Flow Characteristics And Control Analysis Of Gas-liquid Two-phase Flow In Catenary Riser

With the development of deep-sea oil and gas fields,offshore platforms have developed from traditional tension leg platforms to floating production platforms.However,due to their motion characteristics in the marine environment,horizontal pipe-catenary system emerges as the times require.But for the marine catenary system,under the action of gravity,the accumulation of liquid at the bottom of the riser prevents gas from entering the riser,resulting in slug flow,which makes the deep-sea catenary system vibrate violently,causes mechanical fatigue,and may even cause pipeline rupture.The following work is carried out for the simulation of Severe Slug Flow in catenary:Firstly,by consulting a large number of domestic and foreign literatures,the current research status of slug flow characteristics in deep-sea catenary system is analyzed,and the characteristics of different flow patterns in the underground pipeline-catenary riser system are determined.Secondly,the flow state,pressure/temperature/distribution along the pipeline,gas/liquid flow rate along the pipeline,water content,outlet pressure and total flow rate at the entrance of horizontal pipeline are analyzed by OLGA software,and the influence of different factors on the flow parameters in the pipeline is analyzed.The following conclusions are drawn: In the marine catenary system,slug flow is easier to form in the pipeline due to large diameter,low flow velocity,low water content and low outlet pressure.The changes of the four parameters are divided into distinct stages according to the change of flow pattern in the pipeline,and the variation of the parameters in the pipeline is the greatest at the slug stage,while the gas flow at the outlet is the greatest at the slug stage.Measurement is affected by pipe diameter,total flow rate at the inlet,outlet pressure and water content;inlet pressure and bottom pressure of riser are mainly affected by the change of flow state in thepipe.Finally,the flow state,pressure/temperature/distribution and gas/liquid flow rate in deep-sea catenary system under different opening conditions are analyzed by OLGA software.The variation laws of pressure,gas/liquid flow rate at outlet and liquid holdup at bottom of riser under different throttle valve opening conditions are explored.The optimum opening of throttle valve under the condition can effectively restrain Severe Slug flow.The following conclusions are drawn: For the throttling method to suppress Severe Slug flow,it is necessary to consider comprehensively the effects of the gas/liquid flow at the outlet,the real liquid holdup at the bottom of riser and the period and range of pressure fluctuation.