Abstract:
A method and system for lifting drilling mud from subsea to a drilling vessel, which uses a pump having a body with a chamber, and a bladder in the chamber. The bladder attaches to the body and defines water and mud sides in the chamber. A mud inlet valve allows mud into the mud side of the chamber; which moves the bladder into the water side and urges water in the water side from the chamber and through a water exit valve. Pressurized water enters the chamber through a water inlet valve, which in turn pushes the bladder and mud from the chamber through a mud exit valve. The bladder separates the mud and water as it reciprocates in the chamber. The travel of the bladder in the chamber is controlled to prevent damage from contact with the chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/791,258, filed Mar. 15, 2013, the full disclosure of which is hereby incorporated by reference herein for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present disclosure relates in general to a system and method for maintaining volume in a bladder pump at the end of each pump stroke. 
         [0004]    2. Description of Prior Art 
         [0005]    Subsea drilling systems typically employ a vessel at the sea surface, a riser connecting the vessel with a wellhead housing on the seafloor, and a drill string. A drill bit is attached on a lower end of the drill string, and used for excavating a borehole through the formation below the seafloor. The drill string is suspended subsea from the vessel into the riser, and is protected from seawater while inside of the riser. Past the lower end of the riser, the drill string inserts through the wellhead housing just above where it contacts the formation. Generally, a rotary table or top drive is provided on the vessel for rotating the string and bit. Drilling mud is usually pumped under pressure into the drill string, and is discharged from nozzles in the drill bit. The drilling mud, through its density and pressure, controls pressure in the well and cools the bit. The mud also removes formation cuttings from the well as it is circulated back to the vessel. Traditionally, the mud exiting the well is routed through an annulus between the drill string and riser. However, as well control depends at least in part on the column of fluid in the riser, the effects of corrective action in response to a well kick or other anomaly can be delayed. 
         [0006]    Fluid lift systems have been deployed subsea for pressurizing the drilling mud exiting the wellbore. Piping systems outside of the riser carry the mud pressurized by the subsea lift systems. The lift systems include pumps disposed proximate the wellhead, which reduce the time for well control actions to take effect. 
       SUMMARY OF THE INVENTION 
       [0007]    A method and system for lifting drilling mud from subsea to a drilling vessel. Drilling mud exiting a wellbore is directed to a subsea pump that includes a body, a chamber in the body, and a bladder in the chamber. An outer periphery of the bladder sealingly attaches to the body, and defines a water side and a mud side in the chamber. A mud inlet valve selectively opens to allow mud to flow into the mud side of the chamber. As mud enters the chamber, the bladder is moved into the water side, and urges water in the water side from the chamber and through a selectively opened water exit valve. Pressurized water enters the chamber through a selectively opened water inlet valve, which in turn exerts a force against the bladder that urges the mud from the chamber through a selectively opened mud exit valve. The bladder maintains a barrier between the mud and water as it reciprocates in the chamber. The travel of the bladder in the chamber is controlled to prevent damage from contact with the chamber. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a side sectional view of an example of a subsea drilling system in accordance with the present invention. 
           [0010]      FIGS. 2 and 3  are partial side sectional views of an example of a subsea pump for use with the drilling system of  FIG. 1  in different pumping modes and in accordance with the present invention. 
           [0011]      FIG. 4  is a side view of an embodiment of a subsea drilling system with a riser and pump kit, and in accordance with an embodiment of the invention. 
       
    
    
       [0012]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0013]    The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
         [0014]    It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
         [0015]    Shown in  FIG. 1  is a side partial sectional view of an example embodiment of a drilling system  10  for forming a wellbore  12  subsea. The wellbore  12  intersects a formation  14  that lies beneath the sea floor  16 . The wellbore  12  is formed by a rotating bit  18  coupled on an end of a drill string  20  shown extending subsea from a vessel  22  floating on the sea surface  24 . The drill string  20  is isolated from seawater by an annular riser  26 ; whose upper end connects to the vessel  22  and lower end attaches onto a blowout preventer (BOP)  28 . The BOP  28  mounts onto a wellhead housing  30  that is set into the sea floor  16  over the wellbore  12 . A mud return line  32  is shown having an end connected to the riser  26  above BOP  28 , which routes drilling mud exiting the wellbore  12  to a lift pump assembly  34  schematically illustrated subsea. Within the lift pump assembly  34 , drilling mud is pressurized for delivery back to the vessel  22  via mud return line  36 . 
         [0016]      FIG. 2  includes a side sectional view of an example of a pump  38  for use with lift pump assembly  34  ( FIG. 1 ). Pump  38  includes a generally hollow and elliptically shaped pump housing  40 . Other shapes for the housing  40  include circular and rectangular, to name a few. An embodiment of a flexible bladder  42  is shown within the housing  40 ; which partitions the space within the housing  40  to define a mud space  44  on one side of the bladder  42 , and a water space  46  on an opposing side of bladder  42 . As will be described in more detail below, bladder  42  provides a sealing barrier between mud space  44  and water space  46 . In the example of  FIG. 2 , bladder  42  has a generally elliptical shape and an upper open space  48  formed through a side wall. Upper open space  48  is shown coaxially registered with an opening  50  formed through a side wall of pump housing  40 . A disk-like cap  52  bolts onto opening  50 , where cap  52  has an axially downward depending lip  53  that coaxially inserts within opening  50  and upper open space  48 . A portion of the bladder  42  adjacent its upper open space  48  is wedged between lip  53  and opening  50  to form a sealing surface between bladder  42  and pump housing  40 . 
         [0017]    A lower open space  54  is formed on a lower end of bladder  42  distal from upper open space  48 , which in the example of  FIG. 2  is coaxial with upper open space  48 . An elliptical bumper  56  is shown coaxially set in the lower open space  54 . The bumper  56  includes upper and lower segments  58 ,  60  coupled together in a clamshell like arrangement, and that respectively seal against upper and lower radial surfaces on the lower open space  54 . The combination of sealing engagement of cap  52  and bumper  56  with upper and lower open spaces  42 ,  54  of bladder  42 , effectively define a flow barrier across the opposing surfaces of bladder  42 . Further shown in the example of  FIG. 2  is an axial rod  62  that attaches coaxially to upper segment  56  and extends axially away from lower segment  58  and through opening  50 . 
         [0018]    Still referring to  FIG. 2 , a mud line  64  is shown having an inlet end connected to mud return line  32 , and an exit end connected with mud return line  36 . A mud inlet valve  66  in mud line  64  provides selective fluid communication from mud return line  32  to a mud lead line  68  shown branching from mud line  64 . Lead line  68  attaches to an annular connector  70 , which in the illustrated example is bolted onto housing  40 . Connector  70  mounts coaxially over an opening  72  shown formed through a sidewall of housing  40  and allows communication between mud space  44  and mud line  64  through lead line  68 . A mud exit valve  74  is shown in mud line  64  and provides selective communication between mud line  64  and mud return line  36 . 
         [0019]    Water may be selectively delivered into water space  46  via a water supply line  76  ( FIG. 1 ) shown depending from vessel  22  and connecting to lift pump assembly  34 . Referring back to  FIG. 2 , a water inlet lead line  78  has an end coupled with water supply line  76  and an opposing end attached with a manifold assembly  80  that mounts onto cap  52 . The embodiment of the manifold assembly  80  of  FIG. 2  includes a connector  82 , mounted onto a free end of a tubular manifold inlet  84 , an annular body  86 , and a tubular manifold outlet  88 , where the inlet and outlet  84 ,  88  mount on opposing lateral sides of the body  86  and are in fluid communication with body  86 . Connector  82  provides a connection point for an end of water inlet lead line  78  to manifold inlet  84  so that lead line  78  is in communication with body  86 . A lower end of manifold body  86  couples onto cap  52 ; the annulus of the manifold body  86  is in fluid communication with water space  46  through a hole in the cap  52  that registers with opening  50 . An outlet connector  90  is provided on an end of manifold outlet  88  distal from manifold body  86 , which has an end opposite its connection to manifold outlet  88  that is attached to a water outlet lead line  92 . On an end opposite from connector  90 , water outlet lead line  92  attaches to a water discharge line  94 ; that as shown in  FIG. 1 , may optionally provide a flow path directly subsea. 
         [0020]    A water inlet valve  96  shown in water inlet lead line  78  provides selective water communication from vessel  22  ( FIG. 1 ) to water space  46  via water inlet lead line  78  and manifold assembly  80 . A water outlet valve  98  shown in water outlet lead line  92  selectively provides communication between water space  46  and water discharge line  94  through manifold assembly  80  and water outlet lead line  92 . 
         [0021]    In one example of operation of pump  38  of  FIG. 2 , mud inlet valve  66  is in an open configuration, so that mud in mud return line  32  communicates into mud line  64  and mud lead line  68  as indicated by arrow A Mi . Further in this example, mud exit valve  74  is in a closed position thereby diverting mud flow into connector  70 , through opening  72 , and into mud space  44 . As illustrated by arrow A U , bladder  42  is urged in a direction away from opening  72  by the influx of mud, thereby imparting a force against water within water space  46 . In the example, water outlet valve  98  is in an open position, so that water forced from water space  46  by bladder  42  can flow through manifold body  86  and manifold outlet  88  as illustrated by arrow A Wo . After exiting manifold outlet  88 , water is routed through water outlet lead line  92  and into water discharge line  94 . 
         [0022]    An example of pressurizing mud within mud space  44  is illustrated in  FIG. 3 , wherein valves  66 ,  98  are in a closed position and valves  96 ,  74  are in an open position. In this example, pressurized water from water supply line  76  is free to enter manifold assembly  80  where as illustrated by arrow A Wi , the water is diverted through opening  50  and into water space  46 . Introducing pressurized water into water space  46  urges bladder  42  in a direction shown by arrow A D . Pressurized water in the water space  46  urges bladder  42  against the mud, which pressurizes mud in mud space  44  and directs it through opening  72 . After exiting opening  72 , the pressurized mud flows into lead  68 , where it is diverted to mud return line  36  through open mud exit valve  74  as illustrated by arrow A Mo . Thus, providing water at a designated pressure into water supply line  76  can sufficiently pressurize mud within mud return line  36  to force mud to flow back to vessel  22  ( FIG. 1 ). 
         [0023]    As illustrated in  FIGS. 2 and 3 , bumper  56  travels axially within housing  40 , and has end strokes proximate to the inner surface of housing  40 . An optional controller  100  ( FIG. 1 ) may be provided for limiting travel of bladder  42  and bumper  56  to avoid collisions of bladder  42  or bumper  56  with the inner surface of housing  40 . In an embodiment, controller  100  includes an information handling system, and receives or contains instructions to selectively operate valves  66 ,  74 ,  78 ,  98 . Optionally, valves  66 ,  74 ,  78 ,  98  can include actuators (not shown) in communication with and/or controlled by controller  100 , that manipulate the valves  66 ,  74 ,  78 ,  98  to limit travel of the bumper  56 . The controller  100  can be set based upon an increase or decrease in fill volume that alters velocity of flow in one of the chambers  44 ,  46 . User defined set points can be input to the controller  100  for establishing limits of travel of the bladder  42 . This can be manifested via control of the valves  66 ,  74 ,  96 ,  98  so that they open and close at designated times and sequences so that travel of bladder  42  and/or bumper  56  prevents or avoids collision with housing  40 . Moreover, a set bias may be included with commands in the controller so that the control system automatically adjusts the set points to a higher or lower value to bring bladder travel within a safe range and thereby avoid any damaging contact. Examples exist wherein volume in one of the chambers  44 ,  46  at a maximum stroke ranges from about 15 gallons to about 55 gallons. By setting the set points with an included bias, the set points are adjusted during use so that in a subsequent cycle of pumping, the extent of bladder travel is decreased to avoid any overshoot from a designated position. 
         [0024]    Referring now to  FIG. 4 , an alternate embodiment of drilling system  10 A is shown in side partial sectional view and wherein lift pump assembly  34 A includes a mud pump kit  102  mounted integral onto riser  26 A. In this example, mud pump kit  102  includes a subsea module  104  shown circumscribing riser  26 A and that includes mud distribution manifold (not shown) and other flow control devices for selectively diverting flow to desired destinations. A riser module  106  is illustrated mounted on an upper surface of subsea module  104 , which also circumscribes riser  26 A. Riser module  106  of  FIG. 4  includes hydraulic power units for pressurizing hydraulic fluid that in an example is used for actuating devices subsea. Riser module  106  also includes hydraulic control systems connection hardware for mounting mud pump kit  102  to riser  26 A. Pumps  38  ( FIG. 2 ) are housed in pump modules  108 ,  110  shown set on riser module  106 . In an embodiment, pump modules  108 ,  110  each include three pumps  38 . A solids recovery unit (SRU)  112  is shown above the pump modules  108 ,  110 , and a subsea rotating device (SRD)  114  attaches to an upper end of SRU  112 . An upper end of SRD  114  flangedly attaches to a riser joint  116 , where in one example a substantial portion of the riser  26 A between SRD  114  and vessel  22  ( FIG. 1 ) is made up of stacked riser joints  116 . 
         [0025]    In the example of  FIG. 4 , mud exiting drill string  20  flows upward in an annulus  118  defined between drill string  20  and wellbore  12 , and which extends further upward between drill string  20  and riser  26 A. The mud flows past mud pump kit  102  and SRU  112  within annulus  118  and into SRD  114  where a packer (not shown) blocks the mud. In an embodiment, the annulus  118  above packer is filled with sea water or other fluid. Mud within annulus  118  below packer is diverted to SRU  112  where cuttings or other solids are removed or particulated. After being processed in the SRU  112 , the mud is directed to the pump modules  108 ,  110  where it is pressurized so it can flow back to vessel  22 . Processing the mud in the SRU  112  can prevent damage to the pumps  38  ( FIG. 2 ) in the modules  108 ,  110 . 
         [0026]    In an example, modules  104 ,  106 ,  108 ,  110  are modular elements that can be transported separately to the vessel  22  ( FIG. 1 ) on site, where the pump kit  102  is assembled. A significant time savings is one advantage of the modularity of modules  104 ,  106 ,  108 ,  110 . Because loading a fully assembled pump kit  102  onto a vessel  102  causes such an asymmetric weight distribution that requires anchoring and stabilization, which is unachievable on site. Whereas the vessel  22  can accommodate individual modules  104 ,  106 ,  108 ,  110  on site and without becoming unstable. Pump modules  108 ,  110  are individually detachable from the pump kit  102 , and thus further enhancing modularity of the pumping system. Dedicated piping (not shown) is routed from SRU  112  and separately to each module  108 ,  110  so that one of the modules  108 ,  110  can remain operational while the other is removed or otherwise out of service. Further, spare modules can be kept on site for one or both modules  108 ,  110 , and can installed in place of a one of the modules  108 ,  110  with little or no stoppage of operation of pumping mud to the vessel  22 . 
         [0027]    In an alternate embodiment, BOP  28 A is a BOP stack, whose upper portion includes an annular blowout preventer and is part of a lower marine riser package (LMRP). Additionally, LMRP can include controls, a multiplexer unit, and pods. In an embodiment, modules  104 ,  106 ,  108 ,  110 , SRU  112 , SRD  114 , BOP  28 A, and riser joints  116  are delivered to the vessel  22  ( FIG. 1 ) while on site and disposed above wellbore  12 . While on the vessel  22 , modules  104 ,  106 ,  108 ,  110  are attached together to form mud pump kit  102  which is coupled with BOP  28 A. SRU  112  and SRD  114  are attached onto mud pump kit  102 ; while suspended from riser joints  116  the assembled unit is lowered subsea onto wellhead housing  30 . 
         [0028]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.