Why is Helium found in natural gas?

Factual Questions
1

Helium deposits in the earth’s crust are thought to have been created by radioctive decay of elements like uranium and thorium. But the largest naturally occuring source of helium is found in natural gas. This fact is used by proponents of abiogenic petroleum to argue that natural gas is not a fossil fuel, because plants do not collect or concentrate helium.

If we reject the claims by Gold, et al, about abiogenesis, how do we account for the association of helium with natural gas? If it is created by radioactive decay, why don’t we find it in large deposits without natural gas?

2

Damn, I meant to post this in GQ. Mod, please twitch your nose.

3

Natural gas is, as might seem obvious, a capturing of gases underground by an impermeable caprockshaped in some sort of reservoir. By far most common are anticlines and faulting producing a cap to a formation.

When plant and animal remnants decay underground andgive off gas, it reaches the surface unless trapped. When trapped it results in a natural gas reservoir.

Meanwhile, alpha decay of long-lived radioactives produces helium. As a gas, it does much the same as the short chain alkanes: methane, ethane, propane, etc. in natural gas, escaping to the surface unless caught and retained in a reservoir.

Hence the same processes that trap and contain natural gas trap and contain helium, generally in the same locations. Therefore it is mixed with the gaseous alkanes that comprise natural gas, and commercially extractable from them.

4

[QUOTE=Polycarp]
Hence the same processes that trap and contain natural gas trap and contain helium, generally in the same locations.
[/QUOTE]
This is what I don’t understand: why in the same locations? The three conditions (radioactive decay, natural gas, and a trapping geology) are presumably independent of each other. This would lead me to believe that somewhere there is radioactive decay in under impermeable caprock formations, where natural gas does not also occur. Shouldn’t we then find significant helium deposits not in association with natural gas?

5

[QUOTE=Fear Itself]
This is what I don’t understand: why in the same locations?

[/QUOTE]

The thing is, you’d be hard-pressed to find some area of land that didn’t have plant life growing on it at some point in Earth’s biological history. So, basically, you’ve got natural gas production happening everywhere at some point in time. But, it’s only going to accumulate in cavities capable of holding it. The rest–actually the vast majority of total production–is just going to percolate up through the ground and escape into the atmosphere over the eons.

Same with nuclear decay resulting in He.

6

I doubt that there is much room for debate on this question.

Off to GQ.

7

[QUOTE=Polycarp]
Natural gas is, as might seem obvious, a capturing of gases underground by an impermeable caprockshaped in some sort of reservoir. By far most common are anticlines and faulting producing a cap to a formation.

When plant and animal remnants decay underground andgive off gas, it reaches the surface unless trapped. When trapped it results in a natural gas reservoir.

Meanwhile, alpha decay of long-lived radioactives produces helium. As a gas, it does much the same as the short chain alkanes: methane, ethane, propane, etc. in natural gas, escaping to the surface unless caught and retained in a reservoir.

Hence the same processes that trap and contain natural gas trap and contain helium, generally in the same locations. Therefore it is mixed with the gaseous alkanes that comprise natural gas, and commercially extractable from them.
[/QUOTE]

I am not doubting your explanation but has anybody done some order of magnitude calculations to check what levels of radioactivities are required to emit that much helium over the time period that it is believed the natural gas formed ? does it all add up ?

ALso has anyone ever checked radiation levels inside a “natural gas reservoir” ?

8

[QUOTE=Fear Itself]
This is what I don’t understand: why in the same locations? The three conditions (radioactive decay, natural gas, and a trapping geology) are presumably independent of each other.
[/QUOTE]

Nope, there is not 3-way independence - natural gas deposits will only be found where you have the trapping geology. Same with helium - no trapping geology, it’d just be lost to atmosphere. Given that the two are both therefore tied to geological traps, it follows that there will be an association. I get that you’re confused that the formation of the 3 things isn’t tied together, but that’s irrelevant, since we’re not looking at every incidence of He or NG formation, only ones where it’s trapped - it’s a biased, pre-sorted sample.

Also, note that (AFAIK) people don’t really prospect for He, it’s a byproduct, so if a trap doesn’t have NG signifiers, it’s not going to be tapped just for He - I doubt the profit margins are there, personally, since enough is currently produced from NG to satisfy demand.

9

[QUOTE=MrDibble]
Nope, there is not 3-way independence - natural gas deposits will only be found where you have the trapping geology. Same with helium - no trapping geology, it’d just be lost to atmosphere.
[/QUOTE]
I accept that there is no natural gas without trapping geology, but I am less convinced on why there cannot be trapping geology without natural gas. I’m still not sure I accept the claim that natural gas was created everywhere because there were plants everywhere. If that were true, there would be oil everywhere, and coal everywhere, because they do not escape to the atmosphere. It seems to me there should be some significant helium deposits under trapping geology without natural gas.

10

Oddly enough on in the USA (Texas, oklahoma) is helium found in natural gas 9in appreciable quantities). There are a few ells in Russia which produce helium, but none in N. Africa (which are major gas deposits).

11

[QUOTE=Fear Itself]
I accept that there is no natural gas without trapping geology, but I am less convinced on why there cannot be trapping geology without natural gas. I’m still not sure I accept the claim that natural gas was created everywhere because there were plants everywhere. If that were true, there would be oil everywhere, and coal everywhere, because they do not escape to the atmosphere. It seems to me there should be some significant helium deposits under trapping geology without natural gas.
[/QUOTE]
sigh Look, it’s quite simple. Natural gas (which is primarily methane) is pruduced during any decay of plant matter. Most of it either escapes into the atmosphere, or is trapped in small pockets that remain unfound until they are voided by geological or manmade upset. However, it becomes trapped and then found in large underground reservoirs where petroleum has been produced by heat and pressure (which forms cavernous sealed fields), hence why natural gas is found with oil deposits, even though methane is produced all over the place. Helium gets trapped in the same reservoir for the same reason, even though its method of production (alpha decay) is entirely independent from the mechanisms that produce natural gas and petroluem.

Could you find a mass of helium by itself in some sealed underground void? Sure, if it contained a natural radioactive that releases alphas and no plant matter is found inside. Helium (and the other noble gases that are normally chemically unreactive) are found in volcanic gas emissions. But unless it is really, really large you’re not going to be mining it for helium; there just wouldn’t be enough to collect there to make it worthwhile. On the other hand, we know that both gas hydrocarbons and helium can often be found along with oil, and so that is where helium extraction is practiced.

Stranger

12

[QUOTE=Stranger On A Train]
sigh Look, it’s quite simple.
[/QUOTE]
You can leave your attitude at the door, Mister. I am really curious about this, and it is an area I am weak in. If that annoys you, you know where to take it.

I do not see why methane would be produced all over the place, and coal and oil are not. Do they not come from the same or similar ancient plant life?

13

And:

Bolding added by me in both quotes.

14

[QUOTE=Fear Itself]
You can leave your attitude at the door, Mister. I am really curious about this, and it is an area I am weak in. If that annoys you, you know where to take it. I do not see why methane would be produced all over the place, and coal and oil are not. Do they not come from the same or similar ancient plant life?
[/QUOTE]

Wikipedia: Methane

Methane is also released from volcanic activity. In addition, there appear to be some other mechanisms for methane production besides the decaying dead plant matter method that also produces oil and natural gas.

15

[QUOTE=Fear Itself]
You can leave your attitude at the door, Mister. I am really curious about this, and it is an area I am weak in. If that annoys you, you know where to take it.
[/quote]
The question has been asked and answered, repeatedly, and your response is essentially, “I don’t believe it.” This, combined with Thomas Gold’s unsubstantiated claims about an abiogenic and self-replenishing origin for petroleum in the o.p, indicates an irritating unwillingness to consider facts or widely accepted theories that are contrary to one’s beliefs. My apologies if that comes off as snark, but I’ve become weary of people attempting to push Intelligent Design, Aquatic Ape hypothesis, or how the gas companies are suppressing a car engine that runs on water who then refused to consider basic scientific reasons why these claims are at best extremely unlikely.

[QUOTE=Fear Itself]
I do not see why methane would be produced all over the place, and coal and oil are not. Do they not come from the same or similar ancient plant life?
[/QUOTE]
Methane is the simplest complete saturated hydrocarbon; a carbon atom whose free valences are filled by four hydrogen atoms. It is the primary product of anaerobic decay of biological organisms, which requires only a lack of oxygen and temperatures low enough to permit anaerobic microorganisms to function. It can also be formed by a number of non-organic processes, provided a sufficient quantity of material and suitable pressures and temperatures, which is where deep field natural gas reservoirs come from, or from the chemical breakdown of more complex hydrocarbons, hence why natural gas is often found with and often trapped below or within liquid petroleum beds. Methane produced at or near the surface will, being lighter than air, escape and be dispersed, eventually being broken down by UV light and reduced by free oxygen or ozone.

Liquid petroleum hydrocarbons and coal/oil shale are formed under substantial pressure in sedimentary rock (although they can later be trapped in porous, non-sedimentary rock like sandstone). This is why they are not found freely on the surface save for some kind of large geological uplift. Peat (decayed organic vegetable material) is the precursor to coal and is found all over the place, especially in wetlands and depressions. Because peat is not under substantial pressure, it retains a lot of non-combustible liquids and is generally not dense enough to be a useful power source.

Helium is produced only by alpha decay in terrestrial conditions. This comes from the decay chain of [sup]238[/sup]U, which is about half alpha decay operations before it reduces to [sup]206[/sup]Pb. Given that the radioactive half-life of [sup]238[/sup]U is about 4.5 billion years (the half-lives of the daughter products down the chain are tiny in comparison) it takes a long time to release a significant amount of helium, and of course helium is both lighter than air and completely chemically non-reactive under terrestrial conditions, which means if it forms near the surface or in a porous basin it will simple escape to the upper atmosphere. At this point, the Earth probably absorbs as much [sup]3[/sup]He from the solar wind as it voids to the atmosphere from alpha decays. Fortunately, the radioactive isotopes that produce helium are mixed all through the crust and mantle, so the gas filters up from the mantle through the crust and accumulates wherever sealed geological pockets exist. These pockets are typically formed as part of creating petroleum; that is, organic material decays into a denser liquid form, and becomes more concentrated by pressure, eventually compacting and leaving a large, well-sealed void which fills with whatever is bubbling up from below. (This is somewhat simplified; these are less like large caverns than a very fine karst or vast thin permeable striations in sedimentary traps.)

In other words, every liquid and gas that is produced within the crust either gets pushed up to the surface and volitizes, or is trapped in these formations. The stuff that escapes never gets noticed (typically) because the concentration is so low, and you only find significant concentrations where the stuff gets trapped and held for geological periods. This doesn’t indicated a common origin, merely that they all get held in the same cookie jar, more or less.

A basic introductory text on geologic and petroleum formation will give you all the details you want in four colors. As for Gold’s theory, well, it’s not impossible that there is some kind of abiogenic origin for some petroleum, but if this accounted for a significant amount of naturally occurring petroleum on Earth it would require a large restructuring of geosciences. This isn’t unheard of–the now universally accepted plate tectonic theory was once considered wildly cracktastical–but what I’ve seen from Gold amounts to nothing more than fairly vague speculation about archaebacteria feeding on natural gas and a lot of handwaving.

Stranger

16

[QUOTE=Fear Itself]
I accept that there is no natural gas without trapping geology, but I am less convinced on why there cannot be trapping geology without natural gas.
[/QUOTE]
There can be. Most traps are just anticlines or diapirs or the like - common enough geological features. Then there’s the combo of permeable capped with impermeable - also common enough. That’s good enough to trap oil and NG. But to trap He? You need a better trap - one that’s even more tightly sealed than most, because He is even more mobile than CH[sub]4[/sub] and the other light alkanes. It needs a salt crust or similar to seal it in - which is why not every NG field is also a He field.

So might there be such traps with just He in them? It’s possible, I guess, but we wouldn’t know because we don’t prospect for He. We prospect for oil, mostly, and the NG and He come as accessory resources.

[QUOTE=Fear Itself]
I’m still not sure I accept the claim that natural gas was created everywhere because there were plants everywhere.
[/QUOTE]
I agree that’s an exaggeration. By the time a lot of sediments petrify, the organic fraction will already be cracked off. And some of it will migrate for 100s of km into … a trap. So don’t make the mistake that the NG has to be generated in situ. And neither does the He.
[QUOTE=Fear Itself]
It seems to me there should be some significant helium deposits under trapping geology without natural gas.
[/QUOTE]
Possibly some, but I doubt “significant” - the peculiarities of petroleum geology and the thoroughness of exploration mean that such peculiar structures as salt domes and the like are well-explored when discovered. I haven’t heard of any such that just trapped large He deposits without NG. So to answer your OP - He *might *not only be found in NG, but it’s the only kind we seem to find, whether crustal or mantle He (and we find both in NG).

17

[QUOTE=Stranger On A Train]
The question has been asked and answered, repeatedly, and your response is essentially, “I don’t believe it.”
[/QUOTE]
I said no such thing. I expressed what I thought were things that needed clarification.

I never supported Gold’s theories of abiogenesis. I specifically predicated my questions on a rejection of Gold. But even if Gold is wrong about abiogensis, I still was curious about the relationship of helium and natural gas.

At first, I attributed your snark to arrogant condescension, but now it sounds much more like defensive projection. Somehow you find it necessary to attribute all sorts of things to me that I never said, in order to quash any suggestion that there might be some gaps in the biogenic theory. If simple inquiries trigger such exasperation, I suggest you look inward to find the source of your uncertainty.