Severe Slugging Prediction And Elimination In Offshore Multiphase Pipelines

In the offshore oil and gas exploitation systems, because of so many changes in throughput and well startup-shutdown operations, the flow pattern in the riser system almost belongs to severe slugging. Severe slugging can cause enormous difficulties to the design, operation and management of the offshore oil/gas gathering and transportation system. The severe slugging in inclined pipeline-riser system is simulated numerically with the software OLGA, and the results are compared with the available experimental datas. The inner relation between the separator operation and control and the upstream multiphase flow characteristics is investigated experimentally in the horizontal/inclined pipeline-riser system.The simulation results and experiment datas are compared and analyzed mainly from the severe slugging flow pattern classification, cyclophysis and pressure characteristics. The comparison demonstrates a good consistency. Simulation result shows a similar classification of severe slugging flow pattern with the experiment data. In experiment results, the cycle time of severe slugging flow decreases rapidly with the increasing gas/liquid superficial velocity. However, the simulation result shows that the cycle time decreases rapidly with the increaseing gas superficial velocity, but when the liquid superficial velocity increases, the cycle time decreases slowly. In the inclined pipeline-riser system, comparison result shows difference in the pressure characteristics, but in the horizontal/inclined pipeline-riser it shows a full agreement. Given all that, OLGA is beneficial to the simulation and prediction of severe slugging in the riser system, especially for the research of characteristics.The separator pressure control program is selected for the experimental investigation. It's indicated that the sepatator liquid level control does not have a significant impact on the upstream multiphase flow, but it's beneficial for the normal operation and pressure control of the separator. When the separator pressure increases, the peak-part of the mid-riser pressure apparently diminishes, and the minimum pressure gradually increases, and the fluctuation amplitude of pressure gradually decreases. During the slug blowing out, the gas/liquid slipping in the riser intensifies. The long gas plug quickly flows through the riser, then tends to be several different lengths of gas plugs and flow slowly in the riser. The inhibiting effect of pressure control strategy on the upstream severe slugging has something to do with the relative size of the superficial gas/liquid rate, but it's not releated to the absolute size of superficial gas/liquid rate.