| As the second rod artificial lift method,electric submersible pump has a wide range of applications and occasions,but it is not suitable for high gas Wells,especially centrifugal electric submersible pump,which can only pump gas-liquid two-phase mixture with gas content less than 10%.When the electric submersible pump transmits gas-liquid two-phase flow,the gas accumulation phenomenon will occur in the impeller passage,and the pump efficiency will decrease.When the gas ratio of the conveying fluid is high,the gas lock will occur,resulting in the normal operation of the electric submersible pump.In recent years,researchers have begun to see a new type of gap drainage impeller,which can significantly enhance the stability of liquid production with high gas-liquid ratio.This paper tries to apply the special impeller in the submersible centrifugal pump,in order to realize the transportation of gas-liquid mixture and liquid production under the condition of high gas content,optimize the structure of the submersible pump under the condition of high gas content,and analyze the transient flow performance of the submersible pump under this condition.Taking Q10 type electric submersible pump as the research object,based on the computational fluid dynamics theory,refer to the basic principle of centrifugal pump work,the modification of electric submersible pump impeller structure,using three-dimensional modeling software to establish slitting blades of the electric submersible pump fluid domain model,using ICEM mesh,two-phase flow mechanics model is determined,according to the actual working condition of the given boundary conditions and initial conditions.The single-phase flow and gas-liquid two-phase flow in electric submersible pump was simulated by using fluid simulation software CFX.The effectiveness of simulation results is verified by comparing with experimental results of ESP.Then,under the condition of 30% gas content and standard flow rate,five factors affecting the two-phase flow performance of submersible electric pump are simulated,including slot position,slot width,slot deflection Angle,slot depth and slot number.The influence of different structural parameters on the internal flow field and external characteristics of submersible electric pump is analyzed.Pressure field,gas phase distribution,streamline and velocity field are used to show the variation law of internal flow field,and head,power and efficiency are used to show the variation law of external characteristics.On this basis,the method combining orthogonal experimental design and CFD technology is used to optimize the blade slit parameters,and the transient analysis is made to reveal the mechanism of the influence of the gap on the performance of the submersible centrifugal pump.The simulation results show that:(1)Under the same working conditions of gas content,there is obvious gas accumulation phenomenon with high gas content in the impeller flow channel of Q10 ESP,while the gas distribution in the impeller of the slotted vane ESP is relatively uniform.The existence of the slits has an impact on the gas phase accumulation zone,homogenized the distribution of the gas phase in the liquid phase to a certain extent,and improved the mixing degree of the gas and liquid phases.There will be no serious gas-liquid separation and gas accumulation in the flow channel.(2)Different slit structures have different effects on the performance of the ESP.When the slit positions are different,the distribution of the pressure field is roughly the same.The larger the radius of the slit position,the larger the area of the low pressure area.With the increase of the radius of the slot position,the gas-phase accumulation area on the back of blade(1)increases,and the gas-phase accumulation area on the back of blade(2)decreases.The maximum fluid velocity at different slit positions is different,and the fluid velocity at the same position of the flow channel is different.When the slit width is different,the pressure distribution is similar,the slit width increases,the area of the high gas-containing area on the back of the blade(2)decreases,the maximum gas phase volume fraction decreases,and the area of the triangular wake area on the back of the blade(2)decreases.The numerical value of the gas phase volume fraction decreases.The area of the vortex area decreases with the increase of the slit width,but when the slit width is too large,the inflowing gas has a great influence on the main flow direction.When the deflection angle of the slit is different,the distribution of pressure on both sides of the slit is related to the positive and negative of the deflection angle.When the deflection angle is negative and positive,the distribution of high pressure and low pressure is opposite.The area of the local high pressure area of the blade head decreases with the increase of the value of the deflection angle of the slot.When the deflection angle is negative,it has little effect on the gas phase accumulation area in the flow channel,and a small part of the fluid will enter the adjacent flow channel through the slit,and the return area is basically unchanged;when the deflection angle is positive,the high gas content area The area decreases as the angle increases,more fluid enters the adjacent flow channel,and the return area decreases as the angle increases.When the depth of the slit is different,the distribution of the pressure field at the middle position when the depth is 0.25 is different from other positions.When the depth of the slit is 0.25,the gas phase gathers in the flow channel at the middle position,and a large-scale triangular gas phase gathering area is formed on the back of the blade.There is a large area of recirculation in the runner.When the slot depth is from 0.5 to 1,with the increase of slot depth,the area of high gas-containing area on the back of blade(1)and blade(2)decreases,the volume fraction of gas phase at the same position decreases,and the recirculation area decreases.When the number of slits is different,the value of the pressure field at the same position in the flow channel decreases with the increase of the number of slits,the area of the high gas content area decreases,and the area of the vortex decreases accordingly.As the number of slits increases,the fluid velocity in the vicinity of the slit area increases to a certain extent,and the area of the recirculation zone decreases.(3)The results of the orthogonal test found that the primary and secondary sequences affecting the lift and efficiency are: slit deflection angle > slit width > slit position > slit depth;The primary and secondary order that affects the volume ratio of the high gas content area is: slit deflection angle > slit depth > slit width > slit position.The optimal design slitting parameters are: slit(1)at a radius of 29 mm,a width of 2mm,a deflection angle of 60°,and a relative depth of 0.75;The slit(2)is at a radius of 24 mm,a width of 1mm,a corner of 60°,and a relative depth of 0.75.The internal flow field characteristics of the slotted vane ESP and the prototype pump were compared and analyzed.At the same position,the pressure value of the slotted blade is lower than that of the prototype pump,the pressure gradient distribution is more uniform,and the volume fraction of the gas phase is much lower than that of the prototype pump,and the slot has a crushing effect on the gas phase accumulation.The slits have a certain impact on the vortex in the flow channel,effectively reducing the accumulation and retention of gas in the flow channel.The cross-sectional area of the flow channel increases,the flow loss is reduced,and the area of the backflow and the secondary circulation in the flow channel is effectively reduced.The velocity of the fluid is significantly higher than that of the prototype pump,and the vane load is reduced overall.In this paper,the sensitivity analysis of the key blade structural parameters affecting the performance of the electric submersible pump is carried out,which provides a reference for the rational design of the slitting factors.A new type of slotted vane fixed electric submersible pump is designed,and a vane orthogonal experimental design method is proposed to improve the mixed-transport performance of the electric submersible pump under high gas content conditions. |
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