which in one embodiment, are positioned at 45°. It is to be understood that other angles are possible. It is also noted that in the system  10 , it is not necessary to harden wickers  32 , as they are not intended to bite into the receiving tubular structure. This is not to say that it is undesirable to harden wickers  32  but merely that it is not necessary to do so. 
   Referring to  FIG. 4 , one of the gripping slips  14  is illustrated. It will be noted that there are two distinguishing features of gripping slip  14  over driving slip  12  as illustrated in  FIG. 3 . These are a length  40  of a T-upright  42 , and a configuration of wickers  44  and  46 . Addressing the wickers first, it will be apparent that in the illustrated embodiment, every other wicker is sharp pointed (wicker  44 ) while the intervening wickers  46  are truncated (single alternating). In this embodiment, the degree of truncation of wickers  46  is roughly equal to the expected penetration of wickers  44  into the receiving tubular structure (not shown). Again the purpose for this construction, like that of the drive slip illustrated in  FIG. 3 , is to distribute the load on the receiving tubular structure imparted by radial motion of slip system  10 . More specifically, upon full penetration of wickers  44  into the receiving tubular structure, wickers  46  come into contact with the inside diameter of the receiving tubular structure thereby distributing stress in that structure. It is to be appreciated that only one embodiment of the slip system contemplated is shown in  FIG. 4 . It is also possible for numbers of wickers  44  and  46  to be grouped such as two wickers  44  alternating with two wickers  46  (double alternating) or three wickers  44  alternating with three wickers  46  (triple alternating) or even a number of sharp wickers  44  alternating with a different number of truncated wickers  46  (random alternating). The overall point of alternating sharp and truncated wickers is to distribute stress otherwise imparted in an undistributed way to the receiving tubular structure. It is further possible to retain all of the wickers on slips  14  in the  44  configuration in some embodiments of the invention, since the truncated wickers  32  on the drive slips  12  will still substantially balance stresses in the receiving tubular structure. It will also be noted that pointed wickers  44  should be hardened such that they are sufficiently durable to penetrate the inside diameter of the receiving tubular structure. 
   Addressing now the upright  42  of the key structure  48 , and referring to both  FIGS. 3 and 4 , it is apparent that the length  40  of the upright section  22  is longer than that of the comparable portion of slip  12 . The reason for the length of this portion of slip  14  is to delay a tensile force being applied to this slip  14  when retraction of the slip system  10  is desired. Referring back to  FIGS. 1 and 2  and reiterating that the T-shaped slots  22  and  24  are distinct, a review of the drawing will make clear that T-shaped slots  24 , upon an axial tensile load on ring  18 , will cause an immediate transfer of the tensile load to the associated slip  14 . This is distinct from the T-shaped slots  22  wherein the same tensile load applied to ring  18 , is not immediately transferred to the associated slip  14  but rather the ring  18  must axially move relative to the associated slip  14  until surface  50  contacts surface  52 . Upon this contact, the tensile load will be transmitted to the associated slip  14 . In such configuration it will be appreciated that every other slip  14 , in the illustrated embodiment, will be pulled in a direct commensurate with retracting the slip system  10  prior to the other slips  14  being so pulled. This reduces the force necessary to retract the slip system  10 . In the illustrated embodiment, the force is roughly halved while in other embodiments with differing numbers of alternating T-shaped slots  22  and  24 , the reduction in tensile force required will be describable as a percentage of the whole proportional to the number of earlier pulled slips relative to the total number of slips associated with the subject ring. 
   It will be noted by the astute reader that ring  16  contains only T-shaped slot  20 . The reason that the staggered T-shaped slots are not required on ring  16  is that all of the associated slips  12  substantially lack gripping wickers and therefore, the tensile force required to unseat them is substantially less than that of the slips  14 . Therefore, there is no need to stagger the T-shaped slots in ring  16 . This is by no means to say that it is inappropriate to stagger T-shaped slots  20 , as it certainly is not only possible and functional, but rather merely to state that it is unnecessary. 
   Referring to  FIG. 5 , an alternate embodiment of ring  18  is illustrated which allows for the T-shaped structures on each of the slips  14  to be identical. In this embodiment, the T-shaped structure  48  is not required to be long, as it is illustrated in the  FIG. 1  and  FIG. 2  embodiments. It will be appreciated that the reason that the elongated section  42  is not needed, is that surface  50  of slots  22  is positioned closer to an end  60  of ring  18  than it is in the  FIG. 1  embodiment. One will also note that the clearances between the T-shaped structure  48  and the slots  22  has also been increased to account for potential axial movement of the system. This additional clearance alleviates unnecessary load on the structure  48  when the system is set. 
   While the figures in this application may suggest to one of ordinary skill in the art the existence of a clear uphole end and downhole end of slip system  10 , based upon conventional illustration methods, it is to be understood that slip system  10  is usable with either end uphole. Generally, it will be desirable to impart a compressive setting force against ring  16  and the drive slips  12  while maintaining ring  18  and gripping slips  14  stationary. This is, however, not a requirement and the slip system  10  is to be understood to be actuable and retractable from either end. It is also to be understood that the system is actuable and retractable from a position downhole of the system of a position uphole of the system. 
   While preferred embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.