Research On Risk Evaluation Of Subsea Tree

With the strategy of marching to deep-water being proposed for the development of oil and gas industry in China,the technology of subsea tree design and manufacturing has become the technical bottleneck for the exploitation of oil and gas in deep-water.To solve this issue,government has set up foundation to support subsea tree research and development.Risk evaluation is the key problem.This thesis has done some research on subsea tree installation and leakage risk analysis.The main work is as follows:Through FMEA on mechanical and control system of subsea tree,the failure modes,causes and impacts of subsea tree are obtained.A statistical analysis on failures occurred in subsea tree has been done.Results show that leakage of oil and gas is the most frequent failure mode.This paper applied the fuzzy FTA method to the process of installation.Introduce the main process of tubing hanger installation: junction,location,locking,and seal test,and the fault tree is built up which top event is the tubing hanger installation failure.In the quantitative analysis,expert opinion and fuzzy sets theory are used to calculate the basic events failure probability.Linguistic Value is converted into fuzzy value,and then defuzzied to obtain failure possibility.The top event failure probability is figured out.Sensitivity analysis can find out the crucial basic events.The result proves that fuzzy FTA method used to evaluate the tubing hanger installation risk is feasibility.And the result is consistent with the experience.AHP-TOPSIS indicator system is built up to evaluate two different leakage patterns.Comprehensive evaluation from environment security,leakage probability and economic loss,weight vectors of each evaluation index are determined by AHP and then combined with the sort of TOPSIS method principle,the comprehensive evaluation indicator system is built up and the two leakage patterns’ risk value are calculated.The result shows that the degree of dominance of internal leakage is lower than external leakage.The case of subsea Christmas tree risk evaluation validates the system method is available and effective.