Two-Phase Slug Flow Experiments with Viscous Liquids

摘要

The challenges behind the multiphase transport of oil and gas mixtures are increasing asudthe oil and gas industry is moving towards production from non-conventional reservoirsudand in remote locations. Transport of high viscosity fluids in long multiphase pipelines isuda particular challenge. Previous experiments have shown that gas-liquid slug flow is audfrequent two-phase flow pattern at high liquid viscosities. The slug flow regime is anudunstable flow, which may lead to operational problems, as the slug lengths and velocitiesudcan become very large. Most of the available experimental data and flow models are basedudon low viscosity fluids, and therefore, the computational models have some uncertaintyudregarding the viscous effects.udWith this in mind, the main objective of this thesis is to extend the knowledge of the twophaseudflow transport of slug flow with viscous liquids by experimental work, data analysisudof available information and evaluation of certain flow concepts within slug flow models,udsuch as bubble propagation, wake effect, severe slugging stability, and flow regimeudtransition.udAll the experiments were carried out at the Multiphase Flow Laboratory of the NorwegianudUniversity of Science and Technology and the experimental data were used to evaluateudthe performance of existing models. Dedicated set-ups and measurement methods wereuddesigned for each of the studied phenomena. Instrumentation has included an array ofudvideo cameras with image analysis, as well as external and internal impedance ringudprobes.udFlow stability was evaluated for gas-liquid severe slugging in a lazy wave shaped riserudwith different liquid viscosities. The experimental results show flow stability at lower gasudvelocities as the liquid viscosity is increased.udThe history effect of the flow in an upstream pipe connected to a downwards inclinedudpipe was studied. The results confirm the existence of a metastable region in the flowudregime map where both stratified and slug flow can be stable flow regimes depending onudthe flow pattern at the inlet. This effect is stronger for liquids that are more viscous. It isuddemonstrated that slug tracking models in principle can capture this phenomenon.udThe bubble propagation velocities for horizontal flows at Reynolds numbers for laminarudflow and for transition to turbulent flow have been measured. An empirical correlation for estimation of the bubble front velocity in the full range from laminar to turbulent flowudis suggested, based on the experimental results.udThe wake effect between two consecutive bubbles in laminar horizontal flow has beenudmeasured. In comparison with the turbulent case, an earlier interaction of the bubbles wasudobserved in terms of the slug length between them.udA new multi-beam gamma densitometer was also designed and fabricated to measureudthree phase fractions along the cross-sectional area of acrylic pipes. The new gammauddensitometer is subject to additional testing.udFurther works might address to extend the metastable region study to include strongerudpipe inclinations and much longer pipes, in order to verify the sustainability of the slugsudgenerated on this region. Moreover, additional sensitivity studies can be made withuddynamic slug tracking models, regarding the effects of the bubble velocity relations andudthe wake effect on the simulations of the slug flow evolution in a pipes.