Abstract:
An emergency riser disconnection system for disconnecting a riser from a subsea installation having disconnect actuators and a signal and power circuit for controlling the actuators. The signal and power circuit is made up of an umbilical with signal lines and hydraulic lines. At an umbilical termination, the signal and hydraulic lines exit the umbilical and can be routed separately to the disconnect actuators. The umbilical termination is disposed above the uppermost break away point on the riser and can be recovered after the riser is disconnected.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to production of oil and gas wells, and in particular to a device and method for unloading, and clean up of fluids from a well. 
       DESCRIPTION OF RELATED ART 
       [0002]    Subsea risers are tubular members extending from the sea surface to seafloor. When encasing a drill string during subsea drilling, a riser typically spans between a drilling rig to a blowout preventer (BOP) and Lower Marine Riser Package (LMRP); that in turn connects to a subsea wellhead. When used during production of hydrocarbons from subsea formations, a riser typically connects between a surface vessel to a subsea wellhead system. Tensioning systems are generally included that axially tension the riser for reducing lateral deflection from sea current side loading. In some instances, such as during a storm or unplanned deviation of location of the support vessel with respect to the well location, lateral loads can exceed structural integrity of the riser. To anticipate riser failure from such loads, risers often include emergency systems to allow a controlled disconnection between the sea surface and seafloor along the riser. 
         [0003]    A prior art example of a subsea exploration/production system  10  is shown in a side schematic view in  FIG. 1 . A riser  12  extends from above the sea surface  13  to a well system  14 . Platform  16  (typically a vessel of some description) provides the upper support for the riser  12  and from which a tensioning system (not shown) may be secured. Well system  14  includes a lower riser package  18  coupled with a production tree  20  that mounts onto a wellhead at the sea floor  22 . The well system  14  is disposed over a bore hole  24  shown intersecting a subsea formation  26 . Also provided is an umbilical  28  that typically includes control lines and power lines for actuating subsea mechanisms. An umbilical termination  30  is often provided on the lower end of the umbilical  28  and provides a mounting point for the umbilical  28  to the well system  14 . Typically at least one signal control line  31  attaches between the umbilical termination  30  and a subsea electronic module  32 . A hydraulic circuit  33  connects to the umbilical termination  30  and to actuation modules  34 ,  36  shown in the lower riser package  18 . An example of a signal and hydraulic control scheme may be found in GB2405163A, which was assigned to the assignee of the present application and is incorporated by reference herein in its entirety. 
       SUMMARY OF THE INVENTION 
       [0004]    Disclosed herein is a riser disconnect system for disconnecting a riser between the sea surface and seafloor, having features that incorporate additional system safety features and employing a distributed controls architecture to simplify the complexity of the safety disconnection interfaces. In an example embodiment, a riser disconnect system includes a break-away safety joint (often referred to as a weak link), located at some distance above the stress joint, it located above the EDP (Emergency Disconnect Package) of an LRP. An umbilical is carried by and attached to the riser, providing control signal line(s) and an actuation power supply. Actuated functions are included at one of a plurality of disconnection points along the riser and are energized in response to communication down the umbilical to the SEM to direct hydraulic power to discrete actuate functions. Also included is an umbilical termination that connects to the umbilical. The umbilical termination is disposed between the uppermost disconnection point and the sea surface, so that when the riser is disconnected to breakaway from the seafloor, the umbilical termination can be recovered. In an example embodiment, the signal line and actuation power line separate from the umbilical at the umbilical termination. The riser disconnect system includes a subsea electronic module (SEM) that has an input side attached to the signal line; additional signal lines attach between outputs of the SEM and a plurality of hydraulic mini-modules providing the direction of accumulated hydraulic control fluid pressure to any or all actuated functions. The actuation power line can, in an alternative embodiment, be a hydraulic fluid line that carries hydraulic fluid to the actuators. In an example, additional hydraulic fluid lines are included that define a hydraulic circuit. Accumulators can optionally be included that receive fluid from the hydraulic circuit and or lines. An output on each accumulator can attach to optionally included additional actuators; where the additional actuators are provided at the disconnection points along the riser In an example embodiment, the actuator is made up of a module coupled to a riser disconnect mechanism. The module can selectively change into an open position that communicates power to the riser disconnect mechanism. A power input can be included with the module that delivers power from the power line. The module can also have a signal input for receiving signals from the signal line. Also optionally included are power output lines with the riser disconnect system that form a power distribution circuit. A controller can receive a signal input and delivering power through one or more of the power output lines. 
         [0005]    The present disclosure also describes an offshore riser system that is made up of a riser, disconnection points along a length of the riser, riser disconnection modules coupled to the disconnection points on the riser, an umbilical suspended beneath the surface of the sea and having an umbilical termination at a lower depth, a signal line extending from the umbilical termination to each of the riser disconnection modules, and a hydraulic power line extending from the umbilical termination to each of the riser disconnection modules. In one example embodiment, the umbilical termination is above an uppermost one of the disconnection points and below the sea surface. This allows recovery of the umbilical termination when the riser is disconnected to breakaway from the seafloor. A subsea electronic module (SEM) can be included that has an input connected to the signal line. An output can be provided with the SEM that connect to output and each of the riser disconnection modules. An emergency disconnect package can be included proximate where the riser connects to a wellhead assembly on the seafloor and a riser safety joint may be included that is disposed above the emergency disconnect package. The emergency disconnect package and riser safety joint can each include an associated disconnection module. In an embodiment, a hydraulic circuit is defined between the umbilical termination and each of the riser disconnection modules. Each riser disconnection module can be coupled to a riser disconnect mechanism at the disconnection point on riser, wherein the riser disconnection module is selectively changeable to an open position to communicate power to the riser disconnect mechanism. In an example embodiment, the riser disconnection module includes a hydraulic input in fluid communication with the hydraulic power line, a signal input in signal communication with the signal line, a valved manifold with a plurality of hydraulic power output lines, and a controller for receiving a signal input and flowing hydraulic fluid through one or more of the hydraulic power output lines. 
         [0006]    Yet further described herein is an example embodiment of a subsea system that is made of a riser projecting upward from a subsea installation on the seafloor. In this example, disconnecting joints may be included on the riser with each having an associated disconnection actuator. An umbilical may be suspended subsea and adjacent the riser that has a signal line connected to the disconnection actuators. The umbilical can also have therein a power line for delivering power to the disconnection actuators and an umbilical termination coupled with the umbilical that is below the sea surface and above a disconnection joint closest to the sea surface. This allows recovery of the umbilical termination when any of the disconnection actuators are actuated to disconnect the riser. An SEM can be coupled to the signal line on an input side of the subsea electronic module and signal lines coupled on one end to an output side of the subsea electronic module and on another end to the disconnection actuators. In an example embodiment, the power line is a hydraulic fluid line that carries hydraulic fluid to the disconnection actuators. The system can also alternatively include accumulators that each connect to the hydraulic fluid lines and supply pressurized hydraulic fluid to an associated disconnection actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a side schematic view of a prior art embodiment of a subsea exploration/production system having a riser disconnect system. 
           [0008]      FIG. 2  is a side schematic view of an example embodiment of a subsea exploration/production system having a riser disconnect system. 
           [0009]      FIG. 3  is a schematic view of an example embodiment of a subsea module for use with a riser disconnect system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    The apparatus and method of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. This subject of the present disclosure may, however, be embodied 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 the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
         [0011]    It is to be understood that the subject 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 of the subject disclosure and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the subject disclosure is therefore to be limited only by the scope of the appended claims. 
         [0012]    Show in a side schematic view in  FIG. 2  is an example embodiment of a subsea exploration and production system  50  in accordance with the present disclosure. The subsea exploration and production system  50  of  FIG. 2  includes an emergency disconnect system or breakaway for a riser  52 . The riser  52  as shown extends subsea beneath the sea surface  53  and shown supported on its upper end along a platform  54 . Examples of the platform  54  include a drilling rig as well as a production vessel, such as a loading production storage and offloading unit. A tensioning system  56  may be included as shown mounted above the platform  54  for imparting an axial tension within the riser  52 . The lower end of the riser  52  couples with a wellhead assembly  58  that includes a lower riser package  60  and production tree  62 . The wellhead assembly  58  of  FIG. 2  is shown mounted on the sea floor  64 . The wellhead assembly  58  is set over a bore hole  66  that extends downward from the sea floor  64  and formed through a subsea formation  68 . 
         [0013]    Joints  69  are shown formed at various locations along the length of the riser  52 . As discussed in greater detail below, actuators may be provided at one or more of these joints  69  to break away or sever the riser  52  at or along a joint  69 . In one example, an emergency disconnect package  70  is shown attached with a connector  71  to the riser  52  set adjacent to where the riser  52  attaches to the wellhead assembly  58 . It is believed that forming and installing a disconnect package  70  is within the capabilities of those skilled in the art. A riser safety joint  72  is an additional example of a breakaway that is shown on the riser  52  and set above the emergency disconnect package  70 . The riser  52  may optionally include an upper riser containment valve  73  as shown within the riser  52  above the riser safety joint  72  and a lower riser containment valve  75  at the emergency disconnect package  70 . Also illustrated in  FIG. 2  is an umbilical  74  that is suspended subsea adjacent the riser  52 . Optionally, the umbilical  74  may be coupled to the riser  52 . The umbilical  74  has a lower end anchored at an umbilical termination  76 . The umbilical termination  76  is in signal communication with a subsea electronic module  78  via a signal line  80  that extends from the umbilical termination  76  to an input connection on the subsea electric module  78 . 
         [0014]    Actuation modules  82 ,  84 ,  86 ,  88  are provided respectively on the riser safety joint  72 , emergency disconnect package  70 , and the wellhead assembly  58 . In an example embodiment, the actuation modules  82 ,  84 ,  86 ,  88  provide for actuation of an actuator(s), an actuation device(s), a valve(s), BOP ram, or a mechanical device(s) located in one or more of the emergency disconnect package  70 , riser safety joint  72 , and wellhead assembly  58 . A signal line  90  shown connected between the subsea electronic module  78  and actuation module  82  may convey control signals for operational control of the actuation module  82 . Similar signal lines  92 ,  94 ,  96  can provide signal communication between the subsea electronic module  78  and actuation modules  84 ,  86 ,  88 . The signal lines  80 ,  90 ,  92 ,  94 ,  96  can be any medium for transmitting signals, where the signals can be electrical, acoustic, or electromagnetic, such as a radio waves or optical signals. 
         [0015]    The actuation modules  82 ,  84 ,  86 ,  88  may be powered by electricity, compressed gas, as well as hydraulic fluid. In the example embodiment of  FIG. 2 , a hydraulic circuit  97  is shown providing fluid communication between the umbilical termination  76  and accumulators  98 ,  100 ,  102 . The accumulators  98 ,  100 ,  102  are in respective fluid communication with each of the actuation modules  82 ,  84 ,  86 ,  88  via hydraulic lead lines  106 ,  108 ,  110 ,  112 . In an example embodiment, the accumulators  98 ,  100 ,  102  include a vessel or other container in which pressurized fluid is stored for use by the actuators  82 ,  84 ,  86 ,  88  when desired. In the example of  FIG. 2 , actuation modules  82  and  88  each have respective dedicated accumulators  98 ,  100 . Whereas, actuation modules  86 ,  88  share a single accumulator  102 . Example embodiments exist wherein each actuation module includes a dedicated accumulator, or more than two actuation modules are in fluid communication with a single accumulator. 
         [0016]    It should be pointed out that the umbilical termination  76  is set above the upper most breakaway point, i.e. the riser safety joint  72  and associated actuation module  82 . Accordingly, in situations when it is necessary to disconnect the riser  52  from the wellhead assembly  58 , the umbilical termination  76  can be recovered along with the disconnected portion of the riser  52 . 
         [0017]    A schematic example of an actuation module  113  is provided in side view in  FIG. 3 , wherein the actuation module  113  is an illustrative example of any or all the actuation modules  82 ,  84 ,  86 ,  88 . In this embodiment, the actuation module  113  includes a hydraulic manifold  114  in fluid communication with a hydraulic power line  115 ; wherein the hydraulic power line  115  is representative of one or more of the hydraulic lead lines  106 ,  108 ,  110 ,  112 . Motor operated valves  116  are shown included within each leg of the manifold  114  for directing fluid flow through each of the legs. The motor operated valves  116  may be controlled to open, close, or partially close via control signals delivered from a signal line  117  to a controller  118 . The signal line  117  is representative of one or more of the signal lines  90 ,  92 ,  94 ,  96 . In the example embodiment of  FIG. 3 , an end (not shown) of the power line  115  opposite the manifold  114  connects to an accumulator that is in fluid communication with the hydraulic circuit  97 . Additionally, the signal line  117  is in signal communication with the subsea electronic module  78 . Optionally, one or both of the power line  115  and signal line  117  may be in direct communication with the umbilical  74 . Exit lines  120  are shown illustrated downstream of the motor operated valves  116 ; each exit line  120  couples with a device, such as an actuator or connector, provided within the subsea exploration/production system  50 . In the example of  FIG. 3 , an actuator  122  is shown attached to a valve  124 , wherein the actuator is selectively powered for opening/closing the valve  124  when fluid is selectively delivered through line  120 . The actuation module  113  may attach directly to a portion of the production system  50 , or can be mounted adjacent the production system  50  and the exit lines  120  extending between the actuation module  113  and the device being powered or actuated. Examples of devices being powered or actuated include the connector  71 , the riser safety joint  72 , and the upper and lower riser containment valves  73 ,  75  ( FIG. 2 ). Supply lines  126 ,  128  can convey actuating fluid from the actuation modules  82 ,  84  to the upper and lower riser containment valves  73 ,  75 . 
         [0018]    In an example of operation of the subsea exploration/production system  50  of  FIG. 2 , the umbilical  74  provides power and control. Power from the umbilical  74  can be transmitted as either electrical, pneumatic, or from pressurized hydraulic fluid. The power can be delivered directly to the actuation modules  82 ,  84 ,  86 ,  88 , or converted to another form of power for delivery to the actuation modules  82 ,  84 ,  86 ,  88  or other devices subsea. In the example of hydraulic fluid power, transmission can occur by flowing pressurized hydraulic fluid through the hydraulic circuit  97  to the accumulators  98 ,  100 ,  102 . Control, such as actuation, deactivation, and operational rate, can take place by transmitting a signal(s) via the signal line  80  to the SEM  78 . In an example embodiment, the SEM  78  distributes the signal(s) received from the signal line  80  to one or more of the signal lines  90 ,  92 ,  94 ,  96  for transmission to a respective actuation module  82 ,  84 ,  86 ,  88 . Thus the SEM  78  can be or operate the same as or similar to a multiplexer. As explained above in the description of  FIG. 3 , in response to the signal delivered to an actuation module  82 ,  84 ,  86 ,  88 , fluid maintained in an accumulator  98 ,  100 ,  102  is routed through an actuation module  82 ,  84 ,  86 ,  88  and delivered to a designated actuator. 
         [0019]    When required or otherwise desired, the riser  52  can be decoupled from the wellhead assembly  58  by signals delivered through one or more of the signal lines  80 ,  90 ,  92 ,  94 ,  96  and optional SEM  78 . Power for decoupling can occur from the hydraulic circuit  97 . Decoupling can involve actuating one or each of the riser safety joint  72  and connector  71  in the emergency disconnect package  70 . Decoupling can also include closing the upper and lower riser containment valves  73 , 75  via the actuation modules  82 ,  84 . After disconnecting the riser  52  from the wellhead assembly  58 , the platform  54  and portion of the riser  52  above the riser safety joint  72  can be relocated to another area if necessary. The signal lines  80  and power lines are severed at a point below the umbilical termination  76  to allow the umbilical  74  (and termination  76 ) to be relocated with the platform  54  and decoupled portion of the riser  52 . 
         [0020]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.