Volumetric Reserves Calculator
Calculate OOIP, OGIP, and recoverable reserves with Monte Carlo uncertainty analysis for P10/P50/P90 estimates.
Oil Volumetric Inputs
Enter best estimate (mean) and low/high for Monte Carlo. Leave low/high empty to use deterministic calculation.
| Parameter | Low (P90) | Best (Mean) | High (P10) |
|---|---|---|---|
| Area (acres) | |||
| Net Pay h (ft) | |||
| Porosity (frac) | |||
| Sw (frac) | |||
| Boi (rb/STB) | |||
| Recovery Factor (frac) |
OOIP = 7758 × A × h × φ × (1 - Sw) / Boi [STB]
OOIP
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Recoverable (Best Est.)
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Pore Volume
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Monte Carlo Results (10,000 iterations)
P90 (Low)
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P50 (Median)
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P10 (High)
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Mean
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Std Dev
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Recoverable Reserves Distribution
Cumulative Probability (Exceedance)
Parameter Sensitivity (Tornado)
How this was calculated
OOIP: 7758 * A * h * phi * (1 - Sw) / Boi [STB]. The constant 7758 converts acre-ft to barrels (43560 ft3/acre / 5.615 ft3/bbl).
OGIP: 43560 * A * h * phi * (1 - Sw) / Bgi [scf]. Where Bgi is the initial gas formation volume factor in rcf/scf.
Monte Carlo: 10,000 iterations using triangular distributions (low, most likely, high) for each parameter. All parameters sampled independently.
P10/P50/P90: P90 = 90% chance of exceeding this value (conservative). P10 = 10% chance of exceeding (optimistic). Per PRMS/SPE convention.
Tornado: Shows which parameter has the most impact on reserves by varying each from its low to high value while holding others at mean.
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Book a free strategy call →Understanding Volumetric Reserves Estimation
The volumetric method estimates original hydrocarbons in place from rock and fluid properties: drainage area, net pay, porosity, water saturation, and formation volume factor. For oil: OOIP = 7758 * A * h * phi * (1-Sw) / Boi. For gas: OGIP = 43560 * A * h * phi * (1-Sw) / Bgi. Every input carries uncertainty, so Monte Carlo simulation samples each from a probability distribution thousands of times, producing P10/P50/P90 estimates per SPE/PRMS conventions. All calculations run in your browser. Built by Groundwork Analytics.