Stratified gas-liquid flow-An analysis of steady state and dynamic simulation for gas-condensate systems

Abstract

In the transport of gas-liquid mixtures, where the amount of liquid condensate is low, a stratified flow-pattern is predicted by mechanistic two-phase flow models. In this case, the momentum balance between liquid and the gas phases is the key relation for the calculation of the steady state flow equilibrium and the existing liquid hold-up. The latter value is particularly important at low production rates for pipelines with a large number of upward and downward inclined pipe segments (making V shaped sections) where liquid can easily accumulate in the lower parts. The error in predicting the liquid inventory has critical consequences on the evaluation of the total pressure drop along the pipeline. The results obtained from steady state simulation can be far from reality or, at least, cannot be reproduced by a dynamic simulation of the same operating conditions. These topics are analysed using a multiphase flow simulator developed by the Author (XPSIM, eXtended Process SIMulation) which can perform compositional and fluid-mechanical analysis at the same time. Steady state and dynamic simulations are developed for the Ormen-Lange pipeline (about 120 km long): large differences are found between the steady state and dynamic solutions.

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