Gas-liquid two-phase severe slugging in a pipeline-riser system with S-shaped flexible riser: Experiments and modeling

The objective of the present work is to investigate the air-water two-phase flow patterns in pipeline-riser system with an S-shaped flexible riser. The test loop with 50 mm ID consists of a horizontal pipeline with 114 m in length, a downward inclined section with 16 m in length, and an S-shaped flexible riser with 24 m in height when downward section inclined at −2° with respective to the horizontal. The inclination angle of the downward section varied from −2° to −5°. The liquid superficial velocity ranged from 0.03 to 1.5 m/s, and the gas superficial velocity from 0.4 to 6.0 m/s. Identification and characterization of flow regimes were attained by pressure at riser-base and liquid holdup at riser top. Severe slugging I, severe slugging II, transition flow and stable flows are observed to exist. Flow pattern maps for each declination are presented and the transition criteria are proposed. It's found that as higher liquid and gas velocity is required for the transition of the flow in the pipeline from stratified to intermittent with increasing the declination angle, severe slugging was observed to occur over a wilder range of flow conditions. The effect of riser geometry and separator pressure on the occurrence of the flow patterns was also examined. It shows that the S-bend tends to suppress the initiation of severe slugging.