Objective  The aim is to solve the technical problem that the gas and liquid produced by a single well cannot be measured accurately in the low permeability gas field with series between wells and mixed wellhead metering mode.

Methods  Based on the single-phase metering principle of the precession vortex flowmeter and V-cone flowmeter, the miscible metering error of the single-phase flowmeter was analyzed under different operating pressures, gas-liquid ratio and apparent gas velocity through the indoor experiment of air-water two-phase flow. Through the application of dimensional analysis, the correlation formulas of precession frequency and pressure drop, as well as relevant dimensionless number were established, respectively. In addition, the parameters under miscible conditions were modified utilizing laboratory experimental data. A two-parameter combined measurement model of moisture gas suitable for low liquid content was proposed by combining two flowmeters in series. The accuracy of the model was verified by using the real flow data of Yan′an gas field.

Results  The results showed that in laboratory experiments, when the liquid volume fraction of wet gas was less than 1%, the precession frequency of the precession vortex decreased with the increase of the liquid volume fraction, resulting in an "underread"phenomenon. In contrast, the V-cone flowmeter's metering pressure drop increased with the volume fraction of liquid, resulting in an "overread" phenomenon. When the liquid volume fraction of the V-cone flowmeter was greater than 1%, the liquid content of the gas phase was too large. As a result, the decline law of the vortex precession signal was not clear, and the results of the combined metering model may be distorted. The field real flow test results showed that the average relative error of the gas phase volume flow of the combined metering model was 2.029%, the average relative error of the liquid phase volume flow was 15.066%, and the average absolute error of the volume liquid content was 0.059%.

Conclusions  The combined measurement model of precession vortex and V-cone flowmeter is used when the liquid content of gas phase is low, the measurement accuracy of the gas phase and liquid phase can meet the needs of on-site production, and the processing design cost is low, which can provide technical support for the gas-liquid mismixing measurement of drainage gas production wells in Yan′an gas field.