Radioactivity and Shale Gas: Some Like It Hot?
- Dec 2, 2010 3:08 pm GMT
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The shale deposits that have the US gas industry so excited were studied after WWII by the Atomic Energy Commission and declared to be the largest uranium resource in the US.
Because the gas industry is now going after gas by drilling into a uranium resource their new gas is contaminated with many times the radiation their former product contained.
According to Dr. V.E.Swanson, author of: Oil Yield and Uranium Content of Black Shales: “the amount of uranium in these shales is extremely large reckoned in billions of tons of metallic uranium.”
Why aren’t companies mining for uranium? There is a catch. Richer deposits were discovered.
Supposedly, when uranium becomes scarce they’re going to mine it from sea water. But first, they’ll go for what is in these shales. Sea water contains about 3 parts per billion uranium. The US shales that have all the new gas average out between 16 – 20 parts per million uranium, which is a concentration 5,000 times higher.
The richest gas and uranium bearing shales are former shallow ocean bottoms. Hence the immense extent. A large area of the US happens to be former ocean bottom. Here is a world map showing the oceans as they looked in Cretaceous times:
Geologists call some deposits that were formerly the bottoms of these oceans “marine black shales”. Bits of dead carbon based lifeforms and their wastes constantly rain down on ocean floors all over the world and accumulate along with clay and bits of rock as sediment. The organic matter preferentially absorbs, i.e. concentrates, some of the dissolved uranium that exists as parts per billion in all ocean water. Over millions of years a thick layer builds up. As conditions change layers of different composition build up on top which compress and heat the deposit. The organic matter is cooked into hydrocarbons: i.e. the gas and oil. The concentrated uranium sits there mixed in with it.
Hundreds of tons of uranium were refined from a shale deposit very similar to the US shales that contain gas, in Sweden from 1950s to the 1980s. (See page 22 in this paper.) The Alum Shale there, compared to all known shales here, is a bit higher grade if evaluated as a uranium deposit. It is now uneconomic to produce uranium from deposits of this type. Ore deposits that become uneconomic get reclassified from “reserve” status and are then called part of the “resource”. As the world runs out of richer deposits, or if prices rise and/or new technology is discovered, parts of the “resource” are reclassified into parts of the “reserve” and mining begins again.
Whatever the classification scheme, all those billions of tons of uranium are in the US shales, intimately mixed in with all the new gas.
Shale gas was once a lowly “resource” like this. The DOE mapped it out just after the energy crisis in the early 1970s. The resource was found then to be colossal, but no one knew how to extract it economically. Higher prices and new technology (“fracking”) turned the “resource” into a “reserve”.
Uranium in shale tends to be most concentrated precisely where the greatest amount of gas in shale is. Perhaps you can see now where this article is headed. Studies were done on the same US shale formations from two very different perspectives, i.e. by those looking for uranium and by those looking for gas. I looked at both.
I was wondering how much radioactivity is in the new shale gas.
A bit-o-background: all natural gas is contaminated with some radioactive radon gas. Radon is produced constantly as the uranium in all rocks undergoes radioactive decay. Natural gas extracted from a uranium deposit contains more radon than natural gas extracted from ordinary rocks. Radon decays rapidly which means it is highly radioactive. It lasts long enough to reach places where the natural gas is consumed, like your home. Burning it mixed with natural gas in, say, in a cookstove doesn’t change it at all. It survives the flames and enters the room air where you can breathe it. If it decays in your lungs, the cells nearby are blasted with ionizing radiation at close range. This is one way cancer is known to be initiated.
There isn’t a lot there. If you cook and heat with gas, you get exposed to a dose of radioactivity a mere 15 times what you’d be exposed to if you lived right next door to a nuclear reactor and you used nuclear electricity to cook and heat with instead of gas. Because reactors emit so little radiation, 15 times as much as what living next to a reactor exposes you to isn’t dangerous.
The authorities I got the 15 times figure from put it online to show people who worry about nuclear reactors how safe they are. They weren’t trying to pin a label of radioactive danger on natural gas. But how will people feel if the new gas exposes them to hundreds of times more radioactivity than a reactor?
Turning to the DOE study: Review of Rn222 In Natural Gas Produced From Unconventional Sources:
“If one were to assume that the US average concentration of 37 pCi/l of Rn222 in natural gas were due to approximately 3 ppm U238 in the reservoir rock, the 151 pCi/l of Rn222 observed in the gas from Devonian shale wells is roughly in proportion to the overall average 16 ppm U238 observed in Devonian shale.”
This gibberish can be turned into useful information. What that paragraph says is if we know how much radioactive uranium is in the “host” formation they are extracting any gas from, we can have a good idea how much radon will be in the gas, and hence, how much of a radiation dose we will get as we use that gas. The radon/uranium ratio was observed to stay relatively constant even as the uranium content varied fairly radically.
That study was intended for the gas industry. It is in the interest of the gas industry and those scouring the US for new places for them to drill to ignore or minimize the existence of uranium. And, the focus was on a shale gas industry when it was still a gleam in some gas driller’s eye. It assumed the average Devonian shale to be only 5 times as radioactive as the average host formations are that the good old regular gas comes from, and ignored radical deviations. Devonian shale is one major type the gas industry is looking at when they talk about the massive new reserves. Devonian is a subcategory of gas bearing shale: geologists refer to “marine black shales” as generally rich in gas.
But let’s go back to Swanson, the Atomic Energy Commission study guy. He said this about marine black shales: “most contain less than .01% U238” That’s 100 p.p.m. That’s 33 times as much radioactivity as the host formations for regular gas.
Swanson described “hundreds of square miles” of Tennessee where there is a 15 foot thick layer of marine black shale bearing U238 at 60 ppm. That’s 20 times as much as an average host formation they extract regular gas from.
Returning to the DOE study. It couldn’t look at shale gas in much detail. The industry did not exist compared to today: the study was written in 1980. As it says: “it has not been possible in every case to directly obtain information… …that could be considered typical of future production.”
The Atomic Energy Commission study guy, Swanson, published another paper He examined an extremely high grade (for a marine black shale) sample containing uranium in Arkansas in 1962. This was a sample that contained 0.55% U238. He described a report on another sample in the area he didn’t see personally which was 0.71% U. Incidentally, that’s 5,500 and 7,100 ppm U238, respectively. These are not typical.
At that time he summed up the US shale situation this way: “marine black shales… have an average uranium content of about .002% and a general range of about .0008 to 025%.
That’s 20 ppm average, a bit higher than the DOE found later. But note the high end of the range. 250 ppm.
Consider how they explore for gas.
I found an online edition of Pennsylvania Geology which contained an article by one of the geologists who originally mapped out the Eastern Gas Shales for the DOE. He had some advice for companies who want to prospect for shale gas. I quote:
“RADIOACTIVITY = ORGANIC RICHNESS = GAS… [ my note: the gas industry prospects for shale gas with a type of geiger counter ] Organic-rich shales have higher radioactivity responses than typical shales because the organic matter tends to concentrate uranium ions that otherwise would be scattered throughout the sediment…. …higher-than normal gamma-ray response also equates to gas-production potential. The correlation might not be 100 percent, but it is very high. This is a very important concept for those looking to produce shale gas. Many companies would look for places where the entire formation is thick, but they should actually be looking for where it is most rich in organic matter.”
In other words, companies are being advised to look for shale that is the most radioactive if they want to find shale with the most gas.
The shale formations they want to find gas in can have as much as 250 ppm U238. If they have that much they are 80 times as radioactive as “normal average”, good old red blooded American conventional gas.
80 times the radioactivity of normal average gas is going to expose consumers to 1,200 times the radiation dose they’d get if they lived right next door to an operating nuclear reactor.
I’ll certainly be sleeping a lot more soundly tonight now that I know this.
Will everyone like their gas this hot? I wonder.
Some old news reports:
Article about process water more radioactive than should be disposed of into the environment.