Study On Sand Deposition Law And Carrying Characteristics Of Fluids In Natural Gas Condensate Pipelines

Sand deposition in flow lines may create partial blockage,erosion and corrosion,which brings safety threaten and economic damage to field production.Nowadays,the most effective and economical way to solve this problem is to find the minimum velocity,known as critical sand deposition velocity,to keep all the particles constantly moving.Based on the previous critical velocity models and experiment,sand deposition law and carrying capacity of fluids in natural gas condensate pipelines were studied,amendment was made to the critical velocity models in natural gas liquids conditions.The main contents and conclusions are as follows:The experimental system of sand depositon for natural gas condensate pipelines was built.Sand particles deposition and movement behaviors were analyzed based on the natural gas condensate pipelines experimental system.Considering particle size and concentration,sand flow regimes were obtained,as well as the transition mechanisms for sand flow regimes.Fluid carrying efficiency was used to study the carrying capacity of fluids.The results show that the mass carrying efficiency as well as the particle carrying efficiency increase with the increasing superficial velocities,while the increment speed slows down.Under the same gas-liquid velocity,the particle carrying efficiency increases first and then decreases with the increase of particle size.Critical velocity is defined as the minimum velocity to keep all the particles constantly moving along the pipeline.Influencing factors as well as the influencing mechanisms were investigated in the experiment,including particle size,particle concentration and liquid viscosity.The flow regime is stratified smooth and stratified wavy flow within the scope of the experiment.The results show that with the increase of particle size,particle concentration and liquid viscosity,the critical velocity increases.Pipeline pressure drop was obtained by LabVIEW data acquisition system,which was used to investigate the effect of sand particles on pipeline pressure drop.It is noted that the pressure drop gradient of pipelines with sand particles are much greater than that of pipelines without sand particles,while sand particle size and particle concentration have little influence on pressure drop gradient.Based on the comprehensive study of existing sand transport models of hydraulic systems and multi-phase flow systems at home and abroad,the modeling method and its advantages and disadvantages were analyzed in this paper.A widely used hydraulic sand transport model was extended to multi-phase flow by utilizing characteristic parameters,the selecting of which is of great significance to model extension.The actual liquid velocity was used as characteristic velocity,while pipe diameter,pipe hydraulic diameter and liquid height were used as the characteristic length,respectively.The experimental data was used to verify the extended models.The results show that the prediction results of the extended model are in good agreement with the experimental data when pipe diameter is used as the characteristic length.