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)