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Abstract

DOI: 10.1306/12171515067

Constraining burial history and petroleum charge in exhumed basins: New insights from the Illizi Basin, Algeria

Kara L. English,1 Jonathan Redfern,2 Dermot V. Corcoran,3 Joseph M. English,4 and Rachida Yahia Cherif5

1Petroceltic International Plc, 3 Grand Canal Plaza, Grand Canal Street Upper, Dublin 4, Ireland; [email protected]
2North Africa Research Group, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, United Kingdom; [email protected]
3Petroceltic International Plc, 3 Grand Canal Plaza, Grand Canal Street Upper, Dublin 4, Ireland; present address: Petrogen Energy Services Ltd., Unit 2A Tigh Phurseil, Freeport, Bearna, Galway, Ireland; [email protected]
4Petroceltic International Plc, 3 Grand Canal Plaza, Grand Canal Street Upper, Dublin 4, Ireland; [email protected]
5Direction Coordination Groupe Associations, Sonatrach, Djenane El-Malik, Hydra, Algiers, Algeria; [email protected]

ABSTRACT

Intracratonic sag basins commonly have relatively simple tectonic histories; however, later tectonic activity involving exhumation can make reconstructing the burial history a challenging task. This is important because the relative timing of hydrocarbon generation and trap formation can be a key factor in risk assessment. If trap formation postdates peak hydrocarbon generation, exploration plays are typically downgraded. Mechanisms for charge in such exhumed basins are critical factors for understanding exploration risk. This study uses data collected from an Ordovician gas-condensate field in the Illizi Basin of Algeria to document the charging of a trap formed, or modified, during exhumation of the basin following maximum burial. Integrated analysis of sonic compaction data, thermal history indicators, and stratigraphic well data was used to constrain the burial and thermal history of the region. Hydrocarbon generation in the lower Silurian source rock is interpreted to have occurred during the Carboniferous (prior to Hercynian exhumation) and during the Late Cretaceous–early Eocene maximum burial (prior to Eocene exhumation). Structural reconstructions indicate that the field was initially located on the southern flank of a long-lived, intrabasinal, Paleozoic paleohigh. The large, low-relief structural closure that defines the present-day accumulation formed as a result of northward tilting of the Illizi Basin during Eocene uplift of the Hoggar massif. The study demonstrates that the timing of trap formation at the Ordovician field postdates the main local hydrocarbon generation events within the basin, suggesting that alternative hydrocarbon charge mechanisms are required. This study indicates considerable potential to charge updip traps on the flanks of exhumed petroliferous basins via redistribution of the preexisting hydrocarbons within the basin.

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