Phase Behavior and ThermodynamicsGas Properties
Real Gas Isothermal Compressibility with Z-Factor Derivative Formula
Real Gas Isothermal Compressibility with Z-Factor Derivative calculates real gas isothermal compressibility for gas properties workflows in phase behavior and thermodynamics.
How engineers use this formula
Use this formula when the listed inputs (P, z, dz_dP) 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, c_g equals 0.000357 1/psi.
Ppsia
3000
zdimensionless
0.85
dz_dP1/psi
-0.00002
Inputs
P
psiaPressure
z
dimensionlessGas Compressibility Factor
dz_dP
1/psiIsothermal Derivative of Z Factor with Respect to Pressure
Outputs
c_g
1/psi
Real Gas Isothermal Compressibility
dz_dP
1/psi
Isothermal Derivative of Z Factor with Respect to Pressure
Source and review
reviewedPenn State PNG 301. Natural Gas Properties, Equations 3.69 through 3.70.
Source