How Oil Is Formed

betzalel

Quote by Ophiolite

What's wrong with decomposition of marine organisms as a source?

As Gold notes it is difficult to explain why the CH4 flowed down into more dense material rather than up. It is difficult to find sufficient biological material to explain the amount of CH4 found. There is evidence of massive layers of almost pure C12 which cannot be explained by biological processes. (I will provide a link to a paper that discusses that anomaly later. Likely the discussion of that paper should be in a separate thread.)

From the late Gold's Deep Hot Biosphere:

For methane hydrate to form, temperatures must be no greater than 7C and pressures no less than 50 atmospheres. ... A large area of the continental shelf has been surveyed in this fashion. Results indicate that the methane hydrates may, in fact be present in all regions where the pressure and temperatures allow them to form. It has been estimated that methane hydrates contain more unoxidized carbon than all other deposits of unoxidized carbon known in the crust, such as crude oil, natural gas, and coal (Reference 11)... ... the hypothesis - that the source of the methane lies beneath, not within, the crustal sediments - is strengthened by evidence of pockets of free methane gas beneath some regions of hydrate ice (reference 13)... ... Gases, after all, do not migrate downward in a liquid of greater density. If there is any flow, it is in the reverse direction.

... Often there is more carbon in the methane atoms trapped in a deposit of hydrates than in all of the sediments associated with that deposit. In such instances the conventional explanation of its source (biological materials buried with the sediments) cannot account for the production of so much methane. The methane embedded in the ice lattices must have risen from below, through innumerable cracks in the bedrock. Once a thin, capping layer forms, the genesis of more such hydrates underneath becomes an inevitability, provided methane continues to upwell.

It is interesting to think of the finding of massive natural gas deposits at great depth within the Canadian Rockies. One of the geological puzzles is the explanation as to why the Canadian Rockies formed.

A possible hypothesis to explain the Canadian Rockies would be the out flow of CH4 from the liquid core as it solidified to form the solid core. (The CH4 is less dense the rocks of the mantel.) Observationally it is known that there has been massive natural gas deposits found in the Canadian Rockies. The following is quote that explains there is not continental plate collision to explain the formation of the Canadian Rockies.

(Comment: I will provide a link to this quote when I am allowed to provide links to quotes.)

The Rocky Mountains, rising from the center of the North American continent, have long presented a puzzle to geologists.

Mountains generally form where continental plates crash into each other: the Himalayas rise where India smashes into Asia, for example. But the nearest plate boundary to the Rockies runs along the west coast of North America, forming the coastal mountain ranges.

"The Rocky Mountains have always been a problem because they look like a collisional mountain range. They look like the Himalayas but we can't find the India," said Basil Tikoff of the University of Wisconsin, Madison.

"It's just a weird situation in the Rocky Mountains that despite the fact that they have extraordinarily good geology and geophysics that we don't get the basic geology of how they formed."

Since the 1980s, the dominant theory has been that the Farrallon plate to the west skidded underneath the North American plate above it at a shallow angle, creating ripples far out in front, like trying to pry a sticky pancake off a griddle. The further you stick the spatula underneath, the more it sticks to the spatula and rumples the pancake ahead of the spatula edge.

Another hypothesis to explain the drop in atmospheric CO2 which occurred when the planet cooled would be the formation of methane hydrates on the ocean floor when the deep ocean cooled to less than 7C.

Ophiolite

Quote by betzalel

Yes. Gold states source of the CH4 is from the liquid core not the mantel.

Would you provide a Chapter and page number from his book The Deep, Hot Biosphere in which he makes this claim please. In his summary in the PNAS paper (Gold,T. The deep, hot biosphere Proc.Natl.Acad.Sci.USA Vol.89, pp.6045-6049, July1992) he makes no mention of the core as the ultimate source of carbon.

Again, I point out that carbon is not a siderophile element. (e.g. Wikipedia) Do you have any evidence to demonstrate that it is? If it is not, then why would it be entrained in the core in quantity? If it is, then why would it subsequently be release by the core? There appears to be a logical impasse here. By what mechanism do you propose to overcome this?

I have not seen any papers that propose the massive natural gas deposit on the planet are due to biological processes.

Astounding! Perhaps you should try looking.

Geochemical Characteristics and Origin of Natural Gas in Tarim Basin, China
The isotopic compositions of molecular nitrogen:implications on their origins in natural gas accumulations
Geochemical Characterization of Natural Gas: A Physical Multivariable Approach and its Applications in Maturity and Migration Estimates
UNDERSTANDING SOURCE, DISTRIBUTION AND PRESERVATION OF AUSTRALIAN NATURAL GAS: A GEOCHEMICAL PERSPECTIVE
Generation of nitrogen and methane from sedimentary organic matter: implications on the dynamics of natural gas accumulations

And so on, in textbooks, journal articles and internal documents of oil and gas companies the biogenic origin of natural gas is the consensus view - regardless of whether or not it is the correct view. Your assertion that you have seen no papers regarding this is a serious condemnation of your capacity to do an elementary literature search.

The Alberta oil sands (54,000 square miles, is larger than the area of England). This heavy oil in this region has flowed to cover the sand. What is the biological source for hydrocarbon that can form and then flow to cover a region that is larger than the area of England?

Again, have you tried to answer that question, or do you just hope that there isn't an answer?
Timing and petroleum sources for the Lower Cretaceous Mannville Group oil sands of northern Alberta based on 4-D modeling

No agreement. 70% of the earth's surface is covered by water, 4.5 billion years after the formation of the earth. The early solar wind was roughly 300 times stronger than the current. The solar wind would have removed the water from the atmosphere of the hot earth. Carbon chondrites do not have sufficient water to provide the necessary water. As others have noted the late thin veneer hypothesis would have created a Venus like atmosphere on the early earth which the sun would have removed all water from.

Even if there was some mechanism to hold the water in the early earth's atmosphere the current solar wind removes hydrogen from the earth's atmosphere. If one extrapolates the loss the planet would not be covered by 70% water.

Please provide citations that demonstrate the period of intense solar wind coincided with provision of a small volume of water to the surface by bolide impact.

Please provide citations for the "others who have noted the late thin veneer hypothesis would have created a Venus like atmosphere".

Please further provide citations to justify your claim that carbonaceous chondrites could not provide suffcient water. This does not seem to be viewed as a problem by most workers in the field: for example, Determining the composition of the Earth.

I recommend you do a calculation of hydrogen loss and reveal to yourself how little has been lost over geologic time. If you think the loss has been substantial, show the calculation here. You are the one making an exceptional claim.

betzalel

Quote by Ophiolite

Would you provide a Chapter and page number from his book The Deep, Hot Biosphere in which he makes this claim please. In his summary in the PNAS paper (Gold,T. The deep, hot biosphere Proc.Natl.Acad.Sci.USA Vol.89, pp.6045-6049, July1992) he makes no mention of the core as the ultimate source of carbon.

You are correct Gold states the origin of the carbon is deep earth but does not state the origin of the CH4 is from the core. Paper's presented at the Carnegie Institute's Sloan Deep Carbon workshop which has sponsored by US department of Energy did.

I must wait until I have posted 10 times before I can provide a link. I would highly recommending watching the lecture series from the Sloan Deep Carbon workshop as well as reading Gold's book "Deep Hot biosphere".

Quote by Ophiolite

Again, I point out that carbon is not a siderophile element. (e.g. Do you have any evidence to demonstrate that it is? If it is not, then why would it be entrained in the core in quantity? If it is, then why would it subsequently be release by the core? There appears to be a logical impasse here. By what mechanism do you propose to overcome this?

The core solidifies and expels the very high pressure CH4. One method of looking for gold is to search for track deposits of hydrocarbons. As Gold notes water does not dissolve gold.

Quote by Ophiolite

Astounding! Perhaps you should try looking.

Quote by Ophiolite

And so on, in textbooks, journal articles and internal documents of oil and gas companies the biogenic origin of natural gas is the consensus view - regardless of whether or not it is the correct view. Your assertion that you have seen no papers regarding this is a serious condemnation of your capacity to do an elementary literature search.

There is significant CH4 found in regions where there are no sedimentary rocks. There have been a series of massive natural gas discoveries at great depth. Year by year Russia has increased there natural gas production and reserves to the largest in the world. (Compare Canada to Russia.)

Your comment is correct, there are papers that state the origin of CH4 is organic.

There are also papers that state it is not and to provide observation evidence and logic to support that assertion. Your appeal to consensus is not logic. Consensus based on what logical argument and observation?

Quote by Ophiolite

Again, have you tried to answer that question, or do you just hope that there isn't an answer?

A basic overview of the Alberta oil sands would be helpful. The Alberta Oil sands has viscosity of 8000 cSt to 10,000 cSt. It will support a fork. The oil sands has a sulfur content of 2% to 3%. The sulfur and the oil has come from a source deep within the earth also picking up heavy metals, in addition to the sulfur (i.e. the move of source hydrocarbon enabled the sulfur and heavy metals to become concentrated). The oil sands cover a region that is larger than England.

The 4-D model explanation as to the Alberta Oil sands source must explain where the sulfur came from, where the heavy metals come from, and a source of hydrocarbons that can cover a region the size of England.

Quote by Ophiolite

Please provide citations that demonstrate the period of intense solar wind coincided with provision of a small volume of water to the surface by bolide impact.

Please provide citations for the "others who have noted the late thin veneer hypothesis would have created a Venus like atmosphere".

Please further provide citations to justify your claim that carbonaceous chondrites could not provide suffcient water. This does not seem to be viewed as a problem by most workers in the field: for example,.

I recommend you do a calculation of hydrogen loss and reveal to yourself how little has been lost over geologic time. If you think the loss has been substantial, show the calculation here. You are the one making an exceptional claim.

The has been a suit of recent papers which challenge the fundamental assumptions concerning the early atmosphere. I will see what I can find. I fully expect there will be more as it appears Gold's hypothesis is correct.

As Gold notes the geological evidence is that carbon increased on the surface overtime and that the source of that carbon was deep earth based for example on C12/C13 analysis. Have look at his observation and explanation for the range of C12/C13 in the atmospheric CO2 as compared as to range of C12/C13 in CH4.

Also explain why there is very high amounts of Helium in that is common found with the CH4 and with oil fields. As Gold notes the helium concentration is significantly high in concentration than can be explained by the radioactive decay of uranium.

Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints
If the Archaean raindrops reached the modern maximum measured size, air density must have been less than 2.3 kgm23, compared to today’s 1.2 kgm23, but because such drops rarely occur, air density was more probably below 1.3 kgm23. The upper estimate for air density renders the pressure broadening explanation1 possible, but it is improbable under the likely lower estimates. Our results also disallow the extreme CO2 levels required for hot Archaean climates8.

This paper limits the maximum atmospheric pressure to twice the modern levels, 2.7 billion years ago, which is not sufficient to explain the early sun paradox. The most likely atmospheric pressure is less than the current atmosphere pressure.

Ophiolite

I will provide a more detailed response later.
In summary, you appear to be cherry picking your data to support the conclusion you have reached that Gold is right. You seem to have reached this conclusion because you like the idea and you enjoy the overturning of 'conventional wisdom'. Tell me I'm wrong.

Secondly, the consensus view is based upon a plethora of evidence and research. That is why I lean towards it, until other evidence points in another direction.

You can post any link you wish, it just won't be a live link, but I can copy and paste it and go there.

Ophiolite

A basic overview of the Alberta oil sands would be helpful. The Alberta Oil sands has viscosity of 8000 cSt to 10,000 cSt. .....The oil sands cover a region that is larger than England.

Probably accurate statements. None of them, however, in any way demonstrate that the oil was sourced from the mantle.

Sulphur in petroleum is thought to be derived from suphates present in the marine source rocks. For example, R.Francois, in A study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis

The 4-D model explanation as to the Alberta Oil sands source must explain where the sulfur came from, where the heavy metals come from, and a source of hydrocarbons that can cover a region the size of England.

The 4-D model is not required to explain the sulphur or heavy metal concentrations. It does need to explain the source of hydrocarbons and that is exactly what it does.

You seem hung up on the notion that the oil sands cover an area the size of England.do you have any idea how small england is? I'll tell you - 130,000 square kilometres. do you have any idea how large Alberta is? 662,000 square kilometres. It is five times the size of England and the source rocks for the oil lie under a substantial part of it. You are raising problems that don't exist.

betzalel

Ophiolite,
We should start with the Sloan Deep Earth hydrocarbon lectures.

The problem with defending one hypothesis over the other is the objective unfortunately becomes to win an argument as opposed to compare hypothesis to hypothesis and to attempt to explain what is observed. My comment that mountain formation is not understood for example as there are multi regions such as the Rockies or the Andes Mountains that occur at regions where there is not a collision of continental plates. The deep earth CH4 hypothesis might explain mountain formation at those regions, as the CH4 from the ocean plates is moved under the continent into the mantel, thereby releasing some of the entrapped CH4. Alternatively the movement of the ocean floor under the continent might provide a passage from the deep earth for CH4.

I continue back to the process which I fear is akin to a debate as opposed to comparison of hypothesis to hypothesis. I will continue this discussion for a couple of comments because I believe the subject is interesting.

You have not explained how the late veneer hypothesis can explain the observations such as the massive amount of water on the planet or the C12/C13 isotope ratio of carbon dioxide in the atmosphere and the lack of change in the C12/C13 ratio in the carbon that is deposited in geological formations. As Gold notes plants preferentially use C12 for photosynthesis. If the carbon in the atmosphere was thin veneer and recycled the atmosphere would over geological time become enriched with C13. That is not what is observed.

Your defense of the late veneer hypothesis is restricted to quoting papers that state emphatically that the source of natural gas or oil is from biological sources. The papers in question do not address the scores of unexplained observations that the biological source hypothesis appears to be unable to answer, related to natural gas or liquid hydrocarbon. (That observation is why I stated that I have not seen a paper that explains how biological sources could explain the massive super large deposits of natural gas and oil. I accept the the observation that the papers state the source of massive deposits is a biological source. The papers in question do not discuss the observations that appear to dispute that hypothesis.) There appears to be no paper that compares hypothesis to hypothesis and that discusses the observations which the late veneer hypothesis and the biogenic theory cannot explain.

The following is a subset of the issues with the thin late veneer hypothesis and the biological origin for massive hydrocarbon deposits.

The depleted ratio of C13 in “natural” gas for example (the carbon in natural gas is mostly C12) although C12 is significantly dominate, there is a higher range in the ratio of C13/C12 in natural gas than in the atmosphere. The C13/C14 ratio in the carbon in calcium carbonate deposits over time do not change over geological time and closely match that of the atmosphere. (The carbon in the calcium carbonate deposits is from the atmosphere and does not change over geological time. There is one exception which I will start a separate thread for. There is a massive deposit of carbon that is depleted in C13 and that matches natural gas.) Gold explained the C12/C13 ratio variance in natural gas from region to region do to isotopic fractionation that occurs as the molecule with the heavy isotope of carbon moves slower through the pores in the deep earth. The porosity of the mantel and the travel time varies from region to region which explains the variance in the ratio. The CH4 that is released to the atmosphere increases in C13 do to the cosmic rays that create C14 that decays to form the stable C13. The carbon dioxide in the atmosphere is deposited as calcium carbonate and in dead plants. If the CH4 has not added to the atmosphere from deep sources it would have become carbon dioxide would have become depleted over time in the atmosphere.

The massive hydrocarbon deposits in specific locations of the planet. The finding of extremely high amounts of helium at natural gas and oil deposits, for example.
This thread is the comparison of two fundamental hypotheses. The late thin veneer hypothesis and the deep earth hydrocarbon hypothesis. The deep earth hydrocarbon hypothesis is a scientific hypothesis. There are scientific papers that advocate that hypothesis.

The origin of CH4, “natural” gas and oil is a secondary and related question.
As Gold notes the deep ocean and the permfrost regions have vast amounts of methane hydrates. The carbon in the methane hydrates and in “natural” gas deposits is significant deficient in the carbon isotope C13. Carbon dioxide in the atmosphere and the carbon that is deposited in geological formations is higher in C13. The ratio of C13/C12 in the atmosphere does not increase in time although plants preferentially use C12 which should over time result in a gradual increase in the ratio of C13/C12 if the origin of hydrocarbons was in accordance to the late veneer hypothesis.

The alternative hypothesis, Gold’s which is an extension to the Soviet abiogenic hypothesis for the origin of oil/natural gas, is the deep earth hydrocarbon hypothesis. Gold’s hypothesis has been further developed by research that shows the liquid core of the planet contains a significant amount of lighter elements. The deep core hypothesis is as the core solidifies the lighter elements are expelled. The very, very, high pressure liquid that is expelled breaks through the mantel and over time rises up to the surface gradually releasing CH4. Experimental work has confirmed under very high pressures CH4 is converted to long chain hydrocarbon molecules.

Observational evidence to support the deep earth hypothesis is that radon and xenon gas in the earth’s atmosphere does not match comets. The deep earth’s hypothesis explanation for that observation is the Mars sized object that struck the earth roughly 50 million year after the formation of the planet. The energy from that collision stripped the early earth’s mantle of its lighter elements including hydrogen (the most abundant element in the solar system/universe) and carbon the fourth most abundant element in the universe. The source of the unoxidized hydrocarbons on the surface of the planet (carbon on surface of the planet is 100 times more concentrated than the mantel. There are massive deposits of carbonates on the continents which supports the assertion that methane gas is released to the atmosphere from a deep earth source. The methane disassociates in the upper atmosphere forming water and carbon dioxide.

The massive methane hydrate deposits on the ocean floor and in permafrost regions is one observation that supports Gold’s hypothesis. The methane hydrates located on the ocean floor is many times greater than all known coal, oil, and natural gas deposits.

Another is the massive, deposits of unoxidized hydrocarbons that is concentrated in specific regions.

Source Article in Discovery of same name that describes the researcher's findings.

Their Game Is Mud
Last summer Jerry Dickens and his fellow geologists were hauling mud-filled pipes up from the seafloor onto the deck of the research vessel Resolution when one of the mud-core samples exploded. Just as we were pulling it up, it blew, and mud shot 100 feet like a cannon, says Dickens. The geologists weren’t entirely surprised. They had lugged up the mud--It looks like green Play-Doh, says Dickens--in sampling tubes after drilling about 1,400 feet into ocean sediments. Each 30-foot-long tube has a one- inch hole where a little extra sediment sometimes squeezes out if the material is under high pressure. Some of their earlier sample tubes had come up empty, leading the crew to wonder if an entire 30-foot-long mud sample could have blown out through the quarter-size hole. We thought, ‘That’s crazy,’ says Dickens. And then we had one blow up on deck. Fortunately, no one was hurt.

Dickens was surprised not only by the abundance of the methane but by the form it took. As much was floating free in bubbles as was caged in hydrates. (It was this free methane that created the mud cannon.) No one is sure how the bubbles got there, but Dickens suggests that as new sediment piles onto the ocean floor, the zone where hydrates can form rises. The hydrates left behind melt and release their methane, but the overlying seal of hydrates traps the bubbles.

Look, says Dickens, there’s no way to explain this with the conventional carbon cycle. It’s impossible; it doesn’t make sense. There must be one form of carbon that can be released rapidly in the oceans. And we do have a reservoir like that. That reservoir could be contained in places like Blake Ridge, says Dickens. Because no two hydrate deposits are alike, it’s hard to extrapolate from the 850-foot-thick hydrate layer at Blake Ridge. But it is conceivable that methane hydrates worldwide contain twice the organic carbon contained in all the known deposits of coal, oil, and natural gas.

Source: Paper of same name.

Methane hydrate — A major reservoir of carbon in the shallow geosphere?

Methane hydrates are solids composed of rigid cages of water molecules that enclose methane. Sediment containing methane hydrates is found within specific pressure-temperature conditions that occur in regions of permafrost and beneath the sea in outer continental margins. Because methane hydrates are globally widespread and concentrate methane within the gas-hydrate structure, the potential amount of methane present in the shallow geosphere at subsurface depths of < ∼2000 m is very large. However, estimates of the amount are speculative and range over about three orders of magnitude, from 2 • 103 to 4 • 106 Gt (gigatons = 1015 g) of carbon, depending on the assumptions made. The estimate I favor is ∼ 1 • 104 Gt of carbon.

The estimated amount of organic carbon in the methane-hydrate reservoir greatly exceeds that in many other reservoirs of the global carbon cycle — for example, the atmosphere (3.6 Gt); terrestrial biota (830 Gt); terrestrial soil, detritus and peat (1960 Gt); marine biota (3 Gt); and marine dissolved materials (980 Gt). In fact, the amount of carbon may exceed that in all fossil fuel deposits (5 • 103 Gt). Because methane hydrates contain so much methane and occur in the shallow geosphere, they are of interest as a potential resource of natural gas and as a possible source of atmospheric methane released by global warming. As a potential resource, methane hydrates pose both engineering and production problems. As a contributor to a changing global climate, destabilized methane hydrates, particularly those in shallow, nearshore regions of the Arctic Ocean, may have some effect, but this effect will probably be minimal, at least during the next 100 years.

Source: Wikipedia

Athabasca oil sands
Together, these oil sand deposits lie under 141,000 square kilometres (54,000 sq mi) of sparsely populated boreal forest and muskeg (peat bogs) and contain about 1.7 trillion barrels (270×109 m3) of bitumen in-place, comparable in magnitude to the world's total proven reserves of conventional petroleum. Although the former CEO of Shell Canada, Clive Mather, estimated Canada's reserves to be 2 trillion barrels (320 km3) or more, the International Energy Agency (IEA) lists Canada's reserves as being 178 billion barrels (2.83×1010 m3).[5]

With modern unconventional oil production technology, at least 10% of these deposits, or about 170 billion barrels (27×109 m3) were considered to be economically recoverable at 2006 prices, making Canada's total proven reserves the second largest in the world, after Saudi Arabia's.[6] The Athabasca deposit is the only large oil sands reservoir in the world which is suitable for large-scale surface mining, although most of it can only be produced using more recently developed in-situ technology.[6]

Natural gas
Venezuela has the ninth largest gas reserves in the world and the biggest reserves in South America. Proved recoverable reserves were estimated at 4,179 billion cubic meter (bcm)[11] at the end of 2005 and increased to 4,838 bcm at the end of 2007. However, inadequate transportation and distribution infrastructure has prevented it from making the most of its resources. More than 70% of domestic gas production is consumed by the petroleum industry.[1] Nearly 35% of gross natural gas output are re-injected in order to boost or maintain reservoir pressures, while smaller amounts (5%) are vented or flared. About 10% of production volumes are subject to shrinkage as a result of the extraction of NGLs.[11] The 2010 estimate is 176 trillion cubic feet (5,000 km3), and the nation reportedly produced about 848 billion cubic feet (2.40×1010 m3) in 2008.[12]

Tar sands and heavy oils
Venezuela has non-conventional oil deposits (extra-heavy crude oil, bitumen and tar sands) at 1,200 billion barrels (1.9×1011 m3) approximately equal to the world's reserves of conventional oil. About 267 billion barrels (4.24×1010 m3) of this may be producible at current prices using current technology.[2] The main deposits are located in the Orinoco Belt in central Venezuela (Orinoco tar sands), some deposits are also found in the Maracaibo Basin and Lake Guanoco, near the Caribbean coast.[11]

*Studiot*

This thread is the comparison of two fundamental hypotheses. The late thin veneer hypothesis and the deep earth hydrocarbon hypothesis. The deep earth hydrocarbon hypothesis is a scientific hypothesis. There are scientific papers that advocate that hypothesis.

Actually that wasn't implied in the original post which was a question to distinguish between two biogenetic sources.

However I thank you for bringing your information to the table, the discussion is most interesting.

It is just a pity you didn't preface you opening salvo with this paragraph.

*Darwin123*

Quote by wilsonb

Quote :
It is true that the Oil is formed from plant and animal instead of Dinosaur?

I don't think that any scientist ever claimed that petroleum came from dinosaurs. The dinosaur was once used as an advertising logo. The iconic dinosaur was a metaphor for "prehistoric life."
Oil presumably formed mostly from various types of microbes. Microbes sometimes don't fit in the kingdoms of animal or plant. For instance, blue-green algae is technically a bacteria. Bacteria are not considered animal or plant.
The conventional theory is that most petroleum comes from microbes. There is a theory that most petroleum comes from nonbiological hydrocarbons. I don't think this theory has been experimentally validated. However, I am not sure how well validated the conventional theory is, either.
Petroleum is a chemical fossil, if it is a fossil. There is no morphological remains that tell us for sure what the original microbes looked like. Furthermore, petroleum has been contaminated by bacteria and protozoa that live in ground water. There are no hard barriers that prevent microbes of more recent times from getting in. So it would be difficult to distinguish the fossil of a primordial bacteria from an intruder who came later.
On the other hand, oil is associated with limestone deposits. The limestone contains fossils, and definitely comes from biological sources. Geologists look for certain shells when they look for petroleum.
The shell icon is used by another oil company. I don't think the shell represents an animal that is thought to originate petroleum. There was a recent bivalve on one of the islands where the founder of the company got his start. So he chose that as a symbol.
As pointed out in another post, there were never enough large animals collecting in one place to explain where all that petroleum came from. However, there have always been a lot of microbes in the ocean.
Petroleum probably came from a lot of single celled organisms: bacteria, plant and protozoa. My conjecture is that petroleum mostly came from various types of bacteria.
There are even more viruses than bacteria in the ocean. However, I don't think they have enough hydrocarbons in their crystalline bodies to form oil. Bacteria are much larger than viruses, and have all sorts of organic materials that could form petroleum. Bacteria outnumber all other cellular life on earth.
If petroleum is a chemical fossil, and I believe it is, then the likely source of most of it is probably bacteria. Perhaps a little of it comes from plants. Plants are far more common than the animals that live off of them. I conjecture that the contribution to petroleum from animals is very low. I wonder about the protozoa, though.
In any case, I am sure much about petroleum still isn't fully known yet. Further research will be done as petroleum resources dwindle.
Here is a link to a Wikipedia article that reviews a biogenetic theory of the formation of petroleum.
http://en.wikipedia.org/wiki/Petroleum#Formation
“Petroleum is a fossil fuel derived from ancient fossilized organic materials, such as zooplankton and algae. Vast quantities of these remains settled to sea or lake bottoms, mixing with sediments and being buried under anoxic conditions. As further layers settled to the sea or lake bed, intense heat and pressure built up in the lower regions. This process caused the organic matter to change, first into a waxy material known as kerogen, which is found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons via a process known as catagenesis. Formation of petroleum occurs from hydrocarbon pyrolysis in a variety of mainly endothermic reactions at high temperature and/or pressure.”

SpaceDreamer

Oil is formed from dead plant and animal biomass, mainly plankton. When these life forms died hundreds of millions of years ago they started to decompose and many of this life was in the ocean and the plants and mainly plankton fell to the bottom of the ocean and as the decomposed they were buried and eventually started to end up deeper, heat and pressure acted on the decomposed biomass forming hydrocarbons. Since carbon made up many of these life forms they became hydrocarbons. Many of the large oil deposits are now under where there were once ancient oceans, for example the Teyths ocean.

*Studiot*

I am not competent to validate the theories of oil origins, all I can do is compare the logic of statements I am being offered.

This guy is pretty solidly in the biogenesis camp.

http://www.sjsu.edu/faculty/watkins/petrorigins.htm

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Studiot	I am not competent to validate the theories of oil origins, all I can do is compare the logic of statements I am being offered. This guy is pretty solidly in the biogenesis camp. http://www.sjsu.edu/faculty/watkins/petrorigins.htm