The relative long wave and depth water in South China Sea poses great difficulties to the applications of the main floatover barge HYSY228 for the 10000-ton mega topsides. This study aims at evaluating the workability of the floatover operations in the South China Sea. Numerical investigations on the dynamic response of the floatover installation for the 10000-ton topsides are presented. The numerical model of the floatover system is built based on the prototype T-shaped barge HYSY228. Two critical floatover phases are considered: pre-mating phase and mating phase. The loads on Leg Mating Unit(LMU) and fenders at pre-mating phase are discussed. Various intermediate mating stages with different drafts and different engagements of the LMU are analyzed. It is found that fender forces, LMU horizontal motions and LMU loads meet the design requirements. But the LMU vertical load is close to the design value, which threatens the safety of the floatover operations. The study provides valuable suggestions on the topside floatover installation for the jacket platform in the South China Sea.
With the development of China's oil and gas resources in the South China Sea, high requirements for offshore engineering have been put forward. The weight of topside has also developed from a few thousand tons to more than 10,000 tons. It is critical to ensure safety, improve efficiency and save costs for the offshore installation of mega topsides.
The topsides installation of the offshore platform is one of the expensive and important tasks. The topsides installation methods include the lifting method and the floatover method. In the lifting method, the individual module or the integrated topsides are lifted up by the floating crane vessel and matted with the substructures. Lifting the individual functional module separately and welding modules together are time-consuming and uneconomical. Lifting the integrated topsides installation requires a large floating crane and an extended crane radius. Those factors result in a great limitation of the lifting operations and constraint the application. The floatover method has great advantages over the lifting method when it comes to the mega topsides exceeding the capacity of the lifting crane. The floatover method allows that more than 20000-ton mega topsides are fabricated and outfitted onshore. The integrated topsides are then placed on the barge deck in one piece and finally transferred onto the substructures by the tide, the ballasting system, or the active jacking system. Besides the capacity, there are plenty of benefits and strengths of the integrated topside floatover method. More flexibility of the barge choice, less long-term offshore hook-up operations, and reductions of schedule interfaces make the floatover method a much safer and more cost-efficient method than the lifting method (Gros and Lescurat, 1982; ONeill et al., 2000; Seij and Groot, 2007; Wang et al., 2010).
