Wax crystals can aggregate and precipitate when the oil temperature decreases to below the wax appearancetemperature(WAT)of waxy crude oil,which has undesirable effects on the transportation of crude oilin pipelines.Thermodynamic models considering the molecular diffusion,shearing dispersion,and shearstripping as well as hydrodynamic models have been developed for predicting the wax deposition incrude oil pipelines.However,the aggregation behavior of wax crystals during crude oil production andtransportation is not well understood.The microscopic rheological parameters have not been related tothe bulk flow parameters in the shearing field,and the prediction of the wax deposition behavior undercomplex conditions is restricted by the vector characteristics of the shearing stress and flow rate.A setof microscopic experiments was performed in this study to obtain the basic information from imagesof wax crystals in shearing fields.A novel method of fractal dimensional analysis was introduced toelucidate the aggregation behavior of wax crystals in different shear flow fields.The fractal methodologyfor characterizing wax crystal aggregation was then developed,and a blanket algorithm was introducedto compute the fractal dimension of the aggregated wax crystals.The flow characteristics of waxy crudeoil in a pipeline were correlated with the shearing stress work,and a wax deposition model focusingon shearing energy analysis was established.The results indicate that a quantitative interpretation of thewax crystal aggregation behavior can be realized using the fractal methodology.The aggregation behaviorof the wax crystals is closely related to the temperature and shearing experienced by the waxy crudeoil.The aggregation behavior will be intensified with decreasing temperature and shearing effect,anda wider fractal dimension distribution appears at lower temperatures when the same shear rate range isemployed.The lower the fractal dimensions obtained at high temperature and strong shear action,the weakerwill be the nonlinear characteristics of the wax crystal aggregation structure,and thus,the potential waxdeposition will be inhibited during waxy crude oil production and transportation.Furthermore,the improvedmodel provides a method for discussing the effects of the operating conditions on wax deposition.Theaverage relative deviation between the improved model prediction results and experimental results fromthe literature is 3.01%-5.32%.The fractal methodology developed in this study and the improvement in wax deposition modeling are beneficial for understanding and optimizing flow assurance operations in thepipeline transportation of waxy crude oils,and the results are expected to facilitate a better understandingof the wax crystallization and deposition mechanism.
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