Abstract:
A pump with a position indicator is disclosed. The pump includes a pump housing, wherein the pump housing includes a flexible bladder disposed therein; a first fluid zone, wherein the first fluid zone is operable to allow flow of a first fluid into and out of the first fluid zone; and a second fluid zone, wherein the second fluid zone is operable to allow flow of a second fluid into and out of the second fluid zone. The pump further includes a flexible position indicator disposed in the first fluid zone and in communication with the flexible bladder, wherein the flexible position indicator is operable to detect a linear position of the flexible bladder, and wherein the flexible bladder fluidly isolates the first fluid zone from the second fluid zone.

Description:
PRIORITY CLAIM 
       [0001]    The present application is a non-provisional application of and claims the benefit of and priority to U.S. Prov. App. Ser. No. 62/203,779, filed Aug. 11, 2015, the entire disclosure of which is hereby expressly incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    In subsea drilling operations, equipment on the seabed is connected to a platform or vessel via a drilling riser. The riser typically provides a return path for drilling mud that has been used in drilling operations to return the mud to the vessel or platform. Oftentimes, the mud returning through the riser can have a density greater than that of the ambient seawater, so that the pressure exerted on a formation in the seabed by the column of mud in the riser is greater than that exerted by seawater in the absence of the riser. 
         [0003]    One way to deal with problems associated with increased pressure on a formation from high density drilling mud is the use of dual gradient drilling. In dual gradient drilling, a pump can be placed on the seabed, and can be powered, for example, by a seawater powered turbine. The pump serves to isolate the well from the hydrostatic pressure of the mud by directing the mud through a separate return line, thereby allowing replacement of the mud in the riser with seawater. 
         [0004]    In order for the pump to function properly, however, an operator must be able to determine the position of pump components, such as, for example, a flexible pump bladder within the pump housing. With this knowledge, the operator can then control the pump, or a series of pumps, to help control pressure in the well. In known pumps, the position of such components is typically measured using an indicator rod, the structure of which is described in greater detail as follows herein. 
       SUMMARY 
       [0005]    Disclosed herein is a pump with a position indicator. The pump includes a pump housing, wherein the pump housing includes a flexible bladder disposed therein; a first fluid zone, wherein the first fluid zone is operable to allow flow of a first fluid into and out of the first fluid zone; and a second fluid zone, wherein the second fluid zone is operable to allow flow of a second fluid into and out of the second fluid zone. The pump further includes a flexible position indicator disposed in the first fluid zone and in communication with the flexible bladder, wherein the flexible position indicator is operable to detect a linear position of the flexible bladder, and wherein the flexible bladder fluidly isolates the first fluid zone from the second fluid zone. 
         [0006]    Additionally disclosed herein is a dual gradient drilling system for subsea operations. The drilling system includes a water supply line comprising a water supply line inlet and a water supply line outlet; a manifold inlet, the manifold inlet in fluid communication with the water supply line; and a mud return line comprising a mud return line inlet and a mud return line outlet. The system further includes a mud lead line, the mud lead line in fluid communication with the mud return line; a pump housing, wherein the pump housing includes a flexible bladder disposed therein, wherein the flexible bladder fluidly isolates the manifold inlet from the mud lead line; and a flexible position indicator disposed proximate the manifold inlet and in communication with the flexible bladder, wherein the flexible position indicator is operable to detect a linear position of the flexible bladder within the pump housing. 
         [0007]    Further disclosed herein is a method for detecting displacement of a displaceable component in a pump housing. The method includes the steps of disposing a flexible position indicator proximate the pump housing and in communication with the displaceable component in the pump housing, the displaceable component operable to be displaced by fluid movement in the pump housing; allowing the flexible position indicator to be displaced responsive to movement of the displaceable component in the pump housing; detecting a displacement of the flexible position indicator; and monitoring a position of the displaceable component in the pump housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure&#39;s scope as it can admit to other equally effective embodiments. 
           [0009]      FIG. 1  is a schematic diagram of a mud pump. 
           [0010]      FIG. 2  is a schematic diagram of a mud pump depicting the pressurizing of mud within a mud space. 
           [0011]      FIG. 3  is a schematic diagram of a mud pump of the present disclosure. 
           [0012]      FIG. 4  is a graphic illustration of a position indicator with a transducer cable. 
           [0013]      FIG. 5  is an enlarged view of a ferrule connector from  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    A schematic diagram of a mud pump is shown in  FIGS. 1 and 2 .  FIG. 1  includes a side sectional view of an example of a pump  10  for use with a lift pump assembly (not shown). Pump  10  includes a generally hollow pump housing  12 . An embodiment of a flexible bladder  14  is shown within the housing  12 , which partitions the space within the housing  12  to define a mud space  16  on one side of the flexible bladder  14 , and a water space  18  on an opposing side of flexible bladder  14 . Flexible bladder  14  provides a fluidly-sealing barrier between mud space  16  and water space  18 . 
         [0015]    In the example of  FIG. 1 , flexible bladder  14  has a generally elliptical shape and an upper open space  20  formed through a side wall. Upper open space  20  is shown coaxially registered with an opening  22  formed through a side wall of pump housing  12 . A disk-like cap  24  bolts onto opening  22 , where cap  24  has an axially downward depending lip  26  that coaxially inserts within opening  22  and upper open space  20 . A portion of the flexible bladder  14  adjacent its upper open space  20  is wedged between lip  26  and opening  22  to form a sealing surface between flexible bladder  14  and pump housing  12 . 
         [0016]    A lower open space  28  is formed on a lower end of flexible bladder  14  distal from upper open space  20 , which in the example of  FIG. 1  is coaxial with upper open space  20 . An elliptical bumper  30  is shown coaxially set in the lower open space  28 . The bumper  30  includes upper and lower segments  32 ,  34 , which are coupled together in a clamshell like arrangement, and respectively seal against upper and lower radial surfaces on the lower open space  28 . The combination of sealing engagement of cap  24  and bumper  30  with upper and lower open spaces  20 ,  28  of flexible bladder  14 , effectively define a flow barrier across the opposing surfaces of flexible bladder  14 . 
         [0017]    Further shown in the example of  FIG. 1  is an axial rod  36  that attaches coaxially to upper segment  32  and extends axially away from lower segment  34  and through opening  22 . The rod  36  acts as a position indicator which, according to its axial position within the housing  12 , can indicate the position of the flexible bladder  14  within the housing  12 . 
         [0018]    Still referring to  FIG. 1 , a mud return line  38  is shown having an inlet end  40  and an outlet end  42 . A mud inlet valve  44  in mud return line  38  provides selective fluid communication from inlet end  40  to a mud lead line  46  shown branching from mud return line  38 . Lead line  46  attaches to an annular connector  48 , which in the illustrated example is bolted onto housing  12 . Connector  48  mounts coaxially over an opening  50  shown formed through a sidewall of housing  12  and allows communication between mud space  16  and mud return line  38  through lead line  46 . A mud exit valve  52  is shown in mud return line  38  and provides selective communication between mud return line  38  and outlet end  42 . 
         [0019]    Water may be selectively delivered into water space  18  via a water supply line  54 . A water inlet lead line  56  has an end coupled with water supply line  54  and an opposing end attached with a manifold assembly  58  that mounts onto cap  24 . The embodiment of the manifold assembly  58  of  FIG. 1  includes a connector  60  mounted onto a free end of a tubular manifold inlet  62 , an annular body  64 , and a tubular manifold outlet  66 , where the inlet and outlet  62 ,  66  mount on opposing lateral sides of the body  64  and are in fluid communication with body  64 . 
         [0020]    Connector  60  provides a connection point for an end of water inlet lead line  56  to manifold inlet  62 , so that lead line  56  is in fluid communication with body  64 . A lower end of manifold body  64  couples onto cap  24 , and the annulus of the manifold body  64  is in fluid communication with water space  18  through a hole in the cap  24  that registers with opening  22 . An outlet connector  68  is provided on an end of manifold outlet  66  distal from manifold body  64 , which has an end opposite its connection to manifold outlet  66  that is attached to a water outlet lead line  70 . On an end opposite from connector  68 , water outlet lead line  70  attaches to a water discharge line  72 . 
         [0021]    A water inlet valve  74  shown in water inlet lead line  56  provides selective water communication from a vessel (not shown) to water space  18  via water inlet lead line  56  and manifold assembly  58 . A water outlet valve  76  shown in water outlet lead line  70  selectively provides communication between water space  18  and water discharge line  72  through manifold assembly  58  and water outlet lead line  70 . 
         [0022]    In one example of operation of pump  10  of  FIG. 1 , mud inlet valve  44  is in an open configuration, so that mud in mud return line  38  communicates into mud return line  38  and mud lead line  46  as indicated by arrow A Mi . Further in this example, mud exit valve  52  is in a closed position thereby diverting mud flow into connector  48 , through opening  50 , and into mud space  16 . As illustrated by arrow A U , flexible bladder  14  is urged in a direction away from opening  50  by the influx of mud, thereby imparting a force against water within water space  18 . In the example, water outlet valve  76  is in an open position, so that water forced from water space  18  by flexible bladder  14  can flow through manifold body  64  and manifold outlet  66  as illustrated by arrow A Wo . After exiting manifold outlet  66 , water is routed through water outlet lead line  70  and into water discharge line  72 . 
         [0023]    An example of pressurizing mud within mud space  16  is illustrated in  FIG. 2 , wherein valves  44 ,  76  are in a closed position and valves  74 ,  52  are in an open position. In this example, pressurized water from water supply line  54  is free to enter manifold assembly  58 , where as illustrated by arrow A Wi , the water is diverted through opening  22  and into water space  18 . Introducing pressurized water into water space  18  urges flexible bladder  14  in a direction shown by arrow A D . Pressurized water in the water space  18  urges flexible bladder  14  against the mud, which pressurizes mud in mud space  16  and directs it through opening  50 . After exiting opening  50 , the pressurized mud flows into lead line  46 , where it is diverted to mud return line  38  through open mud exit valve  52  as illustrated by arrow A Mo . Thus, providing water at a designated pressure into water supply line  54  can sufficiently pressurize mud within mud return line  38  to force mud to flow back to a vessel (not shown). 
         [0024]    As discussed above, and shown in  FIGS. 1 and 2 , axial rod  36  attaches to upper segment  32  of the bumper  30 , which is in turn attached to the lower open space  28  of the flexible bladder  14 . One purpose of the rod  36  is to act as a position indicator, which indicates the position of the flexible bladder  14  within the housing  12 . One problem associated with the rod  36 , however, is that operation of the pump  10  requires the rod to move up and down relative to the housing  12  and other pump components, including portions of the manifold assembly  58 . 
         [0025]    There are several interfaces associated with the rod  36  and other pump components which may become wear points as the flexible bladder  14 , and in turn the rod  36 , move upward and downward. Each interface requires bushings and/or other mechanical pieces to allow movement of the rod  36  relative to the other components of the pump  10 . In addition, the break-in period for a new pump  10  employing the rod  36  as an indicator can be long, requiring careful initial filling of the pump chambers, and often leading to problems such as the flexible bladder  14  becoming wrapped around the rod  36 . 
         [0026]    Accordingly, and as shown in  FIG. 3 , one embodiment of the present invention provides a pump assembly  100  having certain components shown in  FIGS. 1 and 2 . Rod  36  is not present, and instead a flexible cable  136  is shown. Cable  136  extends through the manifold assembly  58  and can connect to the upper segment  32  of the bumper  30 , as shown. 
         [0027]    As shown, cable  136  can act as a position indicator for the flexible bladder  14  with surprising and unexpected advantages over the rod  36 . Unlike the rod  36  which has a diameter of about 1.375 inches, the cable  136  has a significantly smaller diameter. In certain embodiments, the diameter of the cable  136  is about ⅛ of an inch. In other embodiments, the diameter of the cable  136  is about 1/16 of an inch. Unlike the rod  36 , cable  136  is flexible, such that spooling the cable  136  instead of retracting the rod  36  away from the housing  12  results in occupying less space, for example in manifold assembly  58 . 
         [0028]    Because the cable  136  is smaller in diameter and is flexible, in certain embodiments, the cable  136  does not require as many components and interfaces subject to wear and tear as the rod  36  in the prior art embodiment. In certain embodiments, the use of the cable  136  allows less interface stack-up and less manufacturing tolerances because interfaces between bushings and the housing  12 , interfaces between bushing and the rod  36 , and/or interfaces between the housing  12  and sensors do not require fine control. In certain embodiments, lubrication around the interfaces is no longer required. Accordingly, the pump assembly  100  has a longer operating life. Furthermore, the flexible bladder is less likely to wrap around the cable  136 , and the cable  136  will be less sensitive to operator error during flexible bladder break-in, pump chamber filling, and pressure testing. 
         [0029]    As shown, cable  136  is coaxial with and extends through the manifold assembly  58  and can connect to the upper segment  32  of the bumper  30 . However, in other embodiments, cable  136  can be in communication with other components of the flexible bladder  14  and will be displaced responsive to the movement of the bumper  30  and/or other components moving in pump housing  12  in response to fluid flow. Cable  136 , in other embodiments, need not be coaxial with the manifold assembly  58 , and more than one cable can be used, in some embodiments, to detect certain displacements of components in hollow pump housing  12  in response to fluid flow. In certain embodiments, a linear variable displacement transducer (LVDT) can be attached to the cable  136 . Using a greater-accuracy, smaller range-of-motion transducer, for example a LVDT, enhances the accuracy of position measurement. 
       Experiment for Wire Linear Sensor 
       [0030]    The following describes a successful endurance test of a CPI SL1200-506 linear sensor produced by CPI Control Products, Inc. of East Hanover, N.J. The CPI SL1200-506 linear sensor operated successfully for one million full-stroke cycles in a circulating salt water test tank. At the conclusion of testing, the test unit was functioning correctly. The unit was removed and disassembled for inspection and analysis. The concentration of the salt water was 35 grams of salt per liter of water. End-stop measurements were taken to determine the linear sensor&#39;s initial functionality over 25 inch strokes prior to submerging the sensor in salt water and just after submerging the sensor in salt water. The operating stroke length of the linear sensor was approximately 25 inches. Stroke distances during the test were slightly variable due to small variations in operating points of magnetic limit switches affixed to the pneumatic actuator. 
         [0031]    Referring now to  FIG. 4 , a graphic representation of the linear sensor used in the presently described experiment is shown. The sensor had a resolution of 0.0027 inches per millivolt (0.068 mm per millivolt) (26.6 inches total range/10.00 volts). The maximum variation in the fully-extended data was about 72 millivolts. This corresponds to an error of about 0.194 inches maximum over one million cycles. The maximum variation in the fully-retracted data was about 245 millivolts. This corresponds to a maximum error of about 0.66 inches over one million cycles. Linear sensor  400  includes a sensor housing  402 , sensor enclosure panels  404 , a sensor body  406  disposed between the sensor housing  402  and a sensor conduit  408 , a transducer cable  410  axially-aligned with and disposed in the sensor conduit  408 , and a ferrule connector  412 . 
         [0032]    Sensor housing  402  further includes a spool assembly  414  and guide rollers  416  for transducer cable  410 . In embodiments of the present disclosure, ferrule connector  412  can be removeably connected to upper segment  32  of the bumper  30 , and as water space  18  is filled, transducer cable  410  would be pulled out of sensor conduit  408  allowing for detection of displacement of the linear sensor  400 . Alternatively, as mud space  16  is filled applying pressure to flexible bladder  14 , transducer cable  410  would retract into sensor conduit  408  and sensor housing  402  allowing for detection of displacement of the linear sensor  400 . 
         [0033]    In certain embodiments, the sensor housing  402  includes an internal pre-tensioned coil spring (not shown), where the coil spring causes the cable  410  to always be in tension. The tension is not strong enough to physically cause the flexible bladder  14  to move. However, when the bladder is caused to move, either towards the mud space  16  or towards the water space  18 , in response to the water space  18  being filled or the mud space  16  being filled, respectively, tension in the wire is sufficient to both allow the cable to extend (as the bladder moves toward mud space  16 ) and cause the cable  410  to retract quickly enough, preventing the cable  410  from having slack (as the bladder moves toward the water space  18 ). 
         [0034]    During testing, an end loop on transducer cable  410  was redesigned to include ferrule connector  412  to avoid wear and breakage of the cable.  FIG. 5  shows an enlarged view of ferrule connector  412 . As shown, ferrule connector  412  includes threads  418  and cable connector  420 . 
         [0035]    The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise. 
         [0036]    In the drawings and specification, there have been disclosed embodiments of methods and systems for detecting the position of a pump bladder within a pump housing, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the present disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.