Research On End Connection Reliability Of Subsea Production System

The end connection is one of the key technologies to use subsea production system.Connecting under the water is with high risk,because it is influenced by ocean environments.Now,our country’s deepwater oil and gas exploitation is still in a beginning stage,lacking experiences in subsea end connection and reliability of end connection.Therefore,doing research on end connection reliability of subsea production system is significant for our country’s offshore oil and gas exploitation.This paper takes end connection as the research object by using the method of combining summarization and theoretical analysis.For different types of end connections,corresponding methods and steps are summarized.Qualitative risk assessments have been done for end connections by using the method of risk factors analysis.Considering the factors of water depths,X tree gravity,locking load and work pressure,mechanical analysis and mechanics model are built for the subsea connector which is the key equipment of end connection.Based on energy of form-changed criterion,strength checking and disciplinary analysis of the connector are made by simulated calculating with ABAQUS software,and the two key factors are water depth and work pressure.Results show that under the condition of different work pressures,the maximum Mises stress firstly decreases with the increasing water depth and when water depth increases to a critical depth,the maximum Mises stress increases with the increasing water depth.What’s more,the critical depth increases with the increasing work pressure.Under the condition of different water depths,the maximum Mises stress increases linearly with the increasing work pressure.And the increasing velocity of maximum Mises stress decreases with the increasing water depth,which means that work pressure has a large effect on connector strength in shallow water.According to the unascertained measure theory and information entropy,the index of safety assessment model of end connection is constructed,and the credible degree rule is used to judge the grade of risk.By using C# tool,a risk-assessment software for end connection of subsea production system is developed,and the risk-assessment results are showed through histograms.Using the software to calculate a certain subsea production system in South China Sea,results show that the system’s level of risk is III.Considering the risk histogram,some targeted suggestions and risk-off measures are given,such as enhancing the vigor of damage prevention,controlling the number of active vessels on the sea.After taking these improvement measures,another risk assessment is done again,and results show that the system’s level of risk is II,which means lower risk.So the probability of safety accidents decreases and the reliability of subsea production system enhances effectively.The developed risk-assessment software does have a practical guiding significance for reducing the risk grade of subsea production system.