Abstract:
A downhole choke in the form of a sliding sleeve valve operable in a plurality of positions including fully open, fully closed, and positions in between, is disclosed. It features a hydraulic control system that, in one embodiment, provides the motive force to move the sliding sleeve a predetermined amount for a given applied control pressure. Further increments in applied pressure result in further predetermined movements of the sliding sleeve. In another embodiment, the sliding sleeve lands in a series of grooves in the surrounding housing depending on the degree of pressure applied to the control system.

Description:
FIELD OF THE INVENTION 
     The field of this invention is downhole choke valves and more particularly, sliding sleeve valves that can be selectively positioned in an open, closed, or other positions in between, from the surface. 
     BACKGROUND OF THE INVENTION 
     It is often desirable to control the flow rate into production tubing from one or more producing zones. Going in the reverse direction, the injection rates from surface tubing into the formation also need to be controlled. One way this is accomplished is with a choke. A choke is a variable orifice. One form of downhole valve or choke is a sliding sleeve valve. In the early days, these valves featured a sliding sleeve with an opening. The sliding sleeve moved between a fully open and fully closed position and could be shifted in a variety of ways. Tools could be lowered from the surface to shift the sleeve or some sort of hydraulic system could be used for that same purpose. 
     The early sliding sleeve designs lacked the ability to obtain positions intermediate to the fully open and fully closed positions. Accordingly, chokes, not necessarily involving sliding sleeves were developed, which could assume intermediate positions for throttling purposes. One design uses a form of a J-slot mechanism operable by application and removal of hydraulic pressure to selectively align more or less of the ports in a sleeve with the opening in the housing. This design is illustrated in FIGS. 9 a  and  15  of U.S. Pat. No. 6,308,783. Other designs involve a series of valves operable electrically or hydraulically and mounted in a side pocket mandrel. Examples of this style are the WRFC valve offered by Schlumberger. Schlumberger also offers the TRTFC, which is a choke operating on a form of an indexer pin guiding an indexer to put the valve in different positions. Other well control variable choke devices are illustrated in U.S. Pat. Nos.: 5,823,263; 5,927,401; 5,957,207; 5,979,558; and 6,276,458. Finally, Halliburton manufactures the IV-ICV, which it advertises to be infinitely variable when used in interval control service. 
     The present invention provides a downhole choke valve that is adjustable in a variety of positions. It features simplicity in design and responsiveness to incremental increases in control system pressure to attain varying degrees of opening. A fully hydraulic and a combination mechanical and hydraulic embodiment are described below. Those skilled in the art will be better able to appreciate the invention from a review of the preferred embodiment described below. 
     SUMMARY OF THE INVENTION 
     A downhole choke in the form of a sliding sleeve valve operable in a plurality of positions including fully open, fully closed, and positions in between, is disclosed. It features a hydraulic control system that, in one embodiment, provides the motive force to move the sliding sleeve a predetermined amount for a given applied control pressure. Further increments in applied pressure result in further predetermined movements of the sliding sleeve. In another embodiment, the sliding sleeve lands in a series of grooves in the surrounding housing depending on the degree of pressure applied to the control system. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a - 1   f  are a section view illustrating the adjustable choke in the form of a sliding sleeve in two embodiments. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the housing assembly  10  has a top sub  12  connected to a body  14 . The body  14  is connected to diffuser sub  16 , which is, in turn, connected to bottom sub  18 . Tubing from the surface (not shown) is connected to top sub  12 , while other downhole tools (not shown) can be connected to bottom sub  18 . Between top sub  12  and body  14  a top seal  20  is retained. A middle seal  22  is retained by ring  24  and snap ring  26  against seal spacer  28 , which is, in turn, pushed against diffuser sub  16 . Ports  30  can be on 90 degree spacing or any other spacing depending on the number of ports used and flow into any such ports is circumferentially distributed by the diffuser sub  16  into annular space  32  between the body  14  and the sliding sleeve  34 . A lower seal  36  is retained between the diffuser sub  16  and the bottom sub  18 . A diffuser ring  38  is retained by diffuser sub  16 . It created a small annular clearance for the onset of flow from ports  30 . 
     Those skilled in the art will realize that the fully closed position has the sleeve  34  shifted further down than illustrated, such that elongated openings  40  and their elongated extensions  42  are fully below lower seal  36 . As the sleeve  34  is shifted uphole, as will be explained below, the first to clear lower seal  36  are the elongated extensions  42 . Ultimately, extensions  42  clear the diffuser ring  38 . At this time the entire ports  40  have cleared lower seal  36  and the seal  36  is protected from flow effects since ports  40  have moved beyond it. This is the precise position shown in FIG. 1 e . The purpose of the extensions  42  and the flow diffuser  28  is to reduce fluid velocity between ports  30  and  40  until ports  40  pass completely over seals  36  as high velocity fluid impinging on the seals  36  could damage them, especially when high differential pressures are present. Once the ports  40  move past seal  36 , there is no longer a risk of damage to lower seal  36  from high velocity fluids and the diffuser ring  38  and the elongated extensions have served their purpose. This is the view shown in FIG. 1 e.    
     The sliding sleeve  34  has a seal  44  held by a snap ring  46 . Seal  44  divides annular spaces  48  and  50 . Annular space  48  is between middle seal  22  and seal  44 , while annular space  50  is between upper seal  20  and seal  44 . Body  14  also features a piston bore  52 , within which piston  54  reciprocates against the bias of spring  56 . An adjusting screw  58  can alter the preload on spring  56 . Connection  60  allows closing pressure from the surface to be applied via a control line (not shown) to the top  62  of piston  54 . Connection  64  communicates with the bottom  66  of piston  54  and, through passage  68  into annular space  48 . Piston  54  has upper seals  70  and lower seals  72  and  74 . Vent passage  76  extends from top  62  of piston  54 , through seal  70  and laterally out the side of piston  54  between seals  72  and  74 . A plurality of spaced adjusting ports or vent passages  78  extend from piston bore  52  into annular space  48  or  50  depending on position of sleeve  34 , as will be explained below. A close passage  80  connects annular space  50  to piston bore  52  either above or below seal  70 , depending on the position of piston  54 . 
     Looking at the top of sleeve  34 , there is a C-ring  82  in a groove  84 . As the sleeve  34  moves, the C-ring  82  sequentially expands into grooves  86 ,  88 ,  90 ,  92 ,  94 ,  96 , and  98 . As shown in FIG. 1 each groove has a steeper angle that C-ring  82  must climb to advance the sleeve  34  to a larger open position. The angles get progressively larger as the percentage open position increases. These angular differences between adjacent slots, in turn, require incrementally higher pressure at connection  64  to obtain further movement of the sleeve  34 . Thus one way to obtain multiple positions of sleeve  34  is to use the C-ring  82  in conjunction with multiple grooves  86  to  98  with a varying exit angle in each groove. This technique can be used in isolation or in combination with the operation using the adjusting ports  78 , as will be described below. 
     From the fully closed position, control line pressure is applied at connection  64  into piston bore  52 . This pressure also enters annular space  48  through passage  68 . The sliding sleeve  34  is forced up by pressure in annular space  48  against seal  44 , which is attached to sliding sleeve  34 . The upward movement of sleeve  34  is made possible by fluid displacement from annular space  50  through passage  76 . The piston  54  is forced up against spring  56 , whose spring force increases as pressure is increased into connection  64 . The movement of sleeve  34  with piston  54  stationary due to the force of spring  56  eventually moves seal  44  up to passage  76  that extends laterally between seals  72  and  74 . As this happens, annular space  50  is in fluid communication through passage  76  with connection  60  to vent annular space  50  to allow sleeve  34  with seal  44  to move up. When seal  44  reaches or covers passage  76  the driving pressure for sleeve  34  that is in annular space  48  can be vented through passage  76  between seals  72  and  74 . At the same time, annular space  50  can become isolated and the pressure in it builds, stopping further progress of sleeve  34 . Friction from seal  44  can also contribute to stopping sleeve  34 . Piston  54  holds its position against spring  56  unless the applied pressure through port  64  is increased. If that happens, the piston  54  can shift, to move the outlet of passage  76  into alignment with another adjusting port  78  to a position where pressure buildup can occur on annular passage  48  thus moving sleeve  34  again to a more open position by applying pressure to its seal  44 . In this manner, different applied pressure levels at connection  64  can result in different end positions of the piston  54  and the sleeve  34 . To achieve the full open position, pressure to a high level is applied to connection  64 . The piston is displaced far enough to align passage  76  with the uppermost adjusting port  78 . Pressure from connection  64  can pressurize annular space  48  and apply a force to seal  44  while annular space  50  is vented through passage  76  to connection  60 . The fully closed position is reached by pressurizing connection  60  to drive down piston  54 . Close port  80  is exposed to connection  60 . Pressure in connection  60  enters annular space  50  to push down on seal  44 . Annular space  48  displaces fluid out connection  64  as the sleeve  34  is pushed down moving elongated openings  40  and extensions  42  beyond lower seal  36  to isolate ports  30 . This positioning system for the sleeve  34  can be used in isolation or in tandem with the C-ring  82  and its associated grooves. Preferably, the control system with the adjusting ports  78  is used in isolation. Either system has few moving parts and permits reliable and repeatable operation. 
     The range of angles in grooves  86 - 98  can have any desired range and increments until travel stops for sleeve  34  when C-ring  82  enters groove  98 . For example groove  86  can have an angle of 30 degrees, with subsequent grooves having exit angles increasingly steeper such as 40, 45, 50, 60, 75 and 90 degrees in groove  98 . The larger the angle the more force is required to snap the C-ring  82  out of that groove. 
     Upper sub  12  and Lower sub  18  also features grooves to allow a place for any debris to accumulate in a manner that it will not impede the movement of the sliding sleeve  34 . The debris can settle on the inner wall of the housing  10  as the sliding sleeve  34  strokes between its end positions. 
     Those skilled in the art will appreciate that if only the system of the C-ring  82  in conjunction with grooves  86 - 98  are used, the actuating system for the sleeve  34  can be varied and made more simple. In a two control line system, the sleeve  34  can be driven by pressure applied to one control line or the other with the result being a pressurization of either annular space  48  or  50  for motion in the desired direction by sleeve  34 . This system provides feedback at the surface because the control line pressure must rise to get the C-ring  82  to jump out of one of the grooves  86 - 96 . The adjusting ports  78  can be eliminated and even the piston  54  can be eliminated. Pressure applied to connections  60  or  64  can go directly to annular spaces  48  or  50  to urge the sliding sleeve  34  in the desired direction. Additionally, no matter which combination is used, provisions can be made to return the sleeve to a desired fail-safe position, in the event of failure of control line pressure, seal leakage, or other component failure downhole. The sliding sleeve  34  may have a bias applied to it by a spring or pressurized gas referred to as a “dome charge” to urge it to its fail-safe position in the event of loss of control pressure or other downhole malfunction. 
     In using either system alone or both together, a downhole position sensing and transmitting system to the surface, shown schematically as  104 , can be used to tie into the hydraulic system supplying pressure to connections  60  and  64  as a form of feedback for proper positioning of the sliding sleeve  34 . Positioning transducers may be used to send the position signal to the surface where a computer can process such signal and alter the pressures delivered to connections  60  or  64 . 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the invention, whose scope is determined by the claims that appear below.