Patent Publication Number: US-8118101-B2

Title: Ball catcher with retention capability

Description:
FIELD OF THE INVENTION 
     The field of this invention is devices used in tubular strings to catch and retain objects previously dropped against a seat to operate a downhole tool and later ejected from the seat. More specifically, the present invention captures the ejected objects and preferably retains them outside a main bore regardless of the flow direction in the string. 
     BACKGROUND OF THE INVENTION 
     A tubular string extending downhole can have a plurality of seats that accept objects, usually spheres, which land on discrete seats so that pressure can be built up and a downhole tool in that string operated. The balls can be the same or different sizes as are the corresponding seats. Regardless of the configuration it is desirable after operating the downhole tool to eject the ball from a given seat by a variety of known techniques and then to capture the balls. The reason capturing the balls is a benefit is that if left in the tubular string and there is a reversal in flow direction the balls can flow backwards and get wedged or jammed. Ideally, capturing the blown out balls will leave a main flow bore through a ball catcher to allow other tools to pass such as those that are supported on wireline or coiled tubing, to provide some examples. 
     In one design offered by Baker Hughes Incorporated in Catcher Sub Product Family 14077, the central tube catches ejected balls or darts and the differential pressure that develops pushes the ball or dart further into the central tube with flow possible around the central tube. The central tube has a hook feature to prevent escape of the dart or ball if there is a flow reversal. This design left the central passage obstructed which hampered or prevented subsequent operations further downhole from the Catcher Sub. U.S. Pat. No. 6,920,930 captures a ball when landed on a seat and then the seat with the ball breaks one connection and pivots on a remaining connection out of a central passage to allow a shifting sleeve to come down to keep the ball and the seat that traps it out of a main central bore. U.S. Pat. No. 6,732,793 shows a ball retaining device against reverse flow in a ball catcher that locates the captured balls centrally. U.S. Pat. No. 7,416,029 illustrates providing a tortuous path for a deformable ball that moves through a deformable ball seat. 
     U.S. Pat. No. 7,530,400 shows a ball catcher that has a main bore 18 that is split into two parallel bores 26 and 28 with an entry plate sloping at the top that has openings 38 and 40 aligned with bores 26 and 28 respectively. Only small balls will fit through hole 40 and pass through bore 28 unobstructed. Bigger balls 50 that go through hole 38 are captured at the bottom of bore 26 by a restriction 42, 44. If a small ball 52 goes down passage 38 and into bore 26, it has a way to get from bore 26 to bore 28 as those bores overlap to create a pass through channel so that the small ball 52 can get into bore 28 and escape. There are several issues with this design. First, if there is a flow reversal it will force the balls uphole and out of the ball catcher. Second, the way this ball catcher is set up with parallel bores, it has to have the channel between the bores because it has no way to insure the small balls will go in the pass through passage 28. Another disadvantage is that it has a pass through passage for one size of ball as opposed to catching all balls that enter. While it is recognized that the latter may simply be a design objective when a ball catcher is applied to a specific tubular string, it is recognized that in other applications, this feature can be less than ideal. 
     The present invention is a ball catcher that is designed to collect and store all the balls that reach its entrance in an annular storage location that surrounds a main bore so that the main bore is left open for other tools to later pass. The annular space preferably has a spiral guide slot that is small enough to prevent the balls being used from exiting the annular space but that advances such balls as they arrive to make efficient use of the annular space. Arriving balls get stopped at the inlet where flow around them displaces a seat that originally stopped the ball and allows the ball to advance past the seat and into the annular space where it stays trapped. These and other features of the invention will become more readily apparent to those skilled in the art from a review of the description of the preferred embodiment that appears below with the associated drawings while recognizing that the full scope of the invention is given by the claims that are attached below. 
     SUMMARY OF THE INVENTION 
     A ball catcher is designed to stop balls that are the same size or different sizes at an inlet on a seat that is connected to a movable biased sleeve. Once the ball or other shaped object lands at the seat the flow around it increases differential pressure on the seat and sleeve and displaces them against the bias. The ball goes into a surrounding annular space and cannot exit. A preferably spiral sleeve guide the movement of the balls in the annular space so that efficient use of the annular space is made to maximize the number of balls that can be captured per unit length of the annular space. As soon as the ball enters the annular space the sleeve shifts back to the original position to stop the next ball at the inlet. Once in the annular space, the balls cannot escape if there is a flow reversal. The central passage remains open to pass other tools and flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of the ball catcher with a ball stopped on a seat near the housing inlet; 
         FIG. 2  is the view of  FIG. 1  with the seat and sleeve shifted to allow the ball to move into the surrounding annular space; and 
         FIG. 3  is the view of  FIG. 2  with the ball in the annular space and the seat and associated biased sleeve returned to the original position for the next ball. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The ball catcher  10  has an inlet  12  connected to a tubing string that is not shown. When the ball  14  passes through a ball seat (not shown) that is uphole it continues into inlet passage  16 . A movable sleeve  18  has a passage  20  that extends from end  22  at the uphole end to end  24  at the downhole end. Toward the uphole end  22  the passage  20  has a reduced diameter section  26 . Adjacent the reduced diameter section  26  is a lateral passage or exit  28  that is best seen in  FIGS. 2 and 3  after the ball  14  has gone past. In the  FIG. 1  position the housing  30  has a radial surface  32  and a cylindrical surface  34  adjacent and in an uphole direction. The ball  14  goes into the upper end  22  and cannot progress further down passage  20  because of reduced diameter section  26 . There is enough room around the ball  14  when it engages reduced diameter section  26  to be pushed laterally against the lateral passage  28 . This is the  FIG. 1  position. Since the flow continues from inlet passage  16  a pressure differential develops on the ball  14  causing it to push against sleeve  18  and compress the return spring  36  mounted adjacent the outlet  38  to the housing  30 . 
     Ball  14  and sleeve  18  move in tandem to the  FIG. 2  position. In that position the ball  14  can advance down passage  40  because passage  40  has shifted with sleeve  18  to clear cylindrical surface  34  with lateral passage  28  and to compress spring  36  and now ball  14  has a clear passage into annular capture space  42 . Once that happens the ball  14  is at the top  44  of spiral slot  46  that ends at lower end  48 . The purpose of slot  46  is to increase the radial clearance between the outside diameter of sleeve  18  and the inside diameter of housing  30  so that the ball batcher  10  can capture the largest diameter ball  14  as possible. Slot  46  must be narrow enough to retain balls  14  as it guides the balls  14  that enter annular space  42 . The spiral configuration of slot  46  maximizes the number of balls  14  that can be captured in annular space  42  for a given length of the annular space  42 . The width of the spiral slot  46  does not exceed the size of constriction  26  ensuring that a ball  14  that was stopped by the constriction  26  will not fit through slot  46 . 
     As soon as ball  14  rolls or is pushed into spiral slot  46 , the spring  36  can return the sleeve  18  and the lateral passage  28  that moves with it back to the  FIG. 1  position. The next ball simply repeats the process and follows the same path down spiral  46  until it lands on the ball already there at the lower end  48 . 
     It is worth noting that the spiral groove  46  can have other configurations such as axial but it may be more limited in the number of balls  14  that it can hold for a given unit length of the housing  30 . Groove  46  also allows fluid to pass as a way of advancing the ball  14  along the groove  46  using flow in a downhole direction from passage  16  to passage  38 . The groove  46  serving as a ball guide is optional and that feature can be eliminated. A port from annular space  42  into the path  20  will also allow flow through the annular space  42  to move a ball  14  along in a more random path to the port that replaces the groove  46 . In this case the port instead of the groove  46  should be smaller than the balls  14  that get trapped in the ball catcher  10 . Such a port should be preferably located near the outlet passage  38  so that more of the annular space  42  can be used for storage of trapped balls  14 . 
     Note that if balls  14  are used, the ball catcher can accommodate different diameters. If the reduced diameter section  26  is smaller than all the ball sizes used then they all will land on lateral passage  28  and all will be captured in annular space  42 . Space  42  need not be annular and go around sleeve  18  for 360 degrees. Optionally, if in a given system balls below a given size do not need to be captured, then the reduced diameter section can be configured to exceed such a given size and balls smaller than that given size will just continue through and not land on lateral passage  28  and not go into annular space  42  to be captured. The passage  20  can be centrally disposed in the housing  30  so that other tools (not shown) can be delivered through passage  20  with wireline or coiled tubing or another known conveyance. Alternatively, it can be offset from the axis of housing  30 . Although spheres  14  can be caught other shapes are envisioned including darts and wiper plugs or other shapes that can land in lateral passage such as  28  and enter the surrounding annular space  42 . Spring  36  can be a coiled spring, a stack of Belleville washers or a variable volume chamber with a compressible fluid among other ways for creating a return bias force. Other ways to create the bias to the  FIG. 1  position include using buoyancy of the sleeve  18  or a magnetic or some other type of field. 
     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.