Phase Behavior and ThermodynamicsGas Properties
Gas Molecular Weight from Specific Gravity Formula
Gas Molecular Weight from Specific Gravity calculates gas molecular weight for gas properties workflows in phase behavior and thermodynamics.
How engineers use this formula
Use this formula when the listed inputs (gamma_g) are known and the assumptions behind the cited gas properties relationship match the engineering case being checked.
Assumptions
- Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
- The declared units match the field-unit constants used in the formula.
- The cited formula applies to the selected petroleum engineering workflow.
Limitations
- The calculation does not replace a full engineering model or operating procedure.
- Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.
Common mistakes
- Mixing unit systems without converting the inputs.
- Using default example values as field recommendations.
- Applying the formula outside the source assumptions.
Default example
Using the default inputs, M_g equals 18.82855 lb/lbmol.
gamma_gdimensionless
0.65
Inputs
gamma_g
dimensionlessGas Specific Gravity Relative to Air
Outputs
M_g
lb/lbmol
Gas Molecular Weight
gamma_g
dimensionless
Gas Specific Gravity Relative to Air
Source and review
reviewedPenn State PNG 301. Natural Gas Properties, gas gravity definition.
Source