[Rod_Cloutier]

The question arises with daily consumption of 80 million barrels of oil a day of how long it actually took to form these deposits and how vast they actually are.

The cop out position among geologists is that they formed over millions of years, but is that adequate enough? The Earth in a round number is about 4 billion years old. Surely there were several "millions of years" periods in that time frame for oil formation events.

If you take a false depletion estimate for example. 1000 years of natural oil deposition to equal one day's worth of consumption at the current 80 million barrels per day. 4 billion divided by 1000 equals 4 million days of reserves or 10, 951 years of stock. Obviously this figure is wrong given known volumes of reserves.

If we take another false estimate, lets say, 150 years of supply at 80 million barrels a day then divide this figure into the original 4 billion year history of the Earth figure. That would leave us with a figure of 26,666,666 years of deposition to provide for a single day's consumption at the 80 million barrel a day level that we are currently at.

Obviously this is absurd as well. My question is this- are there any real hard numbers for the ratio of deposition to consumption??

[pup55]

I know just enough about geology to be dangerous, so others may wish to comment:

From what I understand, almost all of these deposits were laid down within a relatively short time frame, and also, under specialized conditions of pressure and temperature, and also anaerobically, such that they became oil, rather than coal or gas, or turn into something else not burnable.

To be specific, most of these deposits were formed about the time of the dinosaurs (between 200 and 65 million years ago), a period of about 140 million years, give or take. This was the only time in Earth history that there was abundant enough plant life and/or organic life so as to accumulate this amount of biomass (the climate was quite different from today, a lot warmer and more tropical, apparently). After the deposits were laid down, they had to be buried under sufficiently deep sediment so as to "age" under conditions which were just right for the formation of oil. As I understand it, 100% of the oil deposits are found in sedimentary rocks, mainly limestone, and almost all were formed in this time window, so the way these geology types find the oil is to look for these deposits, and drill deep enough so as to get down to the Jurassic period, and see what you get. Actually, nowadays, they have ways to identify exactly how deep they have to go, and exactly where in the rock formation there is likely to be an accumulation of oil. If you go back and read a lot of Campbell's newsletters, he goes into detail about what types of sedimentary rock, if any, are around in a given country, and whether they are likely to contain very much oil, so all of this is fairly well known.

Also, as an aside, a lot of the dinosaur skeletons that were found originally were stumbled upon by oil prospectors, because they occur in the same kind of rock formations.

So, is there this type of deposit being formed today? Well, I think a good example would be the peat bogs of England and Ireland and also there are some in the US Midwest. If these were to become buried in several hundred feet of sediment, sink sufficiently close to the molten magma that forms the core of the earth so as to heat up the biomass to the point at which it becomes oil, but not overheat to the point at which it becomes gas, and not leach out into the surrounding area, become eroded, or have some other calamity happen to it, it might, in a few hundred thousand years, become useable oil.

Are there deposits formed relatively recently (from a geological point of view) such that they are on the way to forming oil? Probably all of these coal deposits are a good example. If we could wait maybe another 30 million years, we would be in business.

But, the problem is, the climatic and geological conditions that caused the oil to form in the first place, namely a tropical earth, followed by millennia of limestone deposition, are no longer around, so maybe these deposits would never turn into oil, because they never got buried deeply enough. Who is to say?

So, to answer your question, 99% of the geologists think this oil was formed mainly in a one-time-only "event" in earth history, fairly unique, and whether one would consider this resource "vast" depends on your point of view, but I think actually rare.

As many have pointed out, the big deposits of this stuff, nice and close to the surface, and easy to pump, have mainly already been found. Some possible exceptions to this are potential deposits that are under water, under ice, or remote enough in places like Siberia where no one with a drilling rig has been yet.

Is it possible that there are a lot of small deposits around (a couple of miles wide, for example, or maybe swimming pool sized) that we could tap into? Sure. Take, for example, the continent of North America, between the two mountain ranges. This area is almost all sedimentary rock, and out in the Great Plains a lot of it is close to the surface. Who's to say that you might not be out shooting at some food, a la Uncle Jed, and up from the ground come a bubblin' crude? Well, it's true, you might get lucky and find a swimming-pool sized deposit of oil out there someplace, but a more likely scenario is that the swimming-pool sized deposit is 5000 feet down, and it costs X number of million dollars to drill it, and you might only get Y number of barrels of oil from it, so it becomes an economic calculation as to whether or not you and Granny get to move to Beverly Hills, or whether or not you just leave it down there. Of course, if the oil price is $5000 a barrel, instead of $50, the decision to start drilling is completely different.

So how much oil is really underground out there? No one really knows, as far as I can tell, because it's all underground, and there are different opinions among so-called "experts" as to how much is drillable. Also, the extent to which a deposit is "drillable" depends on what the drilling costs are, and how badly you need the oil.

So here, in a nutshell, is the whole reserves argument, which in my opinion is the true root of the PO debate. Decide from this what you will. Like I said, others may wish to comment.

[mindfarkk]

yeah... when you think about it, in order for these huge reserves to be formed, a whole lotta carbon-based life hadda die together as a very, very large mass, which would require some rapid changes. which implies a whole lotta dying at one time doesn't it?

kinda HOPE that's a one-time thing!

[Carmiac]

Last time I remember this topic coming up someone had a link to some papers discussing where the biomass came from to produce oil. Apparently it was from huge algae blooms that covered most of the world's oceans, before chocking themselves out. These mega-blooms happened twice, and the dates are rather tightly pinned down. I will see if I can come up with the links.

[Antimatter]

As Carmiac said the oil and most gas is formed from algae. For the algae to form oil anoxic (no disolved oxygen) ocean conditions are needed or the biomass gets oxidised as it sinks and gets eaten by fish and other critters. Today the deep ocean is kept oxygenated by the circulation of cold salty dense water sinking in the north Atlantic and eventually surfacing again in the Pacific, so bugger all future oil will be deposited. If we are very unlucky though global warming might shut down that circulation as in The Day After Tomorow, and allow us to repeat the cycle 300 million years later

[tavewa]

The largest oilfield on earth, Ghawar in Saudi Arabia, was formed out of bird shit. Must have been a huge bird-toilet these days.

[Grasshopper]

Probably only within the last billion years have there been organisms around which might have been buried in sediment to form into oil. Only certain conditions of deposition and burial will lead to the formation of oil, as some of the posters in this thread have implied. Optimum conditions for algae blooms include nutrient availability, sunlight, temperature and salinity envelopes. Sufficiently rapid deposition of sediment to cover the fallen plankton, and deep enough burial to get to the oil-forming pressure-temperature window is required. Oil source rocks are usually low porosity, but the oil migrates into higher porosity rock like sandstone or porous limestone, and ultimately into a trap, which defines the pool or reservoir. Sometimes, if there is no trap for the oil to be retained in, it continues to migrate through the porous rock to the surface or to the sea floor,where it dissipates and is eventually consumed by bacteria. Because of uplift and subsequent erosion, many one-time pools have disappeared or become degraded due to breaching. The Athabasca Tar Sands are an example of an oil pool that was degraded by evaporation of the lighter fraction of the oil, and possibly by bacterial action.
So, although millions of years have passed, only parts of the ocean at any time have had the conditions for source rock formation, and not all source rock has been subjected to oil forming conditions. If oil has been formed, it may not have migrated to a porous or permeable enough trap to be economically recovered, or it may have been lost to the atmosphere or ocean through seeps. It is quite scarce compared to water, even underground water.