Subsea systems used in combination with host facilities, such as floating, production storage and offloading units (FPSOs), tension leg platforms (TLPs), spars or compliant towers employ supervisory control and data acquisition (SCADA) systems whose architectures differ from SCADA systems found on conventional platforms. in these systems, programmable logic controllers (PLCs) locate on the host facility, provide control of subsea valves on manifolds and satellite wells. PLCs also continuously record data from temperature and pressure sensors located on subsea wells. Since it is expensive to repair the electronic systems on the manifolds and satellite wells, redundancy is typically built into the system.

SCADA systems used in deepwater must also provide for control switching to workover vessels. Such vessels must provide control compatible with the existing deepwater multiplex controls and must endure the safe control of the well.

During 1999, the Minerals Management Service (MMS) in the United States launched a study to assess the current state of SCADA systems used in the territorial waters of the US, with special emphasis on quantifying the reliability of these systems.

This paper describes findings from this study and provides a comparison of trends with other international deepwater SCADA systems.