(32f) Dynamic Models in Multiphase Flow

Transport of oil and gas mixtures in pipelines involves flow dynamics on a wide range of time and length scales. Liquid slugs and waves occur at scales extending from diameter scales (”hydrodynamic slug flow”) and up to riser lengths (”severe slugging”). Dynamic flow models are used for design and for operational studies of multiphase pipelines. The approach in such 1D dynamic multiphase flow modeling depends on the scale to be resolved. The small scale hydrodynamic slugging is normally of minor importance compared with severe slugging, and can often be treated as averaged flow. Some cases, however, show a coupling between the small scale hydrodynamic slug flow and the large scale severe slugging phenomenon.

A hybrid two fluid model and a slug tracking model is described. A two fluid model is applied on a stationary grid in the gas-liquid stratified flow region until a slug is formed (or initiated), when a slug tracking method with a moving a grid takes over. The potentials of the model are demonstrated in relation to cases of different time and length scales. The first cases relates to small scale dynamics, wavy flows, and slug flow after bend initiation (slug length distributions). The second concerns a rapid acceleration of a pig (model systems) and the third case is a severe slugging case where slug flow initiation upstream the riser base affects the severe slugging characteristics.