Patent Publication Number: US-8109339-B2

Title: Zero backlash downhole setting tool and method

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; a body lock ring at the mandrel; a setting sleeve in operable communication with a device to be set; a rotary take-up in tensile force transmissive contact with the device to be set; and a follower housing configured to follow the rotary take-up in a first mode of operation and extend away therefrom in another mode of operation, the follower being engaged with the body lock ring. 
     A zero backlash downhole setting tool including a setting sleeve; a linear to rotary motion converter depending from the setting sleeve; a rotary take-up; a follower housing forming an interface with the rotary take-up; and a body lock ring in operable communication with the follower housing, a backlash of the body lock ring being counteractable by a change in combined length of the rotary take-up and the follower housing. 
     A method for setting a downhole tool with zero backlash including urging a setting sleeve against one or more resilient elements; transmitting a setting force to a device to be set through the one or more resilient elements; pulling a rotary take-up and a follower housing thereby causing a ratcheting of a body lock ring with the follower housing; axially translating a pin connected to the setting sleeve to impart a rotation to the rotary take-up; and extending the combined length of the rotary take-up and the follower housing to counteract backlash in the body lock ring. 
    
    
     
       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 perspective cross sectional view of a zero backlash downhole setting tool as described herein with a setting sleeve shown in phantom to illustrate underlying structure; and 
         FIG. 2  is a perspective view of the tool illustrated in  FIG. 1  without a setting sleeve shown and in the actuated position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a perspective cross-section view of a zero backlash downhole setting tool  10  is illustrated. The tool comprises a setting sleeve  12  (shown in phantom to allow visibility of the underlying components) in force transferable communication with one or more resilient elements  14 . The one or more elements may comprise a coil spring, a series of spring washers, which may be of the frustoconical type, or any other resilient configuration that allows for force transmission sufficient to set a settable device  16  and yet allow for sufficient further compression to allow the setting sleeve to actuate other components as disclosed hereunder. The one or more elements  14  are in force transferable communication with the device  16  to be set in the downhole environment. The device  16  may be a seal or may be any other type of device that can be set downhole upon axial actuation. Further included in the tool  10  are a rotary take-up  18  and follower housing  20 , the follower housing  20  being in operable communication with a body lock ring  22 , which itself is in operable communication with a mandrel  24 . 
     Referring to  FIGS. 1 and 2 , the rotary take-up  18  includes one or more slots  26  that are receptive to a pin  28  that is mounted to the setting sleeve  12 . Movement of the pin  28  in an axial direction of the tool  10  will cause the rotary take-up  18  to rotate. This is due to angled surface  30 , upon which the pin  28  will bear when urged toward the device  16  during setting of the device  16 . Loaded contact between the pin  28  and the surface  30  occurs in use only after the device  16  to be set has been set and stopped moving downhole. Thereafter, the one or more resilient elements  14  are further compressed by the setting sleeve  12 , which translates the pin  28  toward the device  16  and into contact with the surface  30  thereby rotating the rotary take-up  18 . 
     Referring to  FIG. 2 , it is to be noted that the interface between rotary take-up  18  and follower housing  20  is helical. The interface may comprise a single helix or may comprise a number of shorter part helical ramps  40  and  42  as illustrated in  FIG. 2 . It will also be noted that one or more hooks  44  prevent the rotary take-up  18  from being longitudinally separated from the follower housing  20  at least until relative rotation occurs therebetween. The need for this feature will become clearer during discussion of the operation of the tool  10  hereunder. 
     Referring back to  FIG. 1 , there is shown a configuration (here shown as groove  46 ) that is intended to function to cause the rotary take-up  18  to be drawn along with the device  16  when that device is moved downhole pursuant to setting of the device  16 . This puts the rotary take-up and follower housing in tension, relying upon the hooks  44  to maintain the two components connected to one another. The configuration is illustrated as a hook that is integral with the device  16  but it is to be understood that any arrangement that allows affixation of the rotary take-up to the device  16  while permitting relative rotation between the two will be equally effective. This includes but is not limited to set screws extending through one of the rotary take-up  18  and the device  16  into a groove of the other of the same two components. As illustrated, screws  48  extend from the rotary take-up into a groove  46  in the device  16 . As noted above these could easily be configured oppositely. 
     In operation, the tool  10  is run into a borehole (not shown) and a setting load is placed upon the setting sleeve  12  from some remote location such as a surface location. The setting sleeve compresses the one or more resilient elements  14  to a partial degree that is sufficient for the setting force to be transmitted to the device  16  to be set. The device is hence set using that force. During the movement that is a part of the setting action of the device  16 , for example the movement of an uphole end of a seal relative to a downhole end of a seal, the rotary take-up and the follower housing are drawn downhole. The impetus for this first mode of operation is the groove in the device  16  as shown and through the set screws  46  into the rotary take-up  18 , through the hooks  44  and into the follower housing  20 . As the follower housing  20  moves in the downhole direction, it ratchets along the body lock ring  22  which itself ratchets along mandrel  24 . The follower housing  20  is not loaded in compression by anything but rather simply drawn along by tensile load. The ratcheting along the body lock ring provides an anchoring function for the set force and is similar to any common body lock ring operation. It does suffer the drawback of backlash just as do similar devices of the prior art. In accordance with the invention described herein however, the backlash is counteracted with other components of the tool  10  as further described hereunder. 
     Once the device  16  is fully set, it stops moving downhole and the setting force of the setting sleeve mounts on the one or more resilient elements  14 . The elements  14  continue to deform under this load and accordingly occupy less axial space. This allows the setting sleeve  12  to continue to move toward the device  16  without the device  16  moving. Because the pin  28  is connected to the sleeve  12 , it too will translate toward the device  16 . Further, because the rotary take-up  18  and follower housing  20  are only moved axially by tensile load from the device  16 , they do not move directly axially at this stage. Rather, as the pin  28  comes into loaded contact with the surface  30 , a rotary input is caused for the rotary take-up  18 , which responsively rotates. The rotation, a second mode of operation, causes the helical ramp or part helical ramps  40  and  42  as shown to climb each other, effectively lengthening the combined length of rotary take-up  18  and follower housing  20 . The increase in length will cause the follower housing to move away from the device  16  thereby taking up the backlash in the body lock ring  22 . It is noted that because the follower housing  20  nor the rotary take-up  18  are compressively loaded during the process thus far described, the rotary input of the pin  28  will easily rotate the rotary take-up  18  and the ramps  40  and  42  will easily slide past one another. Once the rotation of the rotary take-up is complete however, meaning that all of the backlash in the system has been counteracted by the lengthening of the combined length of the rotary take-up  18  and the follower housing  20 , the rotary take-up and follower housing  20  will be subjected to compressive load upon release of the setting force from the setting sleeve. Under this compressive load, rotation of the rotary take-up is inhibited by friction to the point that such rotation is prevented. The angles alpha of the ramps  40  and  42  are selected to disallow backdriving thereof. Angles providing this result range from greater than about 0 degrees to about 45 degrees, with one specific embodiment being at about 5 degrees. The angle alpha appropriately selected in accordance herewith can be determined using the formula:
 
alpha=arctan(coefficient of friction)
 
     It should be appreciated that the greater the angle, the less the required stroke of the setting sleeve and the less rotation of the rotary take-up needed to counteract backlash however, the greater the angle, the easier for the system to be back driven. For higher angles the ramps  40  and  42  will require friction enhancing surface treatments such as roughness. 
     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.