Compressibility Factor of Gas with High Content of CO2 in Changshen Gas Reservoir

The natural gas in Changshen gas reservoir is high content of CO2. There are no conventional methods to calculate the compressibility factor of natural gas. In view of this particularity, the compressibility factor is determined and analyzed by PVT laboratory experiments. Experimental studies show that the compressibility factor has great difference between hydrocarbon gas and non-hydrocarbon gas under the same conditions and the compressibility factor of CO2 has very strong temperature and pressure sensitivity. And for the natural gas with high content of CO2, the lower the temperature is, the lower the inflexion pressure of compressibility factor curve is. Under the same temperature and the same pressure conditions, the compressibility factors of different gas systems are strongly sensitive to CO2 component. And at 140°C, the inflexion pressure of compressibility factor curve increases with the increase of CO2 content. Under the condition of 20°C, the calculation of Wichert and Aziz's formula will cause great error when the natural gas has high content of CO2 (more than 80%). It suggests adopting laboratory experiment to measure the compressibility factor in order to provide theoretical reference for the reasonable development of gas reservoir.