Modeling Two-Phase Intermittent/Annular Flow Pattern Transition in High Liquid Viscosity Upward Vertical Wells

Abstract

Two-phase flow pattern prediction is required for accurate prediction of liquid holdup and pressure gradient in upward vertical wells. Recent studies of flow pattern models evaluation in high liquid viscosity two-phase in vertical pipe upward flow revealed (Al-Safran et al., 2020) discrepancies in all transition boundaries, including the intermittent (IN)/annular (AN) transition. This study aims to investigate the effect of liquid viscosity to improve Taitel et al. (1980) and Barnea (1987) IN/AN flow pattern transition models predictions. Taitel et al. liquid droplet fallback model is modified by incorporating liquid viscosity effect in the critical Weber number to predict droplet terminal velocity. In addition, this work eliminates the assumption of negligible annular film thickness (due to high viscosity liquid) in predicting the critical gas velocity to transport liquid drop upward, i.e. transition to intermittent flow. Sensitivity analysis revealed that the interfacial friction factor (fi) and liquid entrainment (fE) closure relationships are crucial in Barnea (1987) film bridging and film instability IN/AN transition models. Therefore, a comprehensive evaluation of fi and fE correlations and their combinations revealed that the combination of Pan and Hanratty (2002) fE correlation and Ishii and Grolmes (1975) fi correlation is the best, i.e. produces least prediction error, for wide range of liquid viscosity. A validation study against large experimental database of high liquid viscosity (4 mPa.s to 1600 mPa.s) flow pattern showed high prediction efficiency for the improved Taitel et al. and Barnea IN/AN transition models.