Hydrocarbons in the deep earth

Hydrocarbons in the deep earth
A snapshot taken from a first-principles molecular dynamics simulation of liquid methane in contact with a hydrogen-terminated diamond surface at high temperature and pressure. The spontaneous formation of longer hydrocarbons are readily found during the simulations.
(PhysOrg.com) -- A new computational study published in the Proceedings of the National Academy of Sciences reveals how hydrocarbons may be formed from methane in deep Earth at extreme pressures and temperatures.

The thermodynamic and kinetic properties of hydrocarbons at high pressures and temperatures are important for understanding carbon reservoirs and fluxes in Earth.

The work provides a basis for understanding experiments that demonstrated polymerization of to form high hydrocarbons and earlier methane forming reactions under .

Hydrocarbons (molecules composed of the elements and carbon) are the main building block of and natural gas. Hydrocarbons contribute to the global carbon cycle (one of the most important cycles of the Earth that allows for carbon to be recycled and reused throughout the biosphere and all of its organisms).

The team includes colleagues at UC Davis, Lawrence Livermore National Laboratory and Shell Projects & Technology. One of the researchers, UC Davis Professor Giulia Galli, is the co-chair of the Deep Carbon Observatory's Physics and Chemistry of Deep Carbon Directorate and former LLNL researcher.

Geologists and geochemists believe that nearly all (more than 99 percent) of the hydrocarbons in commercially produced crude oil and natural gas are formed by the decomposition of the remains of living organisms, which were buried under layers of sediments in the Earth's crust, a region approximately 5-10 miles below the Earth's surface.

But hydrocarbons of purely chemical deep crustal or mantle origin (abiogenic) could occur in some geologic settings, such as rifts or subduction zones said Galli, a senior author on the study.

"Our simulation study shows that methane molecules fuse to form larger hydrocarbon molecules when exposed to the very high temperatures and pressures of the Earth's upper mantle," Galli said. "We don't say that higher hydrocarbons actually occur under the realistic 'dirty' Earth mantle conditions, but we say that the pressures and temperatures alone are right for it to happen.

Galli and colleagues used the Mako computer cluster in Berkeley and computers at Lawrence Livermore to simulate the behavior of carbon and hydrogen atoms at the enormous pressures and temperatures found 40 to 95 miles deep inside the Earth. They used sophisticated techniques based on first principles and the computer software system Qbox, developed at UC Davis.

They found that hydrocarbons with multiple carbon atoms can form from methane, (a molecule with only one carbon and four hydrogen atoms) at temperatures greater than 1,500 K (2,240 degrees Fahrenheit) and pressures 50,000 times those at the Earth's surface (conditions found about 70 miles below the surface).

"In the simulation, interactions with metal or carbon surfaces allowed the process to occur faster -- they act as 'catalysts,'" said UC Davis' Leonardo Spanu, the first author of the paper. The research does not address whether hydrocarbons formed deep in the Earth could migrate closer to the surface and contribute to oil or gas deposits. However, the study points to possible microscopic mechanisms of formation under very high temperatures and pressures. Galli's co-authors on the paper are Spanu; Davide Donadio at the Max Planck Institute in Meinz, Germany; Detlef Hohl at Shell Global Solutions, Houston; and Eric Schwegler of Lawrence Livermore National Laboratory.

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Citation: Hydrocarbons in the deep earth (2011, April 15) retrieved 27 May 2019 from https://phys.org/news/2011-04-hydrocarbons-deep-earth.html
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Apr 15, 2011
Can you please add a doi the next time?
For this article it is doi:10.1073/pnas.1014804108

Apr 15, 2011
Looks like they're getting ready to finally dump the notion of "fossil fuels". It's about time. :-)

Apr 15, 2011
Fossil Fuels or not, the fuel is highly toxic to living organisms. (when burned)

Apr 15, 2011
Looks like they're getting ready to finally dump the notion of "fossil fuels". It's about time. :-)

Actually not. The term Fossil doesn't mean that it literally comes from fossils, any more than the term Fossil Water means that somehow the water came from old dead animals/plants.

This term refers to the fact that it takes geologic time scales (millions of years) to regenerate.

Apr 16, 2011
It is truly amazing that people blinded by evironmentalism can not comprehend the fact stated in this article that carbon is part of the life cycle and not some kind of poison. It is not difficult to see that the plants that formed the crude oil got thier carbon from the air (carbon dioxide). This article should be required reading for every school,colledge and government agency. Polymerization of methane might explane why coal instead of oil is formed in some areas.

Apr 17, 2011
Nice... explains why some hydrocarbon deposits are not associated with sedimentary processes.

Apr 17, 2011
They're not called fossil because of geologic scales, limestone isn't (except for the one from shells).

The old name for 'fosile fuel' was MINERAL OIL.

Apr 17, 2011
I thought this idea came up about twenty years ago so they drilled some wells in Sweden where a meteor strike had fractured the crust allowing access to these postulated " deep synthesized" hydrocarbons. That drilling program was dry.

Apr 17, 2011
carbon is part of the life cycle and not some kind of poison
So far anthropogenic CO2 isn't so much poisonous, as it is disruptive to climate.
plants that formed the crude oil got thier carbon from the air (carbon dioxide)
Q: where did the air get it from? A: volcanoes. Q: why is CO2 in air not growing without bound due to ongoing volcanism? A: C from air is being sequestered back into the crust by geological processes, thereby maintaining a sort of equilibrium over geologic time. Q: what happens when humans dredge C from the crust and sustain CO2 emission already more than 100x the natural volcanic rate -- and still accelerating exponentially?
Polymerization of methane might explane why coal instead of oil is formed in some areas
Do yourself a favor and read up on the various types of coal:


Then consider this:


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