Abstract:
An anchor system for high expansion applications is described. It features a gripping member that holds together a pair of links. The movement of the links is regulated to assure the gripping member moves into proper contact with the casing. Meshing gears or a pin and slot can do this, for example. The gripping member is shaped such that it can still transmit load through the links even if the pin connections fail. The gripping member is preferably contoured to the shape of the casing inner wall to enhance grip.

Description:
FIELD OF THE INVENTION 
     The field of this invention is anchor systems for well tools and, more particularly, high expansion bridge plugs or packers. 
     BACKGROUND OF THE INVENTION 
     Well tools frequently need to be anchored in casing for proper operation. In situations where the tool has to be delivered through tubing and set in casing, the anchor assembly must extend substantially from the run in position to grab the casing. This happens because the tool must be no bigger than a small dimension to be run smoothly through tubing and yet must expand substantially in percentage terms to grab the casing. In the case of a plug or packer, substantial directional forces are transmitted to the anchor system when such tools are set. 
     The designs of anchor systems in high expansion service have shown limited abilities to retain grip and some have released their grip under load. Generally these designs involve a release when the wickers on the end of a link that contacts the casing simply shear and the grip is lost. In the past, high expansion anchor systems involved rotating individual links that engage the casing with wickers mounted on an end. Examples of this design are U.S. Pat. Nos. 6,311,778 and 6,318,461. A through tubing design using similar anchor assemblies is shown in U.S. Re 32,831. In applications where high expansion is not an issue, the known technique of pushing slips out with cones has been employed, as shown in U.S. Pat. No. 6,220,348. 
     The problem with past designs is that they had a limited grip area due primarily to their layout of having wickers at the end of a thin link engage the casing wall. Even though multiple links would get independently actuated around the periphery of the packer or plug, the links were narrow and their grip limited for that reason. Even a plurality of such individual links could not support a tool in extreme loading conditions. What is needed and provided by the present invention is a way to increase the bite area of the gripping member that engages the casing wall. This has been accomplished in part due to the placement of the gripping member at the intersection of a plurality of links as well as controls built into the linkage to control the final movement of the gripping surface. Provisions for pin connection failure have been made so that the anchor of the present invention could still retain a grip if such a connection weakened or failed under heavy load. These and other advantages of the present invention will be more apparent to one skilled in the art from a review of the description of the preferred embodiment and the claims below. 
     SUMMARY OF THE INVENTION 
     An anchor system for high expansion applications is described. It features a gripping member that holds together a pair of links. The movement of the links is regulated to assure the gripping member moves into proper contact with the casing. Meshing gears or a pin and slot can do this, for example. The gripping member is shaped such that it can still transmit load through the links even if the pin connections fail. The gripping member is preferably contoured to the shape of the casing inner wall to enhance grip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is the run in position of the anchor using gears between the links; 
     FIG. 2 is the view of FIG. 1 in the set position; 
     FIG. 3 is an alternative embodiment of FIG. 1 shown in the run in position; and 
     FIG. 4 is the view of FIG. 3 in the set position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, only the anchor assembly is illustrated with it being understood that it can be a part of any downhole tool that needs anchoring. The tool will generally have a mandrel  10  with a lower hub  12  and an upper hub  14 . One of those hubs will move in tandem with the mandrel  10  while the other will be held stationary, during the setting procedure. In the embodiment illustrated in FIGS. 1 and 2, the upper hub  14  is movable toward the stationary lower hub  12 . There is a plurality of anchor assemblies A, and only one will be described with the understanding that the others are preferably identical to it. Each assembly A has an upper link  16 , pivotally mounted at its upper end  17  to upper hub  14  by a pin  18 . Lower link  20  is pinned at its lower end  22  to lower hub  12  by pin  24 . Slip  26  has wickers  28  for contacting the casing (not shown). Link  16  is pinned to slip  26  by pin  30 . Link  20  is pinned to slip  26  at pin  32 . Referring to FIG. 2, slip  26  has rounded interior areas  34  and  36  to accept ends  38  and  40  of links  16  and  20  respectively in the event of weakening or failure of either of pins  30  or  32 . Additionally, ends  38  and  40  feature meshing gears  42  and  44  so that the movement of links  16  and  20  is tied together to ensure that the slip  26  comes out flush against the casing (not shown). The gears  42  and  44  remove a degree of freedom for the slip  26  and prevent it from changing the relative positions of pins  30  and  32  as the links  16  and  20  rotate into the position shown in FIG.  2 . 
     As an alternative to gears  42  and  44 , FIGS. 3 and 4 illustrate another way to insure the flush contact of the casing wall by slips  26 . FIG. 3 shows the run in position, but the operation of the alternative design can be more easily seen in FIG.  4 . In this embodiment, there are no gears  42  and  44 . Instead, pinned to link  16  is guide link  46  that has a slot  48 . Pin  50  provides the connection to link  16 . Inserted in slot  48  is pin  49  of guide link  52 , which is connected, by pin  54  to link  20 . With this arrangement, the movements of links  16  and  20  are kept equal as hub  12  moves toward hub  14 . This ensures that slip  26  will engage the casing in a flush manner. The rounded areas  34  and  36  are also more clearly seen in FIG.  4 . It shows that upon failure of pin  30  or  32  the load from links  16  or  20  can be transferred to the curved areas  34  or  36 . In view of the close proximity of the ends  38  and  40 , a failure of either pin  30  or  32  when slip  26  is in contact with the casing could also be absorbed by one end  38  abutting end  40  while bearing against the curved areas  34  or  36 . 
     The slips  26  can be curved to better conform to the casing inner wall. The gap between pins  30  and  32  can be increased to allow making the slip  26  taller to increase its contact area with the casing. The guiding of the movement as between links  16  and  20  allows the slips  26  to move outwardly in a flush orientation to the casing wall for a maximum secure grip. The gears  42  and  44  can be replaced with a friction contact between links  16  and  20 , although a more positive displacement type of contact like meshing gears  42  and  44  or guide links such as  46  and  52  are preferred. The advantage of the present invention over the prior systems where only the wickers at the end of a tilted link are used for anchoring can readily be seen. Because of the unique support system to drive a slip supported by a plurality of links, the contact area is dramatically improved so the grip is enhanced. The curved areas provide a backup incase severe loading causes a pin  30  or  32  to stretch or fail. The positive guiding of the connected links assures contact of the casing in a flush manner over a far greater area than prior designs. The holding forces are substantially increased. The guiding system for links  16  and  20  also facilitates release of the anchor A. As previously stated the anchor A can be used on a variety of downhole tools, whether run in into casing or through tubing. The method of actuating the anchor can be using any known device that can cause the required relative movement to get hubs  12  and  14  to move toward each other. Known devices that can provide the force to separate hubs  12  and  14  can accomplish release. A variety of surface treatments can be used instead of wickers  28  to enhance grip including using hardened inserts. Another advantage of the present invention is that slip  26  resists forces in opposed directions to allow simplification of the overall anchor structure. In the past, anchor structures have had to use separate anchoring mechanisms to resist forces that came from opposite directions. In the present invention the link pairs, with their associated slip can resist forces from opposed directions. The face of the slips  26  can have wickers or other surface treatments that are mirror images on a single slip to facilitate anchoring against forces from opposed directions. They can have one continuous arc or be a series of curves having different radii. Multiple hubs controlling pairs of links that have a slip holding them together as described above can be used to add additional grip. The slips would then translate out at different elevations along the body  10 . The present invention is useful in high expansion applications where driving slips out with cones is insufficient to span the gap necessary to get anchoring forces against the casing. 
     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.