Hydraulic model of steady state multiphase flow in wellbore annuli

Based on the classification and flow behaviors of two phase flow in wellbore annuli, the hydraulic models for slug flow and annular flow in annuli for vertical or inclined wells were established, and the flow regime transition criteria were also obtained. Based on the flow behavior research of multiphase flow in wellbore annuli, the liquid film zone was used as the control volume, and the effect of the tubing liquid film, casing liquid film and the droplets in gas core area on the mass and momentum transfers were considered. The mass and momentum conservation equations of slug and annular flows were obtained. Then the evaluation criterion of flow pattern transitions were established, including dispersed flow to slug flow, bubble flow to slug flow and slug flow to annular flow. The model prediction results were compared under the experimental conditions from the previous literatures. The predictions of flow pattern, liquid holdup and pressure gradient were compared between the new model and the pipe flow model modified by using the hydraulic diameter. The results show that the flow pattern, liquid holdup and pressure gradient can be predicted by the new model more accurately, and the prediction of liquid holdup and pressure gradient are better.