Study On Leakage And Dispersion Law Of Subsea Gas & Oil

Recently,China has stepped up its efforts to exploit offshore oil and gas fields with the flourishment of the economy.In this process,submarine pipelines play an extremely powerful role as the main means of transporting oil and gas.However,erosion and suspended span,the third-party damage and corrosion can cause pipeline failure and lead to oil and gas leakage accident,resulting in environmental pollution and casualties.In order to provide support for emergency response,this paper combines experimental studies,theoretical analysis and numerical simulations to investigate oil and gas leakage and dispersion behaviors,transport laws and the interaction between gas & oil plume and the water surface after a leakage occurs.A two-phase gas-oil leakage experimental system has been built to study the leakage and dispersion behavior under stratified and slug flow considering the influence of leak pressure,leak direction,leak depth and other parameters.From the experimental results,the underwater gas-oil leakage diffusion undergoes three stages: jet,buoyant jet and buoyant plume stage.Plume offset,maximum fountain height and plume axis velocity increase with the increase in release pressure and leakage nozzle,plume rise time decreases with the increase in release pressure and leakage nozzle,plume offset and plume rise time increase with the increase in water depth,different leakage directions also have influence on plume rise time and plume offset.In addition,when the horizontal leakage occurs in stratified flow,with the increase of apparent gas velocity,plume offset and rise time are increasing,and the maximum fountain height is decreasing.The opposite pattern is seen in slug flow,where the plume offset,rise time and maximum fountain height all decrease with increasing apparent gas velocity.Compared to single gas leakage,the overall density of the two-phase plume increases,the plume offset is further away and the rise time becomes larger.With reference to phase splitting model through small holes in the pipe wall and related theories,a prediction model for oil and gas leakage under stratified flow and slug flow has been established.The accuracy of the prediction model was verified through experiment results,which overall error is within ±10%.Based on the Euler-Lagrange method,a three-dimensional CFD numerical model with VOF coupled DPM is established to predict the dispersion behavior of subsea oil and gas leakage.The accuracy of the numerical model is verified through experiment,which shows that the simulations are in better agreement with the experiments,and the predicted values are small,with errors between-20% and-5%.The validated numerical model is extended to shallow sea considering the current.It is shown that the plume bent significantly under the influence of current,time of arrival at surface is prolonged and the plume offset increases.Currents are the main factor causing the plume offset compared to different release directions.The larger the release nozzle is,the shorter the time of arrival at surface,and the smaller the plume offset and maximum plume radius during the plume dispersion.Under the stratified flow,oil and gas are mixed and reach the surface at the same time,while under the slug flow,oil and gas enter the water alternately,and due to the small buoyancy force on the oil droplets,it is difficult for the oil droplets to reach the surface,and they keep dispersing to a farther distance under the action of the current.