The slug capturing technique, which is incorporated in the industrial PROMPT code is used to explore the influence of entrainment of gas bubbles at slug fronts, on slug characteristics such as slug length and frequency. The computations are compared with available field data. It is found that the amount of gas entrained within the slug can substantially affect slug lengths, increasing them (almost doubling) in some cases, while in another it can decrease them. The paper presents the basic methodology, the models governing the motion of the gas entrained within slugs and the results of comparison with the field data.
Intermittent flow, especially the slug flow regime, occurs very frequently in the transport of hydrocarbon fluids in pipelines in the oil and gas industry. The slug flow regime is usually undesirable since the intermittency of slugs causes severe adverse conditions. Firstly, the flow rates of the gas and oil arriving at the receiving equipment (separators and slug-catchers) can fluctuate widely thereby undermining the functioning of the equipment (e.g. separator flooding). To cater for this situation, processing facilities are usually designed with generous "safety margins" at the cost of capital, weight and size. Secondly, the flow intermittency results in highly unsteady loading on the piping system and processing equipment, which can result in serious failure due to metal fatigue. It is therefore important to be able to predict the onset of slug flow; it would be even more beneficial if slug characteristics, such as slug length and frequency could be calculated reliably as well.