International Geologiical Congress - Oslo 2008

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GEP-09 Linking petroleum systems and plays to sedimentary basin evolution - Part 1

 

Basin analysis in onshore petroleum exploration - A case study from the Kufra basin, southeast Libya

 

Hans Morten Bj°rnseth, StatoilHydro ASA (Norway)
Laurent Gindre, StatoilHydro ASA (Norway)
Alexander Schimanski, StatoilHydro ASA (Norway)
Simon Higgins, StatoilHydro ASA (Norway)
Heike R. Gr÷ger, StatoilHydro ASA (Norway)
Claudius VandrÚ, StatoilHydro ASA (Norway)
Markus Geiger, StatoilHydro ASA (Norway)
 

 

The Kufra Basin is a large intracontinental basin in Southeast Libya. Three exploration wells have been drilled, but no petroleum accumulations have so far been found in the basin. Presented here is a basin analysis of the Kufra Basin, focusing on improving the predictions of key parameters for petroleum exploration in the region, as well as developing and testing methods and workflows optimized for onshore basin analysis.

The Cambrian - Silurian tectonic and depositional history of the Kufra Basin appears to be very similar to the adjacent Murzuq Basin to the west. In fact, it can be argued that both basins at this time were part of a huge platform area covering large parts of North Africa. In the Murzuq Basin substantial volumes of oil have been found in fluvial, shallow marine and glacial sandstone reservoirs of Ordovician age. These reservoirs are overlain by a basal transgressive unit of Early Silurian shales, representing an excellent source rock for petroleum generation. Recent field work and evaluations of subsurface geological and geophysical data indicate that the same Ordovician reservoir units seen in the Murzuq Basin are also widely distributed within the Kufra Basin. In contrast, Early Silurian source rocks have not yet been proven in the Kufra Basin. The three wells in the basin all penetrated shales of Early Silurian age, but no shales with source rock potential were encountered. The Early Silurian source rocks in the Murzuq Basin have a very patchy distribution, however, and this may also be the case in the Kufra Basin.

A major change in the configuration of sedimentary basins of North Africa occurred in the Early Devonian. The Tibesti High underwent major uplift at this time, effectively separating the Kufra Basin from the Murzuq Basin to the west. Several other uplift events have later modified the geometry of the Kufra Basin. The most significant phase of uplift and erosion in the Kufra Basin probably occurred late in the basins history as the flanks were significantly uplifted and eroded some time after the Triassic. The central part of the basin does not appear to have experienced the same amount of uplift and erosion. As a result, the present day geometry of the basin does not reflect the basin configuration during deposition of the key Paleozoic reservoirs, seals and source rocks. Reconstructions of the basin configuration and regional depositional geometries through time are therefore included in the analysis of the Kufra Basin.

 

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