Control of hydrocarbon wells

#This application claims the benefit of United Kingdom patent application 0208800.3, filed Apr. 17, 2002.

#The present invention relates to the control of hydrocarbon wells.

#Traditionally, fluid production systems on subsea hydrocarbon wells have been powered by hydraulics fed from a high-pressure source on a surface vessel or platform via expensive umbilical tubing. The historical reason for this is that hydraulic systems were seen to be very reliable compared to electrical systems, mainly because the required electric devices, both actuating and control, such as motors and relays, were considered to be much less reliable than hydraulic equivalents.

#The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

#FIG. 1 is a block diagram of an example of the invention, being a system for distributing and controlling the use of three-phase electric power at a subsea hydrocarbon production well; and

#FIG. 2 is a block diagram of a sensing unit of the system.

#Referring first to FIG. 1, three-phase (3.ø), fixed frequency AC electric power is supplied to the apparatus via a supply line 1, typically an electric umbilical cable, from a platform or vessel to a subsea control module (SCM) 2 of the apparatus, mounted on a well tree. The SCM 2 houses a subsea electronics module (SEM) 3 and an actuator electronic module (AEM) 4. The input AC power feeds via a connector through the SCM 2 to the SEM 3, to provide basic low voltage supplies for the electronic circuitry of the apparatus, and to an input sensing unit 5 in the AEM 4.

#FIG. 2 shows the unit 5 which contains devices 6 to sense voltage (V) in respective ones of the three input phases and devices 7 to sense current (I) in respective ones of the three input phases, to enable measurement of these parameters, which are required by logic circuitry installed in electronic circuitry housed in the SEM 3, outputs of devices 6 and 7 being connected to the SEM 3 for that purpose. The input sensing unit 5 has dual outputs (channels A and B) feeding motor drive units 8 and 9 respectively. Since only one motor drive unit is in operation at a time, the other motor drive unit provides 100% redundancy in the event of a fault.

#The motor drive units 8 and 9 are high power electronic inverter units, each of which provides both a variable voltage and a variable frequency output under the control o f the SEM 3. The output voltage and current of each of motor drive units 8 and 9 (i.e. the voltage (V) applied to and the current (I) taken by the motor connected to the system at the time) are also sensed and fed back to the SEM 3 to enable measurement of these parameters for use by the logic circuitry in the SEM 3.