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Reconstructing a Source Rock System — Silurian Onlap in Time and Space

Spaak, Pieter *1
(1) Exploration, Shell International E&P, The Hague, Netherlands.

With the rising interest in unconventional oil and gas plays, the need for better understanding and detailed reconstructions of source rock systems becomes even more important than for conventional plays. In this presentation, the base Silurian source rock on the Gondwana margin will be reviewed.

The most prolific Palaeozoic source rocks in the Middle East and North Africa (MENA area), are associated with a major second order transgression, following a Late Ordovician-Early Silurian glacial event. These Silurian source beds are responsible for or contribute to numerous hydrocarbon accumulations, including the Arabian ‘super-giants’ (North Dome/South Pars and Ghawar) and major Algerian gas fields (Hassi R’Mel and Hassi Messaoud). Over 300 biostratigraphically constrained data points from this central Gondwana area, allow the reconstruction of the flood in time and space and show a ‘duration’ of onlap of typically 5-9Ma. Some areas only became flooded after 24Ma in the Late Silurian (Ludlow).

These data points are rotated (using PaleoGIS) to their Silurian position and the ‘base’ Silurian transgression is presented in several palinspastic maps, which show clear tectonic and glacial topography. These reconstructions illustrate that source rocks are found in different settings. Some can be clearly linked to the process of oceanic upwelling but the majority is formed on an extensive Gondwana shelf-area. Reduced circulation caused by the mentioned topography and increased nutrient input during deglaciation are thought to be responsible for the source rock formation on the Gondwana shelf.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain