Experimental investigation and prediction of overall and local flow patterns in pipeline-riser systems

A unified model for predicting flow patterns in the pipeline-riser system is essential for the flow assurance of offshore oil and gas pipelines. This paper uses the visual images and pressure signals to obtain the internal correlation and the transition boundaries of the overall and local flow patterns in a 46 mm ID, 1722 m long pipeline S-shaped riser system. The flow pattern map with industrial parameters is plotted, and a fast identification method for unstable flow is proposed based on the differential pressure signal of the riser. The mapping relationship between the overall flow pattern divided by the pressure signals and the local flow pattern distinguished by the visual images is established. The transition mechanism dominated by the liquid phase is whether the gas in the downward-inclined pipeline accelerates after entering the riser base, and the transition mechanism dominated by the gas phase is whether the gas can penetrate the liquid in the riser so that the gas does not accumulate in the downward-inclined pipeline. A unified mechanistic model is proposed for predicting the overall flow pattern transition boundaries in pipeline-riser systems. The model results show a good agreement with 24 kinds of flow pattern maps under various pipeline structures, fluid properties, and separator pressures.