Abstract:
A dog sub is provided for use in an assembly for running liners with weight-set packers and/or other mechanically or hydraulically actuated devices that need to be located. The dogs are retained by a sleeve so that an applied pickup force to determine that the running string had released from the liner can be applied which even results in removal of the dog sub from the extension tube of the weight-set packer. The dogs are held in a retracted position, even if taken out of the extension tube initially. Thereafter, the dog sub is supported off the extension tube and the locking sleeve on the dogs is liberated, with the dogs inside the extension tube. A subsequent pickup force allows the dogs to move outwardly, whereupon a subsequent setdown force locates the dogs on the setting extension tube. A subsequent setdown force sets the packer and breaks a breakable member, such as a shear pin. Upon removal to the surface, surface personnel can see that a shear pin has broken to indicate that the requisite force has been applied to the weight-set packer.

Description:
This application claims priority from a Provisional Patent Application entitled Unlocking Packer Setting Method &amp; Device, filed by the same inventors on Nov. 12, 1998, and accorded Ser. No. 60/108,043. 
    
    
     FIELD OF THE INVENTION 
     The field of this invention relates to devices and methods for setting packers and/or locating other types of tools in a liner string, particularly in the context of weight-set packers in deviated wellbores. 
     BACKGROUND OF THE INVENTION 
     Packers are used in many applications downhole. In one application, packers are run with a liner which is to be hung in the wellbore. In these applications, a running tool is used with a tubing string to position the liner and set the hanger. After the liner hanger is set, it is common practice to release the running tool and raise the work string several feet. The work string is raised prior to cementing the liner to check for weight loss as an indication that the running tool has released from the liner. Thereafter, it is desirable to lower the work string and apply a downward force through the running tool and into the liner during cementing so as to counteract the upward forces due to hydraulics when the cement is pumped through the liner. When a compression-set liner top packer and/or another mechanical or hydraulic device in the string is used, a packer-setting device which consists of a dog sub is usually positioned just above the running tool. The dogs are compressed to fit inside an extension of the weight-set packer during run-in. 
     In the past due to deviation in wellbores, it was uncertain as to where the dogs would wind up when pulling up at the surface to ensure a release of the running tool from the liner. The problem in prior designs was that if the dogs were pulled out of the extension of the weight-set packer when testing for release of the running tool from the liner, a subsequent downward force would prematurely set the packer prior to the onset of the cementing job or prematurely locate the running string opposite another device which is mechanically or hydraulically operated. One solution that had been implemented was to put an unduly long extension tube on the weight-set packer to ensure that no matter how high (within reason) the dog sub was lifted that the dogs would remain inside the tube so that the string could be set down to resist the hydraulic forces occurring during the cementing operation. However, lengthening the extension tube provided a restriction against circulation of mud being displaced by the advancing cement. This would prolong the time required to complete the cementing and thus increase costs for the well owner. It could also adversely affect the quality of the cementing job. 
     In the past, dog subs such as disclosed in U.S. Pat. No. 5,813,458 (“the &#39;458 patent”) could be employed to facilitate the operations of cementing, followed by setting the weight-set packer. Furthermore, as disclosed in the &#39;458 patent, a shear screw in the assembly could be used as a signal to surface personnel when extracting the dog sub to the surface that a sufficient force had been applied to the weight-set packer. However, the dogs in that patent were free to engage the extension tube if they inadvertently got pulled out of the extension tube during the procedure to determine that the running tool had released from the liner. 
     Accordingly, one of the objectives of the present invention is to provide a dog sub which can literally come out of a reasonably sized extension tube without release of the dogs to facilitate the step of determining that the running tool had released from the liner. Another objective is to then allow the dogs to be subsequently released when inside the extension so that thereafter, when removed from the extension, they can be used to set the weight-set packer and to provide the necessary signal to surface personnel that sufficient weight had been used to set the weight-set packer. 
     Another objective of the present invention is to facilitate the sequence of operations which involve setting the liner hanger, picking up the string as much as necessary to ensure disconnection of the running tool from the liner, setting back down into the liner and holding that position during cementing, picking up to allow the dogs to engage the top of the extension tube, setting down weight to set the packer, and to provide a signal to surface personnel that sufficient force has been applied to the weight-set packer. Accordingly, the objective of the present invention is to eliminate uncertainties of the prior art devices which could have catastrophic consequences if, during the pickup of the string to release the running tool from the liner, the dogs emerged form the extension tube on the packer. Should that occur, the running string would have to be pulled out of the hole and the dogs removed, followed by another trip back in the hole with the running string to facilitate the cementing job. Thereafter, the running string would have to be tripped out of the hole and some object located on the bottom end of the running string so that it would ultimately engage the extension tube on the weight-set packer to subsequently set the packer after the cementing job. The problem would be that the time delay involved in these extra trips would cause the formation to come back in around the liner, thus making circulation difficult for placement of the cement around the liner. On top of that, there are operational uncertainties of whether the weight-set packer could even be actuated at the conclusion of the cementing job with makeshift tools. Accordingly, one of the objectives of the present invention is to allow extraction of the dog sub from the extension tube without adverse consequences for the purpose of determining release of the running string from the liner. Those and other advantages of the method and apparatus of the present invention will become more apparent to those skilled in the art from a review of the detailed description of the preferred embodiment which appears below. 
     SUMMARY OF THE INVENTION 
     A dog sub is provided for use in an assembly for running liners with weight-set packers and/or other mechanically or hydraulically actuated devices that need to be located. The dogs are retained by a sleeve so that an applied pickup force to determine that the running string had released from the liner can be applied which even results in removal of the dog sub from the extension tube of the weight-set packer. The dogs are held in a retracted position, even if taken out of the extension tube initially. Thereafter, the dog sub is supported off the extension tube and the locking sleeve on the dogs is liberated, with the dogs inside the extension tube. A subsequent pickup force allows the dogs to move outwardly, whereupon a subsequent setdown force locates the dogs on the setting extension tube. A subsequent setdown force sets the packer and breaks a breakable member, such as a shear pin. Upon removal to the surface, surface personnel can see that a shear pin has broken to indicate that the requisite force has been applied to the weight-set packer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view through the dog sub of the present invention at the elevation of the dogs and fingers. 
     FIGS. 2 a-c  are, respectively, section views along lines A—A B—B, and C—C of FIG. 1 during run-in. 
     FIGS. 3 a-c  show the dog sub lifted out of the extension tube, with the dogs still retained in a retracted position and indicating the outward extension of the fingers. 
     FIGS. 4 a-c  illustrate the breakage of the shear pin retaining the cover sleeve on the dogs. 
     FIGS. 5 a-c  illustrate further downward movement into the extension tube upon further rotation of the fingers to liberate the dogs while inside the extension tube. 
     FIGS. 6 a-c  indicate removal of the dog sub from the extension tube and the engagement by the dogs of the extension tube for setting the weight-set packer. 
     FIGS. 7 a-c  indicate breakage of a shear pin to provide the signal to surface personnel that an appropriate amount of force has been applied to the setting sleeve for the weight-set packer when the dog sub is removed to the surface. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 2 a,  a lower mandrel  10  is secured to the top mandrel  12  at thread  14 . O-ring  16  seals the connection of thread  14 . The lower mandrel  10  is secured to the running tool (not shown), which in turn is connected to the liner and liner hanger (not shown). The weight-set packer (not shown except for its extension tube  18 ) is ultimately connected to the liner (not shown). Those skilled in the art will appreciate that a setdown force on the tube  18  sets the weight-set packer. It should also be noted that the top mandrel  12  is connected to the running string (not shown) for support from the surface. The top mandrel  12  has a longitudinal recess  20  which is aligned with a window  22  in the lower mandrel  10 . A key  24  extends into recess  20  and through window  22  to rotationally lock the top mandrel  12  to the lower mandrel  10 . Key  24  is retained by sleeve  26 , which is in turn held by fastener or fasteners  28 . 
     A series of dogs  30  are each biased outwardly by a spring or other biasing mechanism  32 . In the position shown in FIG. 2 a,  the dogs  30  are retained toward the top mandrel  12  by dog retainer sleeve  34 . Dog  30  is retained between dog support  36  and cover  38 . Cover  38  has an opening  40  through which the dog  30  can pivot outwardly, as shown in FIG. 6 a.  Each of the dogs  30  has a tab  42  which acts in conjunction with the spring  32  to create counterclockwise rotational motion of the dogs  30  when no longer retained by sleeve  34  and extension tube  18 , as will be explained below. 
     A shear ring  44  is held to the top mandrel  12  by a shear pin  46 . Those skilled in the art will appreciate that other techniques can be used to selectively retain the ring  44  to the top mandrel  12  without departing from the spirit of the invention. Ring  44  has an internal seal  48  and an external seal  50 . Seal  50  seals against the cover  38 , while seal  48  seals against the top mandrel  12 . Located below the shear ring  44  is a thrust bearing assembly  52 . The thrust bearing assembly  52  is retained above and below, respectively, by the shear ring  44  and dog support  36 . The thrust bearing assembly  52  is retained internally by the top mandrel  12  and externally by the cover  38 . A fastener  54  extends through the cover  38  and into dog support  36 . A stop ring  56  acts as a travel stop for shear ring  44 , as shown in FIG. 7 a.    
     The thrust bearing assembly  52  allows the work string (not shown), connected to the top mandrel  12 , to be rotated without rotating the dogs  30  to help in setting down weight on extension tube  18  with dogs  30 . This occurs because rotation of top mandrel  12  rotates the lower mandrel  10  because they are rotationally locked at key  24 . However, the assembly retaining the dogs  30 , which includes the dog support  36  and the cover  38 , is free to remain stationary as the top mandrel  12  rotates. With the shear pin  46  intact, as shown in FIG. 2 a,  rotation of the top mandrel  12  will also rotate the shear ring  44  on the other side of the thrust bearing assembly  52  from the stationary dog support  36 . 
     As shown in FIG. 2 c,  the dog retainer sleeve  34  is secured by a shear pin  58  to the cover  38 . It can be seen in FIG. 2 b  that the dog retainer sleeve  34  has a guide block  60  secured to it by fasteners  62  and  64 . A shifting block  66  supports a plurality of latch fingers  68  which are biased in a counterclockwise direction by a torsion spring  70  about a pivot point  72 . A retaining pin  74  extends through shifting block  66  and into a recess  76  in guide block  60 . A spring  78  biases the pin  74  away from recess  76 . The dog support  36  in FIG. 2 b  further comprises a hole  80  which is shown offset from the pin  74 . Those skilled in the art will appreciate that when there is alignment between the hole  80  and the pin  74 , as shown in FIGS. 4 b  and  5   b,  that the pin  74  can be biased by spring  78  to retract out of recess  76  for reasons which will be explained below. The shifting block  66  has a top end  82  which is ultimately engageable with dog support  36  on its surface  84  (see FIG. 4 b ). 
     The major components of the apparatus now having been described, its operation will be reviewed in greater detail. The run-in position is illustrated in FIGS. 2 a-c.  As shown in FIG. 1, those skilled in the art will appreciate that three separate views at the same elevation of the apparatus are revealed in FIGS. 2 a-c.  The dogs  30  are held in a retracted position by the dog retainer sleeve  34 . In the normal sequence of operations, the liner hanger (not shown) has already been set and the surface personnel are now in the position to pick up at the surface to ensure that the running tool (not shown), which is connected to the lower mandrel  10 , is free from the liner (not shown). Based on experience and the weight indicator at the surface, the surface personnel will apply an upward force to the top mandrel  12 , in effect potentially pulling the dogs  30  completely out of the extension tube  18 , if necessary. It should be noted that surface personnel may not actually know if they have pulled the dogs  30  all the way out of the extension tube  18 . This is one of the advantages of the present invention in that even though in the process of picking up to determine that there is a release from the liner by the running tool, the fact that the dogs  30  have been pulled outside of the extension tube  18  is immaterial since they will not expand because they are held by the dog retainer sleeve  34 . Accordingly, the surface personnel can pick up as high as they desire to obtain sufficient feedback to ensure that the running tool is free from the liner. 
     Comparing FIGS. 2 b  and  3   b,  it can be seen that the act of lifting the top mandrel  12  moves the fingers  68  clear of the upper end  86  of extension tube  18 . At this time, the torsion spring  70  rotates the fingers  68  counterclockwise. The dog retainer sleeve  34  temporarily stops the counterclockwise rotation of fingers  68  in the position shown in FIG. 3 b.  At the conclusion of the picking up to determine release of the running tool from the liner, the surface personnel will set down weight. As shown in FIG. 4 a,  the dogs  30  (still held by sleeve  34 ) are now back inside of extension tube  18 . The dog support  36 , which moves in tandem with the top mandrel  12  due to shear pin  46  and bearing assembly  52  below it, eventually reaches a travel limit as shown in FIG. 4 b,  when surface  84  contacts top end  82  of shifting block  66 . At this time the hole  80  aligns with the pin  74 . As shown in FIG. 5 b,  when the pin  74  retracts into hole  80  due to the force of spring  78 , the shifting block  66  is no longer secured to the guide block  60  to facilitate further advancement of the top mandrel  12  and further counterclockwise rotation of the fingers  68  along the upper end  86  of the extension tube  18 . 
     Referring now to FIGS. 3 c  and  4   c,  it can be seen that the shear pin  58  is broken as a result of the fingers  68  which are connected to guide block  66  at pivot point  72 , applying an upward force against the dog retainer sleeve  34  in reaction to a setdown weight. It should be noted that the level of force required to break shear pin  58  is significantly less than that required to set the weight-set packer by pushing down on extension tube  18 . Accordingly, as shown in FIGS. 3 c  and  4   c,  a setdown force applied from the surface, with the fingers  68  riding the top end  86  of the extension tube  18 , results in the breakage of shear pin  58 . As earlier noted and shown in FIG. 4 a,  at the time the shear pin  58  breaks, the dogs  30  are past the upper end  86  of the extension tube  18 . Once the pin  74  is biased back into hole  80 , the continuation of a setdown force from the surface allows the shifting block  66  to move downwardly with respect to the guide block  60 , as shown in FIG. 5 b.  Further force is necessarily applied to the dog retainer sleeve  34  as a result of the continued counterclockwise rotation of fingers  68 . To prevent marring of the inside surface of extension tube  18  when the dogs, unrestrained by sleeve  34 , are pushed down to facilitate cementing, a wear member  31  (see FIG. 5 a ), which can be a soft shear pin or the like, rides on the inside surface of extension tube  18 . 
     FIGS. 6 a-c  show that on a subsequent pickup force, fingers  68  finish their counterclockwise rotational movement and are now pointing directly uphole, having pushed the guide block  60  further up to better ensure the maximum window height availability for the dogs  30  to pivot outwardly outside of tube  18 , as shown in FIG. 6 a.    
     Referring to FIGS. 7 a-c,  it can be now appreciated that a subsequent setdown of weight, with the dogs  30  on the upper end  86  of extension tube  18 , will result in an applied force to the extension tube  18  to set the weight-set packer (not shown). Ideally, the shear pin  46  is set for the desired force to be applied to the extension tube  18  to set the weight-set packer. Accordingly, the act of setting the weight-set packer (not shown) will also break the shear pin  46 . Thus, when the assembly, including the running tool and the dog sub illustrated, is brought to the surface, surface personnel can see that shear pin  46  has broken. That is the signal that the requisite force has been applied to the weight-set packer through the extension tube  18 . 
     Those skilled in the art can now appreciate the operation of the apparatus and the method employed to provide greater reliability for the downhole operation previously described. One of the main features is that upon application of a pickup force for determination that a release of the running tool from the liner has occurred, it is immaterial that the dogs  30  are withdrawn outside of the upper end  86  of the extension tube  18 . Unduly long extension tubes which restrict circulation are not necessary with the apparatus and method of the present invention. The normal steps for subsequent cementing can occur as weight is set down again with the dogs  30  retained by dog retainer sleeve  34 , despite extraction of the dogs from the extension tube  18 . At this point, in the position shown in FIG. 5, the cementing operation can take place because a setdown force to reposition the running tool in the liner has occurred. Coincidentally, the setdown force repositions the dogs back inside the extension tube  18  and allows the shear pin  58  to break so as to liberate the dogs  30  to rotate counterclockwise under the force of springs  32  when they are later picked up out of tube  18 . A subsequent pickup force allows the dogs  30  to be pivoted outwardly by springs  32  so as to catch the upper end  86  of the extension tube  18 . A further setdown force will set the liner packer and ultimately break the shear pin  46  for the subsequent surface signal when the dog sub is brought to the surface. At this point, the tool can be used to locate another mechanical or hydraulic device in the liner string. Alternatively, it can be used in a liner string without a liner top packer where it can locate a mechanical or hydraulic device. It should be noted that the first upward pull to disconnect the running tool from the liner can now be done with confidence because it is known that the dogs  30  will not catch on the top end  86  of the extension tube  18 . It is only after subsequent picking up after breakage of shear pin  58  that the dogs  30  will catch on upper end  86  for setting the liner packer. 
     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.