Modeling Of Liquid Loading In Wet Gas Pipe

Liquid loading is one of the main problems restricting the production of natural gas.When the gas velocity is not sufficient to fully carry the liquid in the pipeline,liquid loading will result in pipeline internal corrosion,back pressure increase,reduction of gas well production or transportation capacity of gas gathering pipeline and other problems,which will cause great risks to the safety of the pipeline.Therefore,accurate prediction of the critical gas velocity is of great importance for the design and operation of the natural gas production system.The stable flow pattern in vertical and inclined pipes is mainly annular flow.The liquid film reversal occurs at the boundary of the transition from annular to churn flow.The maximum superficial gas velocity of unstable annular flow is taken as the critical gas velocity.By combining the analytical solution of the flow field of the uniform liquid film near the pipe wall with gas-phase momentum equation of annular flow,a new critical gas-velocity prediction model is proposed.The effects of inclination angle,diameter,pressure and liquid droplet entrainment in gas core on the critical gas velocity are included in the new model.The new model is compared with Wang model,Shen Weiwei model,Li Jinchao model,Liu model,Shekhar model,Li model,Luo model,Belfroid model and Barnea model in predicting critical gas velocity at different pipe diameters and inclination angles.The comparisons of 128 laboratory scenerios show that the new model demonstrates the best agreement with the experimental data including the horizontal inclination angle of 50°-90°.The average relative error of the new model is 2.28%.For the field operating scenerios of 191 gas wells,the new model outperforms other models.The new model characterizes the impacts of inclination angle,diameter and superficial liquid phase velocity on the critical gas velocity.The steady gas-liquid two phase flow is mainly stratified flow in near horizontal wet gas pipe.When the gas-liquid interface shear stress reaches the minimum,the gas is not enough to carry liquid.A new model for predicting the critical gas velocity in near-horizontal pipe is established by combining the analytical solution of the liquid film velocity field with the flat gas-liquid interface and gas-phase momentum of stratified flow.The Blasius liquid-wall friction coefficient is discarded,which improves the prediction accuracy of the model.The prediction results of the new model,Li Guohao model,Shen Weiwei model,Alsaadi model,Fan model and Brito model for the critical gas velocities of 128 laboratory data with diameters of 1 in-6 in show that the prediction of the new model is the closest to the laboratory data in the range of inclination angle of 0.5°-45°.The average relative error of the new model is 1.04%.The new model correctly captures the effects of pressure,inclination angle and liquid phase velocity on the critical gas velocity.