Abstract:
The present invention provides for an apparatus and method of use for a hydraulic shifting tool to be used in a sealed volume in a subsurface well completion to actuate a downhole device, without a fluid return to surface or the well annulus.

Description:
This application claims the benefit of U.S. Provisional Application 60/410,359, filed on Sep. 13, 2002. 

   BACKGROUND 
   1. Field of Invention 
   The present invention pertains to shifting tools used in subsurface well completions, and particularly to hydraulic shifting tools used in closed hydraulic volumes. 
   2. Related Art 
   Shifting tools are commonly used in well completions in which actuation of a tool is brought about by relative movement of a tool element. This can be, for example, opening or closing a valve (e.g., sleeve, ball, or flapper), setting a packer, or initiating an explosive train. The earliest shifting tools were simple mechanical devices that engaged a profile in the tool element to be moved, and the tool element was moved as an operator manipulated the shifting tool. 
   More sophisticated shifting tools use hydraulic pressure to apply a force to a moveable element, such as a piston, to induce motion of the element. Existing hydraulic shifting tools generally require a fluid path to the surface or well annulus to permit movement of relatively incompressible well fluids. If such tools are run into a sealed volume, the tool will be stopped from advancing, and the piston will be prevented from moving, unless the fluid within the volume is routed to the surface or well annulus. 
   SUMMARY 
   The present invention provides for an apparatus and method of use for a hydraulic shifting tool to be used in a sealed volume in a subsurface well completion to actuate a downhole device, without a fluid return to surface or the well annulus. 
   Advantages and other features of the invention will become apparent from the following description, drawings, and claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIGS. 1A–1E  are cross-sectional diagrams of a volume compensated shifting tool according to an embodiment of the invention, showing the shifting tool in a run in configuration. 
       FIGS. 2A–2E  are cross-sectional diagrams of the shifting tool of  FIGS. 1A–1E , showing the shifting tool in a locked in configuration. 
       FIGS. 3A–3E  are cross-sectional diagrams of the shifting tool of  FIGS. 1A–1E , showing the shifting tool in a shifting configuration. 
       FIGS. 4A–4E  are cross-sectional diagrams of the shifting tool of  FIGS. 1A–1E , showing the shifting tool in a retrievable configuration. 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1A–1E , a volume compensated shifting tool  10  has, in accordance with an embodiment of the invention, an inner sleeve  12 , a compensating piston  14 , an actuator piston  16 , and a housing  18 . 
   Inner sleeve  12  is disposed within housing  18  and releasably engages housing  18  with an upper collet  20 . Housing  18  carries a locking dog  22 , a locator dog  24 , an upper spring  26 , a lower collet  28 , compensating piston  14 , and actuator piston  16 . Compensating piston  14  and actuator piston  16  are disposed in chambers  30  and  32 , respectively, within housing  18 . Chamber  32  is in fluid communication with an interior  34  of a tubing (not shown) via a lower port  36 , and chamber  30  is in fluid communication with the interior of a tool body  38  (only a representative portion of which is shown) via an upper port  40 . Housing  18  also has a balance port  42  on the lower end of housing  18  to allow fluid communication between the interior of tool body  38  and tubing interior  34 . Inner sleeve  12  carries a seal  43  on its lower end that seals against the inner wall of housing  18 . 
   Actuator piston  16  releasably engages housing  18  with lower collet  28 . A shifting element  46  is slidably mounted to housing  18  and moves within a slot therein in response to the movement of actuator piston  16 . Shifting element  46  engages a moveable assembly  48  that is part of tool body  38 . Moveable assembly  48  has a recess  50  terminated on its lower end by a shoulder  52 . Shifting element  46  moves within recess  50 , causing moveable assembly  48  to move down when shifting element  46  bears on shoulder  52 . A lower spring  54  is carried in the lower end of chamber  32  and bears against shifting element  46 . 
   In operation, shifting tool  10  is initially run in on wireline or other common deployment system. Shifting tool  10  is held in its running-in position by collet  20 . Shifting tool  10  is run in until locator dog  24  catches on a matching profile in a nipple or portion of tool body  38  to properly position shifting tool  10 . 
   With locator dog  24  properly engaged, inner sleeve  12  is displaced downward ( FIGS. 2A–2E ) relative to housing  18 , disengaging upper collet  20 . Inner sleeve  12  is displaced, for example by mechanical means, and moved downward until locking dog  22  is locked in place. That secures shifting tool  10  in place. In this position, shifting element  46  is disposed in recess  50 . Also, balance port  42  is sealed closed by seal  43  to prevent fluid communication between interior  34  and the interior of tool body  38 . 
   To move moveable assembly  48  ( FIGS. 3A–3E ), pressure is applied within interior  34 . That pressure is communicated to actuator piston  16  via lower port  36  and displaces actuator piston  16  and shifting element  46  downward. Upon sufficient downward movement, shifting element  46  engages and bears on shoulder  52 , causing moveable assembly  48  to move downward. 
   The fluid in chamber  32  is generally incompressible, and must therefore be displaced as actuator  16  moves downward. Because the fluid is in communication with the interior of tool body  38 , it can be collected in the lower end of chamber  30  via upper port  40 . The fluid pressure acts on compensating piston  14 , causing it to be displaced upward, pushing against spring  26 . The upper end of chamber  30  may be an atmospheric chamber or may hold compressible fluid such as a charge of gas. Thus, energy may be stored in spring  26  and the compressible fluid, if any, in chamber  30 . The upper end of chamber  30  is preferably prepressurized with a compressible fluid to compensate for anticipated hydrostatic pressure within tool body  38 . 
   Compensating piston  14  and the compressible volume in the upper end of chamber  30  allow shifting tool  10  to enter a closed, hydraulically locked volume (i.e., having no hydraulic return path to the surface or into the well annulus). Shifting tool  10  does not merely balance to downhole hydrostatic conditions, but rather carries a displaceable volume into an otherwise hydraulically closed volume. The incompressible fluid in the closed volume must be displaced to allow entry of shifting tool  10  into the closed volume. Shifting tool  10  routes the incompressible fluid into the lower end of chamber  30 , as described above. Compensating piston  14  and chamber  30  also allow work to be done by shifting tool  10 , such as moving a piston in the closed volume. Thus, only a single fluid path is required to activate shifting tool  10  remotely. Shifting tool  10  can be placed in a system without using a fluid conduit (e.g., by slickline or wireline) and actuated by pressurizing the system, without providing a separate vent or return path for displaced wellbore fluids. Similarly, shifting tool  10  can be used to remove a tool from a hydraulically locked system. 
   If an operator wishes to repeat the actuation sequence, perhaps because the operator believes a valve failed to open properly, the operator can pull upward on inner sleeve  12 . This pulls actuator piston  16  upwards and allows shifting element  46  to move upward in response to lower spring  54  ( FIGS. 4A–4E ). Inner sleeve  12  is then lowered to again close port  42 . Tubing pressure may then be reapplied to repeat the downward displacement cycle. Alternatively, simply bleeding and reapplying the tubing pressure can also repeat this operation. The charged volume in chamber  30  will work to return the piston substantially to its original position. Similarly, if the operator is ready to retrieve shifting tool  10 , the operator pulls upward with sufficient force on inner sleeve  12  to release locking dog  22  and locator dog  24 . When shifting tool  10  is pulled out of the hole, balancing port  42  is open to allow flow through shifting tool  10 . This allows shifting tool  10  to be removed from a hydraulic lock or reduces the effect of an overbalanced (downward flow) well situation. It also eliminates the requirement of equalizing the well before and after operation to allow installation or removal. 
   In the preceding description, directional terms, such as “upper,” “lower,” “vertical,” “horizontal,” etc., may have been used for reasons of convenience to describe the completion valve assembly and its associated components. However, such orientations are not needed to practice the invention, and thus, other orientations are possible in other embodiments of the invention. 
   Although only a few example embodiments of the present invention are described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph  6  for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.