Abstract:
A pressure equalizing system allows flow past an upper seal on a movable member downhole that in turn allows pressure to be delivered from uphole into what had previously been an isolated low pressure zone. The pressure differential across the member is equalized before attempting to move the member into another position. The member is a ball in a ball valve for subterranean use.

Description:
FIELD OF THE INVENTION 
     The field of this invention is an equalizing pressure feature for subterranean or downhole valves and more particularly a way to equalize trapped lower pressure in a ball or plug of a valve without having to run a tool in the valve. 
     BACKGROUND OF THE INVENTION 
     Downhole valves are used to isolate portions of the wellbore for a variety of reasons such as for safety systems or to allow building a long bottom hole assembly in the wellbore, to name a few examples. Such valves have featured a rotating ball with a bore through it that can be aligned or misaligned with the path through the tubing string where the valve is mounted. The ball is surrounded by a sliding cage that is operated by a hydraulic control system from the surface. One such design that features opposed pistons actuated by discrete control lines is illustrated in US Publication 2009/0184278. This design was concerned about a pressure imbalance on an operating piston and provided a passage through the piston with two check valves  64 ,  70  in series to allow pressure equalization across the actuating piston with the ball in the closed position. 
     What can happen in this type of a ball valve that has upper and lower seats against the ball in the closed position is that pressure from downhole can rise, which leads to a pressure differential between the passage inside the ball and the downhole pressure. This pressure differential can distort the ball and make it hard or impossible for the piston actuation system to operate the ball back into the open position. One way this was solved is described in a commonly assigned application Ser. No. 12/366,752 filed on Feb. 6, 2009 and having the title Pressure Equalization Device for Downhole Tools. The solution described in this application was to use a tool that goes into the upper sleeve that hold a seat against the ball and separate the seat from the ball while providing pressure from the surface at the same time to equalize the pressure on the ball before trying to rotate it to the open position. The problem with this technique was that it required a run into the well with coiled tubing, latching and shifting the upper sleeve and associated seat enough to give access into the ball for equalizing pressure. One of the downsides of this technique was that the pressure admitted to try to equalize the pressure in the ball could be high enough to unseat the lower seat from the ball so that the higher pressure below the ball would get to above the ball. This technique also took time which cost the operator money and required specialized equipment at the well location, which could be remote or offshore and add yet additional costs to the effort to operate the ball when subjected to high differential pressures that increases opening friction or could distort the ball enough to make it hard for the hydraulic system to rotate it. 
     In flapper type safety valves such as U.S. Pat. No. 5,564,502 the preferred method to get pressure equalization on a closed flapper was to simply apply tubing pressure on top of it to reduce the differential before using the control system to try to rotate the flapper. Of course, the flapper is built to rotate open with pressure applied above so that this technique did not equalize pressure around the flapper when it was closed but simply built up pressure above it when it was closed. Other equalizer valves mounted in the flapper were actuated by the hydraulic system moving down a flow tube that impacted the equalizing valve before the flapper was engaged by the flow tube as seen in U.S. Pat. Nos. 6,848,509 or 4,478,286. 
     Also relevant are US Publications 2001/0045285; 2009/0184278 and U.S. Pat. Nos. 4,130,166; 4,197,879; 4,288,165; 4,446,922; 5,865,246; 6,223,824; 6,708,946; 6,695,286 and 4,368,871. 
     The basic components of the valve of  FIG. 1  are reviewed in more detail in US Publication 2008/0110632 whose description is fully incorporated by reference herein as though full set forth. The portions of such valve relevant to the understanding of the present invention will be reviewed below in sufficient detail and for completeness so as to fully understand the operation of the claimed invention. While the actuation system of the valve in  FIG. 1  in the present case is somewhat different in that it uses mechanically operated rod pistons to move the ball cage, the remainder of the structure of the ball and the way it seals and turns are the same with the further exception that the present invention is employed to equalize pressure as between the inside of the closed ball and the pressure below the ball by virtue of application of uphole pressure to accomplish a bypass of an uphole seal to achieve pressure equalization. 
     Those skilled in the art will better understand how pressure equalization is obtained before the ball is turned from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the technique is by no means limited to downhole ball valves but can be used in a variety of tools where trapped pressure results in differentials that may damage the component to be moved or the actuating system for it if such differentials are not resolved before attempting to move the component. Those skilled in the art will further understand that the full scope of the invention is to be found in the appended claims. 
     SUMMARY OF THE INVENTION 
     A pressure equalizing system allows flow past an upper seal on a movable member downhole that in turn allows pressure to be delivered from uphole into what had previously been an isolated low pressure zone. The pressure differential across the member is equalized before attempting to move the member into another position. In the preferred embodiment the member is a ball in a ball valve for subterranean use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a ball valve in the closed position and including the portion where the pressure equalizing feature is located; 
         FIG. 2  is a close up view of the valve of  FIG. 1  showing the path for pressure equalizing with applied pressure from above; and 
         FIG. 3  is an alternative embodiment to the design of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a multi-component housing  10  that holds a ball  12  pinned at pins  14  to a frame  16 . A cage  18  extends through the open frame  16  and is connected to the ball  12  offset from the center pivot pins  14  so that sliding the cage  18  in opposed directions results in 90 degree rotation of ball  12  between an open position and the illustrated closed position. A connecting rod assembly  20  is secured to cage  18  at connection location  22 . A shifting tool (not shown) can engage the connecting rod assembly  20  to selectively move it back and forth to open or close the ball  12 . 
     A lower seat sleeve  24  has a seat  26  in which a seal  28  is located for contact with the ball  12 . The sleeve  24  is biased against the ball  12  by a spring that is not shown that is located on the housing  10  but further downhole. An upper seat sleeve  30  has a seat  32  in which a seal  34  is located for contact with the ball  12 . The biasing spring that is not shown pushes the assembly of the lower seat sleeve  24 , the ball  12  and its frame  16  and the upper seat sleeve  30  against housing component  36 . The cage  18  moves relatively to the frame  16  and over the frame  16  to operate the ball  12 . Seal  38  seals between the lower seat sleeve  24  and the housing  10 . Together seals  38  and  28  retain downhole pressure in higher pressure zone  40  from reaching the intermediate zone which is also referred to as the lower pressure zone  42 , which extends from below to above cage  18  and further encompasses the passage  44  inside the ball  12 . In the closed position pressure in zone  42  migrates into passage  44  around the pins  14 . Above the ball  12  the zone  42  is further defined by seal  34  located in the upper seat sleeve  30  as well as seal  46  shown in  FIG. 2  and seal  48  around the pushrod assembly  20 . Accordingly, an uphole pressure zone  50  is defined by these seals. The present invention deals with a pressure imbalance where pressure in zone  40  goes up when the ball  12  is in the closed position and a lower pressure is trapped in zone  42  which includes the passage  44  inside the ball  12 . This pressure imbalance can increase opening friction or distort the ball  12  making it hard to rotate such that any attempt to rotate the ball  12  while under such a pressure imbalance can adversely affect the pushrod assembly  20  or its seal  48  or the ball  12  itself. The present invention allows pressure applied to zone  50  before rotating the ball  12  to get past seal  46  and into zone  42  which also includes the passage  44  in ball  12 . Different embodiments are presented in  FIGS. 2 and 3  that are discussed below. 
     As seen in  FIG. 2  the upper seat sleeve  30  has an external shoulder  52  that is biased by the spring previously described and not shown against shoulder  54  of housing component  36 . While shown apart in  FIG. 2  for clarity of illustration of the flow path into zone  42  represented by arrows labeled  56  surfaces  52  and  54  will normally be touching but there is no seal between them. To equalize pressure in zone  42  and include the flow passage  44  in the ball  12 , the pressure is built up in zone  50  generally from the surface with available equipment or pressure sources. Normally, the pressure in zone  42  acts on preferably metallic seal  46  between legs  58  and  60  to spread them apart to retain pressure in zone  42  thus preventing pressure communication from zone  42  into upper zone  50 . Keeping in mind that the objective is to cure the pressure imbalance between zones  42  and  40  by raising the pressure in zone  50  to a point of bypassing the seal  46  those skilled in the art will appreciate that the c-shaped ring seal  46  is configured to resist flow or pressure loss from zone  42  into zone  50  but is also able to permit flow and pressure migration when the pressure in zone  50  is raised substantially over the pressure in zone  42 . During normal operations some leakage from zone  50  into zone  42  is acceptable because the volume will be insignificant to affect the operation of the valve assembly. The seal  46  has a u-shaped cross-section and is a commercially available seal. 
       FIG. 3  is an alternative embodiment showing parts  30  and  36  having a small clearance  62  that is closed off by a seal  64  in a surrounding groove  66 . The equalization concept in  FIG. 3  is the same as in  FIG. 2 . Pressure is introduced from zone  50  which typically will come from the surface. At a predetermined differential between zones  50  and  42  the seal  64  will be pushed further back into groove  66  and flow will bypass the seal  64  increasing the pressure in zone  42  to get it closer to the pressure in zone  40  so that the connecting rod assembly  20  can be safely operated with little to no risk of damage to the assembly  20  or its seal  48  or the ball  12  itself. 
     Those skilled in the art can appreciate that the disclosed modes of pressure equalization are cheaper and faster than running a tool into the valve assembly to provide access into zone  42  by physically shifting a part such as seat sleeve  30  to get seal  34  away from ball  12  so that pressure from the wellhead can then be applied to equalize zone  42  with zone  40 . In the present invention the housing does not need to be expensively machined for internal bypass passages that need one or more check valves which have small moving parts that also need protection from debris that may be in the well fluid. Instead, the mere creation of enough differential across a seal so that flow and pressure can migrate from zone  50  into zone  42  gets the job done and the ball  12  can then be operated in the normal manner. 
     The above description is illustrative of the preferred embodiment and various alternatives and is not intended to embody the broadest scope of the invention, which is determined from the claims appended below, and properly given their full scope literally and equivalently.