# Oil Sludge Deposition in Storage Tanks: A Case Study for Russian Crude Oil in Mo-he Station
###### Abstract
Firstly, the heavy components in crude oil are characterized, the fugacity of solid and liquid phase is calculated by the equation of state, and activity is calculated by the canonical solution model and canonical solution model and universal quasi-chemical model (UNIQUAC) to describe the thermodynamic equilibrium of the system. [PERSON] [17] established a three-phase thermodynamic model considering gas, crude oil, wax crystal and solid and compared the accuracy of predicting wax appearance temperature (WAT) and wax deposition by adjusting several parameters in the solid model. He found that the fusion temperature was the most appropriate parameter to adjust. [PERSON] [17] used the same method to propose a thermodynamic model considering four phases in crude oil to calculate wax and asphaltene deposition. In this model, simplified perturbed chain statistical associating fluid theory (sPC-SAFT) was used to calculate fugacity of the gas phase and liquid phase, UNIQUAC theory was used to calculate activity coefficient, and binary interaction parameter (BIP) prediction was modified to meet the best results. As for the thermodynamic model of asphaltene deposition, the solubility models are also widely used. [PERSON] [17] et al. summarized different thermodynamic models for predicting asphaltene precipitation. According to Flory Huggins model, asphaltene is a macromolecular polymer, which can be represented by virtual components. The liquid properties are obtained by vapor-liquid equilibrium, the oil-rich phase is regarded as a solvent, and asphaltene is regarded as a polymer solute to describe liquid-liquid equilibrium. Modified Flory Huggins (MFH) model divides oil and precipitation into asphaltene and non-asphaltene, the core of the methods is to calculate solubility parameters and molar volume of asphaltene. [PERSON] [17] et al. put forward a more detailed method for prediction by using the perturbed-chain statistical associating fluid theory (PC-SAFT). The model was established according to the definition of Helmholtz free energy reduction. The model accuracy is higher than the traditional cubic-plus-association (CPA) EOS model, however, the crude oil data used is more extensive. CPA EOS model is composed of a cubic equation of the state and SAFT model, which takes into account the attraction and repulsion force between non associated molecules, and also considers the influence of associating parts, such as the hydrogen bond [17]. [PERSON] et al. [18] used the CPA EOS model to determine the starting point of asphaltene deposition in various oil products. They used a simple crude oil component characterization method, which divided oil into asphaltene and heavy components. They considered association between asphaltene molecules and the association between heavy components and asphaltenes. The solid model combines the monodisperse asphaltene model with the Soave-Redlich-Kwong (SRK) EOS for fugacity calculation. [PERSON] compared the prediction results using the above models based on the experimental data of 12 kinds of asphaltene crude oil. It was found that the PC-SAFT EOS model and CPA EOS model have shown better results. Another description of asphaltene deposition is the colloidal model. [PERSON] [17] was the first to study the colloidal structure of asphaltene. Based on the colloidal theory, [PERSON] [17] et al. analyzed the causes of asphaltene sedimentation in crude oil. [PERSON] [17] analyzed the settlement mechanism of asphaltene under different conditions. He proposed a mathematical method to determine the particle size of deposited particles in the colloidal system. According to the sedimentation equilibrium theory, only the diffusion effect caused by gravity and the concentration gradient of particles was considered, and the calculation of the molecular weight of critical particles was deduced from the equilibrium condition that the sinking amount must be equal to the upward diffusion amount. The formula for calculating the gamma distribution of particles and the packing factor was also proposed.