Study On Bearing Capacity Of Cluster Risers System Of TLP Under Extreme Environment Condition

The South China Sea is an important target area for deep-water oil and gas drilling in China.Due to its special environment,such as typhoon and internal wave,the deep sea operation technology and equipment are facing new challenges.This paper is supported by the project of CNOOC named �Research for drilling and completion designing and safe operation technology of cluster riser system for TLP�,Specific to the experience of typhoon and internal wave in the South China Sea,Based on the foreign experience on Deep-water Tension Leg Platform.Taking the coupled system of tension leg platform and risers in a sea area of South China Sea as the research object.Using the professional hydrodynamic analysis software SESAM to carry out the research on the bearing capacity of the coupled system of the tension leg platform and risers in extreme environment,which can provides theoretical reference and technical support for the development of oil and gas resources in the South China Sea.The main achievements are as follows:(1)Establish the finite element model of coupled system of TLP and risers by using the hydrodynamic analysis software SESAM,forming the modeling process of coupled system.Investigate the related configuration and research status of coupled mooring system.Focus on the coupled mechanism of mooring system,hydrodynamic analysis process of TLP,analysis process of riser system and calculation method of environment load.Extract the movement and force of TLP under the self-existence condition.(2)This paper mainly analyzes the mechanical properties of TLP under typhoon condition of the South China Sea.Analyze the movement of TLP based on the research progress at home and abord.Analyze the combined influences of wind,wave and current on the motion of TLP and axial tension of tendons.The results show that wind,wave and current have a great influence on the motion of TLP and axial tension of tendons,that the movement of TLP in vertical direction shows a certain,but there is a significant sinking movement,that the restraint effect of tension leg can effectively control the TLP shake,the constraints on TLP rock is relatively small.(3)This paper mainly analyzes the motion and force of riser system in coupled mooring system under typhoon condition,taking into account the combined influence of TLP movement and wind,wave and current.Focus on he combined influences of wind,wave and current on the static characteristic of riser system.The results show that wind,wave and current have a great influence on the movment and force of the riser system,that when the current flow is increased,the axial tension of the riser system fluctuates obviously and the amplitude of oscillation increases.Based on the reliability analysis method of response surface,this paper determines the limit state equation of coupled system,and take the typhoon 5 years as an examplethen,then calculate the reliability index of the system under typhoon condition,the results show that drift of platform along Y axis is easier to exceed 10% of the water depth,the probility that the axial effective tension of tension joint of drilling riser exceeds the yield strength is relatively small.(4)Combined with the characteristics of solitary waves in the South China Sea,this paper takes different solitary wave theory for numerical simulation.The simulation results shows that the waveforms of KdV,mKdV and eKdV are relatively steep and the duration is short,while the Gardner theory is relatively smooth and the wavelength and duration are relatively long,which is in accordance with th actual characteristic of the South China Sea.This paper simplifies the solitary wave,designs the analysis sonditon under the internal wave condition,then studies the movement and the force of the coupled mooring system.The results show that when the internal wave exists,the current effect increases obviously,and the drift of riers along X,Y axis increase obviously,in the near water surface,the bending moment and the deformation of risers increase,increasing the risk of damage.