Modeling of solid wax content in wax deposits

Abstract

The problem of wax deposition in crude oil pipelines is one of the important concerns for flow assurance in recent 50 years. Herein, the solid wax content in wax deposit was modeled with the precipitation enthalpy and precipitation entropy based on the wax precipitation characteristics to characterize accurately and quantitatively the change of solid wax content with temperature. Meanwhile, the solid wax content model expressed by crystallization activation energy of wax deposits was further derived according to the van't Hoff equation, which is helpful to understanding the precipitation process of wax crystal. In addition, the model was validated by comparing the model's calculation results with the experimental results of field pipeline wax deposits and using the experimental wax deposits at different oil-wax ratios to fit the model. Moreover, the mechanism of different influencing factors acting on the precipitation process of wax crystal in wax deposits was investigated on the basis of the solid wax content model. The results show that both the cooling rate and the carbon number-based composition of wax deposits affect the precipitation process of n-alkanes in wax deposit by changing the free energy of crystallization. Generally, the model can well describe the change of solid wax content in wax deposit with temperature, thus laying a theoretical foundation for the study of the strength of wax deposits and having the value for application in the field of pigging technology for crude oil pipelines.

Keywords

• wax deposits
• solid wax content model
• gibbs free energy
• precipitation enthalpy
• free energy of crystallization