Experimental determination and prediction of the compressibility factor of high CO2 content natural gas with and without water vapor

In order to study the effect of different CO2 contents on gas compressibility factor (Z-factor), the JEFRI-PVT apparatus has been used to measure the Z-factor of dry natural gas with CO2 content range from 10.74 to 70.42 mol% at the temperature range from 301.2 to 407.3 K and pressure range from 7 to 44 MPa. The results show that Z-factor decreases with increasing CO2 content in natural gas at constant temperature and increases with increasing temperature for natural gas with the same CO2 content. In addition, the Z-factor of water-saturated natural gas with high CO2 content has been measured. A comparison of the Z-factor between natural gas with and without saturated water vapor indicates that the former shows a higher Z-factor than the latter. Furthermore, Peng-Robinson, Hall-Yarborough, and Soave-Benedict-Webb-Rubin equations of state (EoS) are used for the calculation of Z-factor of high CO2 content natural gas with and without water vapor. The optimal binary interaction parameters (BIP) for PR EoS are presented. The measured Z-factor is compared with the calculated Z-factor based on three models, which shows that PR EoS combined with van der Waals mixing rule for gas without water and Huron-Vidal mixing rule for water-saturated gas, are in good agreement with the experimental data.