Forecasting the transition to undesirable gas-liquid two-phase flow patterns in pipeline-riser system: A method based on fast identification of global flow patterns

•New experiments of transient inlet flow conditions for pipeline-riser system.•Two mechanisms for transition to undesirable gas-liquid two-phase flow patterns.•Presentation and verification of forecast method for flow pattern transition.•Discussion of false positives and beneficial effect for flow control. The level of flow assurance for gas-liquid two-phase pipeline-riser system in offshore oil and gas fields will be significantly improved once the transition to undesirable flow patterns can be forecasted before its occurrence. In this study, experiments of gas-liquid two-phase flow in a pipeline-riser system were performed at both steady and transient inlet flow conditions, through which the forecast method was investigated. Two mechanisms for the transition to undesirable gas-liquid two-phase flow patterns were discovered; and the feasibility of forecasting was demonstrated by the response of differential pressure signals to the change of inlet flow rates. The forecast method was a combination of a fast identification model and special forecasting rules. The formation position of the liquid slug was also qualitatively predicted. All the cases of the transition to undesirable flow patterns in the experiments were successfully forecasted at least 30 s ahead of the formation of undesirable flow patterns, which proved enough for the response of flow control systems through an additional experiment. False positives were also discussed.