We are all used to diagrams like this:
(hit your browser’s “refresh” button to see this animation again)
It seems as if there is a large cavern underground, where oil swishes and swirls, waiting to be sucked up via the production string. Dream on.
- Oil is contained within rock. The porosity of the rock is variable, take an average of 20%.
- Of the oil in the pores (called hydrocarbon in place), perhaps 15-60% is recoverable if you rely on the reservoir pressure ‘squeezing’ the oil into your production string (called primary recovery), and up to the surface. The rest either sticks to the rock, or is not recoverable when pressure is no longer available.
So, out of 1m3 (1000 kl) of rock, you get between 30-120 kl of oil during primary recovery.
How do we get more of the remaining oil out? That’s in an upcoming entry.