Hydrodynamic slugs in pipelines are usually analyzed by using a steady-state flow assurance simulator as a first approximation. The pipelines are then modeled in transient simulation software to get more accurate values. Comparisons between an empirical and a mechanistic method are made in this work by running simulations in steady-state simulators in order to explain the differences in the calculated slug properties. It has been demonstrated that both methods cannot accurately estimate the maximum slug length in pipelines since the relative errors are significant; nevertheless the mechanistic model is more accurate than the empirical one with lower relative errors.

Additionally, slug sizes for operational slugging have been analyzed by using a new alternative pseudo transient approach to the Lagrangian slug tracking scheme. The model expresses an unsteady state mass balance in a pipeline, formulated utilizing the slip velocity written in terms of the void fraction and superficial gas velocity. Our model includes a constitutive equation for slip velocity, elevation changes to represent the hydraulic profile of the pipeline, a method for the calculation of the maximum slug length, a modified correlation for the slug length calculation and the variation of the fluid density along the pipeline profile. The results yielded by this model have been compared with field data and results performed by using a transient simulation software, showing fairly accurate values.

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