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Petroleum generation and migration in the Ghadames Basin, north Africa: A two-dimensional basin-modeling study

¹ North Africa Research Group, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; ruth_underdown{at}hotmail.com
² North Africa Research Group, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom; jonathan.redfern{at}manchester.ac.uk

Ruth Underdown obtained her first degree in geology from the University of St. Andrews, Scotland, an M.Sc. degree in petroleum geoscience from Imperial College, London, and a Ph.D. from the University of Manchester, United Kingdom, in 2006, funded by the North Africa Research Group. She is currently teaching in the United Kingdom.

Jonathan Redfern obtained his B.Sc. degree in geology from the University of London, Chelsea College, in 1983, and a Ph.D. from Bristol University, United Kingdom, in 1989. He worked in the oil industry for 12 years, initially with Petrofina in the United Kingdom, southeast Asia, and Libya, and subsequently with Hess. He is a senior lecturer at the University of Manchester and leads their North Africa Research Group. His main research interests are in basin analysis, hydrocarbon systems, and continental and glacial sedimentology.

The Ghadames Basin contains important oil- and gas-producing reservoirs distributed across Algeria, Tunisia, and Libya. Regional two-dimensional (2-D) modeling, using data from more than 30 wells, has been undertaken to assess the timing and distribution of hydrocarbon generation in the basin. Four potential petroleum systems have been identified: (1) a Middle–Upper Devonian (Frasnian) and Triassic (Triassic Argilo Gréseux Inférieur [TAG-I]) system in the central-western basin; (2) a Lower Silurian (Tannezuft) and Triassic (TAG-I) system to the far west; (3) a Lower Silurian (Tannezuft) and Upper Silurian (Acacus) system in the eastern and northeastern margins; and (4) a Lower Silurian (Tanezzuft) and Middle–Upper Devonian (Frasnian) system to the east-southeast. The Lower Silurian Tanezzuft source rock underwent two main phases of hydrocarbon generation. The first phase occurred during the Carboniferous, and the second started during the Cretaceous, generating most hydrocarbons in the eastern (Libyan) basin. The Frasnian shales underwent an initial, minor generative phase in the central depression during the Carboniferous. However, the main generation occurred during the Late Jurassic–Cenozoic in the western and central depression. The Frasnian shales are currently only marginally mature in the eastern part of the basin.

Modeling indicates that the Alpine (Eocene) exhumation of the eastern (Libyan) basin margin had a significant control on the timing of hydrocarbon generation from the Lower Silurian source rock. The preferred burial-history model calibrates source rock maturity data by incorporating late exhumation and reduced subsidence prior to the Hercynian (Carboniferous) orogeny. As a result, the Tannezuft shales preserve their generative potential into the Mesozoic–Cenozoic, with renewed hydrocarbon generation during subsequent reburial, which can migrate to post-Hercynian (Carboniferous) traps, hence favoring the preservation of hydrocarbon accumulations.