Study on double differential pressure measurement method of gas-liquid two-phase flow in high gas content wells

Abstract

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. For dynamically monitor the liquid and gas production from a single well, there is an urgent need for a low-cost, small-volume online metering device for wet gas flows through a single well. Aiming at the problem, this paper designs a wet gas flow measurement device for a long-throated Venturi tube based on the double differential pressure method. By combining experiments and numerical simulations, a matching flow calculation model was developed. Based on the experimental data of NEL's 6-inch standard Venturi tube wet gas over-reading, the numerical simulation method is used to carry out the research of high-pressure wet gas measurement under the pressure condition of 2, 4 and 6 MPa. The simulation results of two multiphase flow models, DPM and Euler, are compared with the experimental values of NEL. The results show that the maximum relative error is less than 10%, and the Euler model is more suitable for the numerical simulation of high-pressure wet gas. According to the actual production from the gas well, a long-throated Venturi tube with a throttling ratio of 0.5 and a diameter of DN50 was designed, and a numerical simulation study of wet gas under a pressure of 2, 3 and 4 MPa was carried out. Numerical simulation results show that the change laws of over-reading and liquid-gas mass ratios of high-pressure wet gas are consistent with those of low-pressure wet gas. The numerical simulation results are used to correct the flow calculation model of low-pressure wet gas, and a flow calculation model suitable for high-pressure wet gas in gas wells is obtained. The gas flow prediction accuracy of the flow calculation model was lower than ±3%, and the liquid flow prediction value was lower than ±10%. Compared with other measurement methods without separation of wet gas, the long-throated Venturi tube based on the double differential pressure method has a simple structure and low measurement cost. By further optimizing and expanding the measurement model, after improving the accuracy, it can be installed in the wellhead pipeline to monitor the oil and gas production from a single well in real time. This can provide support for gas reservoir exploitation decisions.