[Tanada]

What formation on Earth producing oil today has the oldest petroleum? I mean literally the oil that was formed longest in the past? Corollary what field has the youngest oil in the world?

I have heard Colin Campbell say in several different interviews over the last decade that most oil was formed during two brief periods (60 and 140 Million Years Ago?) Using the term 'most' implies some oil was formed at other times, perhaps much earlier than 140 million years ago, and maybe more recently than 60 Million years ago.

How can you date a petroleum sample to be sure it formed when you think it did instead of migrating from a younger or older source rock into the reservoir where you find it today?

Rockdoc123? ROCKMAN? Beuler?

[ROCKMAN]

MOST of the world's oil comes from geological sediments laid down since the time when animals and plants had already evolved to highly advanced forms. But a recent discovery in Australia may not only enhance scientific understanding of primitive life forms but may also disclose hitherto untapped sources of oil. A team of geologists working for the Australian Government's Bureau of Mineral Resources reports in the journal Nature that it has discovered oil formed from the decayed remains of organisms that lived 1.4 billion years ago, when the earth was young. After the group drilled a 1,100-foot-deep test hole beneath the McArthur Basin in northern Australia, the oldest oil of its kind ever found bubbled to the surface.

Half of the world's oil production comes from sediments deposited during the Tertiary period, which began 65 million years ago and ended 1.8 million years ago. Most of the rest of the oil comes from the Cretaceous and Jurassic periods, when dinosaurs ruled the land, from 195 million to 65 million years ago. Analysis of the oil found by the Australian group showed that it had been produced from the remains of primitive bacteria and algae, the only forms of life that existed on the earth 1.4 billion years ago. ''These results show that exploration of previously ignored sediments may lead to the discovery of new reserves of oil,'' the Australians said.

[sparky]

.
Checked the story ,
http://www.abc.net.au/science/news/anci ... 385489.htm
the report mention 3.2 billions years ago , that's as soon as the Earth had an atmosphere and a crust

the Permian had deposits and the carboniferous period ,
it seems that making hydrocarbon is the favorite pastime of geology
of course the oldest the deposit the more chances its capping deposits will break or be eroded
it migrate topside
any hydrocarbon exposed to air is gone pretty soon
most of the oil deposited must have disappeared down the ages , what is left is probably a fraction of what was created

[Tanada]

MOST of the world's oil comes from geological sediments laid down since the time when animals and plants had already evolved to highly advanced forms. But a recent discovery in Australia may not only enhance scientific understanding of primitive life forms but may also disclose hitherto untapped sources of oil. A team of geologists working for the Australian Government's Bureau of Mineral Resources reports in the journal Nature that it has discovered oil formed from the decayed remains of organisms that lived 1.4 billion years ago, when the earth was young. After the group drilled a 1,100-foot-deep test hole beneath the McArthur Basin in northern Australia, the oldest oil of its kind ever found bubbled to the surface.

Half of the world's oil production comes from sediments deposited during the Tertiary period, which began 65 million years ago and ended 1.8 million years ago. Most of the rest of the oil comes from the Cretaceous and Jurassic periods, when dinosaurs ruled the land, from 195 million to 65 million years ago. Analysis of the oil found by the Australian group showed that it had been produced from the remains of primitive bacteria and algae, the only forms of life that existed on the earth 1.4 billion years ago. ''These results show that exploration of previously ignored sediments may lead to the discovery of new reserves of oil,'' the Australians said.

So the story I learned a long time ago goes something like this. When looking for oil look for sedimentary rock from 60 or 140 million years ago trapped beneath an impermeable layer or rock . Then drill a well into an upward fold of the sedimentary rock and see if you get oil or natural gas.

(My dad invested in an oil drilling company back in the 1950's and lost his shirt wildcatting. After that he went into business with two brothers in law running a gasoline service station and went broke a second time. He decided business wasn't his thing and went to work for factories as a blue collar worker until he retired at 68 from the early 1960's to the early 1990's)

From what you posted about Australia it sounds like instead of dating the rock to the two 'oil periods' you petroleum geologists need to drill into every layer of sedimentary rock no matter what the age is to see if it has oil in it, not just the stuff that came from the Jurassic and Triassic???

[ROCKMAN]

“…most of the oil deposited must have disappeared down the ages”. Some geologists with way too much time on their hands have estimated that 95% of all hydrocarbons that have been generated leaked to the surface. Which includes a big chunk called the Alberta oil sands.

T – “…petroleum geologists need to drill into every layer of sedimentary rock”. We try but those damn engineers with their economic evaluations keep getting in the way. LOL. Actually when you get to untested layers you first look for evidence of hydrocarbon generation before you begin looking for reservoirs. Many years ago a very expensive well was drilled by a consortium of company from a manmade ice island up near the arctic circle. Tests of the rock sample that came up indicated that this area had not gone through the oil creation phase and thus there was no point looking for traps.

And a similar story: when I started at Mobil Oil I 1975 I read a report about a similar “stratigraphic test” off the US east coast in federal waters. The company that was contracted to drill the well used a little bit of oil in the drilling mud to make the effort go a little faster. Of course every geochem analysis used to determine if there had been an “oil window” developed in this area came back: “Sample contaminated with diesel…no analysis possible”. When the oil companies complained the drilling contractor explained it was their call how to drill the well and this was how they were going to continue doing it. Thus the result of a committee project overseen by the federal gov’t.

[Tanada]

“…most of the oil deposited must have disappeared down the ages”. Some geologists with way too much time on their hands have estimated that 95% of all hydrocarbons that have been generated leaked to the surface. Which includes a big chunk called the Alberta oil sands.

T – “…petroleum geologists need to drill into every layer of sedimentary rock”. We try but those damn engineers with their economic evaluations keep getting in the way. LOL. Actually when you get to untested layers you first look for evidence of hydrocarbon generation before you begin looking for reservoirs. Many years ago a very expensive well was drilled by a consortium of company from a manmade ice island up near the arctic circle. Tests of the rock sample that came up indicated that this area had not gone through the oil creation phase and thus there was no point looking for traps.

Related question, I was also taught way back when that the oil formation window was of moderate depth in the crust, but these days I see talk about sub-salt occasionally, and super deep fields off the coast of Indo-China, and the Bakken being some of the deepest reservoirs ever drilled along with super deep in the GOM like Deepwater Horizon.

There has to be a physical limit below which Petroleum breaks down into natural gas, but darned if I have a clue how deep it is.

[dorlomin]

There has to be a physical limit below which Petroleum breaks down into natural gas, but darned if I have a clue how deep it is.

It will differ place to place but temperature puts a limit on where oil can exist.

[Tanada]

There has to be a physical limit below which Petroleum breaks down into natural gas, but darned if I have a clue how deep it is.

It will differ place to place but temperature puts a limit on where oil can exist.

Handy graph, thanks. So in some places oil can form as much as 20,000 feet below the surface, but that vast bulk of it forms between 10,000 and 15,000 feet down.

That would explain the Bakkan formation, the oil is over 10,000 feet deep but the rock is so tight it was not able to migrate to geological traps at higher depths.

[Tanada]

MOST of the world's oil comes from geological sediments laid down since the time when animals and plants had already evolved to highly advanced forms. But a recent discovery in Australia may not only enhance scientific understanding of primitive life forms but may also disclose hitherto untapped sources of oil. A team of geologists working for the Australian Government's Bureau of Mineral Resources reports in the journal Nature that it has discovered oil formed from the decayed remains of organisms that lived 1.4 billion years ago, when the earth was young. After the group drilled a 1,100-foot-deep test hole beneath the McArthur Basin in northern Australia, the oldest oil of its kind ever found bubbled to the surface.

Half of the world's oil production comes from sediments deposited during the Tertiary period, which began 65 million years ago and ended 1.8 million years ago. Most of the rest of the oil comes from the Cretaceous and Jurassic periods, when dinosaurs ruled the land, from 195 million to 65 million years ago. Analysis of the oil found by the Australian group showed that it had been produced from the remains of primitive bacteria and algae, the only forms of life that existed on the earth 1.4 billion years ago. ''These results show that exploration of previously ignored sediments may lead to the discovery of new reserves of oil,'' the Australians said.

Is this the one you are referring too, or is it something else?
http://www.empireenergygroup.net/Litera ... ?ID=176415

[ROCKMAN]

T - Actually in many cases where there's been sufficient evidence the OIL GENERATION window was rather shallow: 10,000' and even much less. Which would explain why so much oil has leaked out: the oil was generated before the traps were formed. There is also the oil PRESERVATION WINDOW. Actually I just made that term up but the dynamic is real. A trap may be created shallow and filled with oil. But if the rock continues to subside it can reach temperatures that break the oil down. The reason those big oil reservoirs exist at 25,000'+in the GOM is that the sediments were buried so quickly that the temperature hasn't risen to the point where oil wouldn’t be preserved. Remember that the rocks being drilled 5+ miles down were originally deposited in 10’ of water…or less. That's a whole lotta subsidence. The term is GEOSYNCLINE…the Mother of All Holes in the earth. LOL.

At the other end of the spectrum are oil reservoir that are trapped deeper within the earth and then the area is pushed up by tectonic forces and the reservoir is pushed upwards the surface…maybe all the way to ground level. At that time bacteria can begin feeding on the oil and degrade it. Not sure but I think that’s at least one reason for the poorer quality of the Alberta oil sands.

[Synapsid]

Tanada,

I'm not sure if this is part of what you're wondering about but there's a key point mentioned in the Australian report that ROCKMAN quotes, to the effect that the oil formed only from very old types of "bacteria and algae".

There are marker organic molecules that persist in the rock record for a couple of billion years, and that are specific to particular groups of organisms. The report is saying, I think, that the only markers found are from bacteria (I'd set aside the mention of algae, as I can't tell if they're talking about cyanobacteria, which are often erroneously called blue-green algae) so the oil dates to when bacteria were the only critters around, and that was over a billion years ago.

My guess.

[Lone Ranger]

Rockman said:
There is also the oil PRESERVATION WINDOW. Actually I just made that term up but the dynamic is real.
I agree.
I recently returned from the GCAGS convention in Lafayette, one speaker addressed the big oil reservoirs in the GOM at 25-30,000 feet. His take on the maturation window involved heat dissipation at depth by SALT. Salt domes are di-thermal anomalies being cooler at the base than at the top...they act as heat conduits, thereby affecting the thermal maturation.
just google " heat dissipation in sedimentary basins by salt"

[ROCKMAN]

Syn - Interesting. I've seen rocks of fossilized organisms that dated over 1 billion years. But never heard of oil dated much older the 800 million years.

[sparky]

.
on my laundry window sill , I got a piece of stromatolite , I picked it up in Western Australia
the concretions are build by microbial mats since 3.5 billions years ago and still do it today
matter of fact they don't seems to have moved much more than a few hundreds of miles
finding refuge around Shark bay in one of the world most inhospitable environment

those stromatolites were the very first biological system , their metabolism is very slow but for 3 billions years they pretty much had the place to themselves , munching on sunshine and CO2 , generating large amount of oxygen as a effluent

[Synapsid]

ROCKMAN, sparky,

I haven't heard of oil this old either. If the organics really are only bacterial, I can see where the conclusion came from, though.

Those stromatolites are built by cyanobacteria but they aren't alone. As sparky says, there's a whole system--an ecosystem--involved. They are found elsewhere than Shark Bay, the Bahamas for instance, but Shark Bay has had all the publicity.

[sparky]

.
Been searching a bit and it would seems there is oil fields from before the Cambrian
http://www.ogj.com/articles/print/volum ... rocks.html
since that was when life went crazy ,and before there wasn't much happening , most fields are from the Cambrian down to the end of the Dinosaurs 65 millions years ago , younger I don't know , but that's getting tight , cooking wise .