reservoir · volumetrics
Oil Recovery Factor
RF = Edrive × (1−Sw−Sor) / (1−Sw)
click formula to derive ↑
Inputs
—
fraction
fraction
fraction
Description
Estimates primary oil recovery factor from porosity and saturation endpoints, scaled by an empirical efficiency factor for the dominant drive mechanism. Provides a quick-look RF for screening before detailed material balance or simulation work.
Variables
| Symbol | Unit | Description |
|---|---|---|
| RF | fraction | Recovery Factor |
| Drive | — | Numeric code for the dominant drive mechanism: 1 = solution gas drive, 2 = water drive, 3 = gravity drainage. Rounded to the nearest integer. |
| φ | fraction | Average effective porosity of the net pay interval. |
| Sw | fraction | Initial water saturation of the net pay interval. |
| Sor | fraction | Oil saturation remaining after displacement/depletion — from core waterflood (SCAL) tests where available; 0.20-0.35 is typical for sandstone. |
Assumptions
- Sor is representative of the rock/fluid system and ideally calibrated from core SCAL waterflood or depletion tests
- A single dominant drive mechanism persists over the life of the reservoir (no major mechanism shift, e.g., solution gas to gas-cap drive)
- Porosity and saturations are representative areal averages, not single-point wellbore values
Limitations
- The drive-mechanism efficiency factors are generalized defaults, not basin- or reservoir-specific — calibrate against analog field performance where possible
- Does not capture EOR/secondary recovery uplift (waterflood, gas injection) beyond the primary mechanism modeled
- Single-point estimate — for reserves reporting, run as a distribution across plausible Sor and efficiency-factor ranges
Use Cases
- → Early-stage reserves screening: Apply a drive-mechanism-appropriate RF to OOIP before detailed simulation is available, to rank prospects or development scenarios.
- → Drive mechanism sensitivity: Compare RF across solution gas, water drive, and gravity drainage assumptions to bound recoverable volume uncertainty.
- → Waterflood/EOR screening: Use the solution-gas-drive RF as the primary baseline, then evaluate whether a waterflood (water-drive RF) materially improves recovery.
Related Calculations
Region Notes
Permian Basin
Wolfcamp/Spraberry unconventional benches are matrix-dominated with depletion-drive behavior similar to solution gas drive; primary RF is typically 5-10% of OOIP — well below conventional solution-gas-drive sandstone ranges due to nanodarcy permeability.
Gulf of Mexico
Strong aquifer support in many Miocene/Pliocene sandstone reservoirs gives water-drive RF at the high end (50-60%) of the typical range.
North Sea
Brent Group reservoirs under waterflood commonly achieve 40-50% RF; gravity-stable gas injection in some fields pushes RF toward 60%.
Global
Always validate the assumed drive mechanism against pressure/production history (e.g., GOR trend, water cut trend) rather than assuming it from geology alone.
References
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