Numerical Simulation And Risk Assessment Of Gas Leakage And Diffusion On Submarine Pipeline

With the increasing demand for natural gas in China,the scale of underwater oil and gas exploitation is gradually expanding,and the possibility of submarine pipeline leakage is also increasing.Aiming at the potential leakage accidents in oil and gas development projects,this paper studies the movement behavior of underwater gas leakage and diffusion,improves the calculation model and risk assessment method of submarine pipeline leakage and diffusion,and provides assessment tools for preventing leakage accidents and emergency disposal of leakage.Firstly,a calculation model of gas leakage rate of submarine pipeline is put forward to explore the gas flow behavior at the leakage point of the pipeline.Considering the variable compressibility factor in the gas state equation,the calculation model is divided into the small hole model,the pipeline model and the large hole model according to the leakage hole diameter.The subcritical flow in the pipe,the critical flow in the leakage hole and the subcritical flow both in the pipe and the leakage hole are programmed and calculated by MATLAB.The leakage rate and other parameters are calculated by taking a 10 m water depth gas pipeline as an example.Secondly,the model of gas leakage and diffusion in submarine pipeline is established to study the movement behavior of gas leakage in water.The VOF model in Fluent is used to simulate the movement of underwater gas leakage and diffusion,and the calculation results are verified by flume experiment.The influence of internal pressure,current velocity and leakage aperture on gas leakage and diffusion is discussed.The shape of residual gas in seawater under different internal pressure and the influence of gas diffusion on free surface are also studied.Finally,aiming at the problem of submarine pipeline leakage,the safety risk assessment method is studied.ANP evaluation system is established,including 4 firstclass indexes and 14 second-class indexes.Based on Delphi method and triangular fuzzy number,experts are invited to evaluate the mutual influence importance of various risk factors,and MATLAB software is used to complete the programming calculation of limit super matrix and global weight vector.Taking an in-service gas pipeline in Liwan,South China Sea as an example,the fuzzy comprehensive evaluation is carried out.And the calculation results are basically consistent with the accident statistics data,which verifies the rationality of the comprehensive evaluation of failure risk based on fuzzy ANP.In addition,the calculation formula of submarine pipeline leakage probability is given by the event tree analysis method.