Given the unimaginable volume of petroleum products we have been extracting over a century, why does the Earth not crumble on itself from the void?
In: 3
Because the volume of the earth is 1,097,509,500,000,000,000,000 cubic meters.
Gonna have to remove a lot more than just oil for it to cave in on us.
Because it doesn’t exist in any sort of “lake-like” opening that leaves an empty space if you pump it all out.
Oil, for example, is just tiny droplets that fill in pores on rocks deep beneath the surface.
This is a real oversimplification, but imagine filling up a bucket with marbles. Then add water. If you were to then extract the water from the bucket, the marbles aren’t going to collapse in on each other because the water only occupied vacant space in the first place.
The amount of oil we have removed from the earth is rather imaginable: [recent estimates](https://www.petro-online.com/news/fuel-for-thought/13/breaking-news/how-much-oil-have-we-used/34379) place a lower bound on the amount of oil extracted from the earth since 1870 at ~135 billion barrels of oil, a volume of ~21,463,284,815 cubic meters, or **~21.5 cubic kilometers**.
The volume of the earth is **~1,083,206,916,846 cubic kilometers**, ~150 billion times larger.
The [volume of water](https://justinweather.com/wp-content/uploads/2021/10/earth-volume-air-water-adam-nieman.jpg) on, in, and around the earth is **~1,386,000,000 cubic kilometers**, ~780 times smaller than the volume of the earth, but ~62 million times the amount of oil we have extracted from the earth in the past 150 years.
But like underground water, oil doesn’t usually live in open voids in the earth, which, as you pointed out, can (and do) tend to get filled in by the bits of the earth sinking into them. Oil is largely found in porous substrate and interstitial spaces, so the amount of sinkage of the surface of the earth has been extremely minor. Given all of the other forces shaping the surface of the earth, ‘undetectably minor’ might be more appropriate.
So, yeah, if you lived in a 1-square-kilometer town, and a 20 cubic kilometer void appeared underneath it, there would be a hole 20 kilometers deep, which would be problematic. But the real-world situation is that aside from the occasional sinkholes – which are often directly caused by humans mining deep holes in the earth – extracting oil has had a negligible effect on the surface of the earth.
(The *atmosphere*, on the other hand…)
Edit:
According to Mathcad, which craps out beyond 17 decimal places, if:
* Earth was a perfect sphere with a radius of 6371 km, and
* all of the oil we have extracted from the ground in the past 150 years had been uniformly extracted from the entire surface, and
* extracting oil left a void commensurate with the volume of oil extracted
… the surface of the earth would have sunk by 0.042 millimeters.
[It can](https://www.blueridgeoutdoors.com/go-outside/does-oil-drilling-cause-sinkholes-or-earthquakes/). The oil needs to be replaced with other liquids, either intentionally or by natural pressure-equalizing processes. If it’s not replaced, the pressure is sufficient to collapse the void, even though the void is made of a less-dense clump rock rather than a literal cavern. Because it’s the compression of rock, the effect is typically not as dramatic as a sinkhole, and not as fast.
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