Analysis of FPSO station keeping characteristics

Abstract

Nowadays with increasing production and exploration activities offshore, the FPSO system has been widely adopted globally because of its unique design system and adaptability to these offshore environmental conditions. This research project aims to provide the station-keeping characteristics of an FPSO in the West African region, by analysing an FPSO with spread mooring design for multiple load cases, different offset, multiple draught conditions and environmental loads, all acting simultaneously and dynamically on the coupled FPSO system. Static and dynamic analysis were conducted using the Orcaflex software to establish the station-keeping characteristics, the recommended practices by DNV for mooring and global performance analysis were utilized for the mooring lines in the static analysis to obtain the primary equilibrium position before the dynamic analysis was conducted and to estimate a dynamic response of the risers in dynamic analysis. The effective tension of the static and dynamic analysis results for the different draught and environmental conditions shows that the far offset had the maximum effective tension, with the fully laden effective tension been the maximum effective tension of the entire simulation. The increase in effective tension as the loading of the FPSO tanks increased caused a reduction in the bending moment radius and thereby reducing the curvature of mooring lines and riser bends. But it was the near offsets that had the minimum bending radii as expected, however, from the analysis the draught conditions provided the largest responses to the multiple loading cases when compared with the changes in the offset positions.