Patent Application
20120210926
1. Field of the Invention
Embodiments of the present invention generally relate to a direct current (DC) powered remotely operated underwater vehicle (ROV) and umbilical.
2. Description of the Related Art
Work class ROVs employ electric motors of up to several hundred horsepower. Power is typically supplied by four hundred eighty volt three phase alternating current (AC) which requires cables of relatively large diameter. The cable adds significant weight and drag to the ROV, often comprising the majority of the load on the vehicle. This results in a reduction in the speed and maneuverability of the vehicle and in some conditions, may impact the ability to predictably control the ROV. The additional drag also decreases the efficiency of the ROV as additional thruster power is required to overcome the drag on the cable.
Embodiments of the present invention generally relate to a direct current (DC) powered remotely operated underwater vehicle (ROV) and umbilical. In one embodiment, a method of operating an ROV includes launching the ROV from a vessel into water; supplying a DC power signal to the ROV from the vessel via an umbilical; and sending a first command signal to the ROV from the vessel via the umbilical while supplying the DC power signal.
In another embodiment, an ROV includes a chassis; a float connected to the chassis; a thruster connected to the chassis, the thruster including an electric motor; a manipulator connected to the chassis; a video camera connected to the chassis; a light connected to the chassis; a diplexer connected to the chassis and operable to connect to a two conductor tether and split a composite signal from the tether into a DC power signal and a first command signal; a power converter connected to the chassis and operable to receive the DC power signal from the diplexer and supply a second power signal to the thruster motor; and a programmable logic controller connected to the chassis and operable to receive a first command signal from the diplexer, modulate a video signal from the camera, and transmit the video signal to the diplexer.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
A subsea wellbore 10 has been drilled from a floor 1f of the sea 1 into a hydrocarbon-bearing (i.e., crude oil and/or natural gas) reservoir (not shown). A string of casing (not shown) has been run into the wellbore 10 and set therein with cement (not shown). The casing has been perforated to provide to provide fluid communication between the reservoir and a bore of the casing. A wellhead (not shown) has been mounted on an end of the casing string. A string of production tubing may extend from the wellhead to the formation to transport production fluid from the formation to the seafloor 1f. A packer (not shown) may be set between the production tubing and the casing to isolate an annulus formed between the production tubing and the casing from production fluid.
The Christmas or production tree 5 may be connected to the wellhead, such as by a collet, mandrel, or clamp tree connector. The tree 5 may be vertical or horizontal. If the tree 5 is vertical, it may be installed after the production tubing is hung from the wellhead. If the tree 5 is horizontal, the tree may be installed and then the production tubing may be hung from the tree 5. The tree 50 may include fittings and valves to control production from the wellbore into a pipeline (not shown) which may lead to a production facility (not shown), such as a production vessel or platform.
A support vessel 15 may be deployed to a location of the subsea tree 5 to perform an intervention operation. The support vessel 15 may include a dynamic positioning system to maintain position of the vessel 15 on the waterline 1w over the tree 5 and a heave compensator to account for vessel heave due to wave action of the sea 1. The vessel 15 may further include a tower and winches for deploying tools to the tree 5 for performing the intervention operation.
The ROV 100 may be launched into the sea 1 from the support vessel 15 by a launch and recovery system (LARS) 30 to assist the intervention operation. The LARS 30 may be mounted on a working deck of the support vessel 15. The ROV 100 may be controlled and supplied with power from a control van 300 carried onboard the support vessel 15. The control van 300 (see
Alternatively, the power converter 310v may include a transformer (not shown) for stepping the low voltage AC power signal to a medium voltage AC power signal, such as greater than or equal to one kilovolt, and then the power converter may convert the medium voltage AC power signal to a medium voltage DC power signal for transmission over the umbilical. Additionally, the power converter 310v may include a transformer for reducing the low voltage AC power signal to an ultra-low voltage AC signal, such as less than or equal to one-hundred twenty volts, and then the power converter may convert the ultra-low voltage AC signal to an ultra-low voltage DC power signal for powering the control console 302 and PLC 305v or the control van 300 may include an additional power converter (not shown) for powering the control console and PLC.
The PLC 305v may receive commands from the ROV pilot (not shown) via the control console 302 and include a data modem (not shown) and multiplexer (not shown) for modulating and multiplexing the commands into a data signal for delivery to the DIX 315v and transmission to the TMS 50 via the umbilical 200u. The DIX 305v may combine the DC power signal and the data signal into a composite signal and transmit the composite signal to the TMS 50 via the umbilical 200u and to the ROV 100 via tether 200t (and umbilical 200u). The DIX 305v may be in electrical communication with the umbilical 200u via an electrical coupling (not shown), such as brushes or slip rings, to allow power and data transmission through the umbilical while the LARS 30 winds and unwinds the umbilical. The control console 302 may include one or more hand-operable controllers, such as joysticks 302c, and one or more video monitors 302v. The multiplexing scheme may be frequency division and commands to the TMS 50 may have a separate channel than commands for the ROV 100. Communication among the van 300, TMS 50, and ROV 100 may be full duplex. The PLC 305v may also receive data signals from the ROV 100, such as video signals from the cameras 125, via a tether 200t, umbilical 200u, and DIX 315v, demodulate and demultiplex the data signals, and display the data signals on one of the monitors 302v. In this manner, the ROV pilot may operate the ROV 100 from the control van 300. The PLC 305v may also include an autopilot (not shown) to assist the ROV pilot in operation of the ROV 100. The ROV pilot may selectively disengage and engage the autopilot and operate the ROV 100 in tandem with the autopilot.
The LARS 30 may include a frame, a winch 31, a boom, a boom hoist, and a hydraulic power unit (HPU) 320v. The LARS 30 may be the A-frame type (shown) or the crane type (not shown). For the A-frame type LARS 30, the boom may be an A-frame pivoted to the frame and the boom hoist may include a pair of piston and cylinder assemblies (PCAs), each PCA pivoted to each beam of the boom and a respective column of the frame. The HPU 320v may include a hydraulic fluid reservoir, a hydraulic pump, and one or more control valves for selectively providing fluid communication between the reservoir, the pump, and the PCAs. The hydraulic pump may be driven by an electric motor. The winch may include a drum having the umbilical wrapped therearound and a motor for rotating the drum to wind and unwind the umbilical 200u. The winch motor may be electric or hydraulic. A sheave may hang from the A-frame. The umbilical 200u may extend through the sheave and an end of the umbilical may be fastened to a cablehead of the TMS 50. The frame may have a platform for the TMS/ROV 50, 100 to rest. Pivoting of the A-frame boom relative to the platform by the PCAs may lift the TMS/ROV 50, 100 from the platform, over a rail of the vessel 15, and to a position over the waterline 1w. The winch may then be operated to lower the TMS/ROV 50, 100 into the sea 1. Recovery of the ROV/TMS 50, 100 may be performed by reversing the steps.
The ROV 100 may be launched together with the TMS 50. A top of the ROV 100 may be fastened to the TMS 50 for a top-hat type TMS. Alternatively, the ROV may be housed in the TMS for a cage type TMS (not shown). The TMS 50 may be connected to the LARS 30 by the umbilical 200u. The TMS 50 may include a frame, a cablehead, a winch 51, a PLC 305t (see
Similar to the control van PLC 305v, the TMS PLC 305t may include a modem and modulator for receiving command signals from the DIX 315t. The TMS PLC 305v may then release the ROV 100 and operate the tether winch 51 in response to receipt of the appropriate command signals. The TMS 50 may further include one or more sensors (not shown). The TMS PLC 305t may send the sensor data to the van PLC 305v along a dedicated channel. Additionally, the TMS 50 may include one or more thrusters (not shown) so that the vessel 15 may be moved away from over the tree 5 while the ROV 100 remains at the tree. Additionally, the TMS 50 may include one or more accessory tools (not shown) for the ROV 100. Alternatively, the TMS 50 may include an HPU (not shown) and the winch motor may be hydraulic.
The ROV 100 may be connected to the TMS 50 by the tether 200t. The tether 200t may be in power and data communication with the umbilical 200u so that the ROV 100 and TMS 50 are connected to the umbilical 200u in a parallel arrangement. The TMS 50 may include an electrical coupling (not shown) similar to the electrical coupling discussed above providing power and data communication between the tether 200t and the umbilical 200u.
The ROV/TMS 50, 100 may be deployed to a depth proximate to the tree 5. The ROV 100 may then be released from the TMS 50 and driven to the tree by the ROV pilot. The TMS 50 may unwind an excess of the tether 200t to maintain sufficient slack in the tether so that the ROV 100 is isolated from vessel heave. The ROV 100 may transmit video to the pilot for inspection of the tree 50. The ROV 100 may then interface with the tree 5 to assist in the intervention operation. Alternatively, the ROV 100 may be deployed to assist in a drilling operation, completion operation, or abandonment operation. Alternatively, the ROV 100 may be deployed to conduct a subsea pipeline inspection operation.
The thrusters may include one or more longitudinal thrusters 115f, one or more transverse thrusters 115t, and one or more vertical thrusters 115v. The horizontal thrusters 115f,t may be fixed (shown) or vectored (not shown). The thruster motors may be reversible, thereby affording complete three-dimensional movement of the ROV 100. Each thruster 115f,v,t may include a propeller, a shroud, and an electric motor for driving the propeller. Each thruster motor may directly drive each propellor or include a gearbox. Each thruster may have a dedicated motor or two or more thrusters may be driven by one motor and a gearbox. Alternatively, the thruster motors may be hydraulic and driven by the HPU 320r.
The sensors 325 may include one or more of: a depth gage, altimeter (i.e., height-off bottom sonar), scanning sonar, temperature sensor, laser line scanner, gyroscope, Doppler velocity log, and/or magnetometer. The cameras 125 may be monochrome or color, standard definition, enhanced definition, high definition, or low light and may be fixed or have panning and tilting capability. As shown, the ROV 100 may include a pair of front facing cameras 125 for stereo vision. Each camera 125 may include its own channel for multiplexed transmission over the tether 200t and umbilical 200u. Although only a pair of front facing cameras 125 are shown, the ROV may additionally have one or more rear facing, left and right facing, bottom facing, and/or top facing cameras. The lights 120 may include one or more of Hydrargyrum medium-arc iodide (HMI) lights, high intensity discharge (HID) lights, quartz halogen, high intensity light emitting diode (LED) and/or strobe lights. The intensity of the lights 120 may also be adjustable from the surface to accommodate seafloor conditions (i.e., low beam/high beam). As with the cameras 125, although only a set of front facing lights 120 are shown, the ROV 100 may additionally have one or more rear facing, left and right facing, bottom facing, and/or top facing lights. The lights 120 may also be fixed or have pan and tilt capability.
The manipulators 130 may each include an arm and a pair of opposable claws and may each have multi-degree of freedom capability (i.e., shoulder, elbow, and wrist movement). The jaws of each manipulator 130 may also be removable for replacement by other tools, such as a snip or drill, carried by the TMS 50. Each manipulator 130 may include a shoulder, aft arm, forearm, wrist, and hand, each portion pivoted to one or more of the other portions and PCAs and/or hydraulic motors for articulating the portions. The HPU 320r may include a hydraulic fluid reservoir, a hydraulic pump, and one or more control valves for selectively providing fluid communication between the reservoir, the pump, and the PCAs/hydraulic motors. The hydraulic pump may be driven by an electric motor. Alternatively, the manipulators 130 may include electric actuators instead of the PCAs/hydraulic motors, such as lead screws, linear motors, and/or stepper motors, and the HPU 320r may be omitted.
The inner core 205 may be the first conductor and made from an electrically conductive material, such as aluminum, copper, or alloys thereof. The inner core 205 may be solid or stranded. The inner jacket 210 may electrically isolate the core 205 from the shield 215 and be made from a dielectric material, such as a polymer (i.e., polyethylene). The shield 215 may serve as the second conductor and be made from the electrically conductive material. The shield 215 may be tubular, braided, or a foil covered by a braid. The outer jacket 230 may electrically isolate the shield 215 from the armor 235, 240 and be made from a seawater-resistant dielectric material, such as polyethylene or polyurethane. The armor may be made from one or more layers 235, 240 of high strength material (i.e., tensile strength greater than or equal to one hundred, one fifty, or two hundred kpsi) to support the deployment weight (weight of the TMS 50 and ROV 100) so that the umbilical 200u may be used to launch and remove the TMS/ROV into/from the sea. The high strength material may be a metal or alloy and corrosion resistant, such as galvanized steel, aluminum, or a polymer, such as a para-aramid fiber. The armor may include two contra-helically wound layers 235, 240 of wire, fiber, or strip.
Additionally, each of the umbilical 200u and the tether 200t may include a sheath 225 disposed between the shield 215 and the outer jacket 230. The sheath 225 may be made from lubricative material, such as polytetrafluoroethylene (PTFE) or lead, and may be tape helically wound around the shield 215. If lead is used for the sheath 225, a layer of bedding 220 may insulate the shield 215 from the sheath and be made from the dielectric material. Additionally, a buffer 250 may be disposed between the armor layers 235, 240. The buffer 250 may be tape and may be made from the lubricative material. The cover 245 may be made from an abrasion resistant material, such as a polymer, such as polyisoprene or polyethylene.
Due to the coaxial arrangement, each of the umbilical 200u and the tether 200t may have an outer diameter 255 less than or equal to one and one-quarter inches, one inch, or three-quarters of an inch. As discussed above, the each of the umbilical 200u and tether 200t may be capable of delivering at least seventy-five, one hundred twelve, or one hundred fifty kW (for one-hundred, one hundred fifty, or two hundred horsepower thrusters, respectively). As compared to a three conductor (phase) AC umbilical/tether, a significant reduction in weight and diameter is achieved, thereby improving performance of the ROV 100 and improving the portability of the LARS 30 and TMS 50. For example, replacing a three conductor AC tether/umbilical with the coaxial umbilical/tether may reduce the diameter from two inches to point six five inches and reduce the weight from one point eight pounds per foot to one-half pound per foot.
Alternatively, the umbilical 200u and/or the tether 200t may include additional conductors (not shown) for conducting the data signals separately from the power signal. The additional conductors may be electrically conductive and/or optical fiber. If the additional conductors are electrically conductive, they may additionally carry (along same or different conductors) an ultra-low voltage power signal for powering the tether and/or ROV PLCs 305t,v instead of converting the signals from the low voltage power signal. Alternatively, the tether armor may be made from a lower strength material or omitted as the tether 200t may not have to support the weight of the ROV 100 and the TMS 50. The low strength material may be may be a polymer, such as an aliphatic polyamide.
Similar to the tether power converter 310t, the ROV power converter 310r may receive the low voltage DC power signal from the tether 200t via the DIX 315r, include an inverter for converting the DC power signal to an AC power signal, and a transformer for stepping the low voltage AC power signal to the ultra-low voltage AC power signal, and a rectifier for converting the ultra-low voltage AC to ultra-low voltage DC power signal for powering the PLC 305r. The power converter 310r may also include the one or more single phase active bride circuits, discussed above. The circuits may be arranged in series to gradually step the DC voltage from low to ultra-low. The converter 310r may include a three-phase inverter for receiving the low voltage DC power signal and outputting a three phase low voltage AC signal for powering the thruster motors and the HPU motor. The converter 310r may also be capable of reversing the polarity of the AC power signal to the thruster motors and the ROV PLC 305r may control the polarity. The converter 310r may supply the lights 120 with low voltage or ultra-low voltage AC power signals.
Similar to the TMS PLC 305t, the ROV PLC 305r may include a modem and modulator for receiving command signals from the DIX 315r. The ROV PLC 305r may then operate the thrusters and/or the manipulators in response to receipt of the appropriate command signals. The ROV PLC 305r may send the sensor data to the van PLC 305v along a dedicated channel. Each sensor 325 may have a dedicated channel or data from two or more of the sensors may be time division multiplexed on a single channel. The ROV PLC 305r may relay ultra-low voltage DC power signals to the sensors 325 and the cameras 125. The ROV PLC 305r may also be in data communication with the sensors 325 and the cameras 125. The ROV PLC 305r may receive data from the sensors 325 and the cameras 125, modulate and multiplex the data, and transmit the data to the control van PLC 305v via the DIX 315r, the tether 200t, the umbilical 200u, and the DIX 315v. The ROV PLC 305r may also be in communication with the HPU control valves for selectively operating the valves to control movement of the manipulators 130.
The ROV 100 may further include a motor controller (not shown) for operating the thruster motors and the HPU motor. Each thruster motor and the HPU motor may be an induction motor. The motor controller may be integrated with the power converter 310r or each motor may have its own motor controller. The motor controller may be in data communication with the PLC 305r for receiving pilot/autopilot commands from the control van 300 and sending diagnostic data to the control van 300 (i.e., RPM and temperature). The motor controller may be capable of simple control (i.e. constant speed). Alternatively, the motor controller may be capable of controlling the speed of the motors, such as by variable frequency drive. In this alternative, the motor controller may receive the low voltage DC power signal and construct quasi-sinusoidal motor power signals (i.e., three phases) for speed controlled operation of the motors.
Alternatively, the motors may be reluctance motors, such as switched reluctance or synchronous reluctance. The reluctance motors may each include a wound stator and a rotor having a multi-lobed laminate core. The motor controller may output stepped, trapezoidal, or sinusoidal power signals to the reluctance motors and the motor controller may control the speed of the motors by controlling the frequency of the power signal. The motor controller may employ an asymmetric bridge or half-bridge circuit for control of the reluctance motors.
Alternatively, the motors may be permanent magnet motors, such as brushless DC motors (BLDC). The BLDC motors may each include a wound stator, a permanent magnet rotor, and a rotor position sensor. The permanent magnet rotor may be made of a rare earth magnet or a ceramic magnet. The rotor position sensor may be a Hall-effect sensor, a rotary encoder, or sensorless (i.e., measurement of back EMF in undriven coils by the motor controller). The BLDC motor controller may be in communication with the rotor position sensor and include a bank of transistors or thyristors and a chopper drive for complex control (i.e., variable speed drive and/or soft start capability). Alternatively, the motors may be universal motors. Alternatively, the motors may be brushed permanent magnet motors or any other type of AC or DC motors.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
