Saturday, October 31, 2009

"Where does the oil come from?"

Some interesting reading


Haji said...

That should have been obvious all along. We're pumping hundreds of millions of barrels of crude out of the Earth for a very long time. How many dinosaurs and plants could have possibly been on the planet at one time? Sadly, Algore didn't create enough of them to support his mansion in Nashville.

wolfwalker said...

Interesting, but almost certainly wrong. Petroleum geology is a very big business -- it's just about the only career path for a geologist outside government or university work. They've had a lot of success over the last sixty-plus years following the classic explanation of petroleum as a fossil fuel. Lots of new fields found, lots of information about the oil in those fields. And these dudes come along and in just a couple of years turn that all upside down? I don't think so.

Keith said...

As a geologist outside of both oil and Govt...

My knowledge of oil is not brilliant, I think the stuff is boring (no pun).

There was a much publicised conference in Rome in the early 70s where it was found that, shock horror, there were only 25 years reserves of oil, tin, copper...

err yes? "Reserves" have a very precise meaning. Stock markets have clear rules on how much drilling, pump testing etc are required to define a "resource", you then need to prove it's commercial viability before you can call it a "Reserve".

All of this takes a lot of money on drilling, siesmics, permeability testing, insitu stress measurements, pilot plant refining, bankable feasibility studies...

As money has a time value, and the net present value of income 25 years in the future is so small it isn't worth it, no one bothers to prove up "reserves" of virtually anything more than 25 years ahead. the only ones who may, are the likes of the Chinese, but for strategic rather than immediatly financial reasons.

As to the "Well refusing to run dry" oil wells don't, there is only about 20% of the oil that is economic to extract. A point is reached at some time when the volume of oil coming up does not cover the cost of maintaining the well and the pipelines (this might be at the point that the pipeline needs replacing).

The understanding of how oil flows and how to force more of the oil to flow into a well keeps on improving. it is now routine practice to pump water in behind the oil, to keep the fluid pressures high.

Since the oil industry started to employ mining engineers (at about 2x the money the mines do)they've been taught how to manipulate the stress field around a well to keep cracks in the rock open, and stop the pore spaces from crushing closed.

Oil in granite - so?
depending on the composition of the granite, they can be big heat producers from decay of U, Th and K40, which are all enriched in some granites.

This heat can drive big (several tens of kilometres from the granite) convective systems. If you have a sedimentary basin busy generating oil, and the fluids in it are not only cooler than the granite, but also under the pressure of the weight of rock above them (lithostatic pressure / overpressured), then it is hardly suprising that they flow, possibly down through deep faults and fissures, and come up through the granite.

That is where the geology of hydrocarbons and of mineral like lead zinc and fluorspar start to overlap.

In a really beautiful bit of geology, the Late prof Kingsly Dunham, who had mapped out the zonation of minerals in a minimg field in Northern England (The North Pennine Ore field) and was able to draw near circular inner zones in which fluorite was present, and an outer zone where barite was present, there was a poorly developed zone where both or neither was present.

Dunham postulated that there was a burried granite that had generated the hot fluids. This view was supported when a gravity survey showed gravity lows under the centre of each fluorite zone.

When funding for a deep drill hole was obtained, prof Dunham was on site when the first granite core came up, the top of the granite had a fossil soil on it, it was older than the rocks with the mineral veins in them!

Since then a lot of isotope work has shown that the granite probably drove big convective systems. One of the mines even had hot salty water inflows, accompanied by methane and radon, it is about 50 miles from the coast, and surface is over 1,000 feet above sea level.

although not common, bitumen is not unknown in the veins of the NPO. The mines where I have seen lots of bitumen were those in the metamorphic rocks in shropshire, again, I think it migrated there, rather than formed in the immediate country rocks.

Do I think oil will run out?

no,, it will just become more expensive, as it does that, then previously un economic accumulations become economic reserves. It is of course finite, but we'll never see any sort of sharp end to it.

Keith said...

oh, just on the fossil thing, before liquid oil was discovered in Pennsylvania, There was a big industry in central Scotland, mining oil shale and cannel coal and roasting / distilling it for lamp oil and Candle wax

oil shale is pretty much a waxy mudstone that hasn't been warmed enough in the ground to drive the hydrocarbons out of it as oil. its' sedimentary origin is clearly visible as are the diatoms algae etc that's greasy lttle remains are the source of the hydrocarbons.

Firehand, if you are still reading this, you must read Pratchett's "The fifth Elephant"

Firehand said...

I'm reading; I see all the comments, but- being the organized sort I am, who still can't find those damn sunglasses- it takes a while to answer.

I'll put that on the list.

This oil stuff is a very complicated subject; I've seen both this "It's not from decay" idea and "Then why do we find it when we act like it is?" stuff over the last few years. It's an interesting argument.