An Entrained-Droplet Model for Prediction of Minimum Flow Rate for the Continuous Removal of Liquids From Gas Wells

Abstract

Summary Experimental studies show that liquid drop is deformed from initial spherical shape into ellipsoid shape in annular-mist flow, and the available critical Weber number WeCrit determined by the experiment can vary from 2.2 to 60 for low-viscosity liquid. On the basis of the force equilibrium and the critical-Weber-number-calculation method proposed by Azzopardi (1985), this paper develops a new model to predict minimum gas rate. This model introduces a parameter Ck,Wecrit that describes the effect of liquid-drop deformation and the maximum drop-size difference on the minimum gas rate. The effect of liquid-droplet coalescence is also considered indirectly. A function to predict drop-deformation magnitude for different critical Weber numbers is developed on the basis of energy conservation. The function-prediction results are in good agreement with experimental data from the literature and the predicted result from the drop deformation/breakup model, and the average absolute deviation is 6.1%. The Ck,Wecrit calculated by the new model increases with the increase of the pressure and liquid amount and it varies from 3.99 to 7.3, which means the critical gas velocity increases with the increase of the pressure and liquid amount. Numerous gas-well data were used for the validation of these entrained models, including data from 33 low-pressure gas wells (wellhead pressure: 0.26–3.41 MPa) from Coleman et al. (1991) and 91 high-pressure gas wells (wellhead pressure: 0.7–56 MPa) from Turner et al. (1969). The result shows the new entrained model has a good comprehensive performance in judging liquid-loading status in both high- and low-pressure gas wells.