Prediction of the critical points of natural gas mixtures by rigorous and semi-empirical methods

In the first part of this work, the modified Patel-Teja equation-of-state was applied to the rigorous critical point calculation method developed by Heidemann and Khalil. Two binary interaction coefficients (kaijand kbij) were used to fit the binary critical point data and the composition dependency of kij-values is evident. Considering the composition characteristics of natural gas mixtures, an optimal kij-matrix is recommended. The test on 46 natural gases (including a rich gas condensate), and other multicomponent hydrocarbon mixtures, shows a satisfactory prediction of critical properties. second part, the simpler semi-empirical methods based on excess critical property functions were systematically studied and a new interaction parameter (Aij) matrix designed for natural gas mixtures was developed. Test results on 93 binary and multicomponent mixtures are reported. Critical point data of mixtures are important parameters for phase behavior measurements of reservoir fluids.