Friday, March 13, 2009

Oil Shale Will Set Us Free! (right?)

Recently, NPR had a story about the role of oil shale in the American petro-economy complex (I made that phrase up, but I think it sounds kind of neat), likening the Pieance Basin to an "American Saudi Arabia" rich in oil shale. It was an interesting story, particularly in the context of the recent reversal of an old Bush policy that made it easier for Companies to lease and explore oil shale production schemes. Now, I work in rocks of similar age to the Pieance (specifically, the clastic phase of the Wilkins Peak Member of the Green River Fm, famous for it's own oil shale), so I was a little familar with the crazy development schemes some folks have come up for these oil shale deposits. One of the things that always strikes me is the fact that very few discussions about oil shale actually tell you what the stuff is, which is kind of important, as prospecting and (potentially) developing oil shale economically is pretty different from the more traditional hydrocarbon methods. The picture below is a bit of organic-rich oil shale in Outcrop from the Laney Member of the Green River Fm. The richest oil shales are always that blueish-purple in outcrop.

So, what exactly is "Oil Shale"? Well, to paraphrase a geologist who has worked extensively in these deposits, oil shales are neither Oil nor Shale. Actually, they are organic rich micrites, relatively common in some lacustrine deposits (such as those formed by Eocene Lake Gosiute in SW Wyoming). The organic matter is mostly derived from algae living in the lake, and total organic content can range considerably; in the Mahogany Zone, one of the major oil shale intervals of the Uinta Fm in the Pieance Basin, total organic carbon is 40%!

The picture above shows just how rich these rocks are in organics; pretty black stuff, huh? This picture is from oil shales in the Tipton Member of the Green River Fm, SW Wyoming.

This picture above is an interval of Oil Shale from the Wilkins Peak Mbr in core. Again, organic rich, huh?

YET ANOTHER picture, also from the Tipton; these rocks actually smell like petroleum, and sure enough you can set them on fire and they'll burn. Of course, they smell like a tire fire, but that's the price of Energy Independence, I guess.

And there are a LOT of these THICK intervals in the Green River Fm, too; the picture above is from the Tipton, again, showing a thick (whitish) interval of rich oil shale. Start thinking about this in 3-D, and you quickly realize that there is a considerable volume of these oil shales throughout SW Wyoming (in the Green River) and down into the Uinta Fm in the Pieance Basin, in Colorado.

Now, some folks start thinking about all that hydrocarbon, and can't help but get droolin' a little. But how would you get these at these hydrocarbons? Well, as you can see in the Green River (and the Uinta Fm), these intervals are fairly shallowly buried (if not directly exposed). You could mine them directly, and then cook the oil out in some sort of processing, I reckon. Of course, then you're left with a huge, ugly-as-hell open pit hole sitting there.

Other schemes are plentiful, of course, and include in situ heating, hyrdo-fracing, and all sorts of Strangelovian schemes that generally require a substantial input of energy, which changes the ol' equation a bit, you know? I sort of wonder what kind of efficiency you could hope to get out of subsurface extraction?

Oh, and remember how I said that these things smell terrible when burned? Well, turns out there are probably several good reasons for this; oil shales are dirty. Like, filthy. Like, Larry Flynt filthy, man. This study, done on an Estonian power plant that burns Oil Shale for energy, shows that these things have ridiculously high concentrations of heavy metals in them, much higher than even low-grade coals. Kinda grim, really.

All in all, I think I have to applaude Obama's "Hold-on-a-minute-there-pardner!" policy reversal in regards to Oil Shale development. It's fine to push technical and geological innovation, and I certainly think oil shales warrant further study. I can tell you, there are some VERY interesting stratigraphic relationships between these organic rich intervals, clastic phases, and evaporite phases in the Green River Basin (check HERE if you don't believe me!), and careful study of the stratigraphy and depositional processes associated will probably help us understand all sorts of source-rock issues (at least). BUT, I think that there are substantial economic, social, and environmental issues at stake here that really do need careful, considered, and multidisciplinary study before we dig up all of SW Wyoming in some mad bid to become "Energy Independent".


Chris R said...

Cool photos! Do you know if the organic content or composition are affected much by burial and heating or surface exposure? I'd expect the effect to be minimal, as most of the organic phases are pretty insoluble and immobile - one of the reasons its tricky to get more energy from what you extract than the amount you put in to extract it.

Eric said...

Your right Chris - the organic phase is kerogen, so it's pretty much stuck there, and there is fairly little effect of burial or exposure on total content.

Silver Fox said...

Nice post! Glad to learn something down to earth about oil shales. I'm always imagining the ones in Canada, without having really examined any, but can relate to the Green River and Mancos Formations. It seems like it would take a lot of drilling to prove these things out, unless the high-organic zones are highly laterally continuous. It would be interesting to get involved from an exploration standpoint, but even with the price of oil to $4/at the pump, the mining/extraction might be too expensive, especially with whatever 'cleaning' is needed to meet environmental standards.

Eric said...

Silver Fox - commonly, the oil shales are fairly laterally extensive; they are commonly "railroad tracks" in the correlations, although there are changes in TOC in a marginal-distal trend in a lot of these lacustrine oil shales.

Also, I recently dound out that there are some fairly substantial oil shales in Nevada!

Andrew Alden, Oakland Geology blog said...

Physics Today has a world-readable article on the industrial processing of oil shale -- seems like a lot a processing for a barrel of sludge to burn up as fast as possble.

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