This is the first post of what I hope will become a renaissance for this blog. I've tended to neglect it, partly because I've been working hard, and partly because when I do get time to do some blogging, it's much more fun to go moron-baiting over at hawk/handsaw. The intention is to publish something here once a week in future.
This post is about abiogenic oil, a collection of hypotheses by which oil could be created in the mantle, rather than in sedimentary basins at relatively shallow depth. A recent(ish) Hedberg Conference of the American Association of Petroleum Geologists (AAPG) addressed this issue, and the results were written up in the AAPG Bulletin earlier this year.
First of all, why is this important? For two reasons. If significant quantities of oil are produced through inorganic chemical processes in the mantle, it is possible that there is far, far more oil available for production than is conventionally thought. The much-dreaded peak oil could be put off for a considerable period of time. Secondly, current exploration is based on the biogenic origin of hydrocarbons; that hydrocarbons are created during the burial of organic material. This hypothesis makes predictions about where hydrocarbons should be found. If a significant amount of oil really is abiogenic in origin, then we need to urgently revisit how we explore for oil and gas resources.
How could abiogenic processes produce hydrocarbons? There are two possibilities: firstly, degassing of the mantle, followed by polymerisation the low-molecular-weight compounds released. Secondly, the serpentinisation of ultramafic rocks combined with a Fischer-Tropsch reaction, in which carbon monoxide and hydrogen are combined, using a catalyst, to form hydrocarbons. What both these hypotheses have in common is that hydrocarbons are produced deep in the crust or in the mantle, and must migrate considerable vertical distances to reach the relatively shallow reservoirs in sedimentary basins where hydrocarbons are normally found.
Unfortunately, the evidence for large accumulations of abiogenic hydrocarbons seems to be somewhat thin. No-one disputes that non-commercial deposits of abiogenic hydrocarbons do exist, but commercial quantities seem to be elusive. The problem is really one of Occam's Razor; where there are suggestions that hydrocarbon accumulations might be abiogenic, they can also be explained within the biogenic paradigm. For example, hydrocarbons have been found in fractured basement rocks such as granite. At first glance, this seems to be contrary to the biogenic model. On closer analysis, though, these occurences can be explained coventionally. The hydrocarbon source rock is subjected to heat and pressure, generating hydrocarbons, which then migrate via fractures. If the horizon they are generated in is overpressured, they can be forced downward. Alternatively, uplifted areas of granitic basement might have source rocks adjacent to them across faults, for example.
Another problem for the abiogenic oil hypothesis is the presence of age-restricted biomarkers. These are organic compounds that are only produced from certain types of organism. For example, a compound called oleanane is derived only from angiosperms (flowering plants). It is therefore restricted to hydrocarbons derived from Late Cretaceous or younger source rocks. Not only that, but the radiation of angiosperms through time should mean that the proportion of oleanane increases as the source rock becomes younger. This is exactly what is observed in real hydrocarbon provinces. This is consistent with the biogenic origin of oil, and not with the abiogenic origin of oil.
A third problem is the existence of oil shales. These can be explained by the biogenic paradigm: they are the strata that contain the organic material that gets buried, matures into hydrocarbons, and migrates into reservoir units of high porosity and permeability. But the shales themselves are of very low porosity and permeability. So how could fluids migrate from deep in the crust or mantle and accumulate in them?
Does all this mean that there is no such thing as commercial abiogenic oil? Not necessarily. If you wanted to find abiogenic oil in exploitable quantities, you would have to look in areas where crustal-scale fault or fracture systems could allow fluids generated deep in the Earth to migrate towards the surface, perhaps in areas of basement where there are no sedimentary basins. No-one has been looking in those places, because the biogenic model works perfectly well. It would be hugely risky to go looking for hydrocarbons using the abiogenic theory as your guide, but it could ultimately be worth it. Especially if oil prices rise much further...
Playground example of gravity-driven deformation
9 years ago
12 comments:
Interesting stuff. I came across this idea in Robert Ehrlich's book "Nine Crazy Ideas in Science" (2001). I'm not sure how his review has stood the test of time, or how good it was in the first place, but it's certainly entertaining. (He gave it a "zero cuckoo" score, for what it's worth.
Don't you still need sediments to trap your abiotic oil? I mean, there are reports of abiotic hydrocarbons from mid-ocean ridge vents, but that isn't going to help anyone since those just belch straight into the ocean.
And serpentization generally happens in places with unfriendly or absent stratigraphy (e.g. young ocean floor)
Chuck:
You don't necessarily need sediments, but you do need a reservoir and a trap. While most reservoirs are in nice permeable sandstones, that isn't always the case: there are fractured basement reservoirs, where the hydrocarbons are stored in a network of fractures in an otherwise impermeable rock.
Basically, you still need all the elements of a petroleum system: source, reservoir, seal and trap. The difference is in the source.
Paul ... I'm glad to come across your blog.
Earlier this summer I attempted to discuss this issue with a few abiogenic 'enthusiasts' on both my blog and then mostly on theirs ... I brought up a lot of what you discuss above. Ultimately, I was told I was arrogant and a disgrace to the profession of geology for presenting information that goes against their worldview (e.g., oil shale). Therefore, I put them within the "strong" abiogenic oil camp -- that is, they are of the opinion that ALL hydrocarbons are abiogenic and biogenic oil is fundamentally impossible. Like you say above, the vast majority of serious people and actual scientists acknowledge the occurrence of biogenic AND abiogenic hydrocarbons, with the main issue, as you point out, being volumes.
To me this isn't so much a question of producing or trapping an economically viable source of abiogenic oil, it is more a question of preserving it in basement.
Even relatively undeformed basement has undergone multiple deformation events and several cycles of prograde and retrograde metamorphism. In addition, each time this happens, fracture (and fault) networks open and close, and a variety of fluids of various P-T and X flush through those rocks.
Having only been in the industry a short time, I am not that familiar with the stability fields of the numerous hydrocarbons that we explore for. However, (assuming they remain trapped - a whole other bag of worms!) I'm pretty certain that they wouldn't survive the life cycle of your average basement rock!
I doubt that much abiogenic oil survives to be found - not in basement at any rate.
Are geologists allowed to have gut feelings?
brianr
Yes, you hit the nail on the head: sure there are accumulations of abiogenic hydrocarbons, but are they voluminous enough for the oil industry to get excited about? Probably not.
Hi Michelle:
That seems like a reasonable point. It's really all down to timing. Presumably if you can charge a basement fracture system with hydrocarbons during or after the latest deformation/metamorphism event, you could preserve the hydrocarbons. This issue applies to conventional biogenic reserves too: for example if you get reactivation of fault systems after the trap is charged, you can end up destroying the trap.
If there really were large accumulations of hydrocarbons sitting in crystalline basement, surely you would find remnants of them in dissected basement terranes? After all, some of these terranes have been sitting around without significant deformation for hundreds of millions of years. As far as I know, there isn't any evidence of such remnants. And if there was, you can bet the oil companies would be looking into it...
Hello, Dr. Wilson:
I came across your website in the course of my internet researches.
I appreciate your forum.
This post discusses abiotic oil.
I would like to make a few comments, reflecting on your post and abiotic oil.
Dr. Wilson states: "Unfortunately, the evidence for large accumulations of abiogenic hydrocarbons seems to be somewhat thin. No-one disputes that non-commercial deposits of abiogenic hydrocarbons do exist, but commercial quantities seem to be elusive."
I appreciate your acknowledging abiotic processes exist because I've engaged in enough discussions where there was no recognition of any abiotic processes.
(I suppose they really didn't know because most "popular" opponents of abiotic oil theory don't acknowledge abiotic hydrocarbons exist at all.)
Yes, your post reflects the current thinking among a majority of geologists, but I note a growing minority of geologists and geophysicists who do subscribe to the idea that commercial quanities of abiotic oil exist.
This is reflected a growing body of scientific literature supporting abiotic oil theory.
So, if the hydrocarbon process exists, as you acknowledge, what is the limiting factor? Because we know eruption of volatiles and other minerals can be robust.
"Eruption" can mean other phenomenon than the spectacular volcanic emissions typically associated with the word in the popular imagination.
Wouldn't hydrocarbons, as a volatile, take its place in proportion with all other volatiles, and minerals known to be associated with hydrothermal, volcanic, and tectonic activity?
Certainly, the raw material for hydrocarbon formation exists in abundance in the mantle and deep crust.
Hydrogen and carbon are present in the upper mantle and deep crust in various mineralogical formations.
The atomic and electron structure of the two elements, hydrogen and carbon, respectively, results in a chemical affinity between the two for thermo-molecular bonding as a function of ultra-high heat and pressure in the mantle in accord with general laws of mineral formation and in the deep crust as a result of serpentization and catalyst processes. Iron seems to be the best catalyst candidate.
All the above factors would seem to suggest the robust presence of abiotic hydrocarbons in various geological formations.
Thus, a limiting factor, as such, needs to be cited and identified to explain the postulate that abiotic hydrocarbon production is confined to small amounts.
(An unnamed or unknown limiting factor can not be assumed.)
Otherwise, physical observations consistent with principles of abiotic oil and physical observations inconsistent with "fossil" theory lead to the conclusion there is no, as such, limiting factor, and, therefore, what is acknowledged as happening on a small scale (hydrocarbon formation), happens on a larger scale, too.
Dr. Wilson, you go on to state: "The problem is really one of Occam's Razor; where there are suggestions that hydrocarbon accumulations might be abiogenic, they can also be explained within the biogenic paradigm."
This statement is problematic, but maybe indicative of why a majority of geologists still subscribe to "fossil" theory: Their assumption, apparently your assumption, is that petroleum is formed from organic detritus, and they rely on that assumption to maintain their belief.
Occam's razor, in short, postulates: Stay with the simple and describable process. But that is where "fossil" theory runs afoul. There is no "simple and describable process" for how organic detritus, a low potential chemical energy molecule becomes kerogen, a high potential chemical energy molecule, consisting of mostly inert minerals and heavy atomic weight hydrocarbon C215H330 and biocontaminates.
Diagenesis, is not a quantifiable description, it's an assumption.
An assumption that goes against recognized physical laws. When a theory requires one to apparently accept violation of recognized physical laws it is encumbent on that theory to provide a detailed quantifiable process to explain why it is consistent with recognized physical laws.
"Fossil" theory can't provide a detailed quantifiable process for diagenesis therefore, fails rhe Occam's razor maxim.
Dr. Wilson states: "Another problem for the abiogenic oil hypothesis is the presence of age-restricted biomarkers."
Reading your explanation carefully, I fail to understand why this provides any constraint on the presence of abiotic hydrocarbons.
You go on to state: "This is consistent with the biogenic origin of oil, and not with the abiogenic origin of oil."
How so?
The decription you provide doesn't rule out abiotic oil at all. As abiotic oil travels up to the surface from depth, it picks up biocontaminates, therefore, abiotic oil closer to the surface would have more of this oleanane biocontaminate.
Dr. Wilson states: "But the shales themselves are of very low porosity and permeability. So how could fluids migrate from deep in the crust or mantle and accumulate in them?"
Of course, the reverse is also true, if "shales themselves are of very low porosity and permeability" how would the oil escape the shale? Also, shale is a sediment, am I right? So, the abiotic hydroccarbon is embedded at the time the shale is forming at the bottom of the water body.
Particularly bodies of water that are the result of tectonic rifts would be excellent candidates for heavy hydrocarbons like those consistent with the California oil seeps to supply heavy hydrocarbons at the time of formation, which of course would also provide for biocontaminates to be embedded in the shale.
I suggest the above process is why heavy hydrocarbons, C215H330, and biocontaminates are found together in oil shales and kerogen.
And remember there are many examples of shales that have no heavy hydrocarbons at all.
This is not meant to be exhaustive and I apologize if I've unduly stretched out my comment.
But it seems important to identify assumptions and gaps that mitigate against the general tenor of your post.
I comment frequently on the Oil Is Mastery website which is devoted to abiotic hydrocarbon theory.
Dr. Wilson, thank you for the forum to offer my thoughts on the subject of abiotic hydrocarbon theory.
Dr. Wilson:
I was encouraged by your statement:
"Unfortunately, the evidence for large accumulations of abiogenic hydrocarbons seems to be somewhat thin. No-one disputes that non-commercial deposits of abiogenic hydrocarbons do exist, but commercial quantities seem to be elusive."
Specifically: "No-one disputes that non-commercial deposits of abiogenic hydrocarbons do exist..."
Your statement was also consistent with a couple of statements I've previously read:
"No one doubts that inorganic hydrocarbons may occur in association with hydrothermal systems." -- Michael D. Lewan, geologist, 2005
And:
"I don't think anybody has ever doubted that there is an inorganic source of hydrocarbons." -- Michael D. Lewan, geologist, 2002
Michael D. Lewan is a geologist with the United States Geological Survey. He is well known and respected in the petroleum geology community and is the author of many scientific papers.
But I also had a nagging feeling that not everybody agreed with your statement.
Then I remembered this scientific paper: Petroleum: To Be Or Not To Be Abiogenic, by M.R. Mello and J.M. Moldowan (2005).
Where the authors state:
"Present-day analysis of petroleum systems, when performed integrated with direct geochemistry, remote sense and high resolution geochemistry technology (HRGT), can provide irrefutable proof that 99.99999% of all the oil and gas accumulations found up to know in the planet earth have a biologic origin."
Specifically: "...can provide irrefutable proof that 99.99999% of all the oil and gas...have a biologic origin."
Carrying out to the fith place on the decimal point sure seems like these two authors state there is no abiotic hydrocarbons at all.
Both authors have been published multiple times in the petroleum literature and are also well known and respected in the petroleum geology community.
So it seems there is disagreement in the petroleum geology community.
"No-one disputes that non-commercial deposits of abiogenic hydrocarbons do exist..."
Clearly, the above statement isn't correct.
Remember, Mello and Moldowan state: "...99.99999% of ALL (emphasis added) the oil and gas...have a biologic origin."
Not just commercial oil & gas.
It's hard to get around it when authors run it out to 99.99999%...
That's about as absolute as one can get in the world of scientific probability...
So it would seem that the two conflicting views need to be reconciled in the "fossil" theory community.
But in reality it reflects the fact that there is no conclusive scientific evidence that supports "fossil" theory.
(See above quote: "Diagenesis, is not a quantifiable description, it's an assumption.")
So, it would seem, some petroleum geologists decide: "We cant't open the door even a crack to the possibility of the existence of abiotic oil because then the door would get 'pushed open then broken down'..."
Admittedly, the above quote is imaginary and speculative on my part, but what's for sure is that the geology community is divided about abiotic oil theory even in the majority that supports "fossil" theory.
Could this divide be because the science for "fossil" theory is not conclusive?
Dr. Wilson:
I noted you do research for StatoilHydro.
Do you know Martin Hovland? He works for StatoilHydro. Martin Hovland has some interesting and provocative theories that he has published, which are available on his website.
Anaconda:
Thanks for your comments. I'm not ignoring you, it's just that I have many other things to do imminently. I will try to address some of your points a bit later.
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