Abstract:
An actuator for a subterranean tool is releasably retained by a collet. The actuation system features opposing actuation pistons with ports communicating to the tubing. The spaced ports are sequentially straddled for initial setting and a subsequent release using a predetermined applied pressure. The applied pressure overcomes the retaining force of the collet and actuates a one of two opposed pistons to set the tool, which is preferably a liner hanger. Upon shifting the actuation tool to communication to another port leading to an actuating piston pushing in another direction with applied pressure releases the tool and re-latches a retaining collet. The tool can be set, released and repositioned for another cycle in the same trip in the hole.

Description:
FIELD OF THE INVENTION 
     The field of the invention is actuators for subterranean tools and more particularly those that are initially in pressure balance to tubing pressure through spaced ports leading to opposed pistons and more specifically where the access ports to tubing pressure can be sequentially exposed for unlocking, setting and releasing the tool such as a liner hanger. 
     BACKGROUND OF THE INVENTION 
     Hydraulic actuators in the past have been made insensitive to tubing pressure using opposed pistons that create opposing forces to any tubing pressure so that the net result is no movement of the actuator mechanism so that the tool is not set even if there are pressure surges in the tubing. To insure that there is no premature setting the sleeve to be moved to set the tool can be held with a shear pin that breaks under a predetermined net force. Tool actuation involves isolating an upper inlet to one of the pistons from a lower inlet to an opposing piston, such as with an object dropped on a seat in the tubing. This is followed with elevating the pressure to one of the pistons that has access to tubing pressure above the seated object so that one piston creates a net force in the setting direction for setting the tool. A retainer for the setting sleeve can be broken in the setting process as the tool is set with the actuator. This design is shown in schematic terms in U.S. Pat. No. 7,766,088. While this reference mentions in passing an application for unsetting a tool, the details provided focus on how to set and no details are provided as to how to unset with the described actuation tool. 
     U.S. Pat. No. 7,686,090 shows the use of a floating piston in a liner hanger actuation tool with a balance piston referenced to the annulus. US Publication 2010/0319927 shows the use of a ball seat that can be displaced with a seated ball on it into a larger diameter for release of the ball. 
     The present invention goes a step further by initial isolation of one actuating piston to set a tool such as a liner hanger and then isolation of an opposing piston to tubing pressure to reverse the movement of an actuation mechanism for release of the tool such as a liner hanger. Those skilled in the art will more readily appreciate various aspects of the invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims. 
     SUMMARY OF THE INVENTION 
     An actuator for a subterranean tool is releasably retained by a collet. The actuation system features opposing actuation pistons with ports communicating to the tubing. The spaced ports are sequentially straddled for initial setting and a subsequent release using a predetermined applied pressure. The applied pressure overcomes the retaining force of the collet and actuates a one of two opposed pistons to set the tool, which is preferably a liner hanger. Upon shifting the actuation tool to communication to another port leading to an actuating piston pushing in another direction with applied pressure releases the tool and re-latches a retaining collet. The tool can be set, released and repositioned for another cycle in the same trip in the hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the actuator tool in the run in position; 
         FIG. 2  shows an upper port in the actuator tool isolated with an internal straddle device so that pressure applied to the isolated port will set the downhole tool that is operably connected to the actuator tool; 
         FIG. 3  is the view of  FIG. 2  with the straddle device shifted to straddle another isolated port so that applied pressure will cause the downhole tool to release; 
         FIG. 4  shows the released downhole tool in position for being pulled out of the hole or relocated for another setting; and 
         FIG. 5  is an enlarged view of the detail in the circle of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows the actuation tool  10  that has a mandrel  12  that defines a tubing passage  14  that extends to a well surface through a tubular string that is not shown. An actuating sleeve  16  is connected at an upper end  18  to a schematically represented tool  20  which preferably is a liner hanger but it can be a variety of other tools. The sleeve  16  is moved axially in opposed directions to set and release the tool  20 . 
     For running in with ports  22  and  24  accessible in passage  14  there will be no movement of sleeve  16  because the piston area in chamber  26  defined by seals  28  and  30  is equal to the piston area in chamber  32  defined by seals  34  and  36  and opposing in direction. The volume in chambers  26  and  32  varies as the sleeve  16  is forced to move axially. Before any axial movement of sleeve  16  can occur, to set the tool  20 , enough pressure has to be applied to port  22  to make collet  38  jump out of groove  40 . Groove  40  is retained to mandrel  12  with ring  42 . Collet  38  is secured at thread  44  to the sleeve  16 . The purpose of the collet  38  being in groove  40  is to allow a predetermined force to build up through ports  22  before there is sleeve  16  movement. Additionally, during run in, if the sleeve  16  is bumped on a surrounding tubular or connection in the wellbore then the collet  38  in groove  40  will resist sliding movement and pre-setting of tool  20  due to the engagement of collets  38  in groove  40 . 
       FIG. 2  shows a running and actuation tool that is associated with the mandrel  12  and the string that is not shown and attached to the lower end  46 . The running and actuation tool has several features that are schematically illustrated. There is a gripping device shown schematically as  48  that grabs the mandrel  12  and selectively releases when the mandrel  12  becomes independently supported to the surrounding tubular  50  or some other way supported in the wellbore. At the same time the gripping device  48  allows for run in and release of the mandrel  12  when there is support such as by actuation of a tool  20  that in the preferred embodiment is a liner hanger. When running in, spaced seals  52  and  54  can be located in a straddle about openings  22  and  24  or both ports  22  and  24  can be open to the passage  14 . Seals  52  and  54  are an isolation assembly and can be a variety of designs that are either run in with a sealing position or that need to be actuated when in the proper location. These seals can be cup seals, inflatable, ball seats S that accept balls or other styles that allow selective straddling of the ports  22  or  24 . Application of pressure through passage  56  goes into ports  22  but that same pressure is isolated from ports  24  due to seal  54 . As pressure is applied the collets  38  jump out of groove  40  when a predetermined pressure is applied in chamber  26  which then starts to increase in volume as the collets  38  jump groove  40 . If the tool  20  is a liner hanger, then movement of sleeve  16  in the direction of arrow  58  will set the liner hanger and support the mandrel  12 . The running tool gripping device  48  is released from the mandrel  12  in conjunction with the shifting of the sleeve  16 . At this point the running and straddle tool assembly can be moved relative to the mandrel  12  to assume the  FIG. 3  position from which it is possible to urge the sleeve  16  in the direction of arrow  60  to release the tool  20  or to reverse its previous motion, depending on the nature of the tool. Such reverse movement will bring collets  38  back to groove  40  and release the slips of the liner hanger (not shown) so that the mandrel  12  can be moved within the borehole or pulled out of the hole. Such movement in the direction of arrow  60  must also be preceded with regaining a grip on the mandrel  12  as the tool  20  such as a hanger is released. In  FIG. 3  the openings  24  are straddled so that pressure applied to chamber  32  moves the sleeve  16  in the direction of arrow  60 . 
     In  FIG. 4  the mandrel  12  is supported by the grip  48  up above so that the liner supported by mandrel  12  will not drop if the liner hanger or other tool  20  is released. In essence, after releasing the hanger  20  while gripping the mandrel  12  with the seals straddling ports  24  the gripper  48  is engaged to the mandrel  12 . If the mandrel  12  is to be pulled out of the hole then an upward force is applied to the running tool that now supports the mandrel  12  in the  FIG. 3  position and the string and mandrel  12  with the tool  20  come out of the hole as an assembly. 
     On the other hand if after a release of tool  20  in  FIG. 3  it is desired to reposition the mandrel  12  with the tool  20  in another well location without coming out of the hole then there needs to be an ability to retain support for mandrel  12  while repositioning seals  52  and  54  to again straddle ports  22  so that the tool  20  can be reset again before the gripper  48  releases the mandrel  12 . This repositioning of the seals  52  and  54  can be done with a telescoping member responsive to fluid pressure or any other method that can then draw up the seals  52  and  54  to the  FIG. 4  position and the process can be repeated. 
     Seal  54  can be a packer that can be set mechanically, hydraulically or by inflation to name a few options. Alternatively, seal  54  can be a ball seat that permits circulation or reverse circulation as long as there is no seated ball. To set the tool a ball can be dropped to the ball seat and pressure built in the  FIG. 2  position for setting the tool  20 . The ball can then be extruded through the seat such that a bigger ball can land on the same seat when the position of  FIG. 3  is obtained so that the tool  20  can be released in the manner previously described. The same ball seat can accept many balls of increasing size, or can be a stack of different size ball seats, to allow the pressure cycling to be repeated several times for subsequent setting and releases of the tool  20  in different wellbore locations in the same trip. Such a design is well known in the art. 
     The present invention allows setting and releasing a tool multiple times in a single rip with a feature of making the setting sleeve  16  insensitive to tubing pressure or mechanical shocks from a surrounding tubular when running in. The grip and straddle tool allows setting a tool such as a liner hanger while releasing the grip of the mandrel. The mandrel can be gripped again when it is desired to release a tool such as a liner hanger by straddling different ports to reverse the movement of the actuating sleeve while at the same time gripping the mandrel so as to retain a liner string once the hanger releases. At this point the hanger and liner attached to it can be pulled out of the hole. Alternatively, while retaining the grip obtained, to initiate the release, the straddle seals can be repositioned by use of a telescoping member, among other techniques, to locate the seals  52  and  54  back over ports  22  and repeat the cycle without coming out of the hole. 
     The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: