actually when we think about oil well at least what I used to think - a big gaping hole deep underground where all the oil gather there conveniently and a well shaft is plunge to suck up this liquid - not so.
what happens is deep deep underground the oil exists as millions of small tiny droplets trapped in between spaces of rocks called strata, also deep underground there is tremendous powerful upward pressure, the oil in droplets wants to get out but there is no where to go it is 'trapped'.
so when a well is drilled deep down it creates an 'air opening' and pressure is suddenly getting released. The pressure will force the small droplets to move thru cracks and fissures in the rock and gravitate toward the opening then it comes out oil on it's own usually with a bang in the form of geyser.
shale is different. shale is 'younger' than liquid oil and still existing as a rock. oil forms from shale naturally under the same hot pressure in the earth after billions of years. The technology is to quicken that natural process.
I think of shale as this huge 10 km long frozen ice berg that's hard as rock then to melt the ice to get the water heating probes are inserted into it over the 10 km. So for shale it's also similar after a period of 3 years of heating with hot probes over a large area out comes the oil then water is pumped to flush out that oil.
the problem with that is the reservoir goes into depletion quickly because it's being tapped over a big area, is like killing the goose to get all those golden eggs at once. So there could be several large parcels of land that are being tapped and wastes of a lot of fresh water and creates pollution.
There's a huge water crisis problem is US now that some are saying could be linked to shale. Some places like california food basket of america are dry as bone.
http://www.theguardian.com/environment/2...ht-oil-gas
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