When oil is taken from a well what replaces it?

Question

I'm not sure of the figures but if 2 million barrels of oil are pumped from the ground a day, what is put back in the hole.

Surely with the amount of oil that has been removed this would have some effect?

2 million was a just a starting figure.

Answer 1

1/ There is still oil in the reservoir even when the exploitation is finished. Basically 30 to 70% of the oil remains.
The rock impregnated of oil is like the sand impregnated with water on sea side. When you dig, you will pass from totally dry sand to wet sand without free water and finally wet sand with free water. The wet sand without free water is a sand where the capillary forces are keeping the water bound to the sand grain. You will never succeed to get this water by normal forces.
2/ When you remove the free water or the free oil, first there is a compaction of the rock. Which means that the porous rock will "collapse on its on weight", In some places in the world, the compaction leads to important surface collapse of metric significance.
3/ Then, part of the oil will be replace by water which is "pushing" often the oil outside the reservoir (water drive reservoir) or by gas (gas drive).
4/ In some cases, the human are re-injecting water or gas to maintain the pressure of the reservoir. Part of the oil will be swept and replaced by injected water.

Answer 2

Nothing goes in the hole, which is held open by using steel pipe. The rock underground is like a sponge. To get liquid out of a sponge, you squeeze and the sponge gets smaller. Oil flowing out the pipe reduces the pressure in the rock, so the over-all rock formation compresses. This is noticed in some oilfields by the ground surface subsiding, getting lower in elevation. When the pressure is high enough, it can push the oil up the pipe like a gusher, but eventually that lowers so a pump has to be used to produce the oil. The reduced pressure also allows other liquids to flow in so that eventually it is water or saline water that will be produced at the well. When too much water dilutes the oil, the well is shut in and abandoned. It is very rare for a well to actually go dry, that is all the liquid removed from the rock.

Answer 3

A very basic, understandable explanation

Oil is generally produced by a 'Water Drive'.
This is water moving upwards below the oil and gas in a reservoir. (Water is not pumped in at the start of a well's production).

The fluids, oil and natural gas were formed millions of years ago from decaying organic matter, and rose above the water passing through small pores in permeable rocks until it became trapped by an impermeable 'Cap-Rock' or a rock 'Fault'.

As the fluids built up under the cap, pressure also builds up until geologists discover the formation and wells are drilled.
The pressure is sufficient to drive the oil and gases to the surface, under control of a 'Well-head' (a system of valves and control units), from where they pass into separation units and processed.

The idea that the oil and gas are contained in a 'cave-like' structure is wrong. The rocks underground contain the fluids in their pores.
As the pressure is released, water gradually takes up the spaces (pores) left by the oil and gas until water begins to be produced with the oil and, when it becomes too much, the well bottom will be cemented to a certain level and the piping re-perforated at a higher point to decrease the amount of water produced.
At some point, the natural pressure of the well will be insufficient to produce more oil.
Surveys are carried out to determine whether or not enough oil is still available and the well can be re-activated by a 'gas-lift injection' or a 'Water Flood' injection or 'Down-hole pumps' to continue producing oil.
The rocks holding the oil may be 're-fractured to increase the size of the pores which have 'silted up' blocking the migration of fluids through the formation. This is done by 'acidising' the rocks - injection of acid to dissolve the blockages and increase the pore size again.

The production of millions of barrels of oil does not form cave-like holes in the formation.

Answer 4

They pump water in to get the oil out.

Also, your 2 million barrels is low. I worked in Saudi Arabia for some time, and they were producing 6-10 million barrels a day on their own.

One crazy statistic that will amaze you, is that at the height of production in the Persian Gulf, it was said that there was an oil tanker every 40 miles on route between the Gulf and Japan.

And USA would be getting even more than that.

Answer 5

Water

Answer 6

Non contaminated water is forced in to the well before they extract the oil. This pumping process is done slightly away from the place where they extract oil.

Answer 7

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