Design And Analysis Of The Production Riser System For A Semi-submersible Platform

With the development of our country’s economy,the demand for petroleum and natural gas is increasing,which makes the exploration of deepwater oil and gas resources necessary for the relief of energy tense situation.As an important portion of deep sea oil and gas resources development system,the marine riser is an essential engineering equipment.Steel catenary riser(SCR)is the first choice for wet tree semi-submersible platform.In order to ensure the safety and entirety of a riser,it is of great importance to conduct design and analysis work which includes strength and fatigue analysis.Until now,there have been many researches about design and analysis of steel catenary risers,which formed a lot of mature theories and techniques.But there are still some problems needed to be solved,thereinto,how to model pipe-soil interaction in time domain analysis and strength and fatigue analysis of flowline segment on slope are still two key problems.Based on nonlinear pipe-soil interaction model,this paper developed external codes of software Orcaflex by C++ language to realize nonlinear pipe-soil interaction in time domain analysis of steel catenary riser.Combine with punished time domain analysis code of steel catenary riser,and discuss the influence of nonlinear pipe-soil interaction model to touch down zone mechanical behavior.It is found that the nonlinear pipe-soil interaction modeling codes have considered stiffness degeration,formation of trench,soil suction,passive soil resistance and berm resistance caused by cyclic motion of riser itself,modeling more realistic pipe-soil interaction,which improves the accuracy of strength and fatigue analysis of touch down area.This paper also explored the influence of different soil parameters and design parameters to riser strength and fatigue analysis.The results show that the soil stiffness value has a great impact on the strength and fatigue property of touch down area,while shear strength and soil suction parameters have great impact on riser strength property but small impact on riser fatigue property.Moreover,wall thickness and hanging angle will change the whole riser’s strength and fatigue damage,and appropriate increase of these two parameters’ value is good for strength and fatigue performance.Besides of these,this paper improved the pipe-soil interaction modeling codes in time domain to carry out dynamic strength and stability analysis of flowline segment on slope.Respectively for the transverse and longitudinal slopes,the influence of different slope inclinations,soil stiffness and riser sizes on riser stiffness and stability performance were discussed.The results present that the existence of slope increases the equivalent stress of flow line segment.And the increase of slope inclination leads to the increase of max von mises stress,transverse displacement and effective tension of risers on transverse and longitudinal slopes.Soil stiffness value has non-ignorable influence on the riser flow line segment’s stability performance.Bigger wall sickness and smaller riser diameter would contribute to the strength and stability performance of steel catenary riser.This paper offers technical reference for reasonable design and analysis of steel catenary riser and solution of several key problems,and has certain reference value for engineering application.