in terms Geology: subsurface formation of porous,
permeable rock (usually sandstone,
limestone, or
dolomite) containing oil or gas within the rock pores. A typical oil
reservoir contains gas, oil, and water, which occupy the upper, middle, and
lower regions of the reservoir, respectively. The flow of reservoir fluids
from the rock to the borehole is driven by gas
pressure or water pressure.
Also see enhanced
recovery, rotary drilling.
Lubrication: primary lubricant repository in a
lubrication system, e.g., crankcase, gear box.