Patent Publication Number: US-8534361-B2

Title: Multi-stage pressure equalization valve assembly for subterranean valves

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 features opposed pistons actuated by discrete control lines. This design was concerned about a pressure imbalance on an operating piston and provided a passage through the piston with two check valves  54 ,  76  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 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. 
     The present invention manages to equalize pressure by simple application of pressure from the surface that can communicate to inside the ball in the closed position for pressure equalization. That pressure communicated through a passage in the housing that selectively communicates the zone above the closed ball to the isolated passage within the ball when the ball is in the closed position. That communication preferably occurs through a check valve assembly that preferably has a series redundant feature and screens to assure that on removal of the applied pressure that the check valve passage will reclose allowing for normal ball operation to open the ball with the hydraulically actuated operating piston or pistons. These and other features of the present invention will be more readily appreciated by those skilled in the art from a review of the specification and associated drawings while understanding that the full scope of the invention is to be found in the appended claims. 
     SUMMARY OF THE INVENTION 
     A downhole valve that operates on turning of a member having a passage through it with a control system also features a passage from above an uphole seat for the member which communicates to the isolated passage within the member when the valve is closed. The passage features a check valve assembly that preferably has redundant sealing features and filters to prevent debris entry. Pressure applied from above the closed member gets through the check valve assembly to equalize the higher pressure below the ball with the pressure raised in the ball from pressure application at the surface. Removal of the applied pressure reseats the check valve or valves to allow the hydraulic system to rotate the member while the member is no longer subject to a high differential pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view through a ball valve showing the major component and taken at a section rotated from the section of  FIG. 2  where the check valve assembly is located; 
         FIG. 2  is a section through a housing component shown in  FIG. 1  but rotated to a different plane to illustrate the passage and the check valve assembly within the passage that allows pressure equalization within the ball when it is closed prior to actuating the hydraulic system to open the ball. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
       FIG. 1  shows a ball valve in the closed position. The ball  10  has a lower seat sleeve  12  below it and an upper seat sleeve  14  above it. Seat  16  with seal  18  is pushed by a spring assembly (not shown) against the ball  10 . Seat  20  with seal  22  is supported against axial movement by the housing  24  such that the bias on the lower sleeve  12  pushes the seat  16  against the ball  10  and in turn pushes the ball  10  against the seat  20 . Control lines (not shown) are in fluid communication with inlet passages  26  and  28  that respectively lead to operating pistons  30  and  32 . Pistons  30  and  32  are preferably rod pistons that at the opposite ends from passages  26  and  28  are connected to a sliding cage  34  at the opposed ends of cage  34  so as to selectively reciprocate the cage  34  axially in opposed directions for normal opening and closing of the ball  10 . Ball  10  is held in a stationary frame  36  that is an open structure to accept the passage of cage  34  as it is pushed to axially reciprocate by pistons  30  and  32 . Frame  36  supports the ball  10  to rotate on its central axis on opposed pin supports that are not shown. The ball  10  is also pinned to the cage  34  at a location away from the central axis of the ball so that relative axial movement of the cage  34  with respect to the frame  36  rotates the ball  10  90 degrees in opposed directions depending on the direction of the relative movement of cage  34  caused by selective pressure application to passage  26  or  28 . Note that seal  38  keeps pressure in the tubing below the closed ball  10  from entering passage  40  and a similar seal  41  against the upper sleeve  14  keeps pressure in the tubing above the closed ball  10  out of inlet passage  40 . With ball  10  in the closed position of  FIG. 1  its passage  40  is isolated from tubing pressure below the ball  10  by seals  18  and  38 . This pressure differential can be high enough to cause distortion of ball  10  to the point where there can be damage to the hydraulic system that is trying to turn the ball  10  while exposed to such high pressure differentials. 
     The present invention addresses how to equalize ball  10  when subject to a high differential pressure before trying to move it. While the preferred embodiment is a 90 degree ball, the present invention is applicable to other downhole devices that because of their configuration can become exposed to pressure differentials that need equalization to prevent actuation system damage or damage to the element to be operated by the actuation system. The present invention allows the use of tubing pressure from above to equalize pressure so that the member or ball can then be rotated or operated in the normal manner without damage to any components. 
     Generally speaking, a bypass passage starts at an inlet  42  and continues to an outlet  44 . Inlet  42  is in housing component  13  and is not seen in the section view of  FIG. 1  because it is rotated about 90 degrees from the bore for piston  32 . Inlet  42  needs to communicate with tubing pressure and will be located above the end of sleeve  14  such that pressure applied from above the closed ball  10  into passage  46  will reach the inlet  42 . At the other end at outlet  44  the passage  45  communicates with the low pressure passage  40  in ball  10  when ball  10  is in the closed position. 
     All fluids entering inlet  42  go through filter  48  into its internal passage  50  and then into chamber  52 . Check valve member  54  has a taper  56  with a seal  58  with an elongated end  60  that keeps valve member  54  centered as it moves axially against the bias of spring  62  that pushes on tab  64  on one end and housing  66  at the opposite end. Member  54  also has ports  68  that allow flow to enter once member  54  is pushed enough against spring  62  to lift the seal  58  away from the opposing tapered sealing surface on the housing  66 . Flow around member  54  goes through opening  70  in retainer  72  that is attached to check valve member  76  and then through passage  74 . Flow continues through passages  78  where it pushes seal  80  mounted on a tapered surface away from a mating tapered surface on housing  82  so that flow can go around the outside of the member  76  to reach the screen  84  held to housing  82  by retainer nut  86  through which is found the outlet  44 . Removal of applied pressure at inlet  42  allows springs  62  and  89  to respectively move members  54  and  76  to put seals  56  and  80  against their respective tapered surfaces in housings  66  and  82 . The ball  10  is equalized as between the pressure in passage  40  and the pressure at  88  below the ball  10  using the flow through passage  45  resulting from pressure applied above ball  10  to passage  46 . The ball  10  can then be operated in the normal manner with the previously described hydraulic system. 
     Those skilled in the art will appreciate that there are two stacked check valve assemblies and that a single or more than two assemblies in series are contemplated. Filters  48  and  84  prevent debris from entering passage  45  when flow direction reverses to enhance the sealing integrity of the seals  56  and  80 . 
     The equalizing system that is described works on applied tubing pressure from above that is simple to provide and it is the applied pressure that operates the equalizing valve or valves to get pressure balance on the final controlled element such as ball  10  so that it can then be operated in the usual manner with a surface controlled hydraulic system. The application of the invention is to a broad range of tools that operate downhole where in a given position there could exist substantial pressure differential across a powered component that has to be overcome before trying to actuate that component so that damage to the actuating system or the component can be avoided. In the preferred embodiment the final controlled element is ball  10  and the actuating system is hydraulic and operated from the surface with a control line or lines actuating one or more pistons to cause ball rotation. The pressure differential across a ball  10  when closed can cause elastic ball distortion that can make it difficult or impossible within the capacity of the hydraulic actuating system components to operate the ball  10  when subject to such differential pressures without damage to the ball  10  itself or more likely the components of the hydraulic system such as pistons  30  or  32  or seals associated with such pistons. The equalizing system does not depend on forcing pistons against components and for that reason can be simply operated from the surface of a well without additional specialty equipment. The applied pressure directly operates the equalizing system, making it far more reliable than another system that adds movement of mechanical components just to open the equalizing valve or valves. 
     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.