Abstract:
An electrically actuated fail-safe valve for controlling fluid flow in deepwater drilling operations comprises a body having a bore therethrough, a closure element mounted in the bore and actuable between a closed position and an open position, a flow tube slidably mounted in the bore, the tube being actuable between a first position in which it does not interfere with the normal bias of the closure and a second position in which it opposes the normal bias of the closure, and a drive mechanism causing the tube to advance from its first to its second position. The drive mechanism comprises a gear drive, a rotating sleeve including a helical groove, and a follower pin on the flow tube and received in the helical groove. Power supplied to the drive causes the sleeve to rotate, bearing on the follower pin and advancing the flow tube to its second position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. Provisional Application Serial No. 60/437,070, filed Dec. 30, 2002 and entitled “Electric Downhole Safety Valve,” which is incorporated herein by reference. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         FIELD OF THE INVENTION  
         [0003]    The present invention relates generally to downhole safety valves and more particularly to a downhole safety valve that is electrically operated.  
         BACKGROUND OF THE INVENTION  
         [0004]    The invention relates to a surface controlled subsurface safety valve (SCSSV) for a sub-terranean well and, more particularly, to a safety valve utilizing an electrical actuation mechanism controlled from the surface or by a downhole intelligent controller.  
           [0005]    Oil and gas wells typically employ at least one safety valve that can be actuated to stop or control the flow of fluid through a pipe. These valves are normally positioned downhole to close the bore of the tubing string extending from one or more production zones to the well surface. Safety valves of this type include a spring that biases the valve to a fail-safe mode, such that an interruption in the force acting to keep the valve open will cause the valve to close.  
           [0006]    Conventional downhole safety valves are hydraulically operated. As oil and gas reserves are developed in deepwater, however, the column of fluid needed for hydraulic actuation becomes impractically long. Specifically, the hydrostatic head developed in a conventional hydraulically controlled valve results in high operating pressures and requires an unworkably large failsafe spring.  
           [0007]    Because of the problems with hydraulically controlled safety valves, electrically operated safety valves are an attractive alternative. In addition, intelligent completion systems are being developed that are equipped with a variety of electrically driven flow control devices. Hence, it is currently desirable to provide an all-electric control system and remove the requirement for any hydraulic supply. Electrically controlled downhole safety valves have been developed, but they generally require high power consumption and/or unfavorably large geometry, and are vulnerable to problems with electrical connections to the surface.  
           [0008]    Hence, it remains desirable to provide an electrically operated downhole safety valve that can operate effectively and reliably at deep setting depths, using available power downhole.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides an electrically operated downhole safety valve that can operate effectively and reliably using available power downhole. In a preferred embodiment, the present system fits into a casing no larger than would be required for a comparable hydraulic unit.  
           [0010]    The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    For a more detailed description of the preferred embodiments of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a schematic cross-section of a device constructed in accordance with a preferred embodiment of the present invention, showing the valve in a closed position;  
         [0013]    [0013]FIG. 2 is a schematic cross-section of the device of FIG. 1, showing the valve in a open position;  
         [0014]    [0014]FIG. 3 is a cross-section taken along lines  3 - 3  of FIG. 2; and  
         [0015]    [0015]FIGS. 4 and 5 are cross-sections taken along lines  4 - 4  and  5 - 5  of FIG. 2, showing the restraining mechanism in its de-energized and energized states, respectively. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring initially to FIG. 1, a device constructed in accordance with a preferred embodiment of the present invention comprises a generally cylindrical body  10  having a central bore  12  therethrough and a concentric flow tube  50  slidably mounted in bore  12 . Body  10  includes a first end  13  and a second end  14 , and preferably includes female threads  15  at each end. In addition, bore  12  includes a valve receptacle  16 , a spring receptacle  26 , an eccentric gearbox receptacle  36 , and a guide groove  46 , all described in detail below.  
         [0017]    Flow tube  50  comprises a cylindrical tube having a first end  53  and a second end  54 . The outer surface of flow tube  50  includes a first, annular extension  56  spaced a first distance from first end  53  and a second, non-annular extension  58  spaced a further distance from first end  53 . In addition, the outer surface of flow tube  50  includes an outwardly extending follower pin  59  between annular extension  56  and non-annular extension  58 .  
         [0018]    Referring still to FIG. 2 and in particular to bore  12  in body  10 , valve receptacle  16  comprises a first increased diameter portion in bore  12 . Valve receptacle  16  is bounded by a lower, frustoconical shoulder  17  and an upper, annular shoulder  18 . The inside diameter of valve receptacle  16  is greater than the outer diameter of flow tube  50 , creating a chamber  19  therebetween. A closure element  20  is housed in chamber  19 , along with a spring  22 . Closure element  20  is pivotally mounted such that it can pivot about a transverse axis between a closed position, shown in FIG. 1, in which it bears on annular shoulder  18 , and an open position, shown in FIG. 2. In its closed position, closure element  20  preferably substantially obstructs the flow of fluid through bore  12  and in its open position it does not. It will be understood that the closed and open positions need not be completely closed or completely open. In other words, the closed and open positions may be merely relative; namely, the closed position being one in which less fluid is allowed to pass than is allowed in the open position. Spring  22  is preferably mounted between closure element  20  and body  10  such that it bears on closure element and urges it into its closed position. Sprint  22  is shown as a coil spring, but it will be understood that spring  22  can comprise any suitable biasing member.  
         [0019]    Spring receptacle  26  comprises a second increased diameter portion in bore  12  spaced farther from end  13  than valve receptacle  16 . Spring receptacle  26  is bounded by a lower annular shoulder  27  and an upper annular shoulder  28 . The inner diameter of spring receptacle  26  is greater than the outer diameter of flow tube  50 , creating an annular chamber  29  therebetween. A coil spring  30  is preferably disposed in chamber  29  between lower annular shoulder  27  of spring receptacle  26  and annular extension  56  of flow tube  50 . Spring  30  is preferably sized such that it is compressed and urges flow tube  50  away from first end  13  even when annular extension  56  bears on upper annular shoulder  28 .  
         [0020]    Eccentric gearbox receptacle  36  comprises a third enlarged portion in bore  12  and is spaced farther from end  13  than spring receptacle  26 . Eccentric gearbox receptacle  36  comprises a lower portion  37  and an upper portion  38 . Lower portion  37  houses at least one and preferably a plurality of drive motors  40 , gearboxes  42 , and gears  44 . Upper portion  38  houses a rotating sleeve  46 . Rotating sleeve  46  includes a looped groove  48 , which includes a helical portion  47 , a short, transverse portion  51 , and a straight portion  49 . Looped groove  48  receives follower pin  59  on flow tube  50 . When closure element  20  is in the closed position shown in FIG. 1, follower pin  59  is disposed at a junction between straight portion  49  and helical portion  47 .  
         [0021]    Drive motors  40 , gearboxes  42 , gears  44  and rotating sleeve  46  are preferably operably connected such that power supplied to drive motors  40  causes motors  40  drive gearboxes  42 , which in turn drive gears  44 , which in turn cause rotating sleeve  46  to rotate about the axis of body  10  and flow tube  50 . FIG. 3 is a cross-sectional view along the axis of the device with the rotating sleeve  46  removed so as to show the plurality of gearboxes  42  and gears  44 . FIG. 3 also illustrates the extension of follower pin  59  from the outer surface of flow tube  50 .  
         [0022]    Guide groove  46  extends longitudinally along a portion of bore  12  and receives non-annular extension  58  of flow tube  50 . Referring briefly to FIGS. 4 and 5, guide groove  46  preferably is wide enough to include at least a pair of retaining members  68 . Retaining members  68  are actuable between an open position, shown in FIG. 4, and a closed position, shown in FIG. 5. In their closed position, retaining members  68  engage extension  58  so as to prevent flow tube  50  from moving relative to body  10 .  
         [0023]    Retaining members  68  and drive motors  40  receive electrical power from electrical leads  7 ,  9 , respectively. Conductors  7 ,  9  preferably enter body  10  through electrical penetrator  8 . Conductors  7 ,  9  electrically connect to a local control unit  100 , which is in turn electrically connected to a remote control unit  102 .  
         [0024]    A plurality of seals  70  are preferably provided between body  10  and flow tube  50  so as to isolate guide groove  46 , eccentric gearbox receptacle  36 , and spring receptacle  26  and prevent the ingress of fluid thereinto.  
         [0025]    Operation  
         [0026]    When it is desired to open bore  12  and allow fluid flow therethrough, a preferred first step is to equalize pressure on both sides of closure element  20 . With pressure equalized, power is supplied to motors  40  via conductors  9 . Motors  40  drive gearboxes  42 , which in turn advance gears  44 , causing sleeve  46  to rotate such that follower pin  59  enters the helical portion  47  of loop  48 . As sleeve  46  rotates, helical groove  47  bears on pin  59 , urging flow tube  50  toward first end  13  of body  10 . Because flow tube  50  is prevented from rotating by engagement of extension  58  with guide groove  46 , the rotation of sleeve  46  causes flow tube  50  to advance longitudinally through body  10 . As flow tube  50  advances relative to body  10  in response to the force applied by rotating sleeve  46 , annular extension  56  compresses spring  30  and first end  53  bears on closure element  20 , forcing it open. If pressure is not equalized before the opening sequence, more power may be required to open the valve.  
         [0027]    When the opening process is complete, the tool is in the position shown in FIG. 2. Specifically, end  53  of flow tube  50  rests on frustoconical shoulder  17  and closure element  20  is contained between body  10  and flow tube  50 . Bore  12  is open along the length of the tool, spring  30  is compressed, and follower pin  59  rests at the juncture of helical portion  47  and straight portion  49 , as shown in phantom. At this point, power is supplied to retaining members  68 , causing them to come together and engage extension  58  of flow tube  50  so as to prevent it from moving axially within body  10 . Rotation of sleeve  46  is then preferably continued, without further advancing flow tube  50 , as follower pin  59  traverses transverse portion  51  of loop  48 , until follower pin  59  rests at the juncture of transverse portion  51  and straight portion  49 , as shown in FIG. 2.  
         [0028]    Because the present invention is normally closed, it is a fail-safe valve. Once the device has attained the open state shown in FIG. 2, flow can continue through it until either the device is closed deliberately, the power supplied to retaining members  68  is interrupted, or retaining members  68  fail. When any of these events occurs, retaining members  68  cease to hold extension  58  and thus cease to prevent flow tube  50  from moving axially. This allows spring  30  to drive flow tube  50  away from first end  13 . As flow tube  50  advances toward second end  14 , follower pin  59  traverses straight portion  49  of loop  48 . Flow tube  50  is sized such that when annular extension  56  bears on upper annular shoulder  28 , its first end  53  clears upper annular shoulder  18 , allowing closure element  20  to fully close bore  12 .  
         [0029]    Because the device preferably includes a plurality of motors  40 , a plurality of gearboxes  42 , and a plurality of gears  44 , it is multiply redundant, ensuring that it remains operable even in the event that one or more of its components fail. In addition, the gear train may be fitted with multiple slip clutches that will allow the device to operate even if one or more of the redundant drive motors fail.  
         [0030]    Retaining members  68  can be any electrically actuable device and are shown as a pair of electrically actuated dogs. In a preferred embodiment, retaining members  68  each comprise at least one flux carrier in conjunction with at least one coil. The coils are connected to conductors  7 . When power is supplied to the coils, they induce flux in the flux carriers, which in turn advance toward extension  58  and ultimately engage it. By using electrical actuation and electrical power, the present device avoids the need for hydraulic systems.  
         [0031]    Flow tube  50  preferably includes a static sealing member at its first end  53 , which forms a seal with frustoconical shoulder  17  when the device is open. Flow tube  50  can be rotated to remove deposits that would otherwise impede travel of the tube. In some embodiments, flow tube  50  includes a toothed cutting edge to facilitate removal of deposits.  
         [0032]    In still another alternative embodiment, the relative positions of the drive mechanism and spring  30  may be reversed, such that the flow tube is pulled into the open position against the spring force. In this embodiment it is still preferred that the device be normally closed, so that it can function as a fail-safe device. Nonetheless, it is contemplated that in other embodiments, the configuration may be modified such that the device is normally open. In these embodiments, the relative positions of spring  30  and the drive mechanism may again be such that the drive mechanism either pulls or pushes the flow tube into the closed position.  
         [0033]    While certain preferred embodiments of the present invention has been shown and described, it will be understood that a variety of modifications could be made thereto without departing from the scope of the present invention. For example, the guiding and retaining functions performed by extension  58  could be performed by separate elements. Closure element  20 , shown above as a single component could comprise multiple components and/or could operate in various other ways. For example, closure element  20  could comprise a shutter-type closure, a ball valve, a stopcock-type closure, or any other suitable closure device. Likewise, the spring- loaded pivoting mechanism described above could comprise any suitable biasing means such as are known in the art.  
         [0034]    The drive mechanism described above as formed by the combination of gears, rotating sleeve, and follower pin could be replaced with a drive mechanism comprising solely gears, with the drive motors rotating a set of gears to either directly or indirectly advance the flow tube. For example, the flow tube could include gear teeth on a portion of its outer surface. Similarly, a plurality of powered drive mechanisms can be included and can include one-way drive clutches. The drive mechanism(s) can be configured so as to allow nonfunctioning drive mechanisms to be mechanically decoupled.  
         [0035]    Coil spring  30  can be replaced with a biasing means that is better suited to operate in tension, rather than in compression, if desired. Flow tube  50  can be replaced with a non-tubular element, although a tubular element is preferred because it is mechanically robust and protects the various components of the device from contact with the fluid. Similarly, retaining members  68  could be replaced with a single member, or multiple members, mounted inline with extension  58 , which when face to face with extension  58  can retain extension  58  when energized.  
         [0036]    The embodiments described herein are exemplary only and are not limiting. One skilled in the art will understand that the mechanisms described herein could each be replaced with alternative mechanisms, so long as the invention is within the scope of the claims that follow. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims. Also, in the claims that follow, the sequential recitation of steps is not intended to require that the steps be performed in the order recited, or that any given step be completed before another step is begun.