SEWilco's Journal: Oil From Rock...ongoing...

Well, this discussion on the origin of oil from deep rock rather than dead stuff has been going on for days...I'm dropping a copy of my latest reply here because I think I hit a Slash limit in posting it...

Gold is pointing out that carbon can be much deeper, and availability at the surface is dependent upon deep geology rather than past surface pools of muck.

No one has suggested that oil avaliability is dependant on 'past surface pools of muck'; I really don't understand where you are getting this from.

"Surface" as in "origin not in deep rock". "Pools of muck" as in "plant and animal matter buried in low-oxygen conditions" (has to be low-oxygen or the long chains with hydrogen will not exist and no long-chain hydrocarbons can appear).

Why hydrocarbons should have been retained in the mantle when every other volatile has been effectively stripped (due to melting and cycling through oceanic crust) is unexplained.

By "stripped", I assume you mean broken down from long chain molecules to simpler structures. Methane (CH4) is rather simple. Gold repeatedly points out that methane is more common at greater depth, and hydrocarbons become more complex with decreasing depth. Just what would be expected if the material is being altered as it rises.

Carbon in subducted rock has to go someplace. There are five possibilities:

• Carbon might sink and be lost (unlikely as it is less dense than nickel-iron)
• Carbon might be trapped and never rise (unlikely, as volcanoes often bring material up from subducted areas).
• Carbon might bubble up early in the process and leak right at the fault.
• Carbon might travel great distances under crust, whether dissolved in mantle material, in deposits under crust, or in lower levels of crust.
• Carbon might accumulate near subduction areas and push upward.

Gold's ignorance of the last 40 years of geology shines through; dismissing the entire science of petroleum geology is bad enough for a non-geologist, dismissing plate tectonics, standard planet formation theories, basic physics, and in fact anything that gets in the way of his theory is worse.

Yup, awful crimes. How was Copernicus punished?
I haven't seen him dismissing plate tectonics, although I don't know if he believes that the 4 billion-year-old continental cratons contain carbon from Earth's formation, or if the deep carbon in them is from subducted ocean floor (ocean floor before 200 Ma is gone).

As an astronomer, he probably knows planetary formation and physics quite well. He does state that no gases were incorporated in Earth, so carbon, water, and nitrogen must have come from material within the planet. I don't know what he thinks happened to lighter elements during the Earth-shattering impact which created the Moon (my observation is that the Moon's density is significantly less than Earth, so much separation of dense material must have already happened before impact -- or dense material didn't splash high enough to stay in orbit).

Middle East has been greatly disrupted by tectonic activity (90 degree rotation is somewhat drastic), and obviously there are many faults to deeper areas. So the search for "source" rock has actually been the search for rock which met expectations near the reservoirs.

90 degree rotation is not very drastic.

Well, I thought for recent time it was. Although perhaps the subduction under the Arabian plate since 650 Ma was more important in carbon sources than the movement. The pressures by surrounding plates are interesting, but I don't know if that caused any fractures in the oil-producing areas -- volcanic rock is to the west, not within the oil fields.

And the fact that source rocks have been found, with appropriate thermal conditions and migration pathways is pretty strong evidence, especially as when these rocks are NOT found, there is no oil.

The biogenic theory requires certain source rocks, so finding such rocks includes the biogenic theory as a possibility in the Arabian area (even in the basement rocks in Yemen, due to proximity of biogenic source rocks). Abiogenic theories don't care what kind of rock is near the surface, although obviously an impermeable cap is needed for a reservoir where we tap one. There also are issues about the temperature and pressures being insufficient to create biogenic oil in shallow sedimentary rocks.

Biogenic origin theory does not explain finds where there are no expected formations. There are hundreds of producing wells in basement rocks, and some hydrocarbons have been found in rather unconventional areas. Gold has plenty of references to his experiences drilling in the Swedish impact ring. Anhydride Petroleum continues exploring the basement oil/gas which Hunt believes are part of the source of the Athabasca Tar Sands.

Have a read of this: Petroleum geology, Saudi Arabia. [sc.edu]

Nice description of the biogenic interpretation.

To read from Gold's site:

If the major volume of the Earth has never been molten, the mantle of the Earth underneath the crust must still contain the diversity of chemistry, the chemical energy sources and the sources of gases and liquids that would be the legacy of an accretion process from diverse and initially cold solids.

Except that mid ocean ridge basalts [which sample the mantle beneath effectively] exhibit an extreme uniformity of compositions. Basic physics also gives us raleigh numbers for the mantle indicating that it is well mixed.

Yes, the mid-Atlantic ridge is a spreading zone, so it should have metal-rich magma rather than the silicon-rich lava in a compression zone. So if mantle magma is well-mixed, whether there is carbon in it depends upon whether carbon can mix or dissolve in nickel-iron, and it can be expected to be everywhere. Carbon dioxide is in mantle magma, so carbon is indeed part of the global molten mix.

So the same weak points along the Southeast Asia plate edges which cause volcanoes also cause hydrocarbons to become available near the surface.

No, the hydrocarbons are found in the back-arc settings. These are not 'weak points causing volcanoes', it's subducting slab dehydration melting the mantle above. Hawaii is not mentioned by Gold probably for the reason that it is known to have a deep component to it's magma and yet emits little or no methane.

Actually, Gold mentions Hawaii briefly (your browser might have a Control-F search command), and as I mentioned above carbon dioxide emissions have been studied in Hawaii. Carbon dioxide is not methane, but it shows carbon at 40 km depth from a mantle source.