--> Abstract: Distribution of the World's Oil and Gas Source Rocks in Space and Time – Perspectives for Exploration in Frontier Basins, by Peter J. McCabe; #90073 (2007)

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Distribution of the World's Oil and Gas Source Rocks in Space and Time – Perspectives for Exploration in Frontier Basins

Peter J. McCabe
Petroleum Resources Division, CSIRO, North Ryde, NSW, Australia ([email protected])

It is widely believed that there were periods of geologic time that were highly favorable for the accumulation of petroleum source rocks due to factors such as global sea level conditions, global climatic patterns, or oceanic anoxic events. To examine this premise, data was compiled from USGS assessments made over the last 12 years. The amount of known oil (discovered) was tabulated by the age of presumed source rocks for oil and gas accumulations for 288 of the world’s major petroleum provinces.
Upper Jurassic strata contain the most productive source rocks for both oil and gas and there is a general decreasing productivity trend through younger strata up to the Miocene, although the Maastrichtian and Paleocene have very few source rocks. 80% of the world’s known oil and 64% of the world’s known natural gas is sourced from Upper Jurassic and younger strata. Productivity of source rocks decreases dramatically in strata older than Middle Jurassic with a few exceptions, such as the Lower Silurian that have significant source rocks for natural gas.
The data do not suggest that on a global basis there were periods of geologic time that were particularly favorable for the accumulation of source rocks. The primary trend suggests a simple pattern: source rocks younger than Jurassic are more likely to be under-mature for petroleum whereas those that are older are more likely to be over-mature. However, there are periods of geologic time that were important for the accumulation of source rocks in certain regions. For example, about 95% of the oil in South America is thought to be derived from Cretaceous source rocks and 65% of the oil in the Asia Pacific region is ascribed to Cenozoic source rocks. Rather than global-scale events it the timing of regional tectonism, especially rifting, that determines the potential for source rocks.
These observations are critical in ascertaining the potential for source rocks, and hence petroleum generation, in frontier basins. An integrated understanding of regional tectonic history, paleogeography, and paleoclimatology is much more important for evaluating the probability of the presence of adequate source rock in a basin than is any consideration of global-scale processes.

 

AAPG Search and Discovery Article #90073 © 2007 AAPG Foundation Distinguished Lecturer Series 2007-2008