Yesterday we talked about some common rock types, granite and basalt and some others. Today, let’s talk about a very special rock type, but one that’s specific to the Ordovician.
Kukersite is oil shale – one of the richest oil shales in the world, with as much as 40% organic material in it. It’s found in Estonia.
First, let’s distinguish between oil shale and shale oil. Shale is a very fine grained rock, solidified from mud. Oil shale is a rock – not liquid – in which a lot of organic material, called kerogen, has been incorporated with the sediment. Shale oil, like the famous Bakken in North Dakota, is entirely different – it’s liquid oil, trapped in very tiny, very poorly interconnected spaces, in contrast to a good oil reservoir like a sandstone with lots of open pore space and plenty of interconnectedness to allow the oil to flow. Some of the Bakken isn’t even in shale, but it in dolomite. The main difference is that oil shale is a rock that does not contain ANY liquid oil. To get the organic matter out, you have to mine the rock, then cook it. The organic stuff might burn directly, like it does in peat or coal, or you can use a distillation system to convert the solid kerogen to liquid oil. See also this post.
The geology of the Ordovician kukersite in Estonia suggests that there were episodic periods when the waters there were anoxic – lacking in oxygen. The alternation with periods of more oxygenated water resulted in maybe 50 separate beds of kukersite, separated from each other by layers of limestone and other rock. The individual kukersite layers are typically around 20-30 centimeters thick, but some are a couple meters thick.
The setting was probably something like a low, flat tidal zone along the sea coast that was periodically cut off from circulation, so that stagnant, swampy conditions developed. What was in those swamps? This was the Ordovician, so don’t visualize the Okeefenokee Swamp, with big trees, lily pads, and such. The life that put its organic matter into these sediments was algae. In fact, algae and other microbial plants are the greatest contributors to the source rocks that make all oil and natural gas. The volume of dead animals was usually far too small to add significantly to the stuff that would become oil – so forget that attractive idea of dinosaurs in your gas tank. It was algae.
The Estonian kukersite – a rock that burns – was known as long ago as 1700, or even earlier, but its commercial development began in 1918 in the face of fuel shortages resulting from World War I and the Russian Revolution. Production has continued pretty much up to this day, with both open-pit mines and underground mines. It’s an important energy resource for Estonia. In 2011, Estonia manufactured about 11,000 barrels of oil per day from its oil shale – a bit less than half of its needs. 90% of Estonia’s electricity comes from plants fueled with oil derived from oil shale.
It’s important as a local resource, but producing oil from oil shale is expensive, given that you have to mine it, like you mine coal, then you have to input a lot of energy to heat it up to distill the oil out of it. We know how to do this technologically; the issue is the cost. Building a high-volume oil shale reduction plant might cost something comparable to an oil refinery – maybe several billion dollars or more, with many, many years before you get a real return on your investment. Conventional crude oil’s energy return on investment is 20 to 40 to one, while oil shale’s return is more like 2 to 1. You don’t make much money, and it takes a lot longer to make it. For an oil shale plant to be economic, I’ve read figures all over the map for a sustained price of oil, from $80 per barrel to $150 per barrel. I think something like a cost to produce of $90 to $100 per barrel for oil shale is reasonable. If that’s the production cost, then you have to add taxes, royalties, and so on, plus a reasonable 10% profit margin – and you end up with oil from oil shale being worth it when the price of oil is something like $130 per barrel.
So, yes, there is a LOT of oil tied up in oil shale – estimates of as much as a trillion barrels are common. But it will be expensive to produce it.
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March 27 is the anniversary of the earthquake in Alaska in 1964 that killed 139 people. Here's a link to a couple good videos.
—Richard I. Gibson
Map from USGS