Study Of Dynamic Transport And Evolution Of Gas Phase During Commissioning Process Of Undulating Liquid Pipelines With Large Drops

Due to the complex and changing terrain in China,some of the oil and gas long-distance pipelines will cross plateaus,mountains and basins,etc.The topography of these pipelines is affected with the continuous undulation and repeated large drops,which are called“undulating pipeline with large drop”.During the commissioning process(i.e.,the process of liquid-gas replacement),the complex pipeline topography will lead to the accumulation of a large amount of gas in the pipe,which will form severe gas resistance,and the distribution of these gas resistance is complex,thus the effective gas-discharging is quite challenging.This can lead to different operating parameters of the pipeline far beyond the design range,resulting in breakdowns and,in severe cases,even pipeline failure.In this paper,we study the transport of various forms of gas phases in undulating liquid pipelines with large drops,their mutual mass transfer,and their evolution in complex flow fields to reveal how the dynamic transport and distribution of gas phases vary along the undulating pipeline sections such as up and down slope sections and up and down bend sections during the commissioning process of such pipelines.Firstly,this paper investigates the process of bubble transport and evolution for tracing in undulating large drop pipelines.By introducing the population balance model,and providing an independent physical description of each group of bubbles,the migration and evolution of bubbles in undulating pipelines with large drops are studied based on the Eulerian-Lagrangian coupling scheme.Experimental data are used in order to verify the accuracy of the bubble tracking model.Secondly,the air pockets,formed by the bubble re-coalescence,will be captured and tracked.The momentum equation of air pockets is established to calculate the transport of air pockets in undulating pipeline based on the force analysis of air pockets.Meanwhile,this model describes the chasing and merging of multiple air pockets with each other in the pipeline,including the bubble entrainment occurring at the tails of air pockets,leading to the mass transfer process from air pocket phase to the bubble phase.The experimental data are used to verify the accuracy of the validated model of air pockets capture and tracking.Thirdly,this paper creatively introduces a collocated multi-grid system with EulerianLagrangian scheme for multiple gas phase calculation.By applying this grid system,the simultaneous and homotopic description of the continuous liquid phase,discrete bubble phase and discrete air pocket phase in the pipe can be achieved.The system can describe multiple discrete phases in the continuous phase as well.Finally,based on the analysis of the transport and dynamic distribution of various gas phases in the pipe in the actual commissioning process of M crude oil pipeline,this paper establishes a gas phase dynamic description model,which is applicable to the actual commissioning process.In addition,this paper develops a joint exhaust solution based on gas-phase dynamic analysis for the commissioning of M crude oil pipeline by combining various exhaust methods at the actual commissioning site,and compares it with the original commissioning exhaust solution to analyze the advantages of this joint exhaust solution.