Study On Risk Assessment And Control Of Top Tension Risers For Tension Leg Platform

Tension leg platform(TLP)has been widely used in deepwater oil field development in recent years,and top tensioned riser(TTR)is one of the important parts for TLP design,which connects platform and subsea wellhead.Because of the complex equipments,difficulty technology,harsh operation environment and serious failure consequence of TTR,there are huge risks in the riser operation process,The success of drilling and production operation is directively related with control effect of risks.Currently,the application of TLP in our country is still in blank,and there are little researches in security of the riser operation.This study is supported by CNOOC comprehensive research projects,“Operation and technology on drilling and completion of tension leg platform top tension rise in deepwater”.According to the site actual demanding of TLP in the South China Sea,researches on the risk assessment and control steps of TLP risers are firstly carried out.The main research contents and achievements are as follows.In this paper,in view of the high frequency of two natural disasters in South China Sea,violent typhoon and internal waves,the finite element dynamic response analysis and reliability technology are combined to develop a method for structural risk assessment and reliability analysis of TLP cluster risers in extreme environment.Firstly,the riser survival limit guidelines and operation limit guidelines are determined by researching on relative information and standard.The finite element analysis model of serial riser system is established with ABAQUS.Then,the reseach on structural risk assessment is carried out in the combined action of extreme environmental loads and platform offset.The main risk factor and the weak location of risk system under the influence of typhoons and internal waves are confirmed.Secondly,based on structure reliability method and extreme value theory,considering the the influence of the uncertainty of the material properties,the geometric parameters,the design parameters and the the external load model on the the finite element analysis model of TLP TTR.using monte carlo method、AFOSM and response surface method to analyze the cluster riser strength reliability and interference reliability under violent typhoon and internal waves.The aim is to fully and systematically reflect the safety status of TTR.Through the establishment of riser leak fault tree,the potential Failure Mode and Effects Analysis method is applied to analyze the risk of the key equipment of TTR,the analytic hierarchy from failure mode,failure reason,failure consequence to recommended practices are discussed and the FMEA analyzing process is confirmed.Then,combined with expert advice,the consequences of failure ratings is defined.Hazard and Operability Analysis is applied to analyze the risk of drilling and production operations.According to the practical operation,the guide word,risk evaluation matrix and analysis process of HAZOP analysis are defined.The risk degree is defined combined with expert advice.Finally,the risk factor of TLP riser operation process is comprehensively analyzed,then,the riser risk assessment index system is established.The fuzzy analytic hierarchy process is used to assess riser operation risk.Based on the security barrier method,the risk control process is proposed.