# Oil Sludge Deposition in Storage Tanks: A Case Study for Russian Crude Oil in Mo-he Station
###### Abstract  
The oil tank can form a considerable amount of sludge deposition after continuous accumulation, which cause a seriously negative impact on both the storage capacity and the safe operation of the oil tank. Therefore, it is important to anticipate the rate of sludge deposition in advance so that proper measures can be planned to remove this heavy layer on the bottom. This paper proposes a method using a relatively simple formula for predicting the sludge deposits. The sedimentation mechanism of wax and asphaltene is introduced and summarized from both the micro and macro aspects, the factors causing the interaction between particles and the influence on coalescence were analyzed. We applied our prediction methods to calculate the sludge deposition of four oil tanks in Mo-he Station and compared our results with the data measured by experiments. The results show that our method had a good general accuracy to experimental data and can be used directly for on-site engineers to anticipate real sludge height before measuring the oil level inside the tank. wax; asphaltene; oil sludge; deposition; oil tank +
Footnote †: journal: Applied sciences  
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**? ** ] studied the viscous sediment suspension system, from the overall consideration of the formation of particles after flocculation, according to the experimental observation. They found that if the volume concentration reaches a certain value, the floc size tends to be consistent because the streamline interferes with each other in the sedimentation process. The muddy water interface will appear, that is, the muddy liquid surface. On this basis, they put forward a formula for calculating the settling velocity of muddy liquid surface. In 1999, [PERSON] [**? **] used the relationship between effective stress, permeability and porosity to describe the physical properties of slurry, and established a numerical model for slurry settlement. The settlement of kaolin soil suspension in distilled water was used as verification, and the correlation of model prediction was satisfactory. He also pointed out that the model is sensitive to the properties of the slurry. In 2000, [PERSON] [**? **] et al. established a numerical model of particle settlement consolidation using Kynch's solid flux density function and effective stress of solid. This model also requires that the solid concentration, permeability, and effective stress obtained from experiments be known a priori. From the perspective of oil sludge composition analysis, [PERSON] [**? **] et al. carried out a detailed analysis of crude oil sediment components, including suspended matter particles, molecular weight and four components content (saturated hydrocarbon, aromatic hydrocarbon, resin and asphaltene), which laid a foundation for the study of sedimentation mechanism and theoretical prediction. The formation of oil sludge is closely related to its asphaltene and wax components, especially microcrystalline wax [**? **], not only because the specific gravity of wax in the oil sludge be much larger than that in the crude oil, but also related to the characteristics of wax crystals, which are easy to form composite structures. The theoretical basis for idealized particle deposition is the Stokes formula, which relates the settling velocity of particles and liquid density, liquid viscosity and particle diameter under the action of gravity. However, in the actual oil tank, the assumptions for the Stokes law are usually not valid, for instance the no-interaction between the settling particles assumptions or the spherical particles assumption. When the temperature in the tank reaches the wax precipitation point, wax crystals precipitate and its settlement in the tank is different from that in the pipe flow. In the pipeline, the fluid is moving forward at a fast speed, the shear dispersion and molecular diffusion play dominant roles.