A Simplified Model for Steady-State Pseudo-Slug Flow

Abstract

Abstract Pseudo-slug flow is widely encountered in petroleum production systems, such as in upward inclined pipelines and deviated wells with liquid loading issues. To author's knowledge, there is no model yet available to predict the behavior of this flow pattern. This study presents a simple model to predict the design parameters of pseudo-slug flow (pressure gradient and liquid holdup). The modeling approach relies on the fact that pseudo-slug structure involves a continuous gas passage despite of apparent intermittency as a whole. Consequently, pseudo-slug flow is treated as a segregated flow with very large waves rather than a conventional slug unit cell. A modeling approach combining drift-flux and two-fluid models is proposed in this study. This method eliminates the need to arbitrarily prescribe the interfacial friction factor correlations for pseudo-slug, which would conceivably differ from those of stratified/ wavy/ roll-waves flow reported in literature. A new closure relationship is needed for pseudo-slug flow drift-flux coefficients, which are easily derivable from experimental data in literature. Iterative procedure requirement to run the proposed model is minimal, which is an advantage for practical application. Additionally, this modeling approach does not produce multiple solutions, which may be exhibited by conventional two-fluid model. Pseudo-slug flow experimental data are collected from literature for benchmarking purpose. The accuracy of pressure gradient and holdup predictions of the proposed model is better than two state-of-the-art multiphase flow simulators, which generally treat pseudo-slug as slug flow. The values of interfacial friction factor naturally emerge in the calculation instead of being prescribed by a closure relationship. These calculated values exhibit sensible physical relations with pseudo-slug characteristics observed experimentally. The closure relationships for drift-flux coefficients remain to be improved in the future as more pseudo-slug experimental data become available.