Abstract: Accurately predicting the liquid-loading timing in gas wells and taking reasonable corresponding deliquification technologies in advance can effectively reduce the risk of liquid loading. Existing liquid-loading prediction models lack comparative analysis with liquid-loading features in gas wells, resulting in poor adaptability. Therefore, visual experimental tests were carried out to study the flowing behavior of liquid film at different gas velocities, a new criterion of liquid-loading initiation was defined subsequently. Based on the force balance of liquid film, an analytical model of critical gas velocity for liquid loading was established. And the following research results were obtained. First, the liquid does not accumulate at the bottom of the pipe when the liquid film reverses and travels upward as instead liquid waves. The more serious the liquid film reversal is, the more obvious the fluctuation is. Second, when the liquid film reverses, the flow is relatively stable in the pipe, which is not consistent with the features of liquid loading in gas wells, leading to the prediction of critical gas velocity in liquid-reversal criterion too conservative. Third, it captures the liquid-loading dynamics in gas wells when liquid-loading criterion is defined as the equal liquid flow rate of upward and downward in the laminar liquid film. Fourth, the new model has a good changing trend with the liquid-film model at different affecting parameters, and its prediction accuracy is the highest against the published well data in the literature. In conclusion, the new model can be used to judge liquid loading in gas wells.

Key words: liquid loading, Turner model, liquid-film model, visual experiment, critical gas velocity for liquid loading