Abstract:
A method of supplying electrical power to at least one device at a tree of an underwater fluid extraction well is disclosed. The method comprises using magnetic resonance coupling for wirelessly transmitting power from a supply to each device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate to the supply of electrical power to underwater devices, in particular those at a tree of an underwater fluid extraction well. 
         [0003]    2. Description of the Prior Art 
         [0004]    On a subsea fluid extraction well Christmas tree, the supply of electrical power to pressure and/or temperature (P/T) sensors and to directional control valves (DCVs) within a subsea control module (SCM) is typically supplied. from a subsea electronics module (SEM). Likewise, electrical power to sensors mounted on the Christmas tree itself, external to the SCM, are also fed from the SEM via the SCM. Such power is supplied via simple wiring. However, the wiring, along with the connectors which have to operate under high barometric pressures and low temperatures, are expensive. Embodiments of the present invention provide a cheaper alternative to the power wiring and connectors. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    According to embodiments of the present invention, there is provided a method of supplying electrical power to at least one device at a tree of an underwater fluid extraction well, the method comprising using magnetic resonance coupling for wirelessly transmitting power from a supply to each device. 
         [0006]    According to embodiments of the present invention, there is provided an apparatus for supplying electrical power to at least one device at a tree of an underwater fluid extraction well, the apparatus comprising circuitry configured for using magnetic resonance coupling for wirelessly transmitting power from a supply to each device. 
         [0007]    There could be a plurality of such devices, each powered via a respective receiver circuit coupled by magnetic resonance coupling with a transmitter circuit of the supply. In this case power from the supply could be modulated by a code unique to at least one of the devices, detection of the code at the receiver circuit of the device causing power to be supplied to the device. Alternatively, a code unique to at least one of the devices could be transmitted by wireless means to the receiver circuit of the device, detection of the code at the receiver circuit of the device causing power to be supplied to the device. 
         [0008]    There could be a plurality of the supplies each resonant at a respective one of a plurality of frequencies and a plurality of the devices each powered by a respective receiver circuit resonant at a respective one of the frequencies. 
         [0009]    At least one such supply could be in a subsea control module of the tree. 
         [0010]    Additionally or alternatively, at least one such supply could be in a subsea electronics module of a subsea control module of the tree. In these cases, at least one such device could be in the subsea control module and/or at least one such device could be located externally of the subsea control module. 
         [0011]    At least one such supply could be mounted externally of the tree, for example on a remotely operated vehicle or adapted for carrying by a diver, or mounted at a surface location. 
         [0012]    At least one such device could comprise a sensor. 
         [0013]    At least one such device could comprise a directional control valve. 
         [0014]    The invention reduces the need for expensive wiring and feed through connectors between devices in an SCM and external devices requiring power to operate. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0015]      FIG. 1  is a figure for illustrating the principle of the embodiments of the present invention; 
           [0016]      FIG. 2  is a schematic diagram of an embodiment of the invention; 
           [0017]      FIG. 3  schematically illustrates another embodiment of the invention; 
           [0018]      FIG. 4  schematically illustrates a further embodiment of the invention; and 
           [0019]      FIG. 5  schematically shows a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The concept of transmitting electric power by magnetic resonance is as old as the discovery of electricity in that Tesla himself proposed the technique. In practice, the technique has had no place in electrical engineering technology until recent times, mainly because the cheap electronics required to achieve power transfer by magnetic resonance have only recently become available. 
         [0021]    The basic principle of magnetic resonance involves a transformer where the core is not a ferrous material but air (or a vacuum). Within the transformer, the primary and secondary windings are resonant at the operating frequency of the primary current supplied from a source. The high ‘magnetic gain’ i.e. ‘High Q’ of the resonant secondary winding allows it to be separated from the primary winding by several metres, thus resulting in power transmission wirelessly. 
         [0022]    The technique has been recently demonstrated by the company Witricity to charge laptop and mobile phone batteries without a wired connection from the power source to the appliance. Typically the frequency of the power source deemed to be practical and effective is of the order of 10 MHz, and is typically provided by an electronic sine wave oscillator and power output stage.  FIG. 1  illustrates the principle underlying the invention, in which a standard 50 Hz power source  1  feeds an AC to DC power supply  2  which feeds an oscillator  3 , operating at a frequency which matches the resonant frequency of a primary circuit  4  comprising a primary winding  4   a  in series with a capacitor  4   b.  The primary circuit  4  functions as a magnetic antenna. At the receiving end, a voltage is induced in a secondary winding  5   a  of a secondary circuit  5  comprising the winding  5   a  and a series capacitor  5   b.  The secondary circuit  5  is resonant at the same frequency as the primary circuit  4 . The induced voltage is rectified by a rectifier  6  to provide the required DC supply for equipment  7  which could comprise sensors and/or DCVs. 
         [0023]      FIG. 2  shows a typical arrangement of an embodiment of the invention. A wireless magnetic power supply  8  (operating at frequency f 1 ) including a resonant primary circuit is housed in an SEM  9  located within an SCM  10  on a subsea well tree  11  of a subsea fluid extraction well. Sensors, as shown P/T devices  12 , are each connected to a respective one of resonant magnetic receivers  13  each including a resonant secondary circuit and a rectifier, also operating at frequency f 1 . Thus, the single wireless magnetic power supply  8  supplies electric power wirelessly to a plurality of P/T devices  12  within the SCM  10 , typically monitoring hydraulic control supplies on an SCM distribution manifold  14 . Also, the supply  8  supplies electric power wirelessly to at least one other, external P/T device  15 , typically monitoring the production fluid within the production flow control line  16  on the well tree  11 , via a respective secondary receiver  17  including a resonant secondary circuit resonant at the frequency f 1 . 
         [0024]    DCVs  18 , again within the SCM  10  and typically mounted on the hydraulic manifold  14 , are supplied with electric power individually as required by the control circuitry of the SEM  9 . Thus, for a wireless power feed to the DCVs  18 , each SEM control output feeds an individual wireless magnetic power supply  19 , operating at a frequency that matches the resonant frequency of the secondary circuit of a respective magnetic secondary receiver  20 . Since the Q of the wireless power transmitting and receiving devices is high, the power transmitting links to the DCVs can operate at different frequencies, thus permitting individual control of the DCVs from the Individual control outputs from the SEM. Only two DCVs  18  with receivers  20  whose secondary circuits are resonant at frequencies f 2  and f 3  respectively are shown in  FIG. 2  for diagrammatic simplicity. 
         [0025]    An alternative arrangement for operating DCVs is to have a common wireless magnetic power supply at a single frequency and operate individual DCVs by modulating the supplied power with an identification code. This technique has the advantage of only needing a single wireless magnetic power supply for all DCVs and wireless powered sensors, and a common design of DCV wireless magnetic receiver. The principle of the technique is illustrated in  FIG. 3  in which items which correspond with those in  FIG. 1  have the same reference numerals as in  FIG. 1 . The output of the oscillator  3  of a wireless magnetic power supply connects to a resonant magnetic primary circuit  4  via a modulator  21 , which superimposes a digital code on the oscillator output. The code is generated in a code generating circuit  22 , which generates the code appropriate for a specific DCV according to a demand on a line  23  from DCV control circuitry in the SEM. The wireless magnetic power receiver for each DCV  24  is fitted with a demodulator and decoder circuit  25 . When the code transmitted by the wireless power supply matches that pre-set in the demodulator and decoder circuit  25 , the output of the receiver is connected to the DCV via a switch  26 , to operate the DCV  24 . If the decoding of the transmitted code is effected by a processor, then the code can be inserted with software allowing a standard device design to be employed for all DCVs. Sensors, such as P/T sensors  27  are powered from wireless magnetic power receivers  5 ,  6  without demodulator and decoder circuits, deriving their power from the common shared wireless magnetic power supply. The primary disadvantage of this configuration is that the shared power supply may become too bulky to be conveniently accommodated in the required subsea location such as an SEM. 
         [0026]    A further, alternative arrangement for operating DCVs is to have a common magnetic power supply at a single frequency and operate individual DCVs by a separate independent wireless transmission using a protocol such as Wi-Fi. Bluetooth or wireless USB, etc. Such an arrangement is illustrated in  FIG. 4  in which items which correspond with those in  FIG. 3  have the same reference numerals as in  FIG. 3 . As with the  FIG. 3  embodiment, a code is generated in a code generating circuit  22  which generates the code appropriate for a specific DCV, according to a demand on line  23  from DCV control circuitry in the SEM. This code is sent to modulate an independent transmitter  28  which sends a modulated transmission via an antenna  29 , which transmission is received by an antenna  30  on a receiving, demodulating and decoding circuit  31 , which operates the switch  26  when the transmitted code matches that stored in the decoder in the circuit  31 . Closing of the switch  26  enables the wireless magnetic power receiver  5 ,  6  to operate the DCV  24 . 
         [0027]    In the above embodiments, data from the P/T sensors is also transmitted wirelessly to the SEM using conventional techniques such as Bluetooth, Wi-Fi or wireless USB (Universal Serial Bus) etc. 
         [0028]    A further embodiment is schematically shown in  FIG. 5 . Here, a wireless magnetic power supply  8  is located not at a well tree, but instead is carried by a remotely operated vehicle (ROV)  32 . In  FIG. 5 , reference numeral  33  designates a surface vessel and reference numeral  34  designates an umbilical supplying the ROV with power. Also, reference numeral  35  designates a well tree provided with a resonant magnet receiver  36  for co-operating with power supply  8  for providing power for the tree. With this arrangement, subsea devices are able to be powered wirelessly when an ROV  32  is positioned sufficiently close to the device to enable power transfer. Such an arrangement may have various uses, for example if power (e.g. wired power) to a subsea-located device fails, for example due to an umbilical failure, it could be powered via an ROV  32  without the need for removing or changing the wires enabling the well to keep flowing during a platform power outage for example. The device may also be diagnosed and/or tested via the ROV using the power supply equipment  8  or other components (not shown). In addition, equipping an ROV with such power (and communications) pick-ups would allow the ROV greater power and tool availability subsea, since a higher power or further diagnostic tools may be employed than would typically be possible via the umbilical. This could allow the ROV to communicate with, control and monitor the tree in real time. 
         [0029]    In a further, related embodiment (not shown), a wireless magnetic power supply  8  may be carried by a diver rather than an ROV. 
         [0030]    In a yet further related embodiment (not shown), a wireless magnetic power supply  8  may be provided at a shipside location, i.e. on a vessel, platform or other surface location. This would permit pre-deployment testing to be carried out without connecting wires to the equipment. Such remote powering of the equipment would allow for power and communications, for testing and diagnostics. 
         [0031]    Various modifications and alternatives are possible within the scope of the invention. For example, considering the embodiment shown in  FIG. 2 , it would equally be possible for the transmitters  8 ,  19  to be located externally to the SEM  9 , but remaining within the SCM  10 . Such an arrangement may enable the distance between transmitters and receivers to be reduced, and the transfer efficiency consequentially improved.