Abstract:
A zero backlash downhole setting tool includes a mandrel having a number of recesses therein. A subassembly having a number of fingers is at least partially receivable in the recesses. The subassembly is in force transmissive communication with a device to be set. A lock wedge is in radially deflecting communication with the fingers and a setting sleeve is in operable communication with the device to be set and the lock wedge. Also included is a method for setting a device with zero backlash.

Description:
BACKGROUND 
     Common in the downhole drilling and completion arts is the traditional body lock ring. The ring is well known and includes a finely threaded section commonly referred to as “wicker threads” or “wickers” on an inside dimension of the body lock ring that are configured to be engageable with a set of wickers on an outside dimension surface of another component. The body lock ring may be urged along the other component under an applied force to ratchet into a final set position. Because there is a finite distance between adjacent peaks of wicker threads, there is necessarily a potential backlash. In the event that the applied force brings the wickers to very close but not quite the next wicker trough, the device being actuated will relax in backlash by the distance between the wickers. It is possible to reduce backlash by reducing the peak-to-peak distance between adjacent wickers. A reduction in this dimension, however, is often accompanied by a reduction in every tooth dimension including height and flank surface area as well. A reduction in tooth flank surface area tends to proportionally reduce the “holding ability” of such flanks. While the backlash is necessarily reduced in this type of construction, the potential for slippage of the body lock so constructed is increased. Since slippage is unquestionably undesirable, wickers with reduced peak-to-peak dimensions are not often the selected solution to the backlash problem. 
     In some situations the backlash is inconsequential while in others it can be catastrophic to the function of the particular tool or device. For example, if the device is a sealing tool, the backlash may allow sufficient energy in the seal to relax that the seal function is substantially lost. In other devices, while the entire or any substantial part of the functionality may not be lost, it clearly would be better for the ring to retain the input energy than to lose energy. Hence, it is axiomatic that the art would well receive improved apparatus where backlash is reduced or eliminated. 
     SUMMARY 
     A zero backlash downhole setting tool including a mandrel having a number of recesses therein; a subassembly having a number of fingers at least partially receivable in the recesses, the subassembly in force transmissive communication with a device to be set; a lock wedge in radially deflecting communication with the fingers; and a setting sleeve in operable communication with the device to be set and the lock wedge. 
     A method for setting a device with zero backlash including running the zero backlash downhole setting tool including a mandrel having a number of recesses therein; a subassembly having a number of fingers at least partially receivable in the recesses, the subassembly in force transmissive communication with a device to be set; a lock wedge in radially deflecting communication with the fingers; and a setting sleeve in operable communication with the device to be set and the lock wedge into a borehole with a device to be set; urging a setting sleeve in a direction to set the device; moving a lock wedge with the setting sleeve into contact with the fingers; and deflecting the fingers into the recesses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
         FIG. 1  is a schematic cross sectional view of a zero backlash downhole setting tool in an unset position; 
         FIG. 2  is a perspective view of the fingers illustrated and identified in  FIG. 1 ; 
         FIG. 3  is a perspective view of a mandrel upon which other components of the downhole setting tool mount, and that is configured to receive the fingers illustrated in  FIG. 2 ; 
         FIG. 4  is an illustration similar to that of  FIG. 1  but somewhat magnified and in the set position; and 
         FIG. 5  illustrates alternate surface treatments for the fingers illustrated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a zero backlash downhole setting tool  10  includes a mandrel  12  having a number of recesses  14  therein. The recesses are illustrated in the Figures hereof as four in number but it is to be understood that other numbers of recesses  14  are also employable. Each recess  14  includes two ends  16  and  18  (see also  FIG. 3 ). Ends  16  are larger cross sectionally than ends  18 . More specifically, and addressing the shape actually illustrated (but recognizing that the specific shape is not intended to be construed as limiting), the cross section of end  16  is in the shape of a trapezoid. End  18  is also in the shape of a trapezoid but the area defined by the trapezoid at  16  is greater than the area defined by the trapezoid at  18 . In one embodiment each side of trapezoids at end  16  are larger than each side of the trapezoids at end  18 . 
     Mounted at the mandrel  12  and still referring to  FIG. 1 , is a device  20  (such as a seal or any other axial force settable tool) to be set by the downhole setting tool  10 . As illustrated the device  20  is a seal but it is to be understood that any device requiring axial compression for setting can be set by the downhole setting tool  10 . As illustrated the device  20  is integral with a plurality of fingers  22 . The fingers are deflectable radially inwardly at least partially into recesses  14  during use of the downhole setting tool  10 . Facilitating flexibility of the fingers  22  in the illustrated embodiment is a flexibility groove  24  extending from an inside dimension surface  26  toward an outside surface  26  without reaching the outside surface  26  creating a living hinge  28 . In an alternate embodiment that would illustrate the same as the  FIG. 1  embodiment can be configured with the fingers  22  supported not by the device  20  but by their own ring  25  that will be adjacent the position the living hinge  28  occupies in device  20  (see  FIG. 2 ). Such embodiment will be distinct from device  20  at line  27 . The alternate subassembly  29  of the fingers will other than in  FIG. 2  appear similar to that illustrated since that subassembly will be directly adjacent the device  20 . 
     Still referring to  FIG. 1 , one or more resilient elements  30  are positioned to be axially compressively loadable during use of the downhole setting tool  10 . In one embodiment the resilient elements are a series of spring washers. As illustrated, the spring washers are frustoconical washers. Adjacent the fingers  22  is a lock wedge  32  having a frustoconical inside surface  33  that is moveable into contact with the fingers to maintain a particular selected position of the fingers during use of the device. The surface has an angle alpha of greater than about 0 degrees and about 45 degrees to facilitate self locking of the frustoconical surface with the fingers. In a specific embodiment the angle is about 7 degrees. The angle alpha appropriately selected in accordance herewith can be determined using the formula:
 
alpha=arctan(coefficient of friction)
 
     The embodiment of  FIG. 2  illustrates a smooth surface having, accordingly, a relatively low coefficient of friction. In other embodiments, two illustrated in  FIG. 5  at numeral  35  and  37 , a surface having a greater coefficient of friction is presented enabling different angles. Numeral  37  indicates a wickered (toothed profile) surface that will bite into the frustoconical surface  33  of the lock wedge  32 . It should be noted that the surface  33  can be textured similarly, if desired. Further it is noted that each of the fingers  22  may have the same surface texture or may have different surface textures, as desired. 
     The downhole setting tool  10  further includes a setting sleeve  34  having an inside diameter surface  36  that is large enough to extend over an outside dimension of the lock wedge  32 . 
     In operation, a setting force is applied from somewhere to the left of the drawing in  FIG. 1  on setting sleeve  34 . The setting force may be from a surface location or other remote location. Upon initial axial load, the force is transmitted to the one or more resilient elements and through those to the device  20 . The one or more resilient elements are to be selectively compressed by the action of the setting sleeve  34  primarily so that a significant amount of biasing force remains available in the system post setting. It will be appreciated that the setting sleeve  34  inside dimension surface  36  extends axially farther than the lock wedge does leaving an annular volume  38 . The volume  38  functions to ensure that the one or more resilient elements  30  are selectively compressed while the setting sleeve  34  is being set and before making contact with the lock wedge  32 . Once the one or more elements  30  are compressed to the selected degree, the degree being related to substantial set of the device  20 , setting sleeve  34  closes the volume  38  and causes a contact between sleeve shoulder  40  and lock wedge end  42 . Because the one or more resilient members are not fully compressed prior to or even at the contact between sleeve shoulder  40  and lock wedge  42 , there is still the possibility of relative movement between the setting sleeve  34  and the finger  22 , which relative movement is needed to allow the lock  32  to move toward the device  20  and deflect the finger(s)  22  radially inwardly into contact with the recesses  14 . 
     It is to be understood that the finger(s)  22  deflect at the living hinge  28  and hence do not directly radially inwardly move as a unit but rather tips  44  of the fingers  22  will move more radially inwardly than bases  46 , see  FIG. 2 . 
     The set position of the downhole setting tool  10  is illustrated in  FIG. 4  where the position of the tips  44  of the fingers  22  are shown more deeply received in the recess  14  than the bases  46  of the fingers  22 . At this point the particular shape of the recesses  14  and the particular shape of the fingers  22  will be better understood. Because of the trapezoidal shape, or other shapes having similar functionality as conveyed hereunder, walls  48  the fingers  22  will have contact with walls  50  of the recesses  14  no matter what relative axial position the fingers and recesses have. The further the tips  44  are from end  18  the deeper into the recesses  14  the tips  44  will go before wall-to-wall contact is achieved. The closer the tips  44  are to the end  18  of the recesses  14  the shallower the radially movement of the tips  44  needs to be before achieving wall-to-wall contact. Once wall to wall contact is achieved, and the lock wedge is jammed radially outwardly of the fingers  22 , the system cannot move and hence the setting force put into the device  20  will be maintained indefinitely. The holding force supplied by the downhole setting tool  10  is frictional between the walls of the fingers and the walls of the recesses. Since there are no peaks such as wickers have, there is no backlash. The downhole setting tool  10  described has no backlash and in addition has the benefit of a compressed spring force acting to hold the device  20  in a set position. 
     While one or more 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.