Density at Operating Conditions
Typical: 0.55-0.70 (sweet gas), 0.70-0.90 (rich gas)
Typical range: 0.70-1.00. Obtain from AGA-8 or Standing-Katz chart.
Real gas: Use for P > 100 psig or custody transfer
Ideal gas: Only for preliminary estimates at low pressure
Understand ideal gas law, real gas behavior, Z-factor correlations, and equation of state methods
Natural gas density is calculated using the Real Gas Equation of State: ρ = (P × MW) / (Z × R × T), where P is absolute pressure, MW is molecular weight, Z is the compressibility factor, R is the gas constant, and T is absolute temperature.
The Z-factor (compressibility factor) is a correction term that accounts for the deviation of a real gas from ideal gas behavior. At high pressures, natural gas becomes denser than an ideal gas would predict, making Z less than 1.0.
Gas density is critical for determining mass flow rates, calculating pipeline inventory (line pack), sizing compressors, and performing accurate custody transfer measurements.