New explicit correlation for the compressibility factor of natural gas: linearized z-factor isotherms

Abstract

The compressibility factor (z-factor) of gases is a thermodynamic property used to account for the deviation of real gas behavior from that of an ideal gas. Correlations based on the equation of state are often implicit, because they require iteration and are computationally expensive. A number of explicit correlations have been derived to enhance simplicity; however, no single explicit correlation has been developed for the full range of pseudo-reduced temperatures $$\left( {1.05 \le T_{pr} \le 3} \right)$$ and pseudo-reduced pressures $$\left( {0.2 \le P_{pr} \le 15} \right)$$ , which represents a significant research gap. This work presents a new z-factor correlation that can be expressed in linear form. On the basis of Hall and Yarborough’s implicit correlation, we developed the new correlation from 5346 experimental data points extracted from 5940 data points published in the SPE natural gas reservoir engineering textbook and created a linear z-factor chart for a full range of pseudo-reduced temperatures $$(1.15 \le T_{pr} \le 3)$$ and pseudo-reduced pressures $$(0.2 \le P_{pr} \le 15)$$ .