oil is a viscous material that does not flow easily. How is it that it will flow out of a bore hole?

Answer 1

The reservoir is usually hot, which makes the oil thinner and runnier.

The pressure of the reservoir also usually forces quite a lot of gas (mostly methane) to become dissolved in the oil, which makes it even runnier.

But the main thing is that as the oil comes up the well and the pressure on it is reduced, the dissolved gas comes out of solution (like when you unscrew a bottle of fizzy drink) and there is SO MUCH of it that what is actually coming up the well is a stream of gas with tiny droplets of oil in it like a mist.

Good question.

Answer 2

I have to take exception to your statement. Oil is slightly viscous and it does flow easily. Jello is more viscous and does not flow as easily. Glass is very viscous and it takes about a hundred years before any flow can be seen. Finally, the mantle is extremely viscous and the only reason it flows is because of the extreme heat and pressure causing it to circulate.

Answer 3

The Fluids in a reservoir have been subjected to high pressures for Millenia and are therefore at high temperature giving rise to low viscosity.
The pressure of a reservoir can be in thousands of Psi which will push the oil and other fluids (Water and Natural gas) to the surface where its pressure is decreased and controlled by the 'Xmas-tree' arrangement of piping and valves that ensure the safety of people, the well and of equipment.

Answer 4

Pressure, if not on its own then by gas injection.

Answer 5

pressure