olelog

There is widespread evidence that petroleum originates from biological processes. Whether hydrocarbons (oil and gas) can also be produced from abiogenic precursor molecules under the high-pressure, high-temperature conditions characteristic of the upper mantle remains a disputed question.

A hypothesis that oil can be created by non-biological mechanisms originated in Russian and Ukrainian scientific circles in the 1950s. Put briefly, it proposed that petroleum forms deep in the Earth’s mantle under extremely high pressure and temperature through a reaction between carbonates, iron oxides and water. This process goes on continuously, and the petroleum migrates upwards through the lithosphere. At issue is the formation of complex hydrocarbons. There has never been any doubt that simple hydrocarbons such as methane can be formed by inorganic processes.

If true it was speculated it might be possible to find oil deep under the Siljan Impact Crater (Sweden), and they drilled here in the 1980’s and 1990’s, among other things in the hope to find oil. The hypothesis went that (inorganic) methane (gas) migrates upwards from the mantle and transforms into oil in the upper crust in igneous rocks (like granite). The Siljan ring is a crater of granitic rocks overlain by soil formed by a large meteorite impact 360 million years ago. The impact was postulated to have created fractures at great depth through which gas and oil would have been able to migrate. Although a little bit of oil was found, the drilling was more or less a failure – as far as oil and gas is concerned. Many scientists (though not everybody) thought that that was the final end of the abiotic oil story.

Apparently the dream has been awakened again.

As I said Scientists have debated for years whether some of our oil and gas (hydrocarbons) could also have been created deeper in the Earth and formed without organic matter. Now for the first time, according to a study published in the July 26, advanced on-line issue of Nature Geoscience, scientists have found that ethane and heavier hydrocarbons can be synthesised under the pressure-temperature conditions of the upper mantle —the layer of Earth under the crust and on top of the core (red in the figure below).


Click on image to enlarge!

Using a diamond anvil cell and a laser heat source, scientists first subjected methane to pressures exceeding 20 thousand times the atmospheric pressure at sea level and temperatures ranging from 704°C to over 1 227 °C. These conditions mimic those found 65 to 150 km deep inside the Earth. The methane reacted and formed ethane, propane, butane, molecular hydrogen, and graphite. The scientists then subjected ethane to the same conditions and it produced methane. The transformations suggest heavier hydrocarbons could exist deep down. The reversibility implies that the synthesis of saturated hydrocarbons is thermodynamically controlled and does not require organic matter.

The results from the study seem to support the suggestion that hydrocarbons heavier than methane can be produced by abiogenic processes in the upper mantle.

Reference:
Kolesnikov et al.
Methane-derived hydrocarbons produced under upper-mantle conditions
Nature Geoscience
Published online: 26 July 2009
doi:10.1038/ngeo591

• http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo591.html
• http://www.ciw.edu/news/hydrocarbons_deep_earth
• http://www.scientificblogging.com/news_articles/peak_oil_not_if_deep_earth_hydrocarbon_theory_true
• http://www.npd.no/English/Aktuelt/Nyheter/22.5.2007+Fossilt+drivstoff+uten+fossiler.htm?print=true
• http://www.physorg.com/news167835116.html
• http://www.eurekalert.org/pub_releases/2009-07/ci-hit072409.php
• http://www.eurekalert.org/multimedia/pub/15568.php?from=141472
• http://www.sciencecodex.com/deep_earth_hydrocarbon_discovery_oil_and_methane_without_organic_matter
• http://www.planetthoughts.org/?pg=pt/Whole&qid=2982&src=rss
• http://www.sciencedaily.com/releases/2009/07/090726150843.htm
• http://www.energy-daily.com/reports/Hydrocarbons_In_The_Deep_Earth_999.html
• http://www.abc.net.au/science/articles/2009/07/28/2638484.htm

In Danish:
• http://ing.dk/artikel/100215-olieproduktion-i-laboratorier-nye-forsoeg-vaekker-forskernes-haab?utm_medium=rss&utm_campaign=nyheder



PS of 28 July 2009:
Glenn Reynolds files the story under “THINGS I’D LIKE TO BE TRUE” at http://pajamasmedia.com/instapundit/82538/

No I am not referring to the Golden Triangle. This is about oil and gas. The Golden Zone is the name of a an underground zone where temperatures range between 60° and 120°C. The name refers to a new discovery that 90 per cent of the world's oil and gas reserves are to be found just there.

Earlier it was assumed that the formation of oil and gas was related to temperature. The new discovery is that temperature decides where most of the lighter oil and gas is trapped in the reservoirs.

Hydrocarbons (oil and gas) are formed in source rocks at temperatures higher than 120°C (in the ‘expulsion zone’). They are expulsed and migrate upwards through hydraulically formed fractures to accumulate in reservoir rocks higher up where the temperature is lower than 120°C - this is the accumulation zone or “golden zone”. The upper limit of major entrapment is at 60 °C where hydraulic fractures are generally thought to peter out, simply because the permeability is insufficiently low for hydrocarbons to propagate through the rock.

The accumulation zone or golden zone is a zone of transition between the thermo-chemical compaction regime of the expulsion zone and the overlying mechanical compaction regime of the so-called 'sealing zone’. Here, at temperatures below 60 °C, hydrocarbon volumes are low because the sealing zone is largely beyond the influence of vertical, fracture-controlled re-migration.

Oil in the sealing zone is vulnerable to bacterial degradation (biodegradation). Bacteria consume the lighter oil fractions, leaving behind a viscous mass of heavier oil fractions.

The fact that oil and gas coexist within the same temperature zone is a new discovery and a surprise. Gas is formed at higher temperatures than oil. Consequently it has been a standard rule that there should be more gas than oil the deeper one drilled into the reservoir. The reason why this is not the case is covered by the new theory which predicts that both oil and gas escape through fissures formed at 120°C.

What the researchers stress is that only one parameter, namely temperature, governs all the fundamental processes in the expulsion zone. The fluids (water, oil and gas) are expulsed by thermally controlled processes.

• http://www.uis.no/news/article7071-50.html
  

The theory was nicely described 3 years ago in the Norwegian journal GEO (a copy in Norwegian can be downloaded from http://geony.imaker.no/pertra/dag47/ ).
It is now described in English in a paper (Memoir No. 7) from Statoil. The paper can be downloaded by clicking here (
DISTRIBUTION OF HYDROCARBONS IN SEDIMENTARY BASINS
File Format: PDF/Adobe Acrobat - 16 pages, 872 KB -
http://www.statoil.no/statoilcom/technology/svg03268.nsf/Attachments/memoir+7/$FILE/Memoir_7.pdf)

Yesterday, 27 October 2007, Clastic Detritus had an interesting blog post on Global warming and Petroleum geology at http://clasticdetritus.com/2007/10/27/global-warming-and-petroleum-geology/