A simple analytical model to predict liquid unloading in the horizontal gas well

An accurate prediction of the critical gas velocity for the liquid loading is of great importance for operators to select the tubing diameter for the newly drilled gas wells, or to optimize the production rate for production wells. It is clear from previous experimental studies of the liquid entrainment rate in the gas core that the liquid is mainly carried in the form of film under the critical condition of the liquid loading onset. It is more reasonable to establish a mathematical model based on the film reversal rather than based on the droplet reversal. In our previous paper entitled “Prediction of the critical gas velocity of liquid unloading in the horizontal gas well”, a new analytical model was established based on the force balance between the gas-liquid interfacial friction force and the bottom film gravity, but the model is not very convenient to use because of the complexity of calculating the average film thickness. In the present study, a new method is proposed to calculate the average film thickness from the bubble drift velocity in the mixture, so the new analytical model becomes much easier to use. The new analytical model is evaluated against 103 sets of experimental data, the data in 124 vertical gas wells and one horizontal gas well. Meanwhile, the effect of the liquid loading on the production of the horizontal gas well is also analyzed.