UPWARD VERTICAL TWO-PHASE FLOW THROUGH AN ANNULUS (PATTERN, GRADIENT, FRICTION)

Upward gas-liquid flow through vertical concentric and fully eccentric annuli was studied both experimentally and theoretically.;A comprehensive experimental investigation was conducted for both concentric and fully eccentric annuli configurations using air-water and air-kerosene. Included were definition and classification of the flow patterns. Transition boundaries between the existing flow patterns were determined and presented on flow patterns maps. Measurements of volumetric average liquid holdup and average total pressure gradient were made for each flow pattern for a wide range of flow conditions. Additional data include single-phase friction factor values and Taylor bubble rise velocities in a stagnant liquid column.;Data analysis revealed that application of the hydraulic diameter concept for annulus configurations is not always adequate, especially at low Reynolds number flow conditions. A more rigorous approach was thus required for accurate prediction of the flow behavior, especially for two-phase flow.;The model developed by Taitel et al.('49) for flow pattern prediction in upward vertical pipe flow has been modified to predict flow patterns in an annuli. Mechanistic models have been developed for each of the existing flow patterns, namely bubble flow, dispersed bubble flow, slug flow and annular flow. These models are based on two-phase flow physical phenomena and incorporate annulus characteristics such as casing and tubing diameters and degree of eccentricity. The models also apply new predictive means for friction factor and bubble rise velocity. Given a set of flow conditions, the models are capable of predicting the flow behavior, including the average volumetric liquid holdup and the average total pressure gradient for the existing flow pattern. In general, good agreement was observed between the experimental data and model predictions.;A flow system was designed and constructed. The system consists of a 16 m (52.5 ft) long vertical annulus with 76.2 mm (3 in.) inside diameter casing and 42.2 mm (1.66 in.) outside diameter tubing. The system was capable of operating under both single-phase and two-phase flow conditions.;The models are integrated into a computer program that uses black-oil PVT properties. The program can be used to predict flow pattern, liquid holdup and pressure traverses in a vertical wellbore annulus.