The soft yoke mooring system is considered to be one of the best mooring methods for Floating Production Storage and Offloading (FPSO) on shallow seas, which is widely used in the Bohai Sea, China. Ice load is the main environmental load in this area. The effect of sea ice on single-point mooring is the key problem to the design and secure operation of the whole mooring system. In this paper, the main failure mode of FPSO single point mooring is defined based on the site monitoring of an FPSO single point mooring in Bohai Sea. Combined with the interaction between sea ice and FPSO, the influence of sea ice on the mooring system is analyzed. Finally, taking a typical FPSO single point mooring system as an example, the safety of performance of an FPSO under extreme ice conditions is analyzed using ANSYS numerical simulation.
During the development of marine oil and gas, an FPSO is a very important piece of engineering equipment. A mooring system will let the FPSO stay in a fixed marine oil and gas position, which can ensure the FPSO's continuous production. Unlike using the ship's anchor or taking measures to avoid sailing in the bad marine environment, an FPSO is usually used in the form of permanent mooring. Under stress from wind, wave and current, an FPSO mooring system needs to resist certain environmental loads; it is a key component of the FPSO, which characterizes its high technology content (Yuan et al., 2005; Allen et al., 2006).
The water depth in the Bohai Sea is relatively shallow, with mainly small and medium sized oil fields, which are more distributed, and belongs to the typical marginal oil field. The depth range is usually 15∼20 m. For shallow water marginal oilfields, the approach of single point mooring FPSO combined jacket platform was developed. This model, through which oil or gas transportation is carried out regularly, is economical and practical (Wu, 2012). It consists of a mooring frame, mooring leg, yoke and single point, and has 13 hinge points such as universal joint and thrust bearing, which are located at floating production, storage and unloading (Lyu et al., 2019). In China's Bohai Sea, an FPSO situated by soft yoke mooring is a commonly used combination.