Abstract:
An electrical mudline system that includes a turbine-type power generation assembly that can be lowered by wireline and installed at the seabed or mudline. A generator may be installed on a wellhead for support and located on a lower part of the generation assembly or may be installed through a tree if a cap on the tree is removed. A frame is included to provide additional support for the generation assembly and protect the turbine blades on the periphery of the turbine. The turbine rotates in response to water currents and thereby rotates a shaft coupled to the turbine to generate electrical power. The electrical power is generated local to the well to power various types of equipment at the well or in the vicinity of the well.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional application 61/251,619, filed Oct. 14, 2009. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to generating electrical power from water currents, and in particular, to providing electrical power to subsea equipment with a subsea current power generator. 
       BACKGROUND OF THE INVENTION 
       [0003]    Typically, subsea equipment used in oil and gas well completions requires electrical power to operate. Power is typically provided by an umbilical from a platform. After a platform has fulfilled its use in the production of oil or gas, however, the platform may be removed to the mudline and relocated or discarded. 
         [0004]    If no platform is available, electrical power can also be provided to subsea equipment by an umbilical from an onshore facility. The umbilical must be sufficiently long to reach the subsea equipment to be used and may be many miles in length. 
         [0005]    The power source can thus be located some distance from the subsea equipment offshore platforms and can result in the need for a long, heavy umbilical that is expensive to fabricate, transport, and install. 
         [0006]    Attempts have been made to address the expense associated with an extremely long umbilical. One attempt, for example, is the offshore generation of power through the use of turbines. The energy in the water currents can be transformed into electrical power via a shaft coupled to the turbine. The turbine&#39;s rotation in response to the water currents rotates the shaft and a standard generator coupled to the other end of the shaft to produce electrical power. This approach to solving the problem of costly umbilicals requires extensive infrastructure, such as platforms or subsea support structures, to support the power generators. The infrastructure thus can also be costly. 
         [0007]    Providing electrical power to subsea equipment requires that umbilicals extend from a platform or onshore facility, or that power be locally generated by power generation units requiring additional infrastructure to support. Current methods are expensive approaches to address the expense of electrical umbilicals. A need exists for a technique to minimize the length and thus expense of umbilicals in a cost-effective manner. 
       SUMMARY OF THE INVENTION 
       [0008]    In an embodiment of the invention, the electrical mudline system includes a power generation assembly that can be lowered by wireline and installed at the seabed or mudline. A generator may be installed on a wellhead for support and located on a lower part of the generation assembly. 
         [0009]    In this embodiment, the electrical mudline system may further include a tubular housing at the wellhead that protrudes above seafloor and may have a subsea tree attached to it. Once the well has been isolated or plugged, the tree can be removed and the generation assembly can be landed on the wellhead. The present invention further includes a frame that protects a turbine that has blades disposed on the periphery of the turbine that cause the turbine to rotate in response to water currents. The frame further provides additional support for the generation assembly. 
         [0010]    In this embodiment, in response to the rotation of the shaft coupled to the turbine, the generator generates electrical power. Thus electrical power is generated localized in the well to power various types of equipment. In addition, the use of existing wellheads to provide support advantageously lowers the cost associated with installing additional support structures. Further, an umbilical may be connected to the generation assembly and run out to a desired location at sea to provide electrical power to subsea equipment, thus advantageously decreasing the length, weight, and cost of the umbilical when compared to one extending from onshore facilities. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1 , illustrates a partial sectional view of an embodiment of the power generation assembly in accordance with the invention; 
           [0012]      FIG. 2 , illustrates a top sectional view of a turbine wheel located within the power generation assembly of  FIG. 1 , in accordance with the invention; 
           [0013]      FIG. 2A , illustrates a sectional view of the turbine wheel of  FIG. 2 , in accordance with the invention; 
           [0014]      FIG. 3A , illustrates a top view of the power generation assembly of  FIG. 1 , in accordance with the invention; 
           [0015]      FIG. 3B , illustrates a bottom sectional view of the power generation assembly of  FIG. 1 , in accordance with the invention; 
           [0016]      FIG. 4 , illustrates a sectional view of another embodiment of the power generation assembly in accordance with the invention. 
           [0017]      FIG. 4A , illustrates a top view of the embodiment of  FIG. 4 , in accordance with the invention. 
           [0018]      FIG. 5 , illustrates a sectional view of another embodiment of the power generation assembly in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  shows a partial sectional view of an embodiment of a power generation assembly  10  of the invention installed at the seabed or mudline  12 . In this embodiment, the power generation assembly  10  could be lowered by wireline from a rig or vessel (not shown) and landed on an existing or abandoned wellhead  14  located at the mudline  12 . The wellhead  14  may be adapted to receive and secure a generator  16  located on a lower part of the generation assembly  10 . The wellhead  14  provides support to the generation assembly  10 . In this embodiment, a tubular housing at the wellhead  14  protrudes above seafloor and may have an attached subsea tree (not shown). The well may be plugged if needed and the tree can be removed to allow for landing of the power generation assembly  10  on the wellhead  14 . 
         [0020]    Continuing to refer to  FIG. 1 , the generation assembly  10  comprises a protective frame  20 . Frame  20  extends over wellhead  14  and mounted on legs  22  that are supported by the mudline  12  and preferably are disposed around the periphery of the assembly  10  and extend away from the assembly  10 . The legs  22  may also penetrate the mudline for additional support. A lower portion of the frame  24  connects to the existing wellhead  14 . In addition to support, the protective frame  20  protects a wheel or turbine  26  enveloped by the frame  20 . For example, the frame  20  may reduce the likelihood that fishing nets will snag onto the turbine  26  and other equipment. Further, the frame  20  may act as a duct to help direct water current directly onto the turbine  26 , which may result in improved turbine  26  performance. The turbine  26 , in this example, has blades or fins  27  disposed on the periphery of the turbine  26  that cause the turbine to rotate in response to water currents. A shaft  28  connects the turbine  26  to the generator  16 .  FIG. 2  shows a top view of the turbine  26  on the shaft  28  and the blades or fins  27  disposed on the turbine  26 . The blades  27  may protrude past the outer surface of the turbine  26  and may curve from one end to another along the outer surface of the turbine  26  to facilitate rotation. The rotation axis of the turbine  26  in this embodiment is vertical to the water currents to facilitate coupling with one end of a shaft  28 . This orientation of the turbine  26  further protects the turbine from impact from debris in the water currents and eliminates the need to pivot the turbine  26  in the direction of current, allowing the turbine to rotate in response to subsea currents having an incidence angle ranging from 0 to 360 degree with respect to the turbine  26  and thus minimizing stalling of the turbine  26  due to cancellation of forces. Other types of turbines  26 , such as windmill-type turbines may also be used.  FIG. 2A  shows a sectional view of the turbine  26  where the blades  27  may be disposed on the turbine  26  through any region of an angle θ, which may range slightly more than zero to 180 degrees. 
         [0021]    Continuing to refer to  FIG. 1 , a housing or bushing  30  provides radial support for the shaft  28 . In this embodiment, the generator  16  forms the lower portion of the generator assembly  10 . In response to the rotation of the shaft  28 , the generator  16  generates electrical power. The electrical power generated by generator  16  is thus localized in wellhead  14 . Leads (not shown) in the generator can electrically communicate with a conventional electrical penetrator or connector  40  that is located on an upper portion of the generator  16  and above the mudline  12 . An umbilical  42 , in electrical communication with the connector  40  is shown extending to subsea equipment  50  for providing electrical power to the subsea equipment  50 . Subsea equipment  50  may be, for example, a booster pump or a gas separation unit. The length, weight, and cost of the umbilical  42  is thus minimized when compared to currently used umbilicals coming from onshore facilities. Additionally, minimal support structure is required as the existing wellhead  14  provides some of the structural support. 
         [0022]    Referring to  FIG. 3A , a top view of the assembly  10  shown in  FIG. 1  is illustrated. The frame legs  22  of the frame  20  are inclined outward from top to bottom. This provides a balanced frame  20  to provide better support for the assembly  10  with the turbine  26  centrally located within the frame  20 . 
         [0023]    Referring to  FIG. 3B , a bottom view of the assembly  10  shown in  FIG. 1  is illustrated. In this example, a main frame or member  21  may be connected to each side of the housing  30  and extend diagonally to provide support for each leg  22 , for example by welding. A nose end  23  on the member  21  is connected to the lower frame member  24  which extends radially outward and connects at its other end  29  to the frame  20  at a point where the frame  20  meets the legs  22 . The connections of the components comprising the frame  20  may be connected via welding or soldering, for example. As previously explained, the frame legs  22  of the frame  20  are inclined outward from top to bottom to provide a balanced frame  20 . 
         [0024]    In another embodiment shown in  FIG. 4 , panels  25  are attached to the frame  20 . The panels  25  are located across from each other on the frame  20  so that the turbine  26  is located between the panels  25 . In this embodiment, the panels  25  direct the flow of the water current to the turbine  26  of the assembly  10  described above. The panels  25  thus provide additional protection to the turbine  26  and its blades  27  and also funnel the water current towards the turbine  26 , which may result in increased efficiency of the turbine  26 . A top view of the embodiment of  FIG. 4  is shown in  FIG. 4A  and illustrates the channeling of the subsea currents by the panels  25 . 
         [0025]    In another embodiment shown in  FIG. 5 , the assembly  10  described above is installed in a dummy well or caisson  60  instead of a wellhead  14  ( FIG. 1 ). The caisson  60  can be existing or new and in the embodiment of  FIG. 5  is at least partially below the mudline  12 . In this embodiment, at least a portion of the generation assembly  10  is supported by a structural member  70 . In this embodiment of  FIG. 5 , the structural member  70  is shown as a section of pipe, secured to the bottom of the caisson  60  and protruding above the mudline  12 . The structural member  70  can be adapted to receive and secure the generator  16  of the assembly  10 . 
         [0026]    The invention eliminates the problems associated with generating power for subsea equipment  50  fed by elongate and inefficient umbilicals. The power generation assembly  10  generates electrical power for subsea equipment  50  using shorter, lighter, and thus less expensive umbilicals  42  when compared to umbilicals coming from platforms or onshore facilities. Furthermore, the assembly  10  does not require the use of platforms or other extensive infrastructure as it utilizes, at least partially, the wellhead  14  or caisson  60  as support structures. The assembly  10  thus eliminates the cost of extensive infrastructure. As in the embodiment of  FIG. 1 , the umbilical  42  of  FIG. 5  may be connected to the connector  40  and run out to provide electrical power to subsea equipment  50 . 
         [0027]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These embodiments are not intended to limit the scope of the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.