Geologic Time, Oil Formation and Secretary Chu

Last week ,as Climate Audit caught, the Seretary of Energy was asked about how oil and gas got into the Arctic Rocks. Now there is a little catch to the question, in that for oil to be formed the local environment has to be quite warm particularly relative to today’s Arctic temperatures (as explained below). Thus, to explain how the oil got there, the Secretary would have to admit that there was a period when the Arctic was warmer than today. However Dr Chu did not want to give that answer, and so he proclaimed that the rock and oil-forming algae were deposited elsewhere and then migrated, under Continental Drift, until they ended up in the Arctic. Steve gave a condensed answer pointing out how wrong the Secretary is on this, but I thought I would use the error as a base for explaining the origins of oil and natural gas in a post that I can then relate to later.

The majority of world opinion on the matter, has concluded that oil and natural gas originated in the bodies of small organisms, such as modern algae, which can include up to around 56% lipid material (their version of fat). This is referred to occasionally as the biotic source, as opposed to an alternate theory, the “abiotic” theory. This latter theory, which came out of Russia and gained some acceptance in the West, in essence says that oil is generated deep underground by chemical reactions, similar to the Fischer-Tropsch process used to make synthetic oil. While the relevance of this process to oil supply has been disputed, it relies in part on the idea that there are deep pools of oil that fill old reservoirs back up after they are depleted and that if we just drilled deep enough to find them we would have an almost inexhaustible supply. And the catch with that relates to the formation of oil and gas through the biotic explanation.


The biotic explanation for oil and gas formation proposes several steps along the way. First we have the rivers and shallow seas where the algae flourished and died. Sinking to the bottom they mixed with the sediment that is also deposited in such places (and which can be seen in parts of the world today). With time, as with the formation of coal, the sedimentary beds that hold the nascent hydrocarbon fuels are buried deeper. With an increasing depth of burial comes an increase in pressure and temperature. As a very rough rule I use 1 psi of pressure for each foot of burial, and 1 degreeF for every 60 ft of depth startin at 60 deg at 60 ft. So that, for example, at a depth of 3,000 ft the ground pressure is 3,000 psi and the temperature will be 110 deg F.

An early step along the way, as our hydrocarbon starts to cook is its transformation to a kerogen. This is the “oil” of the oil shales of Colorado, New Mexico and Utah. It is not yet a liquid and does not flow. To get to that stage it has to be buried deeper and heated longer. That is what Shell is planning to emulate with their process for oil recovery from the shale. By inserting long heaters into holes down through the rock, and raising the temperature to 650 – 700 deg F and holding at that temperature for 2-3 years they hope to complete the transformation. The temperature is higher than that which would be needed for the natural process, because the process must happen faster. With nature and depending on the part of the world you are in (since the geothermal gradient varies) the transition will occur when beds lie in the 3,000 ft to 15,000 depth.) (Temperatures up to 300 deg F range. ) This depth range is often referred to as the oil window, since shallower rocks aren’t cooked well enough and we get kerogen, and if the rock goes deeper then the higher temperatures will “crack” the oil into natural gas.

(Which is where the problem of deeper pools of oil for abiotic oil comes up, since the deeper pools that the theory calls for would exist at depths where the oil would be cooked into gas, and thus no longer available to supply the oil).

As the oil heats it also thins and becomes less sticky so that it can start to slide through the grains of the surrounding rock, passing along small cracks and being pushed up, in part by the water that was trapped in the rock with it, and which starts to collect below the oil. The oil will move up through the layers of rock until it either reaches the surface, or it is trapped below a rock which does not have the passageways (permeability) wide enough for the oil and water to pass through.

Similarly the deeper deposits that have turned into gas will also begin to move up until they too are trapped beneath an impermeable cover or cap rock.

OK, so when did this happen? Well it depends on the place you’re at. But, for example if we go up to the North Slope of Alaska, the rocks that generated the oil are known as source rocks, and the USGS has identified rocks of the Triassic (the Shublick) ; the Jurassic (Kingak) and the Cretaceous periods may all have contributed oil.

Source USGS

Now a quick peek at a geologic column tells us that these are periods of the Mezozoic Era which ran from the end of the Cretaceous ( 65 million years ago) through the Jurassic (ending 165 million years ago) to the Triassic which ended 208 million years ago. They are younger than the Carboniferous, when coal beds were laid down, by some 40 million years or more.

However, to get back to Dr Chu’s point about Continental Drift having carried the oil bearing rocks up to Alaska, after they were formed, if you go to any of the models which show how the plates have moved, the North American plate (which includes Alaska) was already up in place as far as the North is concerned (but then drifted West) by the beginning of the Jurassic.

So while this was a good try by Dr Chu, a Climate Warming devotee, to get around some geological truths, the facts argue against him. (Not to mention more recent findings within the Holocene, our current geological Era), but we'll save those for another day.
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