Study On Double Differential Pressure Measurement Method Of Gas-liquid Two-phase Flow In High Content Gas Wells

The production of natural gas wells contains natural gas and a small amount of liquid,which is a wet gas composed of oil,gas and water.In order to dynamically monitor the liquid and gas production of a single well,there is an urgent need for a low-cost,smallvolume online metering device for wet gas flow in a single well.To solve this problem,this paper designs a wet gas flow measurement device for a long Venturi based on the double differential pressure method,and develops a supporting flow calculation model by combining experiment and numerical simulation.Firstly,with reference to the Venturi design standard,the long throat Venturi with three pressure taps with throttling ratio of 0.5 and diameter of DN20 is designed independently.Set up a supporting wet gas metering experimental platform to carry out the differential pressure measurement experiment of wet gas flowing through the long throat Venturi under different pressure conditions of 0.1 ～ 0.3 MPa.The experimental results show that the over-reading,liquid gas mass ratio and differential pressure ratio have a good numerical correspondence when measuring wet gas with a long throat Venturi,and the correspondence is affected by the Froude number of gas phase.According to this relationship,using the experimental data of low-pressure wet gas,a set of low-pressure wet gas flow calculation model based on double differential pressure method is established.Secondly,based on the experimental data of measuring the over-reading characteristics of wet gas with NEL’s 6-inch standard Venturi,the numerical simulation method is used to carry out the simulation research of high-pressure wet gas measurement under the pressure conditions of 2 ～ 6 MPa.Comparing the simulation results of DPM and Euler multiphase flow models with NEL experimental values,the maximum relative error is less than 10%,and the maximum relative error and root mean square error of Euler model are lower than DPM model.It is concluded that Euler model is more suitable for numerical simulation of high-pressure wet gas.Furthermore,according to the actual production of the gas well,the long throat Venturi with three pressure taps with throttling ratio of 0.5 and diameter of DN50 is designed,and the numerical simulation of wet gas under the pressure of 2 ～ 4 MPa is carried out.The numerical simulation results show that the variation law of high-pressure wet gas over-reading and liquid gas mass ratio is consistent with low-pressure wet gas.The numerical simulation results are used to modify the low-pressure wet gas flow calculation model to obtain the flow calculation model suitable for high-pressure wet gas in gas wells.The high-pressure wet gas calculation model is verified by using 30 groups of high-pressure wet gas working condition simulation data of gas wells.The calculation error of gas phase flow is less than 3% and that of liquid phase flow is less than 10%.Compared with other measurement methods without wet gas separation,the long throat Venturi based on double differential pressure method has simple structure and low measurement cost.After further optimizing and expanding the measurement model and improving the accuracy,it can be installed in the wellhead pipeline to monitor the oil and gas production of a single well in real time,so as to provide support for gas reservoir production decision-making.