[thackney]

If I recall correctly.... my understanding about oil wells is that, as years of production pass, the light sweet crude (the easily refined stuff) comes out of the ground first and is (obviously) the first to be depleted. What's left ("at the bottom") as an oil well ages is heavy, sour crude -- a sludgy concoction with lots of sulfur and other impurities.

You do not recall correctly.

[NYorkerInHouston]

Thackney,

When you get a chance take a look at this pdf and tell me what you make of it. It takes an alternate view of the prospects of shale (mind you I'm still optimistic about Shell's new process, cautiously optimistic but optimistic).

http://www.aspousa.org/assets/pdf/OilShale.pdf