Friday Rock Blogging: Oil Shale
This is a thin section from some Colorado shale. It’s part of the Green River Formation, which is a series of rocks laid down about fifty million years ago when the West was wet. The shales come from a set of lakes that occupied part of what is now Colorado, Wyoming, and Utah.
If you look carefully – behind the white blotches, where the contrast is too blown out to say much but they might be grains of sand or bits of shell that fell into the lake where this was forming – you’ll see that the shale was deposited in alternating layers of dark stuff and light stuff. The dark stuff is organic matter and the light stuff is inorganic, and the layering is probably an annual cycle of algal bloom and death.
There’s a trillion barrels of oil inside this rock.
The problem, for those who would like to release all those beautiful carbon atoms into the atmosphere, is that the oil is only half-cooked, so the organic matter is still solid. For oil to be oil – and more to the point, for it to be a commercially viable form of energy mining with current technology, and at current market prices – it really can’t be solid. You can’t pump a solid, you have to strip-mine it and haul it away for processing (which is expensive) and then you’ve got a bunch of useless gravel left over and dump trucks are expensive and all those pesky environmentalists are whining about how you’ve denuded the landscape.
If you cook the shale, though, the organic gunk will break down into lighter liquid components. In more petrochemically convenient circumstances, the earth does this for us – if you bury the rocks deeply enough, geothermal heat will cook the oil down for you, and then it can slowly percolate back up through cracks in the rock until it hits one of our wells. But that never happened to the Green River Formation.
With oil prices on the rise, several companies have started pilot projects in the Green River Formation to test methods of extracting the oil, either by installing large underground ovens, or by pumping in other chemical reagents designed to convert the oil to a handy liquid form. See this 2006 New York Times story for more information, or check out the ginormous bibliography of relevant technical articles maintained by the USGS.