Subsea production system hardware has control and instrumentation needs to serve the following functions Control of tree valves, isolation valves, variable-orifice chokes, pigging/TFL valve diverters, crossover valves.
Measurement of production pressure and temperature, valve and choke actuator positions, downhole sensing, pig/tool passage detection, hydrocarbon leak detection
The provision of these control and instrumentation needs has evolved over the past ten or so years, towards some fairly standard approaches to implementing the remote control and monitoring function.
Typically, for an electrohydraulic multiplexed control and monitoring system (E-H mux system), distributed control pods (or control modules) provide the location of remotely commanded electronics units which can operate electrical pilot valves and read data from sensors The electronics units require electrical power and signals to be provided from a surface facility.
Generally, a single seabed umbilical feeds electrical power from a surface electrical power generation and conditioning facility, located on a fixed or floating production facility, often over significant distances, say 5 or 10 or even 15 km (see Fig 1 for a schematic installation)
(Fig 1 is available in full paper) The umbilical, which may well carry redundant power feed circuits, "plugs in" to the electrical distribution network on the production template, using some form of umbilical tie-in module/pull-in connector or termination assembly.
The electrical distribution network is installed to feed electrical power (and signals) to distributed control pods which contain electronic multiplex data acquisition and control units. Figure 2 shows a typical pressure-isolating, one-atmosphere enclosure for the electronic circuits, and Fig. 3 shows how this might typically be contained within the envelope of the production control pod.
(Fig 2 and Fig 3 are available in full paper) The quantity and location of these control pods is optimized to meet functional modularity requirements, as well as size, weight and installation and retrieval procedures for the control pod The electrical power drawn at each location on the network is quite small and is determined largely by the number of sensors used for internal monitoring of the pod hydraulic circuits and external sensors (pressure, temperature etc) on the trees and manifolds, rather than by the electronic unit multiplexing circuits (which are typically implemented using low-power CMOS technology) Various energy-saving strategies are available to reduce the total power drawn by sensors and, although the peak power drawn by solenoid driving circuits for pilot valves can be 10-20 watts, the average power is low since these are typically operated rather infrequently
The electrical distribution network can typically take two forms, Either
an on-template distribution bus or ring main (see Fig 4A), or
individual "jumper" connections from the umbilical termination assembly (see Fig 4B)