Numerical Simulation And Measurement Of Multiphase Flow In Pipes During Oil And Gas Production

Currently,most oilfields are produced with high water cut and oil-gas-water gathering and transportation have became the first choice for crude oil transportation due to their low cost.The technology of oil-gas-water three-phase metering in the gathering and transportation process is a key research topic in petroleum industry.In this paper,a new type of oil-gas-water three-phase flowmeter is designed to measure the inflow of oil wells online.The main structure of the three-phase flowmeter includes a gas-liquid separator and an oil-water mixer.The gas-phase flowmeter is installed in the outlet of the gas-liquid separator to obtain the gas-phase flow.The liquid-phase flowmeter to installed in the bottom of the separator following the mixer to obtain the liquid-phase flow.The water content is obtained by microwave measurment.Therefore,the respective flow rates of oil and water can be obtained.In this paper,the columnar gas-liquid separator is used as the primary separation structure.Due to the limitation of the size of the columnar gas-liquid separator,in order to meet the gas-liquid inflow under larger working conditions,the exhaust pipe after the primary separation is designed with a guide.The leaf-type gas-liquid separation device is used as a secondary separation,and a core tube is added at the primary separation as a flow stabilizer to deal with intermittent flow,and a SK static mixer is installed in the discharge pipe to enhance the oil-water mixing effect.The parameters of the guide vane gas-liquid separator such as the diameter of the guide vane,the pitch of the guide vane,the inner diameter and other parameters are optimized by numerical simulation,and the pressure drop and separation efficiency are used as the evaluation criteria of the separator.The pitch of the flow vane is 150mm and the inner diameter is 25mm,which is the optimal size for secondary separation.The internal flow field characteristics,pressure drop characteristics and separation efficiency of the two-stage gas-liquid separator are qualitatively evaluated,The research results show that the pressure drop ratio of the primary separation is 11-12 times that of the secondary separation,indicating that the reason affecting the performance of the gas phase separation occurs at the primary separation.the secondary separation can improve the separation efficiency of droplets of each particle size by about 0～40%,which greatly improves the upper limit of the liquid phase separation efficiency.The structure of the SK static mixer is optimized by using the Mixture model.Based on the evaluation of pressure drop and mixing effect,the number of mixing elements is 4 and the length-diameter ratio is 1,and the mixing effect of the SK static mixer with the selected structure is analyzed.It shows that the structure meets the requirements of oil-water mixing,and the mixing effect and experimental consistency are better when the water content is low.Based on the above proposed metering structure,the applicability of the oil-gas-water three-phase metering device was experimentally studied.The research results show that when the flow rate is 9m~3/h,there is a certain amount of gas in the discharge pipe.The critical flow rate for complete liquid phase separation is about 4.5m~3/h.Under the condition that the liquid flow rate is 0-2m~3/h,when the gas phase flow rate is greater than10m~3/h,the discharge pipe starts to blow-by gas;under the condition that the liquid phase flow rate is 2-4m~3/h,the gas phase flow rate is 15m~3/h,The gas blow-by starts at/h;the moisture content measured by the microwave sensor is close to the real value,but the error is larger when the water content is low,less than 10%,and the error is less than 4%when the water content is high,and the overall water content measurement error meet the measurement requirements.