Guest post by David Middleton

Introduction

I am a petroleum geologist/geophysicist with about 36 years of experience in oil & gas exploration mostly in the Gulf of Mexico. In light of Andy May’s recent post, Oil – Will we run out?, I thought I might post an essay on oil formation.

Over the past six years, I have been fortunate to have the opportunity to write guest posts for Watts Up With That thanks to Anthony Watts. Many of my posts have been about issues related to oil production and each of these posts usually triggers comments from Abiogenic Oil advocates. So, this post’s main thrust will be to explain why the Abiogenic Oil hypothesis is not widely accepted and why we think that the original source of crude oil is organic matter.

It’s possible that oil forms in the mantle all the time. The chemical equations can be balanced. So, as an olive branch to Abiogenic Oil aficionados, I will unequivocally state that their favored hypothesis is not impossible.

Biogenic vs abiogenic is really a poor way to characterize the issue. It implies that the formation of crude oil is either a biological or non-biological process. The process is thermogenic. The original source material is considered to be of organic origin because all of the evidence supports this.

The Generally Accepted Theory for Hydrocarbon Formation

I’m not going to go into a lot of detail on this. OffshoreEngineering.com has a very good basic primer here.

The basic steps are:

Algae, plankton and other marine and lacustrine photosynthesizers die and sink to the bottom of the ocean. They are buried in mud under anoxic conditions. As more sediment is deposited, they are buried deeper. The geothermal gradient gradually raises the temperature of the buried critters. Diagenesis and catagenesis lead to the formation of kerogen, then oil, then wet gas. Metagenesis leads to the formation of dry gas and then high temperature methane.

Every phase of the process can be observed in nature it has been repeated under laboratory conditions.

Oil Does Not Come From Dinosaurs or Dead Vegetation

Irrespective of Sinclair Oil’s logo…

Or the old Conoco commercial which showed a Vibroseis crew hunting for a buried dinosaur, this has never been the theory of hydrocarbon formation.

Methane and Other Simple Hydrocarbons vs Crude Oil

What is a Hydrocarbon?

It’s important to note that “organic” doesn’t necessarily mean “related to life,” although it usually is.

Organic chemistry is the chemistry discipline that is concerned with the study of compounds containing carbon that is chemically bonded to hydrogen. Organic chemistry encompasses the synthesis, identification, modeling, and chemical reactions of such compounds. Chemistry.About.com

Methane, ethane and other alkanes, alkenes, alkynes, cycloalkanes and alkadienes are simple hydrocarbons. Inorganically sourced methane is massively abundant on Earth and elsewhere in our Solar System and probably throughout our Galaxy. Other simple hydrocarbons are also often associated with inorganically sourced methane, usually in trace quantities.

The Saturnian moon, Titan, has seas of liquid methane and there is evidence of polycyclic aromatic hydrocarbons (PAHs) in Titan’s atmosphere. PAH’s are pollutants that occur naturally in crude oil and coal deposits and as the result of burning of carbon-based fuels.

The fact that Titan’s methane-rich atmosphere can generate PAH’s and trace amounts of heavier hydrocarbons has no relevancy to how petroleum and natural gas liquids form on Earth. Even if it was relevant to the formation of petroleum, it would be totally irrelevant to how oil and gas accumulate in the Earth’s crust.

Methane and simple hydrocarbons are not even remotely close to crude oil.

Oil is a mixture of complex hydrocarbons:

Petrowiki

Erroneously Cited as Evidence for Abiogenic Oil

There’s a fairly standard litany of Abiogenic Oil “evidence.” I am sure that the following does not cover all of the erroneous “evidence.”

Dniepr–Donets Basin, Ukraine

This is usually cited as proof of Abiogneic Oil because some Russians said there were no source rocks.

Palaeozoic source rocks in the Dniepr–Donets Basin, Ukraine Reinhard F. Sachsenhofer, Viacheslav A. Shymanovskyy, Achim Bechtel, Reinhard Gratzer, Brian Horsfield, Doris Reischenbacher DOI: 10.1144/1354-079309-032 Published on November 2010, First Published on October 20, 2010 ArticleFiguresInfo & Metrics PDF Abstract ABSTRACT The Dniepr–Donets Basin (DDB) is a major petroleum province in Eastern Europe. In order to understand the regional and stratigraphic distribution of source rocks for the dominantly gas-prone petroleum system, 676 fine-grained rocks from 30 wells were analysed for bulk parameters (total organic carbon (TOC), carbonate, sulphur, RockEval). A subset of samples was selected for maceral and biomarker analysis, pyrolysis-gas chromatography and kinetic investigations. Organic-rich sediments occur in different intervals within the basin fill. Maximum TOC contents (5.0 ± 1.9%) occur in the Rudov Beds, several tens of metres thick. The oil-prone rocks (Type III–II kerogen) were deposited in basinal settings above an unconformity separating Lower and Upper Visean sections. While maximum TOC contents occur in the Rudov Beds, high TOC contents are observed in the entire Tournaisian and Visean section. However, these rocks are mainly gas condensate-prone. Highly oil-prone black shales with up to 16% TOC and hydrogen index values up to 550 mgHC g–1TOC occur in Serpukhovian intervals in the northwestern part of the DDB. Oil-prone Lower Serpukhovian and gas condensate-prone Middle Carboniferous coal is widespread in the southern and southeastern part of the basin. Although no source rocks with a Devonian age were detected, their presence cannot be excluded. http://pg.geoscienceworld.org/content/16/4/377.abstract

The Dneiper-Donets Basin has clearly identifiable sedimentary source rocks.

Eugene Island 330 Field, Gulf of Mexico

The sudden, mysterious, inexplicable reversal of fortunes for the Eugene Island 330 field has often been cited as evidence for Abiogenic Oil…

Something mysterious is going on at Eugene Island 330. Production at the oil field, deep in the Gulf of Mexico off the coast of Louisiana, was supposed to have declined years ago. And for a while, it behaved like any normal field: Following its 1973 discovery, Eugene Island 330’s output peaked at about 15,000 barrels per day (2,400 m3/d). By 1989, production had slowed to about 4,000 barrels per day (640 m3/d). Then suddenly — some say almost inexplicably — Eugene Island’s fortunes reversed. The field, operated by PennzEnergy Co., is now producing 13,000 barrels per day (2,100 m3/d), and probable reserves have rocketed to more than 400 million barrels from 60 million.[5] — Christopher Cooper, Wall Street Journal http://interactive.wsj.com/archive/retrieve.cgi?id=SB924151147795357823.djm Christopher Cooper, “Odd Reservoir Off Louisiana Prods Oil Experts to Seek a Deeper Meaning?”, Wall Street Journal, April 16, 1999 Via Wikipedia

Firstly, there is nothing unusual about EI 330’s production curve…

Eugene Island 330 is one of the largest oilfields in the Gulf of Mexico. However, there is nothing unusual about its production curve. The “bump” in the late 1990’s was largely due to drilling activities. The field is still in decline. From 1972 through 2016, the field has produced 452 million bbl of oil, 1.88 TCF of gas and 484 million barrels of salt water. Last year, the field averaged about 11,500 BOPD, 14,400 MCFD and *28,400 BSWD*. Most of the reservoirs are strong water drives. These types of reservoirs can exhibit 50% or better primary recoveries.

The only odd thing about EI 330 has been relatively clear evidence (4d seismic) of oil migrating up a fault plane (which is how the oil got there in the first place). The source rocks in the Gulf of Mexico are still generating hydrocarbons, which are still migrating into geologic traps.

Ultradeep Oil Accumulations Are Too Deep and Hot to be in the Oil Window

Oil comes from organic material, mostly algae,which was quickly buried in mud at the bottom of oceans and lakes – So, it never had a chance to fossilize. Pressure, heat and time converted the organic material into kerogen, oil and natural gas…

As the biomass is buried more deeply in the sedimentary column, increasing pressure compacts it, increasing temperature cooks it and over time, the hydrocarbons slowly migrate toward the surface because they are less dense than connate/formation water. The kerogen first cooks to heavy oil, then light oil, then wet thermogenic gas, then thermogenic light gas, then high temperature methane…

Crude oil cracks at temperatures above about 300°F. It generally can’t exist at depths anywhere close to the mantle.

Walker Ridge 758 Chevron #1 is the deepest active oil producer in the Gulf of Mexico; drilled to a true vertical depth (TVD) of 28,497’ (8.7 km) in a water depth of 6,959’. It was completed in a Lower Tertiary Wilcox sandstone (26,831’ – 27,385’). The bottom hole temperature was 226°F. The oil migrated upward from deeper Mesozoic and Lower Tertiary source rocks. Even deeper oil reservoirs have been discovered in the oil window, many of these will be coming on production over the next few years.

There are no oil wells in the Gulf of Mexico with bottom hole temperatures outside of the oil window. The ultra-deepwater Lower Tertiary oil discoveries are well within the oil window. The shallow water Lower Tertiary gas discovery at Davy Jones is well out of the oil window, but in the gas window…

The depths on the chart are approximations based on a generalized geothermal gradient. The geothermal gradient is highly variable. Water and halite (salt) are less dense than most rocks. When the overburden consists of 8,000’ of seawater and 2,000’ of halite, 30,000’ of overburden weighs a lot less than it does when it’s all composed of more dense rocks.

The ultra-deepwater Lower Tertiary play in the Gulf of Mexico and the deep subsalt plays offshore Brazil are often cited as examples of abiotic oil because the reservoirs are supposedly too deep, too hot and/or too highly pressured to be in the oil window. This is simply wrong.

Tabular salt acts like a radiator. It conducts heat away from the substrata toward the surface. The combination of thick layers of salt and deep water depths enable oil to exist at depths previously unexpected. Salt and water are also less dense than most other overburden. This enables reservoir quality rocks to exist at deeper depths than previously expected.

I’ve drilled wells deeper than 20,000’ in the Gulf of Mexico. The bottom hole temperatures were in the range of 215°F (100°C). Ten wells in the Gulf of Mexico, drilled to true vertical depths greater than 20,000’ have each produced more than 20 million barrels of oil. The maximum bottom hole temperature (213°F) was encountered in the Mississippi Canyon (MC) 777 TF001 well, drilled by BP. The average bottom hole temperature of those ten 20 million barrel producers was 197°F.

For further reading about the geology and petroleum systems of the Gulf of Mexico, I recommend:

The Prize Beneath the Salt by Dribus, Jackson and Kapoor

Hydrocarbon Systems Analysis of the Northern Gulf of Mexico: Delineation of Hydrocarbon Migration Pathways Using Seepsand Seismic Imaging by Hood, Wnger, Gross and Harrison

Gulf of Mexico by Galloway

Offshore Vietnam and other Fractured Basement Reservoirs

Some oilfields produce from fractured basement rocks, usually granitic rocks. The Cuu Long Basin, offshore Vietnam is often cited as an example of Abiogenic Oil.

Petroleum Geology of Cuu Long Basin – Offshore Vietnam* By Nguyen Du Hung and Hung Van Le Search and Discovery Article #10062 (2004) *Adapted from “extended abstract,” entitled “Hydrocarbon Geology of Cuu Long Basin – Offshore Vietnam,” for presentation at the AAPG International Conference, Barcelona, Spain, September 21-24, 2003. […] Source Rocks The effective source rocks are the Upper Oligocene shale that is present throughout the basin and the Lower Oligocene interbedded shale. They contain mostly kerogen type I/II generated from lacustrine sediments. The average TOC is from more than 1% up to nearly 10%; the hydrogen index ranges from 300 to more than 600 mg/gTOC (Figure 5). Fractured Basement Reservoir Fractured basement reservoirs are the unique characteristics of the Cuu Long basin, although there are other oil discoveries in clastics and volcanics plays. The first oil discovery in basement was made by Vietsopetro in the Bach Ho field in 1988. Oil was stored in macro-fractures, micro-fractures, and vuggy pores. The matrix porosity of the magmatic body is negligible. Fractures inside the basement may originate from one or a combination of the following factors: 1) The cooling of the magmatic body 2) Tectonic activity 3) Hydrothermal processes 4) Weathering and exfoliation. AAPG Search and Discovery

Organic markers in the oil match the kerogen in the Oligocene shale. For the “abiotic theory” to work, the oil would have had to migrate out of the granite, leach the organic material from the shale and then migrate back into the granite.

There’s Not Enough Organic Matter Buried in the Oceans to Account for all of the Oil

Here’s the math…

The crust is ~1% of the Earth’s volume.

Sedimentary rocks comprise ~5% of the volume of the crust.

Total world crude production since 1900 has been ~1.3 trillion barrels.

If there are ~3.0 trillion barrels remaining to be found and produced, sedimentary rocks contain an average of 0.01 barrels of recoverable crude oil per acre*ft.

A typical oil reservoir has a recovery factor of ~300 barrels per acre*ft.

This means that only 0.003% of the Earth’s sedimentary rocks would have to be charged with crude oil to explain all of the crude oil ever likely to be produced on Earth.

The volume of organic carbon-rich sediment in the Earth’s crust is massively large. The Gulf of Mexico has accumulated more than 60,000′ of sedimentary column over the last 200 million years. The Cenozoic section, alone, is more than 40,000′ thick in places. The Quaternary can be more than 30,000′ thick in some locations. Most of the sedimentary column is composed of thick, organic-rich shale.

Oil is still being formed and migrating from source to reservoir rocks in the Gulf of Mexico. The Pleistocene reservoirs are less than 2.5 million years old and many have only been charged over the last 275,000 years. The reservoirs simply aren’t being charged as quickly as we are producing them.

Red areas indicate ~20,000 meter sediment thickness.

Oceanic Sedimentary Isopach Map

Marine black shales, deposited under anoxic conditions are loaded with the stuff that oil is made of…

Total organic carbon (TOC) averaged 10% by weight.

The Cretaceous, in particular, was a hydrocarbon “kitchen.” Marine conditions couldn’t have been more favorable for the deposition of source rocks even if they had been designed for such a purpose…

“DSDP sites at which Cretaceous sediments rich in organic matter were encountered. From Dean and Arthur, 1986.”

Cretaceous Proto-Atlantic

The Lower Tertiary Eocene was also a hydrocarbon kitchen (up to 21% TOC).

There is no shortage of organic matter in the sedimentary basins of the Earth’s crust.

The Siljan Ring

Proof of abiogenic oil would consist of the discovery of a significant volume of abiogenic oil.

So far, the closest thing to evidence has been the recovery of an “asphaltenic-type material removed from the drillstem at 5945 m [19,505 ft] in Well Gravberg-1 from the Precambrian granite, Siljan, Sweden.”

The chemical characterization showed that this material contains small amounts of hydrocarbons maximizing in the diesel range. No heavy hydrocarbons were identified, except for trace amounts of polycyclic aliphatics. From the chemical and stable isotopic characterizations, we concluded that the black gelatinous material is derived predominantly from the alteration of biodegradable nontoxic lubricant (BNTL) additives by caustic soda, admixed with diesel oil and trace amounts of polycyclic hydrocarbons from recirculating local lake water. No evidence for an indigenous or deep source for the hydrocarbons could be justified. https://www.onepetro.org/journal-paper/SPE-19898-PA

Unfortunately, the “asphaltenic-type material” was most likely derived from the drilling fluid used in the well.

Other Odd Arguments

These arguments, supposedly from Thomas Gold’s book, demonstrate a total ignorance of the conventional theory of hydrocarbon formation and accumulation…

(8) Petroleum and methane are found frequently in geographic patterns of long lines or arcs, which are related more to deep-seated large-scale structural features of the crust, than to the smaller scale patchwork of the sedimentary deposits.

Oil is generally trapped by structural features, commonly fault systems. Structural trends tend to follow linear and arc-like patterns…

(9) Hydrocarbon-rich areas tend to be hydrocarbon-rich at many different levels, corresponding to quite different geological epochs, and extending down to the crystalline basement that underlies the sediment. An invasion of an area by hydrocarbon fluids from below could better account for this than the chance of successive deposition.

This is just plain ignorance. The conventional theory of oil formation and accumulation doesn’t state that oil forms in situ. It forms in deeper sedimentary rocks and migrates upwards to accumulate in structural and stratigraphic traps… In other words, “an invasion of an area by hydrocarbon fluids from below.”

“Hydrocarbon-rich areas tend to be hydrocarbon-rich at many different levels” because structural deformation creates traps at many levels and the oil migrates into them from below.

(10) Some petroleum from deeper and hotter levels almost completely lack the biological evidence. Optical activity and the odd-even carbon number effect are sometimes totally absent, and it would be difficult to suppose that such a thorough destruction of the biological molecules had occurred as would be required to account for this, yet leaving the bulk substance quite similar to other crude oils.

Abject nonsense.

(11) Methane is found in many locations where a biogenic origin is improbable or where biological deposits seem inadequate: in great ocean rifts in the absence of any substantial sediments; in fissures in igneous and metamorphic rocks, even at great depth; in active volcanic regions, even where there is a minimum of sediments; and there are massive amounts of methane hydrates (methane-water ice combinations) in permafrost and ocean deposits, where it is doubtful that an adequate quantity and distribution of biological source material is present.

The methane straw man. No one has argued against inorganically sourced methane.

(12) The hydrocarbon deposits of a large area often show common chemical or isotopic features, quite independent of the varied composition or the geological ages of the formations in which they are found. Such chemical signatures may be seen in the abundance ratios of some minor constituents such as traces of certain metals that are carried in petroleum; or a common tendency may be seen in the ratio of isotopes of some elements, or in the abundance ratio of some of the different molecules that make up petroleum. Thus a chemical analysis of a sample of petroleum could often allow the general area of its origin to be identified, even though quite different formations in that area may be producing petroleum. For example a crude oil from anywhere in the Middle East can be distinguished from an oil originating in any part of South America, or from the oils of West Africa; almost any of the oils from California can be distinguished from that of other regions by the carbon isotope ratio.

This is because the source rocks are “independent of the varied composition or the geological ages of the formations in which” the oil has been tapped.

This argument from Kenny et al., 2002 fundamentally misstates the conventional theory of hydrocarbon formation, migration and accumulation and then argues against a strawman of their own construction.:

The spontaneous genesis of hydrocarbons that comprise natural petroleum have been analyzed by chemical thermodynamic-stability theory. The constraints imposed on chemical evolution by the second law of thermodynamics are briefly reviewed, and the effective prohibition of transformation, in the regime of temperatures and pressures characteristic of the near-surface crust of the Earth, of biological molecules into hydrocarbon molecules heavier than methane is recognized. http://www.pnas.org/content/99/17/10976.long

The conventional theory of hydrocarbon does not bear any resemblance to a “spontaneous genesis of hydrocarbons” and the sources of energy are heat, pressure and chemical reaction resulting from heat and pressure.

Conclusions

One of the more inane criticisms of the generally accepted theory of hydrocarbon formation is the notion our adherence to an ancient theory prevents us from finding Abiogenic Oil. This is abject nonsense. We don’t look for oil using any theories about hydrocarbon formation. The theory was developed from the observations of hydrocarbon accumulations. When exploring a new basin, we do look for total petroleum systems; however, when I am prospecting in the Gulf of Mexico, I’m not looking for the source rocks.

Geologists generally adhere to Chamberlin’s Method of Multiple Working Hypotheses and most of us have an open mind to the Abiogenic Oil hypothesis. The American Association of Petroleum Geologists (AAPG) has even hosted conferences on the subject…

It boils down to two things:

The conventional theory explains all of the observations. It wouldn’t affect the process of oil & gas exploration.

The process of hydrocarbon formation is very organized, has been observed at all stages in nature, can be quantified in a rigorous scientific theory and can be largely simulated under laboratory conditions. The only part of the process that cannot be directly repeated in the laboratory is time.

Petroleum generation by laboratory-scale pyrolysis over six years simulating conditions in a subsiding basin J. D. SAXBY & K. W. RILEY CSIRO Division of Fossil Fuels, PO Box 136, North Ryde, New South Wales 2113, Australia […] Consequently, we have heated potential source material from 100 to 400 °C over six years, increasing the temperature by 1 °C per week. This was done in an attempt to simulate the thermal history of a sample being buried in a continuously subsiding basin with a constant geothermal gradient. After four years, a product indistinguishable from a paraffinic crude oil was generated from a torbanite, while a brown coal gave a product distribution that could be related to a wet natural gas. Of great significance is the absence of olefins and carbon monoxide in all products. We believe the present experiments, which are possibly as slow as can be realistically planned within a human time scale, have for the first time successfully duplicated hydrocarbon generation in a continuously subsiding sedimentary basin. http://www.nature.com/nature/journal/v308/n5955/abs/308177a0.html

While it is possible for oil to form through mantle serpentinization or the Fischer–Tropsch process, there simply isn’t any evidence that any crude oil has ever naturally formed through these processes on Earth. If oil was forming in the mantle, it would be flowing out of mid-ocean ridges (methane flowing out of mid-ocean ridges is not oil).

There are very few crude oil accumulations that are even consistent with the abiogenic hypotheses and no significant accumulations inconsistent with the generally accepted theory of hydrocarbon formation.

Ultimately, the entire debate is academic. “Oil is where you find it.” However it originally formed, it has to be found in economic accumulations. Igneous and metamorphic rocks are rarely porous and permeable… And rarely contain crude oil. Even if oil was commonly formed inorganically… It wouldn’t alter how and where oil companies look for oil. It still has to be trapped in porous and permeable reservoirs – Sandstones, limestones, shales and other sedimentary rocks. Even the oil that’s trapped in fractured granites and other basement rocks, had to migrate through and be trapped by sedimentary rocks.

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Much of the material in this post was adapted from the comments section of:

Peak Oil Indefinitely Postponed.

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