Reservoirs
Crude oil reservoirs
Hydrocarbon trap
Three conditions must be present for oil reservoirs to form: a source rock rich in hydrocarbon material buried deep enough for subterranean heat to cook it into oil, a porous and permeable reservoir rock for it to accumulate in, and a cap rock (seal) or other mechanism that prevents it
from escaping to the surface. Within these reservoirs, fluids will typically
organize themselves like a three-layer cake with a layer of water below
the oil layer and a layer of gas above it, although the different layers
vary in size between reservoirs