A thermodynamic model for wax deposition phenomena

Wax precipitation is a serious problem in the petroleum industry because it may cause obstruction in well bores, production facilities and transportation pipelines during oil/gas production. To avoid this problem it is necessary to predict the wax appearance temperature (WAT) accurately. Consequently, a reliable thermodynamic model for predicting WAT is crucial in the design of production and transportation facilities. In this work, a thermodynamic model, based on multi-solid phase theory, has been developed. In this model the vapor and liquid phase fugacities are calculated using the Modified Peng Robinson (MPR) equation of state. The solid phase fugacities of pure components are evaluated indirectly from equation of state by the fugacity ratio. Fraction properties are estimated by using PNA analysis, and a correlation is developed for evaluating enthalpy of fusion. The major aim for performing this research was to develop a thermodynamic-computerized model for predicting WAT and the amount of precipitated wax in petroleum mixtures. The model has been applied to calculate wax appearance temperature and the amount of precipitated wax for some North Sea and synthetic oils. The predicted results are in a very good agreement with experimental data.