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Monday, January 31, 2011

The Flood geology of oil

Oil is an interesting subject in geology for many reasons, not the least of which derives from its modern importance to domestic and foreign policies on energy, environmental safety, climate change, and perhaps even military action (at least in the public perception). In other words, the study of oil directly affects us all in some manner. As I see it, the sociological consequence is twofold: on the one hand, geology gains public reputation as a vital scientific discipline; on the other hand, everyone seems to have a strong opinion—albeit commonly misinformed—on the topic of oil.

But lucky for you, I am not here as a political commentator. For this post, I am more interested in discussing the geological origin of oil and gas resources.

The study of oil’s origin and subsequent migration, accumulation, and recovery falls under the discipline of petroleum geology, which elegantly combines aspects of stratigraphy, sedimentology, paleoclimatology, oceanography, geochemistry, geophysics, structural geology, and even engineering. As such, it is also a complex and in-depth subject, so I would summarize it in this way: 1) organic matter is preserved through its burial in sediments, which undergo pressure and heat at depth (like an oven); 2) oil is buoyant compared to other fluids in the rocks and migrates through pore spaces and fractures in the overlying rocks; 3) if migrating oil meets an impermeable barrier (which can take on many forms), it will be trapped and accumulate until the barrier is compromised. Simple, right? Well, petroleum geologists must also be aware of several guiding principles, which account for the fact that only a tiny percentage of Earth’s past life has produced oil:

1) Organic matter decays in the presence of oxygen (this is intuitive, especially for gardeners that produce their own compost). Thus organic matter must be isolated from an oxic environment before it returns to the atmosphere and ocean (and for reference, more than 99% of organic matter is oxidized and escapes burial in the modern carbon cycle).

2) Organic matter must undergo thermal maturation, but not too much. This is much like understanding the basics of baking a cake: too little heat and/or time and the cake is ruined; too much heat and/or time and the cake is ruined. If organic-rich sediments are not buried deeply enough or for long enough, the result is immature kerogen, while burying the rocks too deeply or for too long results in postmature kerogen. Neither is economically useful to us.

3) Organic matter must be concentrated in the sediments. A “good” source rock is one that contains more than 1% Total Organic Carbon (TOC) by weight. This may not sound like much, but even 1% TOC can turn a rock quite dark in color and produce sufficient quantities of oil. Given that organic matter is readily oxidized in a well-mixed water column, only specific environments allow for the concentration of TOC.

4) Oil must be able to migrate freely, but must also be trapped in order to accumulate. If the oil can not escape its source rock, it is buried further and becomes postmature (like a cake that remains locked in the oven after the timer goes off). On the other hand, oil will continue to migrate toward the surface unless trapped by an impermeable boundary. As a fluid, oil disperses throughout the pore spaces and fluids already present in overlying reservoir rocks. The trap must not only be in place at the time of oil migration, but its geometry must allow for the concentration of oil in the sediments.

5) The trap must not have been compromised since the time of accumulation. Like the foundation of a house, petroleum traps are subject to geological forces (like faulting from tectonic movements, or uplift and erosion). In time, the likelihood that a trap will continue to hold significant quantities of oil can decrease substantially.

In summary, petroleum geology is about understanding a system of elements, in which timing is everything. From environmental factors (e.g. nutrient supply, temperature, salinity, dissolved oxygen and carbon dioxide) during the life cycle of marine organisms to the burial history of rocks to seemingly unrelated, subsequent sedimentary events (like the deposition of an impermeable rock millions of years after the fact), the preservation of petroleum systems is a delicate process. So at this point, I hope I have not bored you with details. Rather, my intention was to communicate the intricate nature of petroleum exploration, by which I am quite fascinated.

And which, by the way, involves more than a bad aim with a rifle or randomly drilling million-dollar holes in the ground.

Flood geology and the occurrence of oil

Until recently, I had not considered the implications of petroleum systems for Flood geology (and I suspect I’m not the only one). My search for a young-Earth response yielded a single full-length article by Dr. Andrew Snelling, entitled The Origin of Oil, which made some reference to an ICR article by David McQueen, entitled The Chemistry of Oil – Explained by Flood Geology. The former provides a basic hypothesis of oil formation as a result of the Flood, while the latter focuses on the presence of porphyrins (an organic molecule) as evidence for catastrophic burial of sedimentary rocks. Both argue that petroleum systems are better explained by the Flood model, and that the conventional understanding of geology cannot explain the range of geochemical data. In conjunction, they form the following line of reasoning:

1) Many oils contain porphyrins, which is a type of organic compound derived from plant and animal matter. It occurs in trace amounts (up to 400 ppm), but its presence can be demonstrated clearly.

2) Organic matter containing porphyrins must rapidly escape degradation (being oxidized), since porphyrins are unstable in the presence of oxygen. Anoxic conditions are not common in the ocean today, so geologists must consider areas of high sedimentation rate (like deltas) to explain porphyrins in the geological record.

3) Deltas bury sediments more rapidly than other environments, but contain abundant oxygen. Therefore, we should not expect to find porphyrins preserved in deltaic sediments.

4) Conventional geology cannot explain the widespread preservation of porphyrins. A catastrophic flood, however, would have rapidly buried massive quantities of organic matter and preserved these delicate molecules.

5) And since Flood geology can better explain the preservation of key biomolecules, we need not comment on the thermal maturation of organic matter (except that heat from burial during the Flood was responsible), or subsequent migration of oil into trapped reservoirs.

I admit, that last point was a bit tongue-in-cheek and results from my disappointment with the authors’ oversimplification of petroleum systems. Nonetheless, their case is in the form of a scientific argument, which can be tested by outstanding evidence. Does the argument hold? Have petroleum geologists ignored a catastrophic origin of oil source rocks in favor of an evolutionary timescale? Let’s take a look.

Distribution of porphyrins in petroleum reservoirs: a case for catastrophism?

Neither young-Earth author is mistaken in noting that porphyrins are commonly found in oil recovered from petroleum systems. In fact, porphyrins were the first biomarkers to be discovered in oil, and have since been used to interpret the source, depositional environment, and maturity of oil (e.g. Sundaraman and Raedeke, 1993). How does this work? Porphyrins found in petroleum systems are derived from chlorophyll in bacteria, algae, and other plant material. The organic molecule is a type of ligand, which means that its geometry and atomic structure allows for a metal cation, like iron, to be bound in the center.

And if that doesn’t make sense, just imagine a donut (ligand) with a ping-pong ball stuck in the center (metal cation).

In petroleum systems, porphyrins are most commonly bound to nickel or vanadium (actually, a vanadyl ion: VO2+), and the relative abundance of each reflects whether the depositional environment was oxidizing or reducing (e.g. Chen and Philp, 1991; Huseby et al., 1996). Vanadyl porphyrins are more stable, for example, in reducing conditions, where nickel preferentially bonds to sulfur and free cations become less abundant (Chen and Philp, 1991). Thus a relatively high ratio of vanadyl porphyrin vs. nickel-bound porphyrin suggests that the source rock was deposited in a low-oxygen marine environment, while the opposite relationship may indicate a deltaic/shelf environment, or a terrestrial source of organic matter (Premovic et al., 1998). As the sediments are buried more deeply, the temperatures increases and both types of porphyrin begin to break down into simpler organic compounds. Again, vanadyl porphyrins are more stable at higher temperature (Huseby et al., 1996), so their enrichment against nickel-bound porphyrins and preferential depletion versus more stable algal lipids can be used as a proxy for thermal maturity (e.g. Sundararaman and Raedeke, 1993). This method is particularly important in source rocks of marine origin, since the most common maturity indicators (Vitrinite Reflectance – Ro, and Thermal Alteration Index – TAI) use terrestrial (land-derived) organic matter.

Although the interpretation is not always straightforward (Premovic and Jovanovic, 1997), geologists have long been able to interpret and predict the distribution of oil-related porphyrins according conventional geological timescales. So why Dr. Snelling and Mr. McQueen focus on the preservation of porphyrins as evidence in their favor? Consider the following statement from Dr. Snelling:

“...experiments have shown that plant porphyrin breaks down in as little as three days when exposed to temperatures of only 410°F (210°C) for only 12 hours. Therefore, the petroleum source rocks and the crude oils generated from them can’t have been deeply buried to such temperatures for millions of years.”

On this point, Dr. Snelling’s assessment is spot on: exposure to high temperatures for any significant period of time would deplete any petroleum reservoir of porphyrins. Even vanadyl porphyrins of marine origin are only thermally stable up to ~300°C (Premovic and Jovanovic, 1997), so how do conventional geologists solve the dilemma?

It’s simple: they don’t, because there is no dilemma.

Oil is produced at temperatures between ~60°C–150°C. In the average tectonic setting, this translates to burial between 2.4–6 km below the Earth’s surface. If a source rock is buried much deeper or exposed to higher temperatures (e.g. from magmatic intrusions or hydrothermal fluids), then the rock quickly becomes postmature and will not produce any usable oil. Actually, the argument is easily turned against Dr. Snelling and Mr. McQueen. This range of temperatures is called the oil window, and demonstrates the predictive power of petroleum geology. If one can estimate the time at which the source rock reached the oil window (that is, using the geologic timescale), one can predict when and where the oil migrated. Does the method work? I would suggest that more than 100 billion barrels of burnt oil and the continued profits of Exxon, Chevron, and others clearly demonstrate the method’s validity.

Dr. Snelling also notes that “experiments have produced a concentration of 0.5% porphyrin (of the type found in crude oils) from plant material in just one day.” Since immature kerogen with relatively high concentrations of porphyrins contain at most 400 ppm porphyrin (12.5 times less), Flood geologists must rather explain the rarity of metal-bound porphyrins in petroleum systems, assuming that the organic material was buried catastrophically less than 6,000 years ago and never exceeded 60°C (as indicated by independent maturity and temperature proxies).

Ocean anoxia and the preservation of organic matter

Both Dr. Snelling and Mr. McQueen argue that anoxic conditions are too rare to account for the massive quantities of preserved organic matter. Rather than elucidating whether this is actually true, they engage in a hook, line, and sinker tactic by noting that many authors cite high sedimentation rates as a probable cause for organic-rich sediments. Mr. McQueen writes,

‘If a "high sedimentation rate" will preserve organic material, a catastrophic sedimentation rate, such as we envision for the worldwide Flood, would uproot, kill, and bury organic material so rapidly as to cut the porphyrins off from oxidizing agents which would destroy them in the ocean water.’

Unfortunately, he misunderstands the mechanism behind the original authors’ reasoning. First, dissolved-oxygen content rapidly decreases below the sediment-water interface due to microbial activity (i.e. bacteria eating dead organic matter to produce methane, CO2, and/or H2S), even when the overlying water is oxygenated. Yes, deltaic environments are oxidizing in the water column, but this actually results in poorer quality of oil compared to deeper-water settings, not the absence of oil. Second, catastrophic burial of organic matter in well-mixed ocean water would actually leave sufficient oxidants to chemically degrade most of the organic matter, thus Mr. McQueen’s extrapolation is unwarranted speculation. Third, most organic-rich rocks show geochemical (biomarker) evidence for thorough bacterial “eating” or reworking of the organic matter. If the sediments were buried catastrophically to several kilometers’ depth, how did this process occur?

Fourth, the preservation of organic matter depends on several factors, of which sedimentation rate and dissolved oxygen content are only two: local productivity, nutrient supply, clay fraction of sediments, source of organic matter, and bacterial population also play a major role. Each factor varies in importance for different depositional environments. For example, in a deltaic environment, the input of terrestrial organic matter, amount of clay minerals (which bond to organic molecules), and overall sedimentation rate are most important. In continental shelf and slope settings (further from the coast), primary productivity of marine organisms and the extent of the oxygen minimum zone (OMZ) is most important.

And speaking of the oxygen minimum zone...

Dr. Snelling claims that “[Anoxic] environments are too rare to explain the presence of porphyrins in all the many petroleum deposits found around the world. The only consistent explanation is the catastrophic sedimentation that occurred during the worldwide Genesis Flood.” But how rare are they? Well, to be sure, most of the ocean contains sufficient oxygen to degrade organic matter. Dr. Snelling fails to mention, however, what every introductory geology student already knows about the ocean: that in a small zone between ~200–1,000 m, the water column is anoxic due to the active degradation of organic matter. Anoxia is strongest in areas where upwelling delivers fresh nutrients to heterotrophic marine organisms in this zone (such as the Peruvian or West African coasts) and is less prevalent in areas of downwelling (such as the East Atlantic coast). Therefore, sediments deposited on the western continental shelf (especially near the equatorial zone) can preserve ample organic matter, porphyrins included. As an aside, this means that if petroleum geologists know the paleogeography (ancient position of the continents), they can predict where upwelling was the strongest and better find oil. Along the Peruvian coastline, the anoxic zone extends more than 1,000 km across the shelf.

For reference, a source rock that extends for one thousand kilometers in any direction is spelled with a capital $.

Not only is Dr. Snelling in error about this basic geological feature, he also ignores paleoceanographic conditions during the height of source rock generation (i.e. the chemistry of the ocean when most our oil was deposited as organic-rich sediments). Ocean anoxic events during the Jurassic and Cretaceous periods resulted in widespread deposition of organic-rich sediments, which have produced some of the highest quality oils to date. Of course, Dr. Snelling may reject the geologic timescale and geochemical interpretation of these events, but he cannot make the claim that conventional geology fails to explain the widespread preservation of organic matter in ancient deposits.

Once again, the argument can be turned against the young-Earth authors: how does Flood geology explain the widespread occurrence of Cretaceous black shales, which contain up to 20% TOC sourced from marine organic matter? Catastrophically buried forests may ‘begin’ to explain coal seams, but have nothing to do with geochemically distinct, marine black shales. Furthermore, it is impossible to hydrodynamically concentrate marine organic matter in sediments. On the other hand, the accumulation of organic matter in sediments is readily explained through clay-adsorption at moderately low sedimentation rates (less than a few cm per year) under anoxic conditions.

Petroleum systems involve more than oil and gas generation

After employing a number of misleading arguments to convince the reader that one should not expect to find oil reservoirs on the conventional geologic timescale, Dr. Snelling sweeps away the aspects of petroleum geology most challenging to his position in a simple, anecdotal conclusion. He writes:

“All the available evidence points to a recent catastrophic origin for the world’s vast oil deposits...during the global Flood cataclysm...forests were uprooted and swept away. Huge masses of plant debris were rapidly buried in what thus became coal beds, and organic matter generally was dispersed throughout the many catastrophically deposited sedimentary rock layers...[which] became deeply buried as the Flood progressed. As a result, the temperatures in them increased sufficiently to rapidly generate crude oils and natural gas from the organic matter in them. These subsequently migrated until they were trapped in reservoir rocks and structures, thus accumulating to form today’s oil and gas deposits.”

His concluding paragraph is filled with gratuitous assertions and leaves many important questions unanswered. A more detailed explanation is warranted in the future, so I will comment briefly on the major points.

1) As mentioned, catastrophic burial does not explain the occurrence of petroleum reservoirs, where bacterial degradation, partial oxidation, and long timescales played an important part in turning a biomass much larger than the present-day biosphere into high-quality fuel. Nor does it explain the specific geochemistry, which is the direct consequence of these processes. In essence, Dr. Snelling is claiming that since he can use a microwave to fully cook a piece of fresh beef in minutes, you shouldn’t assume that the $50, prime-cut, seasoned and aged prime rib on your plate actually took any longer to prepare. You can taste the difference when it comes to good cooking; so can petroleum geochemists when it comes to oil and gas.

2) Theories about burying floating forests, or uprooting terrestrial forests, only go so far in petroleum geology, since many oil and gas reservoirs were sourced from marine organic matter. Can terrestrial plant material produce Type I and Type II kerogens? And if not, how was marine organic matter concentrated under catastrophic conditions? Much oil and gas (and the highest quality thereof) is produced from marine algae, phytoplankton, and diatoms, all of which thrive in the surface ocean. How does the Flood geologist account for high TOC in certain types of rocks (shales) and not others (adjacent cap carbonates)? Or in certain types of shales but not others, without invoking a valid sorting mechanism for suspended, single-celled organisms?

3) On a similar note, biomarkers (like porphyrins) are vital to the study of petroleum geology, because they tell us about the source of the oil (marine vs. terrestrial; diatom vs. algal; angiosperm vs. gymnosperm). Evolutionary theory and the geologic timescale provide age constraints on certain biomarkers, and allow us to make predictive assessments of petroleum systems. In other words, if one finds biomarkers from angiosperms, the source rock can not be older than Cretaceous, when angiosperms evolved/diversified; if one finds biomarkers from diatoms, the source rock can not be older than Jurassic, when diatoms first evolved/diversified. Porphyrins are derived from chlorophyll, and should be found in organic-rich sediments of all ages (provided the rocks are not postmature). Such predictions are verified when various petroleum geologists use multiple independent methods to link a petroleum reservoir empirically to its source rock. The same goes for thousands of other biomarkers, which testify to the validity of the geologic timescale and evolutionary theory over against a catastrophic explanation.

4) For organic-rich sediments to produce oil, they must reach a temperature within the oil window (~60°C-150°C). If this occurs through slow burial, temperature increases systematically with depth, since the upper mantle provides a conductive heat source for the crust. If a bulk of sedimentary rocks were deposited during the Flood in the last 4,000-6,000 years, what is the heat source? Imagine taking a hot pan and adding a thin layer of pancake batter every hour for a full day. After your stack is several inches tall, there will be a gradient in temperature from the bottom of the stack (which is in contact with the hot plate) to the top (which is cooled by the room-temperature air). There will also be a gradient of “doneness”, from burnt pancake to raw batter. This process resembles the conventional geologic timescale, where there is ample time for equilibration of the temperature gradient and cooking of the “batter”. On the other hand, if you instantly pour 3 inches of pancake batter into an empty pot on the burner and checked it after only 30 seconds, what would the result be? The edges might be burnt, but there will not have been enough time for heat to reach even the middle of the batter. As I see it, Flood geologists are faced with a serious dilemma: if the upper mantle provided heat to buried sediments, then not nearly enough time has passed for the geothermal gradient to equilibrate in the thick crust (especially if the sediments were soft and water-saturated, like in the Flood model); if hydrothermal fluids provided a heat source during burial (this would also be reflected in oxygen/helium isotopes in cements, but it’s not), then why does the oil window accord roughly to the modern thermal gradient and why can immature oils still be found at depth? In other words, the Flood geology model would predict a majority of oil and gas to be severely “underdone” or “overdone”. In the former case, the oven came on during the Flood but is still on preheat; in the latter case, someone tried to reduce the cooking time by tripling the temperature. But neither explanation predicts what is seen in petroleum systems today.

5) Lastly, once oil and gas are generated, they need time to migrate through the rocks and accumulate in traps. Yet Dr. Snelling has not divulged just how long this process takes in rocks under pressure. Secondary porosity (cracks and fissures) speed up the intermediate process, but oil must still travel through and within the low-permeability source rock, then over a great distance (sometimes several kilometers) before accumulating in a higher permeability reservoir rock. This process alone can take many thousands of years or more, even in a pure quartz sandstone (as modeled by modified groundwater equations and observed in oil seeps).


Petroleum geology provides an elegant, multidisciplinary approach to finding one of the world’s most prized resources. Regardless of your opinion of the oil industry, its success is testimony to the validity of the conventional geologic timescale, evolutionary theory, and theories of oil generation, maturation, migration, and accumulation over multi-million-year timescales. This stands over against the proposed catastrophic explanations of petroleum systems offered by Dr. Snelling and Mr. McQueen, who overlooked many basic geological facts to convince their readers that the occurrence of petroleum systems supports Flood geology. As it stands, Flood geology is neither explanatory of outstanding geochemical evidence from oil and gas resources nor predictive of evidence in the field. Notwithstanding a major restructuring of existing theories by Flood geologists, oil and gas resources provide a powerful argument against a young-Earth interpretation of geologic history.

For the record

Petroleum-associated porphyrins might be structurally similar to heme in human hemoglobin, but are chemically distinct. There is no evidence that oil reservoirs contain trace remnants of “ancient, antediluvian human blood,” as Mr. McQueen postulates as an example of the predictive power of Flood geology. He is correct in noting that scientific hypotheses may be generated from the Flood model, but I would argue that they have already been falsified.

References cited:

Berkel, G.J, and Filby, R.H., 1987, Generation of Nickel and Vanadyl porphyrins from kerogen during simulated catagenesis: American Chemical Society Symposium Series, p. 110-134.

Chen, J.H., and Philp, R.P., 1991, Porphyrin distributions in crude oils from the Jianghan and Biyang basins, China: Chemical Geology, v. 91, p. 139-151.

Huseby, B., Barth, T., Ocampo, R., 1996, Porphyrins in Upper Jurassic source rocks and correlations with other source rock descriptors: Organic Geochemistry, v. 25, p. 273-294.

Premovic, P.I., and Jovanovic, L.S., 1997, Are vanadyl porphyrins products of asphaltene/kerogen thermal breakdown?: Fuel, v. 76, p. 267-272.

Sundararaman, P., and Raedeke, L.D., 1993, Vanadyl porphyrins in exploration: maturity indicators for source rocks and oils: Applied Geochemistry, v. 8, p. 245-254.

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