Design And Analysis Of The Mooring System Of Deepwater Drilling Semi-submersible

Mooring System is very important for the safety of oil drilling and production on the sea. As the oil exploitation in South China Sea goes into deeper and deeper sea, the requirement for the deep and systematic research of taut mooring system using new materials like polyester is higher. This paper addresses the systematic evaluation of station- keeping systems of deepwater drilling semis in South China Sea environment. The main contents of this paper include:Diffraction analysis was first applied to solve the hydrodynamic properties of a selected fifth generation drilling semi-submersible. Static analysis and coupled dynamic analysis in time domain of a polyester mooring system in water depth of 2500m were then carried out. Vessel motion response and line tension response time histories were generated. Based on the selected drilling semi configuration, the mooring systems were analyzed and designed in terms of line strength and station-keeping performance for a range of water depths using different mooring line materials, namely the steel wire rope, the polyester rope and HMPE. Attempts were then made to analyze the effects of some key parameters of mooring system configuration, including top angle, pretension in line and polyester line axial stiffness.The results of analyses and studies indicate that:In terms of mooring line strength and station-keeping performance, polyester mooring system has many advantages compared to the other two in water depth ranges from 1500m to 3000m. Wave frequency components are larger than low frequency components in line tension response and vessel surge motion response. The optimum top angle for polyester mooring systems in water depth of 2500m is around 40 degrees.