Original Oil in Place from General Oil Material Balance Calculator
Enter the required production, expansion, pressure, and influx terms. The calculator returns estimated original oil in place.
Calculation context and source notes
Original oil in place from general oil material balance estimates OOIP by reconciling produced fluids, pressure change, expansion terms, and water influx in a reservoir material-balance relationship.
Use it as a reservoir-engineering consistency check when pressure-production history and PVT expansion terms are available.
Solves for
N (STB)
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Formula, variables, and sourceRelated source-backed guides
Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns N = 400,000 STB. Defaults demonstrate the implementation; they are not recommended field values.
631000
96440
1.15
0.2
0.8
0.0264
Input definitions
F
RBUnderground Withdrawal
W_e
RBCumulative Water Influx
E_o
RB/STBOil and Dissolved Gas Expansion Term
m
dimensionlessInitial Gas Cap to Oil Zone Reservoir Volume Ratio
E_g
RB/STBGas Cap Expansion Term
E_fw
RB/STBConnate Water and Rock Expansion Term
Output definitions
N
Original Oil in Place
F
Underground Withdrawal
W_e
Cumulative Water Influx
E_o
Oil and Dissolved Gas Expansion Term
m
Initial Gas Cap to Oil Zone Reservoir Volume Ratio
E_g
Gas Cap Expansion Term
E_fw
Connate Water and Rock Expansion Term
Engineering use, assumptions, and limits
Use it as a reservoir-engineering consistency check when pressure-production history and PVT expansion terms are available.
Assumptions
- Reservoir pressure, cumulative production, PVT, and water-influx terms are representative.
- The selected material-balance form matches the drive mechanism and available data.
- Production and injection volumes use consistent stock-tank and reservoir-volume conventions.
Limitations
- Material balance is sensitive to pressure data quality, aquifer assumptions, PVT quality, and drive-mechanism interpretation.
- Does not replace a calibrated reservoir model or full reserves evaluation.
Common mistakes
- Ignoring aquifer influx or gas-cap effects when they are material.
- Mixing stock-tank, standard, and reservoir volumes.
- Using sparse or unrepresentative pressure data as if it were average reservoir pressure.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Petroleum Office. Oil Reservoir Material Balance; Havlena-Odeh general oil MBE.
Open source reference