Research On The Separation Performance And Structure Optimization Of The Downhole Gas-liquid Separator

The electric submersible pump unit has been widely applied for its advantages of large displacement,high lift,smooth operation,long working life of the unit and simple process on the ground.The core component of the rotary gas-liquid separator is a downhole gas-liquid separation tool,which is mainly composed of a spiral induction wheel,a transition wheel and a straight impeller.With the deep exploration of major oil fields,along with the gradual depletion of formation energy,with the reduction of formation pressure in each block,the oil layer is degassed,and the well fluid contains a large amount of free gas.Before the well fluid enters the submersible electric pump,it firstly pressurizes through the spiral inducer and then carries out gas-liquid separation through the straight impeller to minimize the adverse effects of the gas on the performance of the submersible centrifugal pump and to avoid the phenomenon of cavitation and air lock.This requires a high separation efficiency of the rotary gas-liquid separator,and requires a significant boosting effect of the spiral inducer.Therefore,using the method of combining the theoretical analysis and numerical simulation,based on computational fluid dynamics,multiphase flow theory,in this paper,the internal flow field of the downhole gas-liquid separator was simulated and analyzed.The influence of different working parameters on the separation performance of the separator was studied.At the same time,the influence of spiral parameters of the spiral induction wheel on the separation performance of the separator was studied,and structural optimization of the spiral inducer.The results of this study can provide some theoretical guidance for the operation of rotary downhole gas-liquid separator.The main contents are as follows:(1)A two-fluid model was selected.Based on the continuity equation,the momentum equation and the energy equation,the RNG turbulence model was used for the liquid phase and the zero-equation turbulence model was used for the gas phase.In this paper,the finite volume method is used to analyze the internal flow field of the downhole gas-liquid separator by simulation.The separation performance of the separator was studied,followed by the simulation of the two-phase separation process,and the separation efficiency and pressure increase of the downhole gas-liquid separator were calculated.At the same time,the changing rules of separation efficiency and pressure increase value for different separators were studied,including different inlet velocity,inlet gas content,bubble size and rotating speed,and provided some theoretical guidance for on-site operation.(2)Using the single variable method,in accordance with the same operating parameters,this paper simulates and analyzes the spiral helix pitch,the spiral outer diameter,the number of spiral pitches,and the spiral thickness of the spiral induced wheel downhole gas-liquid separator at different speeds,and obtains separator efficiency and pressure increase value spiral induction wheel parameters change law.Through this step of research,lay the foundation for the optimization design of downhole gas-liquid separators.(3)The spiral inducing wheel is optimized based on the method of RSM surface response and numerical simulation.The objective function is optimized with the maximum separation efficiency and pressure increase value.The optimization mathematical model is designed with spiral helix pitch,helix diameter,helix number and helix thickness as design variables.By the regression analysis of the quadratic response surface of the separator separation efficiency and pressure increase value,the response surface model of the spiral induction wheel structure is obtained,and the optimal control parameters are further solved to obtain the optimization model of the spiral induction wheel.Finally,the optimized initial structure model of the model is compared and the effect is better.This study provides a reference for further study on the influence of flow field distribution and separation performance on the rotary downhole gas-liquid separator.Combined with the RSM surface response method,the helical induction wheel is optimally designed to improve the reference of the separator structure.