Stability analysis and numerical simulation of riser topside choking on the elimination of severe slugging

Severe slugging is an undesirable operation in offshore pipeline-riser system and riser topside choking is an effective method for the suppression and elimination of severe slugging. A stability analysis is performed and a criterion for the stability of steady state operation is proposed. It is shown theoretically that by increasing the degree of choke setting, the region for unstable flow shrunk down along the superficial liquid and gas velocity axis. A quasi-equilibrium model for the prediction of the dynamic behavior of gas-liquid flow in a pipeline-riser system in the process of riser topside choking is also developed. The effects of the pressure drop across the choke on the variation of the pressure at riser base and the liquid slug penetrating into the pipeline are estimated. It is found that the minimum pressure increases with increase in the pressure drop across the choke. The model predictions are tested against experimental results, showing a reasonable agreement.