A mechanistic model for two‐phase bubble flow in vertical pipes

Abstract

The flow of gas-liquid mixtures in vertical pipes is widely encountered in the petroleum industry. In most oil wells gas is produced simultaneously and the oil production rate is dependent upon the gas rate. As the gas rate is increased from zero, the gas is dispersed as discrete bubbles that increase steadily in number and, with coalescence and pressure drop, may increase in size. This flow pattern is called bubble flow. At progressively higher gas velocities slug, froth, and annular-mist flow patterns occur.For a given gas rate the volume fraction of the gas phase or gas void fraction is dependent upon the oil rate. For a naturally producing oil well, the oil production rate depends upon the difference between the flowing bottom hole pressure and the surface pressure. This difference is dependent upon the flow pattern and the holdup, which are dependent upon the oil and gas rates, the fluid properties, the depth and diameter of the well, and the absolute pressure and temperature.Numerous empirical correlations are available (Brill and Beggs, 1982) for predicting flow pattern, holdup, and pressure drop in oil wells. It has only been in recent years that researchers have begun to consider the basic hydrodynamic phenomena involved in two-phase flow and to develop theoretical models for determining flow pattern, holdup, and pressure drop. Mechanistic models have been developed for flow pattern (Taitel et al., 1980), holdup (Barnea andBrauner, 1985), and pressure drop in slug flow (Fernandes et al., 1983;Sylvester, 1987) and annular-mist flow (Yao and Sylvester, 1987) in vertical pipes.The purpose of this paper is to formulate and evaluate a mechanistic model for two-phase bubble flow in vertical pipes that permits calculation of liquid holdup and pressure drop.(1982) have developed relations that delineate the bubble flow pattern. At low gas and liquid rates bubble flow exists provided the pipe diameter is larger thanAccording to this relation bubble flow does not exist for smalldiameter pipes because the small bubbles rise faster than the Taylor bubbles, which causes coalescence.Taitel et al. considered two distinct bubble flow patterns, bubbly and dispersed bubble flow, depending upon the gas and liquid rates and the gas void fraction. At low liquid and gas rates the transition from bubbly to slug flow is based on a liquid holdup of 0.25. This transition in terms of superficial liquid and gas velocities is given bywhere u, is the slip or bubble rise velocity given by Harmathy (1 960) (3) At higher gas and liquid rates both bubbly and slug flow become dispersed bubble flow. The transition to dispersed bubble flow is given by Flow Pattern Transition BoundariesThe model is formulated based on the assumDtion that theflow is fully developed and stable. It is further assumed that a t any given location the gas is discretely and uniformly dispersed as bubbles in the liquid phase.When gas and liquid flow concurrently upward a t a low gas rate, bubble flow occurs. Taitel et al. (1980) and Barnea et al. This relation was ...

CIC-Erosión: herramienta computacional para la predicción del desgate erosivo en líneas de producción y transporte de hidrocarburos

“…Con respecto a una condición de tubería vertical, se implementó el modelo propuesto por Ansari y Sylvester [23], el cual es también un modelo mecanístico que ha mostrado excelentes resultados en sus predicciones, en comparación con modelos empíricos [24]. Finalmente, para considerar el efecto del patrón de flujo sobre la tasa de erosión, se usaron diversas correlaciones que caracterizan la distribución de las fases (gas, líquid) para cada tipo de régimen de flujo, que posteriormente se relaciona con la velocidad con la cual las partículas de arena golpean la superficie metálica.…”