Original Water In Place with Net-to-Gross Formula
Original Water In Place with Net-to-Gross calculates original water in place for reservoir volumetrics workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (A, h_g, NTG, phi, S_wi, B_wi) are known and the assumptions behind the cited reservoir volumetrics 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, W equals 2,464,305.882353 STB.
160
60
0.75
0.18
0.25
1.02
Inputs
A
acresMapped Reservoir Area
h_g
ftAverage Gross Reservoir Thickness
NTG
fractionNet-to-Gross Thickness Ratio
phi
fractionAverage Reservoir Porosity
S_wi
fractionAverage Initial Water Saturation
B_wi
bbl/STBInitial Water Formation Volume Factor
Outputs
W
Original Water In Place
A
Mapped Reservoir Area
h_g
Average Gross Reservoir Thickness
NTG
Net-to-Gross Thickness Ratio
phi
Average Reservoir Porosity
S_wi
Average Initial Water Saturation
B_wi
Initial Water Formation Volume Factor
Source and review
reviewedPenn State PNG 301. Estimation of STOOIP Using the Volumetric Method, Equations 4.02-4.04c.
Source