Performance Study For Taut Mooring Of A Deepwater Semi-Submersible Drilling Platform

With the development of offshore oil and gas in the direction of deep sea, semi-submersible platform,relying on its advantages: small waterline area,preferable paylaod,strong ability of resisting wind and wave and wider ranger of operational water depth, has get rapid development and wide application. The development of oil and gas resource in deep sea is a complicated systematic project, with technical complexity,high input,high risk characteristic. Because of the complicated environmental in deep sea, it is need to have a reliable mooring system to ensure the platform working normally and security under extreme environmental.Semi-submersible platform generally adopt catenary mooring or taut mooring, Catenary mooring is traditional mooring type,which relying on its gravity to determine platform's position. With the continued increasing of working water depth, the gravity of catennary mooring system increases rapidly and bring a series of problems, which have been no longer meet the mooring requirements of platform. Because of adopting synthetic fibre rope as mooring rope with the advantages of light weight,high strength and corrosion resistant, taut mooring own gravity reduce obviously, has stronger abality of determining position and larger working water depth, therefore, taut mooring has a wider foreground of development. Mooring system must ensure platform movement meet the requirements in various conditons, but also protect the securities of mooring ropes and risers. Therefore, making an analysis of the motion response of platform and dynamic response of mooring ropes has important guiding significance for the design and application of platform.The main research work are as following:1. The angle between mooring rope and sea level and the pretension of mooring ropes are main influence factores for mooring response. This paper separately establish different numerical model to analyse the changing regular of mooring reponse, and choose reasonable mooring parameters.2. Semi-submersible platform generally adopt 8-ropes mooring type ,the angles between mooring ropes have direct influence on mooring capability. On the foundation of first part, establishing several numerical model relying with different angles and analyse the changing regular of mooring response. According to different conditions, semi-submersible platform, sometimes, adopt 16-ropes mooring type. In this paper, two layouts types were calculated and analyse the mooring responses.3. In order to further definite the better mooring capability of tuat mooring than catenary mooring, this paper make numerical simulation for the semi-submersible platform adopting catenary mooring which working on the 1500m water depth., compareing and analyseing the motion response of platform and dynamic response of mooring ropes.The innovations in this paper can be concluded as follows: the analysis for semi-submersible platform adopted taut mooring, so the analysis results have more application value. Considring the coupling function between platform and mooring ropes and making time-history analysis, so the results are more reliable.