Reliability Analysis Of Subsea Tree And Risk Assessment Of Falling Object Impact

With the development of offshore oil and gas resources from shallow sea to deep sea,subsea production system has become the mainstream mode of oil and gas resources development.As an oil and gas production management and safety control equipment,the subsea tree is one of the core equipment to ensure the safe exploitation of subsea oil and gas resources,and its reliability is very important for safe and stable operation of subsea production system.At present,the development and operation evaluation technology of the subsea tree has been monopolized by European and American developed countries for a long time.Domestic research and development technology is still inadequate,mainly because of the harsh environment in the oil and gas exploitation process of the subsea tree,the complex development and design process,difficulty in sealing performance assurance,unclear selection of structural materials,and low accuracy of operation and maintenance reliability evaluation model.For the subsea tree,therefore,break through key technology of the design,manufacture,maintenance,testing and evaluation process,solve the difficulties of the subsea tree in the process of operational reliability evaluation,to break through the foreign technology blockade,realize the localization of subsea tree,provide technical support for the autonomous mining deep-sea oil and gas resources in our country are of great theoretical and practical significance.In order to solve the problem that the traditional reliability analysis method cannot meet the multi-state reliability evaluation of subsea tree under complex environmental loads,based on the analysis of load and failure mode of the subsea tree,the fault tree model of the subsea tree system and its internal components are established considering the time-varying characteristics of operational and maintenance reliability of the subsea tree and the possibility of system degradation during operation.Based on the historical failure data and scenario simulation,the dynamic Bayesian model of the subsea tree system is established,then the variable control analysis of the tree failure mode is carried out,and the influence rule of failure mode and failure rate on the subsea tree reliability is obtained.In order to determine the maintenance priority after a fault occurs,a study on fault prediction based on dynamic Bayesian reverse reasoning is carried out to determine the probability of failure of the subsea tree or components of the subsea tree system,which can be used as a reference for risk decision-making in the operation and maintenance of the subsea tree.In order to solve the problem of high cost of fault simulation test of the tree wellhead connector and difficulty in collecting failure data,based on the traditional fault tree model,fuzzy comprehensive evaluation and Markov method,a fuzzy Markov method is proposed to solve the problem that it is difficult to evaluate risk,reliability,availability and uncertainty simultaneously using a single model.The reliability evaluation algorithm of the wellhead connector is proposed,and more reliable data preprocessed by fault tree and fuzzy theory is input into Markov model,and the calculation accuracy of reliability evaluation algorithm is improved by iterating and adjusting the failure level of model.The influence of different failure modes on the reliability and availability of the wellhead connector is obtained by analyzing the uncertainty of the working environment of the wellhead connector,which is of great significance to the troubleshooting of the wellhead connector.For the risk analysis problem of the impact of falling objects,the three area probability calculation model is established.A numerical method for calculating the reliability probability of the impact of falling objects is presented,which can be applied to many kinds of current subsea equipment and break the limitation of the application object of existing research methods.The reliability evaluation model of the subsea tree after impacted is established,the impact of falling objects is analyzed by numerical simulation and experimental simulation,and the structural damage of the subsea tree after impacted is obtained.In order to solve the explosive problem of multiple failure modes occurring simultaneously in the reliability analysis of the subsea tree loop system and tubing hanger,a method of operation and maintenance reliability analysis based on stochastic Petri net is proposed.Reliability analysis of the tree loop system and the tubing hanger is performed to obtain the influence rule of failure mode on reliability index and availability,and to determine the failure mode that is the greatest impact on the system,it is of great significance for reliability design of the subsea tree loop system and tubing hanger.Based on the proposed dynamic Bayesian model of subsea tree,the fuzzy Markov model of wellhead connector,the Petri net model of loop system and the three-region probability calculation model of subsea tree impacted by falling objects,the reliability analysis software of the subsea tree is developed.By comparing the analysis results of reliability,availability and impact risk of DNV specifications,manufacturers and research institutes,the accuracy of the reliability,availability and impact risk assessment algorithms of the subsea tree,wellhead connector,loop system and tubing hanger proposed in this paper are verified.Automated black box calculation of the subsea tree,wellhead connector,loop system,and tubing hanger reliability is implemented to improve reliability evaluation efficiency and achieve prediction of the subsea tree operations and reduce maintenance costs.