Experimental Study On Rheological Properties Of Hydrates Slurry

The coexistence of hydrates block and wax plug is possible to be appeared during the operation of submarine multiphase mixed pipelines.Therefore,it is of great significance for preventing pipelines plug and improving pipelines transportation efficiency to study the interaction between wax and hydrates.In this paper,the impacts of wax content(0wt%~2wt%),stirring speed(800rpm~1800rpm)and initial pressure(5.8MPa and 7MPa)on natural gas hydrates nucleation induction time and slurry viscosity characteristics in the presence of wax crystal are investigated by using a high-pressure hydrates slurry rheological measurement system to provide the experimental data support and theoretical research basis for the safe operation of mixed pipelines.Through researching hydrates nucleation induction time,three conclusions are drawn:(1)The presence of wax crystal has inhibitory effect on hydrates formation,and its inhibitory effect increases first and then decreases within the wax content of 0wt% ~ 2wt%.(2)When the wax content is lower,hydrates formation is promoted with the increase of stirring speed,which promotion degree is the maximum at the stirring speed of 1300 rpm.However,when the wax content is higher,hydrates formation is inhibited with the increase of stirring speed,which inhibition degree is the maximum at the stirring speed of 1300 rpm.(3)The increase of pressure can shorten the nucleation induction time.Through analyzing the viscosity characteristics of hydrates slurry formed in high-pressure autoclave reactor and rheometer respectively,experimental results demonstrate that natural gas hydrates slurry containing wax crystal shows shear-thinning property.And,hydrates slurry increases with the increase of wax content and initial pressure,while decreases with the increase of stirring speed.Viscosity is less affected by the amount of hydrates formed,but is closely related to the distribution of wax crystal and hydrates particle in the system.In this paper,two methods including classifying wax crystal into continuous phase and regarding wax crystal as solid particle are used.Based on the diameter of hydrates particle and hydrates aggregate,four kinds of natural gas hydrates slurry viscosity model containing wax crystal are established.Through comparatively analyzing these models,the optimal viscosity model of natural gas hydrates slurry containing wax crystal according to the diameter of hydrates aggregate is discovered,which regards wax crystal as solid particle.And,both of the aggregation of hydrates particle and the broken of hydrates aggregate are considered in this optimal model.