OVERVIEW

The ideal-gas law states that the behavior of a gas can be expressed as

where

• p = Pressure, psia

• V = Volume, ft ³

• n = Number of moles

• R = The gas constant, ft ³-psi/( R-lb-moles)

• T = Temperature, Rankine ( R)

As shown below, the ideal-gas law, Equation B-1, can be modified to account for deviation of a real gas from ideal-gas behavior.

where z is compressibility factor. The Theorem of Corresponding States demonstrates that real gas mixtures will have the same z- factor for the same values of pseudo-reduced pressure p _pr and pseudo-reduced temperature T _pr which are defined as

where p _pc and T _pc are the pseudo-critical pressure and temperature for hydrocarbon gases, respectively. Table B-1 lists p _pc and T _pc as a function of gas gravity ? _g for values of ? _g ranging from 0.55 to 1.14. ^[1] Figure A-8 is Standing and Katz chart for determining z-factors for natural gases as a function of pseudo-reduced pressure p _pr and temperature T _pr. ^[2]