The growth in subsea completions at increasing step-out distances and the reduction or elimination of new build topside facilities has continued. When this trend is combined with improved reservoir management using intelligent sensors and the results of current development projects using downhole and seabed metering, separation and process equipment, the volume of control system and sensor data will have expanded beyond the capacity of conventional communication systems. Fibre optics technology offers the necessary long step-out, high speed, high bandwidth data transmission. An added bonus of the move to fibre optics is noise immunity, and consequent high data integrity needed for safe operation in the severe EMI environments created where high power motors and power cables are used subsea. This system uses telecommunications grade single mode optical fibre with laser generated optical pulses at 1550 nm as the information carrier. Multidrop communication at data rates of 2 0 Mbs−1 and with error rates as low as 1 109h as been achieved. The modem supports unrepeated communication over distances in excess of 100 Km Modular systems installation is possible, using proven wet mate hybrid connectors Equipment and installation costs are comparable and in many cases significantly cheaper than for electrical communication, demonstrating that optical communication is a technically and commercially feasible and reliable alternative to existing electrical systems
The high cost and hazardous nature of recovering hydrocarbons offshore, have led to the trend to reduce topsides facilities, and to the growth in subsea production control Subsea control capabilities have been considerably enhanced by the recent generation of microprocessor based systems. These advanced controls facilities, enable the provision of a subsea interface for advanced technology installations such as, artificial reservoir lift systems, multiphase flow measurement, down hole monitoring and intelligent sensors as well as the conventional tree control functions Also recent development projects to install seabed separators with direct water re-injection, and multiphase pumps have required development of the subsea control and monitoring systems.
However these advanced technologies impose increased data processing and communication overheads. These additional communication requirements appear as closed loop motor control, local sensor support and data processing, multichannel communications, downloading of calibration software, intelligent diagnostics and provision of dedicated, uninterrupted communication channels.
This expanded functionality has created a need for increased data transfer. In particular the controls umbilical must now provide a data highway capable of supporting communications between topsides control systems and a network of Subsea Control Modules (SCM) and then extended control functions Traditionally this has been implemented using a number of either dedicated shielded twisted pairs or coaxial conductors, or by utilising the power conductors for Combined Power and Signal (CPS) The available data transmission rates have been necessarily low, often of the order of a few hundred bits/sec, to reduce errors, maintain reliability, and provide an economical solution This transmission performance is no longer sufficient for the inevitable requirements of the offshore industry A high bandwidth communication link is now a critical enabling technology for the continued development of subsea control