Ship Integrated Turret (SIT) is widely used for FPSO in harsh environment and deep water applications. In China, all FPSOs located in South China Sea are equipped with Ship Integrated Turret mooring systems. In 2019-2020, CNOOC has developed offshore Liuhua16-2 oil field project with FPSO HYSY119 equipped with the most sophisticated SIT systems ever been built and integrated in China. The system is designed to host 10 swivel stacks with flow path, power supply, subsea control and chemical injection for over 26 wells. There has been a lot of challenges during the fabrication and integration of this 2800MT turret system. Due to big number of risers attached to the turret and critical vessel to turret load path arrangement, the design had been very challenging with several significant late design changes which essentially created critical path schedule clash issues. The very tight fabrication and integration tolerance of the unique single bearing turret and ten stack swivels into the FPSO presented also unparalleled challenges to the construction team.
The Liuhua16-2 oil field development is comprised of three oil fields namely Liuhua16-2, Liuhua20-2 and Liuhua21-2. The three developments were discovered one after another from 2010 through 2015. The three fields are located in South China Sea with water depth around 420m. They are located in a triangle layout with the far most fields about 30km apart from each other. The field development mode is "FPSO + subsea production systems". The harsh South China Sea environment requires that the FPSO to be equipped with ship integrated internal turret which provides permanent mooring station keeping for the FPSO and weather vanning for the FPSO heading all the time to the favorable environmental direction. The second function of the turret system is to provide interfacing paths from subsea to topside. Due to the large number of oil wells, each well is equipped with dual electrical submersible pumps, each oil field is provided with dual flow lines. All of these made the turret interface with high complexity. In total there are 17 hang off lines on the turret, namely 6 risers, 3 umbilicals and 8 multicore subsea power cables. All of them enter the turret from bottom and run up into the swivel stacks. The Liuhua turret is the biggest and most complex turret ever built and installed in China. Fig.1 shows the general arrangement of the turret.
