Abstract
Two-phase (gas–liquid) flow in vertical pipes has been one of the interests of industrial applications such as power plants, nuclear reactors, boilers, gas well exploration and so on. One of the problems usually encountered in the gas well exploration industries is liquid loading: a condition where the gas velocity is not high enough to carry all the liquid generated in the gas wells. During normal operation, flow in the gas wells shows characteristics of annular flow regime. However, as the gas wells mature, the gas velocities reduce (below a critical value) and gradually lead to the onset of liquid loading (film reversal). At this point, flow in the gas well presents features of churn flow. Thus, during the film reversal point, the liquid film tends to increase in thickness and part of it starts to flow downwards. This paper first summarizes the available mechanistic and numerical models related to liquid loading and then reviews the application of CFD techniques to liquid loading modeling in vertical pipes. Most of the methodologies discussed here focus on annular and churn flow due to the limited information on the application of CFD techniques to liquid loading modeling and the onset of film reversal occurs during the transition from annular flow to churn flow which can lead to liquid loading as observed experimentally by many researchers. It was concluded from the available literature related to liquid loading that a detailed understanding of the fluid flow behavior during liquid loading is not yet fully available and prediction methods of this phenomenon are still rather incipient. Directions for good CFD modeling of these important phenomena are presented in the present paper.
Highlights
Liquid loading in a wellbore of a gas well has been recognized as one of the most severe problems in gas production
Four main improvements are made in this model, namely, (1) it has a new term in its ε equation to improve the accuracy of simulating rapidly strained flows; (2) consideration is made for the effects of swirl and more accurate for swirl flow application; (3) unlike the standard k–ε model, where constant values of the turbulent Prandtl numbers are used, the RNG k–ε model utilizes an analytical formula; and (4) an analytically derived differential equation is provided for the effective viscosity that accounts for low-Reynolds number effects
This study focuses on the finite volume method (FVM) since this approach is mostly adopted in the multiphase flow applications
Summary
Liquid loading in a wellbore of a gas well has been recognized as one of the most severe problems in gas production. The main governing equations for the flow in the Eulerian Multi-Fluid VOF model are the independent momentum and mass conservation equations for the two phases involved (water and air) These are given as (FLUENT ANSYS 2012). Four main improvements are made in this model, namely, (1) it has a new term in its ε equation to improve the accuracy of simulating rapidly strained flows; (2) consideration is made for the effects of swirl and more accurate for swirl flow application; (3) unlike the standard k–ε model, where constant values of the turbulent Prandtl numbers are used, the RNG k–ε model utilizes an analytical formula; and (4) an analytically derived differential equation is provided for the effective viscosity that accounts for low-Reynolds number effects. Two main material studies exist in the literature, namely, simple line interface (SLIC) (Noh and Woodward 1976) and piecewise linear interface construction (PLIC) (Rider and Kothe 1998)
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