Design And Numerical Simulation Of Downhole Enhanced Capture Gas-liquid Separator

At the end of oilfield exploitation,injection-flooding has become the main means of oilfield exploitation.Injection-production in the same well greatly saves the cost of exploitation,but it puts forward new requirements for downhole multiphase separation.Among them,downhole gas-liquid separation is one of the important research directions of oil well exploitation.In the process of exhaust and liquid-holding exploitation,it is necessary to reduce the gas content in the liquid phase to ensure the normal operation of the submersible pump underground.At present,gas-liquid cyclone and vortex separator separation is one of the most commonly used gas-liquid separation methods.This method can separate gas-liquid two-phase with gas content below 60% at high speed,but when the gas content exceeds this value,the separation efficiency will be greatly reduced.Gas anchor separator can efficiently separate gas-liquid two-phase under high gas content,but it requires strict inlet velocity and is not suitable for use under high flow conditions.Therefore,the existing downhole gas-liquid separator still has certain limitations.In this paper,the main difficulties of gas-liquid separation of underground atmospheric liquid ratio are analyzed in depth.Based on the three methods of droplet capture,centrifugation and sedimentation,an enhanced capture gas-liquid separator with multi-stage disc group was designed.According to the actual downhole conditions,the initial structure was designed.Secondly,through the simulation of the separator with different disc structures,the main structural parameters affecting the flow field and efficiency of the separator are determined,and the structure is improved.Finally,the influence of different operating parameters on the separation effect of the separator was studied,and the setting range and method of the operating parameters of the separator were established.The verification shows that the separator can efficiently separate the gas-liquid two phases in different ranges of gas-liquid ratios.The research contents of this paper include :(1)Through the analysis of the difficulties of downhole gas-liquid separation,combined with the actual size and connection requirements of the downhole,a gas-liquid separator with a multistage disc structure was designed.The separator completed the gas-liquid two-phase separation of the downhole high gas-bearing fluid through the coalescence and capture of free droplets by discs and centrifugal sedimentation collection,and the processing materials of the separator were preliminarily selected.(2)The fluid domain of the enhanced capture gas-liquid separator is meshed,and a high-quality mesh suitable for the separator is established.The physical models are compared and analyzed.According to the flow field characteristics of the gas-liquid separator,the physical model in Starccm+ is selected.The simulation of the initial model of the separator is carried out,which preliminarily verifies that the separator has the ability of gas-liquid separation,and the ability of the disc to capture and intercept droplets is good,which is in line with the design concept.(3)Through computational fluid dynamics simulation,the influence of various structural parameters on the flow field of the separator is studied,and the optimal value of each structural parameter is selected.The angle of the disc is 30°,the spacing of the disc is 25 mm,the diameter of the disc is 70 mm,and the outer diameter of the center hole of the disc is 30 mm as the final structural parameter of the separator.(4)The influence of operating parameters on the flow field of the separator was studied,and the adaptability of the separator under different gas-liquid ratio conditions was studied.The formula of split ratio setting based on the inlet gas-liquid ratio is obtained.By using this formula,the stable and sufficient liquid discharge at the liquid outlet can be maintained while ensuring the high separation efficiency of the separator.It is verified that the separator can be separated efficiently in a large gasliquid ratio range,and the practicability of the split ratio calculation formula is verified.In this paper,by combining the actual working conditions and using the computational fluid dynamics method,the downhole gas-liquid separator with this new structure is designed and studied,and the influence of various structural parameters and operating parameters on the flow field of the separator is studied,which provides a new idea for downhole gas-liquid two-phase separation.