Subsea control systems are a necessary, vital element of a subsea completion project. In order to improve the reliability and reduce the costs of the control equipment, the authors have taken a 'zero base' system design approach toward the development of a modular subsea control system. The only allowed constraints have been the functional requirements of the equipment. The resulting designs which are optimized for long term reliable operation have been implemented and the equipment tested to verify its reliable performance according to specifications.
NL Control Systems and Marconi Avionics Ltd., have a teaming agreement signed in the Spring of 1977, and since that time have been involved in a joint product development program aimed to supply high integrity subsea electrohydraulic control systems which can be closely tailored to specific customer requirements but which nevertheless, are based on proven designs, equipment and technological capability.
Every production control system is designed from functionally modular hardware and manufactured to meet each customer's specific requirements. Increasingly the exploration of deeper waters and production from more complex subsea equipment have influenced the trade-offs for control systems toward electronic multiplexed electrohydraulic control.
The detailed system approach being taken in this joint development activity makes use of existing proven parts and modules and allows the design to be aligned to specified needs. This approach offers considerable benefit to a proposed program in terms of minimizing any technical and timescale risk.
Certain key features of the resultant control system can be highlighted to convey the essence of the technical solution.
The system design allows the use of multiplex electronic or hydraulic sequence control for each well plus the ability to select the mode to which the well will revert in the event of the loss of electrical signal.
The tree configuration makes use of the packer seal control pod connector; an effective means of connecting the umbilical control lines to the tree and control pod requiring only one level of electrical make/break, and providing diverless installation of the control pod.
All hydraulic Workover and Completion control pods are available, making use of discrete hydraulic lines to connect to the drillers control panel.
The electronics module is powered from the umbilical supply via inductive couplers of a proprietary Marconi Avionics design which have several attractive features relevant to the subsea application.
The subsea electronic circuits are contained in a pressure isolating vessel, having Lloyds Register design approval, which provides a one atmosphere environment in which to operate the components. The design of the module achieves high reliability through simplicity and utilizes a low packing density for components which are subjected to zero thermal stress and low electrical stress factors.
'Hi-Rel' electronic components are selected to comply with the most stringent standards for harsh physical environments. Reliability predictions are based on authoritative international standards, and make use of reliability data collected over some 15-20 years of equipment service.