Investigation On Severe Slugging Characteristics In A Composite Pipeline-Riser System

During the multiphase transportation of oil and gas form subsea wellhead to the surface processing platform in offshore petroleum exploitation ,oil and gas have to be delivered by pipeline layed on the seabed and vertical riser, as a result,severe slugging phenomenon is commonly encountered and will cause drastic pressure fluctuations and outlet flow with other harmful consequences.Do intensive research on this flow phenomenon has important theoretical and realistic significance.In this study,the severe slugging phenomenon in a horizontal-decline-riser system was studied.The inner diameter of test pipe is 0.026m.The mechanism and flow characteristics of severe slugging were analyzed.The main contents and conclusions are as follows:Three flow patterns are observed in the horizontal pipe, namely,stratified flow, intermittent flow and blocking flow.There are also three flow patterns in the riser pipe section,including terrain severe slugging,hydrodynamic severe slugging,and intermittent flow,while terrain slugging can be divided into type I,type II and type III.The flow pattern map of the two-phase flow of the horizontal pipe and riser were also obtained.The flow characteristics of severe slugging were studied. It was found that typical terrain slugging is on a strict cyclical,and the cycle length decreases with the gas and liquid superficial velocity increase, the pressure fluctuations change with the gas and liquid superficial velocity change,and the maximum value of pressure fluctuation occurs at the boundry of terrain slugging type I and type II.By changing the height of risers,two flow pattern maps of risers were obtained On this basis, the changes of flow patterns are introduced. By analyzing the experimental results,it shows that the mechanism judgement of severe slugging won't change as only change the height of riser,and the flow pattern won't change either,but the region of the severe slugging increases,the length of period,pressure fluctuation and eruption time will also increase.After observations on the hydrodynamic severe slugging which appears in the experiment,it's found that the formation of hydrodynamic severe slugging is stable,and it also has good cycle characteristics, and will also lead to violent gas and liquid flow eruption. As the happening of hydrodynamic severe slugging, the original decreasing of the severe slugging cycle and the pressure fluctuation amplitude increased mutation are abrupt increasing,make the region of the severe slugging increases greatly,so speacail attention also need to be paid on this phenomenon.