Compressibility factor of natural gas determination by means of molecular dynamics simulations

Forecasting of phase behavior and PVT-properties of natural gas is one of the major tasks during the developing and operation of gas and gas condensate fields. Each stage – from an exploration to transportation and storage of gas is followed by continuous changes of thermobaric conditions. This causes changes of thermodynamic properties of gas, one of which is compressibility factor. The comparative study of the existing theoretical methods of compressibility factor determination is given in the presented work: based on the equation of state and empirical correlations. Besides, the alternative approach based on molecular dynamics simulations with the Lennard-Jones potential is offered. The analysis of the received results is carried out on the basis of 165 experimental data for 5 various mixtures of natural gas covering temperatures of 310.9 – 344.4 K and pressure range of 7.074 - 48.443 MPa. The statistical analysis shows that the molecular dynamics method shows the minimum error and is suitable for determination of z-factor of mixtures with methane content more than 90%. For mixtures with the high content of carbon dioxide the Peng-Robinson equation of state with shift-parameter shows the minimum error.