How long does oil take to form?

[zompist]

I asked this once on a much larger forum, and didn't get a good answer. But maybe people want to try!

Let's say we want to think ahead to the next civilization. We'd like them to have some oil and coal. These are, most scientists believe, derived from plants and other primitive stuff (algae, diatoms) that died eons ago.

My question is: how long does this process take? Do you need 3 milllion years, or 30 milllion, or 100 million?

Also, can you accelerate it in any way, if you laid down a bed of the right plant material now?

[KathTheDragon]

I did a bit of cursory searching and the one thing it seems people can agree upon is "we don't know".

[bradrn]

I asked this once on a much larger forum, and didn't get a good answer. But maybe people want to try!

Let's say we want to think ahead to the next civilization. We'd like them to have some oil and coal. These are, most scientists believe, derived from plants and other primitive stuff (algae, diatoms) that died eons ago.

My question is: how long does this process take? Do you need 3 milllion years, or 30 milllion, or 100 million?

I’m certain I learned this in first year geology… hmm, let me check the textbook…

…OK, so apparently, the textbook does not in fact cover this topic. But here’s some relevant excerpts from Bjorlykke (2010):

In the Miocene-Pliocene basins in California, 5–8 km or more of sediments have been deposited in roughly as many million years … which is a very high figure in this context. … In the Ventura Basin which continues into the Santa Barbara Channel, there are about 15 km of young sediments (<4–5 million years) which have been folded and which contain large amounts of oil.

… increasing sedimentation rates will reduce the geothermal gradient because some of the heat flux is used to heat new layers of subsiding sediments. Cold basins with rapid subsidence and low geothermal gradients (<20–25°C/km) require deep burial of the source rocks before they can generate petroleum, both because of low temperature and the short geologic time (<2–3 million years) for petroleum generation.

… With increasing temperature the chemical bonds … are broken and kerogen is transformed into smaller molecules which make up oil and gas. This requires that the temperature must be 100–150°C over long geological time (typically 1–100 million years).

… Four factors are thought to contribute [to the formation of oil]:

1. Temperature
2. Pressure
3. Time
4. Minerals or other substances which increase the rate of reaction (catalysts) or which inhibit reactions (inhibitors).

Temperature is clearly the most important factor, and hydrocarbons can be produced experimentally from kerogen by heating it (pyrolysis). This reaction is time-dependent and in laboratory experiments,where time is more limited than it is in nature, fairly high temperatures (350–550°C) have to be used in pyrolysis. This is the case when oil and gas is produced from oil shales by pyrolysis of immature kerogen in ovens after quarrying … The conversion of organic matter begins at 70–80°C, given long geological time. Between 70 and 90°C the transformation of kerogen proceeds very slowly, and it is only in ancient, organic-rich sediments that significant amounts are formed. Most of the maturation process occurs between 100 and150°C. Here the degree of kerogen transformation is also a function of time. This means that rocks which have been subjected to 100°C for 50 million years are more mature than rocks which have been exposed to this temperature for 10 million years. As the organic-rich sediment (source rock) is buried in a sedimentary basin, it will normally be subjected to increasing temperature as a function of increasing burial depth. If we know the stratigraphy of the overlying sediment sequence and the geothermal gradient and the subsidence curve, we can calculate the temperature as a function of time.

… A theoretical maturity parameter (P) can be calculated by integrating temperature with respect to time: P = ∫₀^t 2^T/10 dT; t, geological time (million years); T, temperature (°C). We see that a doubling of the reaction rate for every 10°C is built into this expression (Geoff 1983). When the temperature rises above about 130–140°C, maturation proceeds very rapidly, and then the time factor is less crucial. There are differing views as to how much emphasis should be placed on time in relation to temperature in the matter of maturation. Oil companies use different formulae for calculating these temperature factors and the 10-degree rule is now found not always to be valid,particularly for very young sedimentary basins with high geothermal gradients. … In basins like the North Sea the rate of heating is typically only 1–2°C/million years but during rapid subsidence and sedimentation in the late Cenozoic the heating rate was higher. During the deposition of 1–1.5 km of upper Pliocene and Pleistocene sediment in 2–3 million years, the gradient was lowered but the heating rate must have been about 10°C/million years.

So in general, it seems that temperature is a far more important factor than time, and you can get oil pretty quickly (geologically speaking) if you have a high enough temperature.

Also, can you accelerate it in any way, if you laid down a bed of the right plant material now?

I doubt it. You’d essentially have to find a way to speed up deposition and erosion — oil forms quickest at great depths (i.e. high temperatures), so you’ll need to find a way to bury it several kilometres underground and then exhume it quickly. On the other hand, as quoted above, it is entirely possible to make oil in the lab by heating kerogen. (But then where do you get the energy for that process from?)

[zompist]

Thanks, Brad, that's a great answer!

The next question is how far down you have to go to get these temperatures. If I'm reading this page right, it's 2 to 3 km.

Or you find places like Larderello, Italy, where you get 200°C just half a km down. It's now a hotspot (ha!) for geothermal energy.

[bradrn]

Thanks, Brad, that's a great answer!

The next question is how far down you have to go to get these temperatures. If I'm reading this page right, it's 2 to 3 km.

Or you find places like Larderello, Italy, where you get 200°C just half a km down. It's now a hotspot (ha!) for geothermal energy.

Yep, temperature gradient is very highly dependent on local geology, and is especially high in volcanic areas. Consulting the textbook again, the average value in the upper crust is 25 °C/km, though of course it varies widely from that average. Bjørlykke (whoops, just realised I misspelt his name last time) gives the following nice diagram of oil and coal generation vs depth/temperature:

oil-formation.png (11.31 KiB) Viewed 7852 times

[Moose-tache]

Apparently in Russia at the Uzon Caldera there is natural petroleum that is only 29k years old, formed near significant hydrothermal activity, supporting the model that relies on temperature.

I might actually be of some help here, since I used to work in a petroleum research lab in the middle east. If you want future people to have oil, it's not enough to just lay down plants. That just gives you organic fertilizer. What makes oil deposits possible is that the vegetable matter accumulates in an anoxic environment, then there is a permeable layer of rock, usually limestone, on top of the source rock, and then an impermeable layer on top of that. This allows the petroleum to percolate up into the porous rock where it can be extracted, but it doesn't just seep into the biosphere to become peat or atmospheric carbon or whatever. In other words, you need carbon sequestration, which is already happening around the world. The most elegant solution just pumps CO2 back into depleted oil fields under enormous pressure. Of course, these are more likely to form carbonate rock than oil, but that's another story. For what it's worth, I'm told the place where future oil is being formed most extensively is under the Black Sea.

So the take away seems to be, you're trying to lay down large amounts of the right type of rock, and you need to go down far enough to achieve very high temperatures. This is getting very complicated. I think it will be much easier to give oil to future generations by growing a bunch of canola and then storing it in plastic barrels.

[zompist]

Apparently in Russia at the Uzon Caldera there is natural petroleum that is only 29k years old, formed near significant hydrothermal activity, supporting the model that relies on temperature.

Ooh, very interesting. For my purposes I'd really like something that can be done in 3 million years or so. It sounds like it's not impossible.

What makes oil deposits possible is that the vegetable matter accumulates in an anoxic environment, then there is a permeable layer of rock, usually limestone, on top of the source rock, and then an impermeable layer on top of that. This allows the petroleum to percolate up into the porous rock where it can be extracted, but it doesn't just seep into the biosphere to become peat or atmospheric carbon or whatever.

Also great info. This sounds like a lot of work. I suppose it would be sloppy to let gravity do most of the work, i.e. digging a huge hole and dropping the rock down...

So the take away seems to be, you're trying to lay down large amounts of the right type of rock, and you need to go down far enough to achieve very high temperatures. This is getting very complicated. I think it will be much easier to give oil to future generations by growing a bunch of canola and then storing it in plastic barrels.

The plants, or the oil? Why would that be better? If it was, wouldn't we be powering everything with canola oil now?

FWIW, I'd prefer schemes that don't require burning more oil than we generate. It's sounding like "fill up an old mine with plant debris" would work, in a geothermal region with the proper rock structure above the mine. But maybe you need mind-boggling amounts of plant material?

[bradrn]

My understanding is that if you don’t have the right rock formations, your oil/gas will form just fine, but then it will move through the crust and escape out into the atmosphere. This may or may not be what you want. (From what resources I can find, it looks like this is what’s happening at Uzon: the oil simply seeps out into the soil, where it presumably evaporates.)

FWIW, I'd prefer schemes that don't require burning more oil than we generate. It's sounding like "fill up an old mine with plant debris" would work, in a geothermal region with the proper rock structure above the mine. But maybe you need mind-boggling amounts of plant material?

I was going to say that this probably wouldn’t work, but then I read that the oil at Uzon probably comes from algae growing on soil around the volcano. Now I’m not sure. However, given that it takes >50 years for conversion into oil to take place, I’d suggest that carrying out pyrolysis in the lab may be more practical. (Indeed, that paper says that ‘The process is technologically feasible: lipid-containing photosynthesizing organisms can be cultivated with the follow-up conversion of biomass into liquid fuel.’)

[zompist]

I was going to say that this probably wouldn’t work, but then I read that the oil at Uzon probably comes from algae growing on soil around the volcano. Now I’m not sure. However, given that it takes >50 years for conversion into oil to take place, I’d suggest that carrying out pyrolysis in the lab may be more practical.

More practical for what? I don't want fuel now, I want it in a few million years.

No to be mysterious; this is an idea for Almea. There was an advanced industrial civilization that long ago. The question isn't "how could they have generated fuel for themselves". It's "How could they re-create deposits of oil for a far future civ", perhaps because they've used up the ones they had.

And yes, I know they could just leave oil in the ground; that in fact is an idea I'm using.

One scenario of interest is accidental deposits: did any oil develop just with 3 million years of time? Sounds like it's possible (cf. Uzon) but it would require some pretty strong coincidences (geothermal activity plus raw materials plus the right roof structure). The other scenario is purposely creating deposits for later.

[bradrn]

I was going to say that this probably wouldn’t work, but then I read that the oil at Uzon probably comes from algae growing on soil around the volcano. Now I’m not sure. However, given that it takes >50 years for conversion into oil to take place, I’d suggest that carrying out pyrolysis in the lab may be more practical.

More practical for what? I don't want fuel now, I want it in a few million years.

Ah, OK, I thought you were looking for a way to generate oil for contemporary use.

No to be mysterious; this is an idea for Almea. There was an advanced industrial civilization that long ago. The question isn't "how could they have generated fuel for themselves". It's "How could they re-create deposits of oil for a far future civ", perhaps because they've used up the ones they had.

And yes, I know they could just leave oil in the ground; that in fact is an idea I'm using.

In that case, I’m going to say that that’s certainly possible. Given what we know about Almea, I’d say the iliu are easily capable of doing it, and if the Count of Years is to believed, they were just as advanced (if not more so) in prehistoric times. (Even humans can turn kerogen into oil in the lab; it’s not like it’s a particularly difficult reaction.)

One scenario of interest is accidental deposits: did any oil develop just with 3 million years of time? Sounds like it's possible (cf. Uzon) but it would require some pretty strong coincidences (geothermal activity plus raw materials plus the right roof structure). The other scenario is purposely creating deposits for later.

As mentioned earlier, the Ventura Basin (<4–5 million years old) contains oil, so that sounds plausible.

[Ares Land]

As an aside, what would happen to the Precusors' landfills and trash? Could it give rise to an oil field, if buried in the right place?

[linguistcat]

I thought another issue with these is that they came from a time when nothing decomposed cellulose in trees. We now have many organisms ranging from microbes to small insects to some large herbivores that help to break down cellulose into CO2 and other byproducts. Even without the issues of needing the plant matter to be in a certain location or a certain temp for however long, in modern times it is likely to just be processed by at least the microbes instead.

[bradrn]

I thought another issue with these is that they came from a time when nothing decomposed cellulose in trees. We now have many organisms ranging from microbes to small insects to some large herbivores that help to break down cellulose into CO2 and other byproducts. Even without the issues of needing the plant matter to be in a certain location or a certain temp for however long, in modern times it is likely to just be processed by at least the microbes instead.

My understanding is that this was a theory once, but seems to have been refuted since then. See e.g. Nelsen et. al., Janusz et. al. Probably a bigger factor was that trees back then were 90% lignin, compared to 10% lignin for modern trees. (One caveat: I can’t seem to find a source for that statement, though I’m certain I remember reading it on Wikipedia.)

[Otto Kretschmer]

Is oil a conlang?

[linguistcat]

My understanding is that this was a theory once, but seems to have been refuted since then. See e.g. Nelsen et. al., Janusz et. al. Probably a bigger factor was that trees back then were 90% lignin, compared to 10% lignin for modern trees. (One caveat: I can’t seem to find a source for that statement, though I’m certain I remember reading it on Wikipedia.)

Ah, that's neat. If you can find the source about the lignin thing, it would be nice to have for world building.

[alice]

Is oil a conlang?

Or is it the same as the "langue d'oil"?

[Moose-tache]

The plants, or the oil? Why would that be better? If it was, wouldn't we be powering everything with canola oil now?

IIUC, your plan was to create oil that future generations can use. Geological methods are slow and inefficient. Using oil made by plants is fast and much more efficient, in the sense that you don't need to spend money moving rocks around. You absolutely could run a civilization on canola oil if you wanted to. We don't, but we could. Remember that period of modern history when the hot new energy source was the rendered flesh of large aquatic mammals? People even used penguin oil as a fuel source for a time (don't google that). Oil is oil.

If you're dead set on petroleum-based oil, then yes, you could fill a mine with plant matter. It wouldn't take an enormous amount, assuming you first extract most of the air and water from it. My recommendation would be to grow trees, burn half of them to turn the other half into charcoal, stuff them down a mine shaft, put a thick sheet of polystyrene on top to seal it, and walk away. Polystyrene is the only common plastic heavier than water, so it won't float away, and it can be made from plants if you have the right equipment.

[Raphael]

Is oil a conlang?

If you go to the main ZBB overview page, you'll see that the full title of this forum is "Conlangery [line break] Conworlds and conlangs".

[bradrn]

My understanding is that this was a theory once, but seems to have been refuted since then. See e.g. Nelsen et. al., Janusz et. al. Probably a bigger factor was that trees back then were 90% lignin, compared to 10% lignin for modern trees. (One caveat: I can’t seem to find a source for that statement, though I’m certain I remember reading it on Wikipedia.)

Ah, that's neat. If you can find the source about the lignin thing, it would be nice to have for world building.

Found one, though it turns out it was bark, rather than lignin:

The main support tissue in the giant lycopsids was bark instead of wood. These trees had thick bark, sometimes more than a foot (~ 30 cm) thick. Packed one upon the other after death and collapse, the bark of these trees makes up most of the coal mined in the Eastern United States and Western Europe. A small cylinder of wood in the center of the trunk transported water throughout the trunk and to the leaves.

Nonetheless, I managed to find at least one dissenting opinion (DʼAntonio & Boyce 2020):

Across all six genera of Pennsylvanian arborescent lycopsids that were investigated, all evidence indicates limited periderm production: typically < 5 cm, always < 15 cm, even in trunks that would have reached 1 m or more in diameter.

[keenir]

I thought pre-Permian oil was from the trees that shed their branches rather than their leaves....i was never sure where post-Permian oil was from. *shrugs*

like this, i think...https://en.wikipedia.org/wiki/Archaeopt ... daptations