Part of current Oil In Place (OIP) which can be recovered to the surface under specific FDP.
The maximum volume of Oil Reserves for a newly explored field is called Estimated Ultimate Oil Recovery (EUOR).
The current Oil Reserves (OR) is often split into Drainable Oil and Non-drainable Oil:
OR = Drainable Oil + Non-drainable Oil
The Non-drainable Oil is a result of deviation from the current Field Development Plan (FDP) or mistakes in FDP itself, for example, the overestimation of OR.
See Also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petroleum Geology / Oil In Place (OIP)
[ Hydrocarbon Reserves ] [ Gas reserves ]