Initial Gas Cap Formula
Initial Gas Cap calculates initial gas cap gas for material balance workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (m, N, B_oi, B_gi) are known and the assumptions behind the cited material balance 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 equals 48,000,000 SCF.
0.2
1000000
1.2
0.005
Inputs
m
dimensionlessInitial Gas Cap to Oil Zone Reservoir Volume Ratio
N
STBOriginal Oil in Place
B_oi
bbl/STBInitial Oil Formation Volume Factor
B_gi
bbl/SCFInitial Gas Formation Volume Factor
Outputs
G
Initial Gas Cap Gas
m
Initial Gas Cap to Oil Zone Reservoir Volume Ratio
N
Original Oil in Place
B_oi
Initial Oil Formation Volume Factor
B_gi
Initial Gas Formation Volume Factor
Source and review
reviewedAhmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter 4, Page 300.
Source