Abstract:
A subsea oil and gas production Christmas tree control system, serviceable by an ROV subsea, comprises an umbilical and a system controller further comprising an HPU that comprises a manipulatable subsea housing; a subsea hydraulic fluid reservoir; a motor disposed in the housing; and a hydraulic power unit disposed in the housing. Hydrocarbon production may controlled subsea by deploying a modular subsea oil and gas production Christmas tree control system using an ROV; supplying the HPU with hydraulic fluid; providing a predetermined control to a subsea Christmas tree using a Christmas tree control system component; monitoring a Christmas tree control system status; enabling a redundant Christmas tree control system component upon detection of a fault in a Christmas tree control system component paired with the redundant component; and providing status data from the Christmas tree control system to a status data receiver using a data communications link.

Description:
PRIORITY  
       [0001]    This application claims priority through United States Provisional Application 61/413,707 filed Nov.  15 ,  2010 . 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention described herein relates a change in the umbilical architecture of most field developments as only low pressure fluids would need to be delivered to the local subsea distribution manifold or subsea tree. The invention more specifically relates to supplying hydraulic power subsea, and more specifically to a subsea hydraulic power unit that uses a biodegradable fluid for hydraulic motive force. 
       BACKGROUND OF THE INVENTION 
       [0003]    Typical control umbilicals for subsea field developments contain numerous components such as electrical signal and power wires. The actual amount used and the size of any of these depends on the configuration of the field development. Hydraulic supplies, e.g. pumps and storage, are typically located at a surface location as opposed to subsea, necessitating hydraulic supply lines to be included in a control umbilical. In a typical field development, the hydraulic fluid is pressurized by a surface located HPU and vented subsea to sea. 
         [0004]    Further, typical field development umbilicals may have chemical lines including dedicated chemical injection hoses for each chemical and for each subsea tree. For example, typically there are two different chemicals used so if there are three subsea trees six lines for chemicals will be required in an umbilical. 
         [0005]    As a result, umbilicals are often non-standard as they have to be tailored to the specific subsea site. Field operators are often unable to retrieve susbea modules to service, replace or reconfigure key components utilized in a subsea oil field development, thus decreasing the reliability of such equipment which, in turn, affects oil production. In the past, other solutions have used discrete high pressure hydraulic lines or employed specialty chemical valves. The essence of the invention is the by locating a pump subsea, the pressure is only increased at a local point close to the fluids final destination, The pump also has the added benefit of being able to locally meter or regulate the amount of fluid that is needed or is necessary. An important benefit is that in high pressure umbilicals, much energy is lost due to friction over long distances, a local electric pump using an electric umbilical experiences much less energy losses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The features, aspects, and advantages of the present invention will become more fully apparent from the following description, appended claims, and accompanying drawings in which: 
           [0007]      FIG. 1  is a planar view of an exemplary system in partial perspective; 
           [0008]      FIG. 2  is a schematic view of an exemplary system; 
           [0009]      FIG. 3  is a cross-sectional view of an exemplary armored cable; and 
           [0010]      FIG. 4  illustrates a further embodiment of a portion of the invention illustrating an exemplary HPU module. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0011]    Referring to  FIGS. 1-2 , in one embodiment system  1  comprises umbilical  10 , HPU module  20 , chemical injector module  30 , accumulator module  40 , low pressure hydraulic module  50 , high pressure hydraulic module  60 , and electrical module  70 . In an embodiment, system  1  further comprises subsea umbilical termination module  80 .  FIGS. 1-2  illustrate deployment of system  1  in a field further comprising surface structure  100 , subsea Christmas trees  4   a - 4   d,  and other structures for illustration. 
         [0012]    Umbilical  10  may comprise lines  12 . As other lines needed for subsea control may originate subsea with system  1 , e.g. hydraulic lines  2   a - 2   d  and/or electrical control lines  3   a - 3   d,  umbilical  10  may be standardized with a set number of lines  12 . For example, umbilical  10  may comprise steel tubes, power lines, and fiber optic cables. Further, moving HPU module  20  from the surface, e.g. located at platform  100 , to a module subsea may eliminate the need for a hydraulic supply line in umbilical  10 . 
         [0013]    Chemical injector module  20  may comprise one or more ROV removable chemical injection valves  21  which may further be used for each tree  4   a,    4 ,  4   c,  and  4   d.  Therefore, only one chemical line  22  for each chemical used may be required within umbilical  10 . In a typical installation, only two chemical lines  22  may be needed for multiple trees. 
         [0014]    Referring now to  FIG. 3 , HPU module  30  is an ROV replaceable module located subsea, comprising at least one pump  32  and one motor  34 . In a preferred embodiment, pump  32  comprises one or more piston pumps slaved to one or more electric motors. 
         [0015]    In a preferred embodiment, HPU module  30  comprises at least two low pressure sections (not shown in the figures) and at least two high pressure sections (not shown in the figures). These sections are independent of each other and redundant. In an embodiment, if anyone motor  34  or pump  32  begins to malfunction, its secondary motor  34  or pump  32  begins to pick up. 
         [0016]    HPU module  30  further comprises instrumentation  36 . Instrumentation  36  may comprise one or more sensors, e.g. flow rate, temperature, pressure and/or on/off state sensors which may be used to sense one or more parameters reflecting the performance of pump  32  and/or motor  34 . 
         [0017]    HPU motor  34  utilizes fluid, typically supplied from reservoir  35 . Reservoir  35  may be used to supply fluid to pump  32  and accept return and vent fluid, e.g. from relief valves  37 . In a preferred embodiment, system  1  is a closed system and the fluid is a biodegradable hydraulic fluid. 
         [0018]    If a leak occurs subsea in system  1 , there is a chance of starving pumps  32 . Therefore, in a currently envisioned alternative an extra line  12   d  ( FIG. 4 ) may be present in umbilical  10  where extra line  12   d  may be used to direct and/or replenish fluid in reservoir  35 , e.g. up until such time as an ROV can be mobilized and replace a leaking HPU module  30 . 
         [0019]    Accumulation module  40  may be present and may be an ROV replaceable module containing one or more accumulators  42  (not shown in the figures) such as may be required to dampen the hydraulics. Accumulators  42  may be further used to contain a sufficient supply of fluid to maintain system pressure. Fluid filters  43  (not shown in the figures) may also be located in accumulation module  40 . Accumulation module  40  may be charged, e.g. with fluid, from HPU module  30 . 
         [0020]    Low pressure valve module  50  and high pressure valve module  60  may contain solenoid actuated hydraulic valves, e.g.  52  and  62 , required to supply hydraulic control to the various tree valve actuators and tree chokes. Hydraulic valves  52 , 62  may be controlled from electronics module  70  and may be supplied with hydraulic fluid from accumulation module  40 . 
         [0021]    In a preferred embodiment, electronics module  70  communicates via fiber optic connection  12   e  ( FIG. 4 ) through umbilical  10 , e.g. to a surface device such as controller  102  ( FIG. 1 ). Electronics module  70  may comprise electronics to perform several functions, by way of example including decode a multiplexed signal, control HPU module  30 , obtain and communicate status for system  1 , fire solenoids in low pressure hydraulic valve module  50  and high pressure hydraulic valve module  60 , send a signal to change one or more settings on chemical valves in chemical injector valve module  20  ( FIG. 1 ), and the like, or a combination thereof. Electronics module  70  may also handle other instrumentation inputs and outputs, e.g. from other devices whether on trees  4   a - 4   d  or in system  1 . 
         [0022]    Long high pressure umbilicals are expensive, many times the cost of this pod, and are more prone to failure the higher the pressure. System  1  reduces the cost and complexity of umbilicals and can be used to meter fluids by specifically controlling amount pumped. 
         [0023]    Referring back to  FIG. 1 , in a further embodiment system  1  is an assembly of components into an ROV operable and replaceable subsea package. This embodiment comprises the primary components: pump  32 , electric or hydraulic motor  34 , pod carriage  82 , and in the case of electric motor, a variable frequency drive VFD  39 . This embodiment may be used to increase pressure to hydraulic or chemical fluids, for the purpose of supplying pressure to hydraulic control systems, or chemicals to processes. In the case on hydraulic fluids, system  1  may be configured as a hydraulic power unit, or HPU. When system  1  is configured for chemical delivery, it could be configured as a chemical injection pump. In both cases, the final configuration would differ by the hydraulic connections, fluid filtering, and need for local accumulators, depending on the specific application. 
         [0024]    In the operation of an exemplary mode, susbea control of hydrocarbon production devices may be provided by deploying system  1  subsea using an ROV (not shown in the figures). HPU  30 , which is part of system  1 , then uses a closed loop hydraulic system for its supply of hydraulic fluid. Therefore, although it may have one, umbilical  10  need not have a hydraulic supply line for HPU  30 . 
         [0025]    Umbilical  10  may be fabricated to be uniform, irrespective of the subsea field device environment. For example, umbilical  10  may have a limited number of chemical lines  12  used to aid in dispersing chemicals to Christmas trees  4   a - 4   d  may be handled by system  1  susbea. HPU module  30  accepts fluid from reservoir  35 . Accumulators  42  in accumulation module  40  may be used to dampen the hydraulics along with contain sufficient supply to maintain system pressure. Accumulators  42  may get their charge/fluid from HPU module  30 . 
         [0026]    One or more other components of system  1 , e.g. low pressure module  50  or high pressure module  60 , may be used to provide a predetermined control to a Christmas tree located subsea, e.g. trees  4   a - 4   d.    27 . These predetermined control may comprise actuation of valves at trees  4   a - 4   d  using hydraulic controls, actuation of valves at trees  4   a - 4   d  using electrical controls, chemical injection, or the like, or a combination thereof. For example, valves in high pressure valve module  60  and low pressure valve module  50 , e.g. solenoid actuated hydraulic valves, may be used to supply hydraulic control to the various tree valve actuators and tree choke of trees  4   a - 4   d.  These valves may get their direction and solenoid motivation from electronics module  70 . Further, these valves may receive their hydraulic fluid from accumulation module  40 . 
         [0027]    Redundancy in system  1  allows system  1  to respond to certain faults, providing a time window during which the fault may be fixed while allowing production to be maintained. For example, during operations, one or more predetermined status indicator of system  1  may be monitored such as by using electronics module  70 . If a fault is detected in a paired redundant component, e.g. pump  32   a,  its redundant component may be enabled and the fault component disabled, e.g. pump  32   a  and motor  34   a  may be disabled and pump  32   b  and motor  34   b  enabled, thus allowing production control to be maintained subsea. A failed module, or any other module such as one needing preventive maintenance or upgrading, may be replaced subsea using an ROV. 
         [0028]    Status data of system  1  may be monitored, either continually, at predetermined intervals, or upon demand such as from a surface device. These data may then be provided, e.g. either continually, at predetermined intervals, or upon demand, to a predetermined receiver of status data using a data communications line, e.g. fiber optics cable  12   e.    
         [0029]    In a preferred mode electronics module  70  utilizes fiber optic cable  12   e  for its connection. As fiber optics comprises a large bandwith, system  1  may be able to communicate more data than prior art systems. Use of fiber optics cable  12   e  may further allow having a full diagnostics system located subsea. Raw data may be sent back to a surface device, e.g. a computer for additional programming, e.g. double checking diagnostics at the surface. 
         [0030]    It will be understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated above in order to explain the nature of this invention may be made by those skilled in the art without departing from the principle and scope of the invention as recited in the following claims.