CONTROL SYSTEM FOR REMOTE SUBSEA COMPLETIONS

The Seahorse and Tarwhine subsea completions are among a number of recent developments in Bass Strait designed to exploit relatively small and remote fields. Both wells have been developed by re-entering and completing the original exploration wells and tying them back to the nearest existing platform, Barracouta, with an insulated production flowline, a gas lift supply line, and an electrohydraulic control umbilical. Seahorse is a little over 11 km north, and Tarwhine almost 18 km south-west of Barracouta, and it is these long offset distances which significantly influenced the decision to adopt an electrohydraulic control system. The advantages of an electrohydraulic system in this application, compared to the other control techniques available, are that it provides a faster response time to surface initiated commands, it has an overall lower cost, and it provides information back to the surface about conditions at the subsea well.Many of the components used in the subsea production control system are innovative and highly specialised, for example, the conductive electrical couplers and the temperature transducers. A significant amount of the equipment also has its origins in the aerospace industry and, like in that industry, demands a high commitment to quality assurance and quality control throughout the manufacturing and assembly phases of the project. Seahorse and Tarwhine have now been producing successfully since September and May 1990, respectively. The success of this project gives the joint venture partners, Esso and BHPP, confidence to use subsea technology to continue developing smaller fields, particularly as developments move into deeper water approaching and beyond the edge of the continental shelf.