Development of Deep Draft Semi-Submersible FPU Hull (Casting-Free) Targets for Oil Field in Gulf of Mexico

Abstract

A deep draft semi-submersible hull has been developed as a standardization concept which can support the topside structures up to the facility weight for the specific level of daily oil production in GOM (Gulf of Mexico). The designed hull has the optimized dimensions of ring pontoon and four columns for coping with the weight change of topside and the innovated hull shape to eliminate the casting which is normally used at the corner node area where high stress concentrated on. The hull form also has the good global motion in waves, winds and currents to be able to use the SCR (Steel Catenary Riser). The mooring systems are designed for water depths of 1,500m as a standard design concept of hull including mooring lines (3 × 4). The global performance is validated for the maximum offset, the mooring line tension and the acceleration. The possibility of SCR usage is also investigated with the fully coupled time-domain analysis to confirm that the designed hull form has the suitable hydrodynamic characteristics to permit the minimum vertical motion performance for SCR. Throughout the global performance and mooring analysis, the designed Semi-FPU fulfills all stability requirements of rules and codes specified in design of basis for both intact and damaged conditions, and has good motion characteristics such as inclination, acceleration, sectional loads and air gap and mooring system compliance with design criteria in the view point of mooring tension, offset and fatigue damage. Also, the global structural strength analysis has been performed to extract stresses and displacements where local points which are pontoon-column connection areas from the global model. The local points need to reinforce during detail design stage from buckling, yielding and fatigue analysis for normal operating and extreme storm conditions.