reservoir · volumetrics
Volumetric Reserves (OOIP/GIIP × RF)
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Inputs
—
STB / scf
fraction
Description
Converts a resource-in-place volume (OOIP or GIIP) into recoverable reserves by applying a recovery factor — the standard SPE/PRMS distinction between the total hydrocarbon in the reservoir and the fraction actually recoverable. This platform does not chain live calculator outputs together, so the resource-in-place and recovery-factor values must be copied in from the OOIP/GIIP and Recovery Factor calculators (or another source).
Variables
| Symbol | Unit | Description |
|---|---|---|
| Reserves | STB / scf | Recoverable Reserves |
| Phase | — | Numeric code for the hydrocarbon phase: 1 = oil (resource in place is N, output in STB), 2 = gas (resource in place is G, output in scf). Rounded to the nearest integer. |
| N/G | STB / scf | Original oil (N) or gas (G) in place, already computed by the OOIP or GIIP calculator (copy the value across — this calculator does not read it automatically). |
| RF | fraction | Recovery factor applicable to the entire resource-in-place volume, from the Oil or Gas Recovery Factor calculator or an analog/simulation estimate. |
Assumptions
- RF is representative of the entire resource-in-place volume entered, not just a single well or sub-area
- The resource-in-place value entered is itself a representative single-point estimate (not a probabilistic distribution)
- The same fluid phase and volume basis (stock-tank/standard conditions) is used consistently between the resource-in-place and RF inputs
Limitations
- Purely a scalar multiplication — does not itself estimate OOIP/GIIP or RF; those must come from the OOIP/GIIP and Recovery Factor calculators or another verified source
- SEC/PRMS reserve reporting requires a probabilistic (P10/P50/P90) treatment across a range of inputs, not a single deterministic point estimate
- Applying one RF to an entire resource-in-place volume ignores compartmentalization and areal heterogeneity — large or complex reservoirs often need area-varying RF and a summed (not single-point) reserves estimate
Use Cases
- → One-step reserves from an existing volumetric estimate: Combine an already-computed OOIP or GIIP with a recovery factor to get recoverable reserves without re-deriving the full volumetric chain.
- → Reserve booking documentation: Provide a quick, auditable recoverable-reserves figure alongside the resource-in-place and RF values used to derive it, for SEC/PRMS reserve reporting support.
- → Economic screening: Multiply recoverable reserves by an oil or gas price for a first-pass economic screening of a prospect or development area.
Related Calculations
Region Notes
Permian Basin
Unconventional wells often report EUR (from decline curve analysis) rather than a volumetric reserves figure — compare this calculator's output against eur_from_decline as a cross-check when both are available.
Gulf of Mexico
Deepwater reservoirs commonly use waterflood or gas injection to raise RF well above primary-recovery values (15-25%) — confirm which recovery mechanism the RF input represents before reporting.
North Sea
UK/Norwegian shelf fields typically report reserves under PRMS with explicit P10/P50/P90 ranges — this single-point calculator supports only one point of that range at a time.
Global
Always keep the resource-in-place and reserves figures clearly labeled and separate in any report — conflating OOIP/GIIP with reserves is one of the most common reserve-reporting errors.
References
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