GEO ExPro

Where does it all come from?

The existence of a source rock is a prerequisite for finding oil and gas. Without a source, the prospect, the play or the basin is bound to be “dry”. An understanding of both source rock distribution and maturation history is therefore key objectives for petroleum explorationists.
This article appeared in Vol. 6, No. 6 - 2009

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Most, if not all, of the oil fields in the North Sea are sourced from Upper Jurassic shales, in particular the Kimmeridge Clay Formation, with its type locality on the Dorset coast of England. Photo: Halfdan Carstens We all know that most of the world’s conventional hydrocarbons are found in the Middle East. Less well known is the fact that most of these conventional hydrocarbons originate in Upper Jurassic to Mid Cretaceous source rocks related to a greenhouse world with warm climates and high sea levels.
 
In this edition of GEO ExPro Rasoul Sorkhabi investigates the distribution of source rocks in time and space. Several independent studies have demonstrated that hydrocarbon-rich source rocks are largely concentrated in just six stratigraphic intervals during the Phanerozoic (compare Geological Time Scale page 14): the Silurian, the Late Devonian, the Late Carboniferous-Late Permian, the Late Jurassic, the Middle Cretaceous, and the Oligocene-Miocene. These six intervals constitute 34% of the Phanerozoic, but they account for more than 90% of the world’s known oil and gas resources.
 
That’s useful to know next time you venture into a new frontier basin.
 
So, we know where it all comes from. The next question is then “how much oil and gas has been generated, and how much can be recovered”. That is not only a geological question; it has turned into a political issue with large numbers of geoscientists - many of them having sound knowledge to share - taking part. Also in this issue, Jane Whaley reports from a debate at the 7th Petroleum Geology Conference (PGCVII) in London earlier this year.  It was another Peak Oil discussion, and it turned out that audience felt that Peak Oil is still a concern. Not necessarily for the oil companies, but certainly for the people inhabiting this planet.

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