Basin Evolution and Geochemical Modeling
An Integrated Basin Modeling Study of the Ghadames Basin, North Africa
Postgraduate research by Dr Ruth Underdown and Dr Jonathan Redfern
Introduction:
The Ghadames Basin is a prolific hydrocarbon province extending over parts of Algeria, Tunisia and Libya, with recoverable oil discovered to date in excess of 3.5 billion barrels. Constraining burial and thermal history is crucial for accurate prediction of the timing of hydrocarbon generation and migration, and of particular importance for future exploration in the relatively undeveloped eastern Libyan part of the basin.
Project methodology:
Extrapolation of observed section thicknesses (palaeo-isopach maps), sonic velocity, apatite fission track and vitrinite reflectance analysis offer four independent analytical techniques to determine burial history and have been used to evaluate the amount of exhumation and associated erosion that have occurred across the basin. Results suggest that much of the basin has experienced widespread apparent exhumation, increasing regionally towards the south and east, with up to ~2000 metres of lost section in the vicinity of the Qarqaf, Tihemboka and Nafusah arches.
Two main phases of tectonic activity have a significant control on basin evolution: the Hercynian (Late Carboniferous-Triassic) and Alpine (Late Mesozoic/Cenozoic). Denudation during the Hercynian increases towards the north and west, whereas the significant regional exhumation recorded along the southern and eastern margins is interpreted to record a period of younger Alpine exhumation. The erosion associated with this late stage exhumational phase has been quantified in this study and incorporated into the basin models. Results suggest a significantly increased generation potential from the Lower Silurian source rock being preserved into the Mesozoic/Cenozoic over the eastern flank of the basin. The integrated basin models have allowed the hydrocarbon generation history to be defined and the major petroleum systems operating within the basin identified.
Modelling Results:
The Lower Silurian (Tanezzuft) source rock experienced two main phases of hydrocarbon generation. The first occurred during the Middle-Upper Carboniferous, when 80-90% of its generation potential was realised prior to Hercynian exhumation over the central basin. By contrast, lower maturities were reached at this time over the eastern flank, when incorporating the late stage Alpine exhumational event, with 30-50% of generation potential being preserved into the Mesozoic/Cenozoic. The second generative phase started during the Cretaceous and is responsible for sourcing the hydrocarbon accumulations found within the Palaeozoic reservoirs of the eastern basin. The Middle-Upper Devonian (Frasnian) source shales also underwent two phases of generation.
The first minor generative phase occurred over the central depression during the Late Carboniferous. However, the main period of generation took place during the Upper Jurassic-Tertiary, peaking during the Late Cretaceous, over the western/central depression. By contrast, the Middle-Upper Devonian source rock over the eastern basin remains immature/early mature at present-day, and has probably not generated sufficient hydrocarbons for expulsion to occur. Regional 2D modeling identifies at least four separate petroleum systems:
- (1) a Frasnian-Triassic system over the central/western basin;
- (2) a Tanezzuft-Triassic system over the far western margin;
- (3) a Tanezzuft-Acacus system over the east/northeast (Libyan) flank;
- (4) a Tanezzuft-Middle/Upper Devonian system to the east/southeast of the basin.
Conference abstracts |
Conference posters |
Papers/Abstracts |
AAPG conference, Calgary 2005 (pdf 10Kb) |
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Saharan conference Geolsoc/NARG 2006 (pdf 17Kb) |
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Underdown, Redfern and Lisker. Basin research (2007) (pdf 1.4 Mb) |