Original Gas in Place from p/z Material Balance Formula
Original Gas in Place from p/z Material Balance calculates original gas in place for material balance workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (G_p, P_z, P_i_z_i) 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 4,000,000,000 SCF.
1000000000
3000
4000
Inputs
G_p
SCFCumulative Gas Production
P_z
psiCurrent Pressure to Gas Compressibility Factor Ratio
P_i_z_i
psiInitial Pressure to Gas Compressibility Factor Ratio
Outputs
G
Original Gas in Place
G_p
Cumulative Gas Production
P_z
Current Pressure to Gas Compressibility Factor Ratio
P_i_z_i
Initial Pressure to Gas Compressibility Factor Ratio
Source and review
reviewedPetroleum Office. Material Balance Overview, p/z method for volumetric gas reservoirs.
Source