Numerical Simulation Research On Downhole Oil-water Separator With Rod Reciprocating Pump

With the development of oil field into the middle and late stages,the oil production has gradually entered the high water cut stage.In addition to ennegy consumption of lifting most water,the produced high water-cut crude oil requires a lot of manpower and resources to achieve the oil-water separation.The sewage needs purifying and injecting,which can also pollute the environment.Downhole oil-water separation technology can achieve the production and injection in the same well to solve the above problems.At present,there are many kinds of downhole oil-water separator,this paper mainly studies the numerical simulation of hydrocyclone.Now oil fields most use beam pumping unit for oil production and the sucker rod pump is used to lift crude oil.When the hydrocyclone is used to separate oil and water in this system,the key problem is that the inlet of the cyclone is intermittent.This paper uses the custom function in Fluent—UDF function—to write program and set the inlet boundary condition,which solves the difficulty.Writing UDF function needs to determine the variation of inlet flow.According to the motion law of horsehead and underground structure and operation mode,the motion law of rod pump plunger driven by sucker rod is transferred to the variation of cyclone inlet flow.This paper uses the single stage double cone hydrocyclone to establish the geometric model and the grid in Gambit.Then it carries out the mesh independent analysis.The turbulence model is LES model in Fluent.This paper also sets the boundary conditions and determines the numerical algorithm.When the inlet flow of hydrocyclone is intermittent liquid,the inlet flow is zero within a certain time interval.Compared with the steady inlet flow of cyclone under the electric submersible pump and screw pump,the intermittent inlet flow is similar to an extreme situation.Currently there is less numerical simulation research in this regard.In this paper,before studying the performance of the hydrocyclone in this situation,the first step is to study the fluctuating inlet flow of cyclone,which is to analyze the influence on the separation performance of the hydrocyclone by changing the steady inlet flow into fluctuating inlet flow.The fluctuation law of inlet flow is decomposed into the variation law of fluctuation frequency and amplitude.With the change of frequency and amplitude,the separation performance and the internal flow field of hydrocyclone are changed.Based on the numerical simulation,the relationship is determined between the separation performance,the variation of the pressure drop and the characteristics of the internal flow field in the hydrocyclone and the fluctuation frequency and amplitude.Secondly,the inlet is set as intermittent flow and the variation law of hydrocyclone separation performance and internal flow field is analyzed.The influence of structural parameters on the separation performance is studied and the structural parameters were optimized by orthogonal experiment.The influence of production parameters and operating parameters on the separation performance is analyzed and it selects the appropriate parameter values.In view of the intermittent inlet flow,not stable separation field in the cyclone and poor separation effect,the inner tube of the cyclone is designed to restrain the short circuit flow and improve the separation efficiency.