Free Gas in Place Formula
Free Gas in Place calculates original free gas-in-place for pvt and rock-fluid properties workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (A, h, phi, Swi, Egi) are known and the assumptions behind the cited pvt and rock-fluid 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, G_f equals 1,047,330,000 SCF.
160
50
0.15
0.25
150
Inputs
A
acresDrainage Area
h
ftReservoir Thickness
phi
fractionPorosity
Swi
fractionInitial Water Saturation
Egi
SCF/bblGas Expansion Factor at Initial Reservoir Pressure
Outputs
G_f
Original Free Gas-in-Place
A
Drainage Area (rearranged)
h
Reservoir Thickness (rearranged)
phi
Porosity (rearranged)
Swi
Initial Water Saturation (rearranged)
Egi
Gas Expansion Factor (rearranged)
Source and review
reviewedAhmed, T., McKinney, P.D. (2005). Advanced Reservoir Engineering. Gulf Publishing of Elsevier, Chapter 3, Page 227.
Source