To find ρg:

 

Petroleum Engineering Equations & Formulas

Gas Density

Density is the most commonly measured property of a gas and is obtained experimentally by measuring the specific gravity of the gas (relative to air = 1). As pressure increases, so does the gas density but the relationship is non linear since dimensionless gas compressibility (z-factor) also varies with pressure.

Gas density ρg can be calculated at any pressure and temperature using the real gas law:

       ρg = MP / zRT

       Where:

       M : is the molecular weight of the gas (lb/mcol or kg/kmol)
       P : is absolute pressure
       z : z-factor
       R : is universal gas constant
       T : absolute temperature (°Rankine)

            
 

$$ \rho_{g} = \frac{MP}{zRT} $$

Where:

  • M is the molecular weight of the gas (lb/mcol or kg/kmol)
  • P is the absolute pressure
  • z is the z-factor
  • R is the universal gas constant
  • T is the absolute temperature (°Rankine)