## 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 ρ_{g} can be calculated at any pressure and temperature using the real gas law:

ρ_{g}= 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)