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# Oil in place

Oil in place (OIP), or oil-in-place (not to be confused with original oil-in-place) is the estimated amount of oil in a reservoir. A variety of techniques, combined with mathematical equations, is used to determine OIP. Only a fraction of the OIP, called the recovery factor, can be recovered from a reservoir.

## Estimation of oil in place

The technique used to estimate the OIP in a given reservoir depends on the type of reservoir and the stage of oil recovery.

### Volumetric balance equation

When fluids are withdrawn from a petroleum reservoir, the space left behind is filled partly by the expansion of the remaining fluids and rock and partly by the flood of water from an adjacent aquifer, if there is one. The volumetric balance equation (VBE) is an expression of this statement. In simplified form, the VBE states:

**Z = AX = BY**

where:

**Z= Total fluid withdrawals in MMRB****A= Original Active Oil=in-Place in MMRB****X= Unit Expansion****B= Water Influx Constant****Y= Water Influx function**

### Statistical confidence intervals

### Restored-state method

### Materials balance method

### Production decline curve method

### Software

## References

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## See also

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