Multi Point Mooring Analysis And Safety Study Of Shuttle Tanker In Marginal Oilfield

Offshore crude oil is usually transported by sub-sea pipeline or shuttle oil tanker.Shuttle tanker is generally positioned by single-point mooring system.But pipelines and single-point mooring system are too expensive to marginal oil field.When jack-up unit is employed in the exploitation of oil field,transporting the crude oil remain a problem for jack-up cannot be berthed by the shuttle tanker.Thus,the multi-point mooring system,which is cheaper,can be considered.The shuttle tanker can be moored by multi-point system at the relative calm sea.The multi-point mooring system is vulnerable to transverse load of wind,wave and current.When the sea environment become rough,the mooring force will be larger,and even the anchor moving will be caused or collision of the vessel and the platform will occur.The research of this dissertation mainly analyzes the feasibility and safety of multi-point mooring of jack-up platform and shuttle tanker.Firstly,the theory of floating motion analysis is summarized,and the correlation equation of the frequency domain and the time domain analysis of floating body are deduced,the method of solving the environmental load of the shuttle tanker and the jack-up platform is described,and the method of analyzing the mooring system is introduced;Secondly,the frequency domain analysis and time domain coupling calculation of shuttle tanker and its mooring system are carried out by using SESAM and Orcaflex software,and the characteristics of tanker movement and mooring system under different conditions are analyzed;Then,the variation of the mooring force of the mooring system under different diameter,length and different anchoring angle is studied,and the force characteristics of the mooring system under different environmental directions are analyzed;Finally,considering the effect of mooring force and environmental load on the mooring platform,the structural strength safety analysis is carried out.The results show that: when the shuttle tanker's draft increased,the hydrodynamic coefficient and motion response and mooring force maximum on the platform with increasing,while the mooring force maximum anchored to the seabed decreases.Increasing the diameter and length of anchor chain and decreasing the diameter of cable is an effective way to improve the operation capability of the mooring system.The mooring performance of the 60 ° angle of anchoring is better than 30 ° and 45 °.The wind direction has little effect on the maximum force of the mooring cable.The mooring cable force reaches the maximum when the direction of wave and current are both 90 °.Considering the existence of mooring force,the anti-overturning stability,anti-slip stability,leg yield and buckling strength and local strength of the platform meet the requirements.This thesis focuses on the influencing factors of mooring force and optimizes the mooring scheme accordingly.Then,the storms of the tanker mooring system under different mooring schemes are analyzed.Finally,the strength of the self-elevating platform under the mooring of oil tankers is checked.