Semi-submersible Drilling Unit Ballast System Design

After long-time exploitation, oil and gas resource on land was exhausted. Exploring oil and gas resource in sea is main direction. Moving toward deep water and super deep water is natural trend for global ocean oil & gas industry development. Drilling vessels and semi-submersible drilling units are only two types of drilling equipment in the deepwater, which can drill in more than 1500 meters depth deep sea. Semi-submersible drilling units is mainstream.The design of ballast system is one of the important crucial technology points of semi-submersible drilling unit, floating condition of rig has very important influence on its performance in any condition. ABS MODU has obligatory requirement on rig ballast/deballast rate. Ballast system is to be efficiently operated when subject to assumed damaged conditions. ABS MODU also has requirement on ballast pump configuration due to lost of one pump room.According to the design requirements of the target rig, this thesis make a research on the ballast system design on the basis to meet the rig’s overall performance and ABS MODU’s requirement by absorbing the foreign advanced technology and experience, and our own engineering design experiences. It makes a detailed analysis and comprehensive comparison from different aspects, such as: system filling and discharge method, level gauging, remote valve control, equipment configuration and pump capacity calculation, system suction performance and resistance estimation, etc.. According to the result of comparison, judgment is made to choose out the best ballast system configuration plan. Two key technical difficulties are resolved: at least two pumps are to be capable of effectively emptying each intact tank at maximum normal operating draft when the unit is subject to the assumed damage conditions, and sufficient available net positive suction head to operate at the max. angles of heel and trim associated with the assumed damage conditions. It is ensured that rig can maintain well-balanced floating state at any condition required by rules and HAZOP.After the ship test, i.e. mooring test, navigation test, it is verified that each index of the target rig meet the design requirements and the design of ballast system is successful.