| Mixed flow electric submersible pump(ESP)has the advantages of large displacement and high efficiency,which is widely used in deep well oil extraction.However,the internal degassing of the oil layer causes the generation of free gas in the oil well,so the problem of gas mixed in the incoming flow when the electric submersible pump is working will be appear.Since the addition of gas phase changes the internal flow field distribution of the electric submersible pump,its performance deteriorates with the increase of the inlet gas volume fraction.When the inlet gas volume fraction reaches a certain level,the electric submersible pump will not be able to discharge liquid and present idling working state,which poses a potential threat to oil wells.So studying the gas-liquid two-phase flow of electric submersible pumps and optimizing the design is an urgent problem to be solved.This paper takes a five-stage mixed-flow electric submersible pump as the research object.Through theoretical analysis,experimental research,and numerical calculation,the internal flow characteristics of the electric submersible pump in pure water and gas-liquid two-phase conditions are deeply studied.This study obtained the change law of external characteristics and reasons for performance deterioration under different inlet gas volume fractions,and optimized the design of geometric parameters.The main research contents and innovative results are as follows:(1)Through in-depth analysis of the development history of electric submersible pumps,the research of gas-liquid two-phase flow in the pump,and the current research status of pump optimization design methods domestic and foreign,it is believed that the mixed-flow electric submersible pump is the research focus of the current submersible pump system.Numerical simulation methods are the key points of current gas-liquid two-phase flow research,and the Musig model can better reflect the changes in gas-liquid two-phase flow status.Orthogonal experiment is an effective method for optimal design of multistage pumps.(2)Taking the efficiency of the mixed-flow electric submersible pump as the optimization goal,based on the speed coefficient method,the geometric parameters of the electric submersible pump is initially determined,and the surface response method suitable for the optimal design of the mixed-flow electric submersible pump is proposed.The inlet placement angle of shroud streamline,middle streamline and hub streamline and outlet placement angle of the blade are optimal designed variables.The mixed-flow electric submersible pump is optimized under pure water conditions.After the optimized design,the efficiency of the single-stage electric submersible pump is increased by 5.09%,the efficiency of the five-stage electric submersible pump increased by 4.85%.(3)The multi-stage pump gas-liquid two-phase flow experiment platform was built,and the external characteristic curve under pure water conditions and different inlet gas volume fraction when rotational speed is 1475 r/min and the liquid volume flow is 7.5m~3/h was carried out.The research results show that the flow-head characteristic curve of the electric submersible pump has a high degree of similarity at different rotational speeds.The operating flow range of the electric submersible pump gradually decreases with the decrease of the rotational speed,and the optimal working condition point at each rotational speed shifts to smaller flow working condition with the decrease of rotational speed.During the gas-containing performance experiment,the pump performance drops sharply after the inlet gas volume fraction is greater than 5%.When the inlet gas volume fraction exceeds 9%,the entire system can still operate normally,but it is particularly unstable.(4)The numerical calculation method for gas-liquid two-phase flow based on Euler-Euler two-fluid model and Musig multi-component model is established,and the numerical calculation of electric submersible pumps under different inlet gas volume fractions is carried out.The research results show that the Musig multi-component model can predict the performance changes of electric submersible pumps more accurately under different inlet gas volume fractions.With the gradual increase of the inlet gas volume fraction,the bubble accumulation phenomenon appear in first stage impeller flow-path,and the bubbles mainly gather in the area near the middle and rear section of the impeller hub,the bubble accumulation area gradually moves to the vicinity of the shroud·of the impeller along with the flow-path of the electric submersible pump.(5)Based on the Musig multi-component gas-liquid two-phase flow model,the submersible pump under multiple inlet gas volume fractions are numerally calculated and the internal flow field changes are analyzed.When the inlet gas volume fraction is 5%,obvious gas-liquid separation occurs in the first stage impeller.At this inlet gas volume fraction,the two-phase flow pattern in the primary and secondary impellers is cavitation flow,and the performance of the electric submersible pump decrease significantly,from the primary impeller to the fifth stage(final stage)Impeller,the intensity of pressure fluctuation gradually increases.(6)When inlet gas volume fraction is 5%and the liquid phase volume flow rate is 7.5 m~3/h,an orthogonal table with 7 factors and 3 levels is used to optimize the design of the mixed-flow electric submersible pump.The research results show that the blade outlet placement angle is the key factor that affects the mixed flow electric submersible pump under gas-containing conditions and the middle streamline outlet placement angle has the strongest influence.After optimization,the efficiency of the mixed flow pump is increased by 2.52%,and the head is increased by 0.15m. |
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