Recovery Factor Calculator: Displacement and Sweep Efficiency to Reserves

Calculate recovery factor from displacement efficiency and areal and vertical sweep efficiency, build a multi-zone field model that sums STOIIP into total recoverable reserves, or solve backward for the STOIIP, recovery factor, or sweep efficiency a reserves target requires. Everything updates live.

Splitting Recovery Factor Into Displacement and Sweep Efficiency

Recovery factor is commonly decomposed into a microscopic displacement efficiency and a macroscopic volumetric sweep efficiency, RF equals Ed times Ev. Displacement efficiency, Ed, measures how much oil is pushed out of the pore space that the drive fluid actually contacts, computed from initial and residual oil saturation as Ed equals initial oil saturation minus residual oil saturation, divided by initial oil saturation. Volumetric sweep efficiency, Ev, measures what fraction of the reservoir volume the drive mechanism actually reaches, and is itself the product of an areal sweep efficiency, Ea, and a vertical or invasion sweep efficiency, Ei.

This decomposition matters because the two terms respond to different levers. Displacement efficiency improves with better fluid properties, lower interfacial tension, or enhanced recovery chemicals, while sweep efficiency improves with well placement, pattern design, and managing reservoir heterogeneity such as high permeability streaks that let injected fluid bypass large volumes of oil.

Building Reserves From STOIIP and Recovery Factor

Recoverable reserves equal STOIIP times recovery factor, so once a field is broken into zones with their own STOIIP and their own recovery factor, the field total recoverable reserves is the sum of each zone’s own reserves rather than STOIIP summed first and a single blended recovery factor applied afterward. Zones with strong water drive or an effective waterflood typically show meaningfully higher recovery factors than zones under simple solution gas drive depletion, so treating the field as uniform can significantly misstate total reserves.

This is the same reservoir characterization discipline that feeds net-to-gross and shale volume cutoffs upstream, and STOIIP or GIIP volumetrics just before recovery factor is applied, each stage narrows a gross number down to a more defensible estimate of what the field will actually deliver.

Solving Backward From a Target Reserves Volume

Sometimes a target reserves number is already fixed, perhaps from a development sanction threshold or a production forecast, and the useful question becomes what STOIIP, recovery factor, or sweep efficiency that target requires given the other parameters. Since reserves equal STOIIP times recovery factor, and recovery factor equals displacement efficiency times areal times vertical sweep efficiency, each of these terms solves directly from the others without iteration.

Common Mistakes

Applying a single field average recovery factor to a multi-zone field instead of computing recoverable reserves zone by zone and summing, which can meaningfully misstate the total when drive mechanism or sweep efficiency vary across the field.

Confusing displacement efficiency with overall recovery factor, a high displacement efficiency in the contacted rock does not help if sweep efficiency is poor and large volumes of the reservoir are never actually contacted by the drive mechanism.

Treating an early recovery factor estimate, often based on analogs, as fixed rather than updating it as waterflood or pressure maintenance performance data becomes available from the actual field.

Ignoring that solving backward for a required sweep efficiency above 100 percent signals the target reserves number is not achievable with the assumed displacement efficiency and development plan, and either the plan or the target needs revisiting.

Who Uses This

Reservoir engineers converting STOIIP or GIIP volumetrics into a recoverable reserves estimate for reporting or planning.

Petroleum economists and planners checking whether a reserves target is achievable given assumed displacement and sweep efficiency.

Students and early career geoscientists learning how displacement efficiency and volumetric sweep efficiency combine into an overall recovery factor.

Analysts building multi-zone field reserves models and comparing waterflood, mixed drive, and depletion drive scenarios.

Try It Above

Use the quick convert tab for a single recovery factor and reserves calculation from displacement and sweep efficiency, move to the field reserves tab to sum recoverable reserves across multiple zones into a field total, or use the solve target reserves tab when a reserves target is set and you need the STOIIP, recovery factor, or sweep efficiency it implies.

Related Calculators and References

Continue building your workflow with the STOIIP / GIIP Calculator. For background on the formulas used above, see AAPG Wiki: Predicting hydrocarbon recovery.