Abstract
The phenomenon of two-phase flows is characterized by its wide range of presence in nature and industrial applications. In gas and oil production, the simultaneous two-phase flow of gases and liquids often occurs in gas wells. The produced gases flow rate decreases over the years until reaching a critical flow rate when they lose their ability to lift the associated liquids upward and the liquid film reverses direction, which triggers liquid loading. Liquid loading causes the produced liquids to accumulate in the bottom of the wellbore, which causes a high back pressure that reduces the well production rate till production is ceased eventually. The critical gas velocity exists in the churn flow regime which is mainly characterized by the oscillatory behavior of the liquids flow field. This study employs CFD techniques to model the churn flow in a 3-inch-diameter vertical pipe near the critical gas flow rate for different liquid flow rates. This work utilizes the two-fluid Eulerian model along with the RNG (Re-Normalization Group) k-ε turbulence model to investigate the behavior of the flow field in a two-dimensional axisymmetric computational domain. Simulations were carried out using the commercial software ANSYS Fluent 18.2 with air and water as the two working fluids. The model results showed a good agreement with the experimental data and proved the mesh and time independence of the model. Oscillatory behaviors of the liquid film flow rate, shear stress, and pressure were observed along with the formation of interfacial waves. Detailed information about the velocity, shear stress, and pressure behaviors is presented. Accordingly, recommendations are suggested for future considerations.
Highlights
Research in the area of two-phase flows continues to be one of the hot research areas due to its wide presence in nature and a broad range of industrial applications
The present flow regime in a given gas well is the annular flow where gases flow at high velocity in the core region while liquids form a film flowing on the pipe wall
The main objective of this study is to model the two-phase annular flow with special emphasis on the onset of the liquid film reversal and the complete reversal of that film
Summary
Research in the area of two-phase flows continues to be one of the hot research areas due to its wide presence in nature and a broad range of industrial applications. Liquid–gas twophase flow is widely present in gas wells where gases and liquids flow simultaneously. The present flow regime in a given gas well is the annular flow where gases flow at high velocity in the core region while liquids form a film flowing on the pipe wall. In the upward vertical two-phase flow in a typical gas well, the pressure difference along the pipe is reduced gradually over time which, The initiation of this entire process that eventually leads to loading the gas well is the reversing of the liquid flow direction from upward to starting falling down, the onset of film reversal.
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