Developed Correlation of Gas Compressibility of High Impurities Natural Gas Reservoirs, UAE Case Study

The gas compressibility factor is a key parameter in determining natural properties. The most common sources of gas compressibility factor (Z) values are experimental measurements, equation of state, and empirical correlations. There are more than twenty correlations available with two variables for calculating the Z-factor from fitting Standing-Katz chart values in EOS or through the fitting technique. The theory of corresponding states dictates that the Z-factor can be uniquely defined as a function of reduced pressure and temperature. Natural gases frequently contain material other than hydrocarbon components, such as nitrogen, carbon dioxide, and hydrogen sulfide. Hydrocarbon gases are classified as sweet or sour depending on the hydrogen sulfide content. Both sweet and sour gases may contain nitrogen, carbon dioxide, or both. The compositions of most natural gases are hydrocarbon of the same family (paraffin hydrocarbons), so the correlation of this type is possible but containing non-hydrocarbon on the gases, make the prediction difficult. 

     This paper focuses on evaluating the correlations to get an accurate gas compressibility factor for natural gas reservoirs with non-hydrocarbon components for gas reservoirs in UAE. It is found that gas pseudo-critical temperature decreases with the increase of N2 and H2S. Also, it is observed that in the tested gas reservoirs which contain C7+ by Stewart Mixing Rules and Kay’s there are some deviations, but this deviation is an error value of Z-factor between two methods that became negligible by using the correction method for non-hydrocarbon. Natural gases, which contain H2S and CO2 frequently, exhibit different compressibility factor behavior than do sweet gases. It is recommended to use Stewart Mixing Rules to investigate the impact of non-hydrocarbon impurities on natural gas properties with high impurities of N2 and H2S.