Chuka, Not sure you're still in need of an answer, and don't follow this thread so I don't know the context in which the question arose, but.....
Oil "sands" and oil "shale" differ in somewhat the same manner as "placer" gold and "desert" gold.
In oil sands, the oil is still just that, an oil on the same continuum as condensate, light oil and heavy oil, primarily a function of the amount of hydrogen attached to the carbon atoms - the less hydrogen, the "heavier" or more viscous the oil. Oil sands (commonly referred to as "tar sands") contain very viscous oil but it is still technically in liquid form, just so viscous that it doesn't want to drain out from the sand grains that have it entrapped. When it's near to the surface, like at Athabasca, it can be mined and separated mechanically (with the addition of heat) and then hydrogenated to increase it's value. If it's somewhat deeper in the ground, like at Peace River or in some California deposits, steam can be injected to "loosen" the oil from the host rock, and then the oil can be piped to special refineries that are designed to treat heavy oils.
With oil shale, the "oil", actually a compound of carbon and hysrogen, is chemically bound with the host material and is not a separate phase. It can be treated thermally or chemically to "break" it down and change it's structure and separate it from the inert host rock. As with the oil in tar sands, it may have to be "enhanced" in some manner to increase it's value and make it suitable for traditional refining.
Note the similarity (in some ways) to the placer gold situation (might be like the condensate or light oils that separate easily or the more fine gold like on the Carlin trend that takes more effort to remove from the host material, but it's still free gold). On the other hand, the "desert gold" might be more "bound up" with the host material and require different processes to free it up before further refining.
This probably goes beyond the concept of your question but it's a slow morning all around<G>. Some of the above is expressed rather simplistically and an "expert" might take exception to some of it, but I tried to answer in layman's terms - since that's what I am at this point.
Alan |
