A Lagrangian three-phase slug tracking model is demonstrated for a severe slugging case with gas, oil and water in an S-shaped riser. The model is an extension of a hybrid twophase flow scheme in which a two-fluid model formulation is used in the stratified flow region. In the slug body region, an incompressible flow model is applied. Mass and momentum conservation equations are solved for open and moving control volumes. This moving grid formulation allows for tracking of discontinuities within the flow, without numerical diffusion. A sub-grid two-fluid model in the bubble region allows for slug initiation directly from the two-fluid model in combination with a fine grid. Alternatively, a mechanistic slug initiation model may be used in combination with a coarse grid. The model is presented and applied to a severe slugging case in which oilwater separation occurs during slug build-up. The third phase is modeled with a mass conservation equation and an oil/water slip model in a mixture liquid momentum equation formulation.


The introduction of nuclear power generation in the mid 1950s increased the need for accurate and reliable methods to predict two-phase steam and water flows in pipe networks. This led to the development of several commercial codes for one-dimensional two-phase pipe simulation. Almost two decades later, a new field of application of the multiphase technology arose with the emergence of oil and gas production from deep water offshore fields. Several codes specifically designed for such systems were developed. These tools were to a large extent based on the modelling and simulation principles originally introduced with the nuclear technology, and were mainly suited for simulation of two-phase oil and gas flows. Here, an algebraic slip model for the relative velocity between the oil and the water was utilized.

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