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This equation " PV=nRT " is one of the most important equations in petroleum engineering, it is simply the ideal gas law, we use it to calculate amount of gas production in gas reservoirs, but is the gas really ideal?
Well, the answer is no!
And this answer is based on many experimental observations which showed that hydrocarbon gas doesn't obey this law ideally but it follows a deviation and the equation can now be (PV=ZnRT) where Z is the compressibility factor .
This factor must be precisely determined because any small error in calculation will cause great problems in production as "petroleum engineers" work with high pressure and temperature so the volume is very high too.
And this problem was solved when Standing And Katz Compressibility Factors Chart was published .
Thanks to these charts calculation are now easier, all what we have to is to follow some steps to calculate the (Z) factor and then put it in the equation to calculate the volume or any other variable of the equation.
But we are explaining here the 1st method only.
This method permits the use of the Standing-Katz Chart by using a pseudo-critical temperature adjustment factor, which is a function of the concentration of CO_{2} and H_{2} in the sour gas. This correction factor is then used to adjust the pseudo-critical temperature and pressure according to the following expressions: