Design Of Caisson Gas-liquid Subsea Separator And Separation Performance Research

The subsea separator is very important equipment in the deepwater subsea production system to improve oil recovery and speed up oil field production.However,the deepwater subsea separator is still in the exploratory stage in our country.In this paper,the structure of inlet section and cylinder section of caisson gas-liquid subsea separator is optimized by means of numerical simulation.According the oil and gas treatment capacity of oil field in the South China Sea,the design formula of separator is put forward and the prototype of separator is manufactured.Then the separation performance of separator is studied.It is very important for the domestic petroleum industry to break through the offshore oil and gas production limitation and break the technology monopoly.The main research contents and conclusions are as follows:A one-dimentional steady-state model is used to calculate the initial parameters of slug flow while the user-defined function is used to define the boundary condition of transient model.Then the liquid slug dissipation in the inlet of separator is simulated on the basis of VOF model.The dissipation of the liquid slug in the inlet pipe of separator has four stages: the stair-head and the annular-tail of liquid slug are developed in the horizontal section,the slug head picks up liquid and slug tail drops the liquid in the riser section,the velocity and intensity of slug decreases in the expanding section,the slug dissipates quickly in the downward inclined or helical section.The simulation result shows that the helical inlet pipe which has angle of 27 degree,expanding diameter ratio of 30-50 and pipe length of 1.6m has better liquid slug dissipation efficiency.The flow field of the cylindrical body is a three-dimensional turbulent flow field which is approximately axisymmetric.The tangential velocity is divided into two layers.One is the inner vortex region,where the tangential velocity increases rapidly with the increase of radius;the other is outer vortex region,where the tangential velocity decreases with the increase of radius.The axial velocity is upward in the center while it changes to be downward in the out.The radial velocity is smaller than the tangential velocity and axial velocity.The distribution law of static pressure and total pressure is higher near the wall and lower in the center.The inlet pipe of caisson gas-liquid subsea separator includes three sections: the horizontal section,riser section and helical section.The riser section includes expanding section,besides,the degree of helical section is 27.A cylindrical body with a tangential inlet is used as the cylinder body of the cyclone.A caisson which has a long length to storage the liquid after separation is installed at the end of the cylinder body.The caisson-electric submersible pump system and data acquisition system are used to control the liquid level in the caisson of the cyclone precisely.The separation performance research is studied by the indoor test on the basis of separator prototype.The increase of gas-liquid flow will make the distance of slug dissipation become longer.Besides,the swirl intensity and liquid film height in the cylinder section increase.The increase of pressure loss and liquid carry-over slowly prove that the separator has good stability and separation efficiency.The liquid level in the separator fluctuates with the sine wave.When the scale factor P is equal to 0.1,the effect of liquid level control is better.