A Study of Flow-Pattern Transitions in High-Viscosity Oil-and-Gas Two-Phase Flow in Horizontal Pipes

Abstract

Summary Two-phase flow pattern is an important parameter for predicting pressure gradient and liquid holdup in mechanistic models, both of which are required to design and operate hydrocarbon production and transportation systems. Existing two-phase-flow mechanistic models have shown various degrees of discrepancy in predicting flow pattern and their transitions for immiscible laboratory-scale flows of gas and high-viscosity Newtonian liquids (mineral oil) caused by the additional complexity that a high liquid viscosity introduces to the two-phase flow behavior. The objective of this study is to improve the high-viscosity oil flow-pattern transition modeling in horizontal pipes for the stratified-smooth (SS)/stratified-wavy (SW) and intermittent/annular transitions. These two transitions were improved by introducing a liquid viscosity-dependent sheltering coefficient model, and a new high-viscosity liquid-level criterion, respectively. An additional objective is to investigate the existing inviscid Kelvin-Helmholtz (IKH), viscous Kelvin-Helmholtz (VKH), and Taitel and Dukler models for the stratified/nonstratified (S–NS) transition, and provide insights on their applications for high-viscosity oil-flow patterns. A validation study of the proposed transition models is carried out with four laboratory-scale two-phase gas/oil flow-pattern experimental data sets covering a wide range of oil viscosities. The validation study revealed that the proposed SS/SW, and intermittent/annular transition models predicted the considered high-viscosity, horizontal flow-pattern data with more accuracy than the Taitel and Dukler and Barnea VKH S/NS models. Furthermore, the validation and comparison of IKH, VKH, and Taitel and Dukler S/NS models show that the IKH model is the simplest one that sufficiently predicts stratified flow for high-viscosity oil, especially for liquid viscosity above 100 mPa·s.