Abstract The A1-NC198 exploration well was drilled in the Kufra Basin in 2007 by RWE Dea and represented only the third well in a large, 400 000 km 2 frontier basin. Despite being dry and lacking any hydrocarbon shows, the well provides important data to improve the understanding of the regional petroleum play. In the 1980s and 1990s the basin's prospectivity was questioned largely because of supposed (1) lack of structuration, (2) lack of source rock and (3) thermal immaturity at Silurian level. Following a series of academic and industry studies over the past 10 years, these assertions can no longer be upheld. The analysis of available seismic has proven the existence of Murzuq-style fault blocks as well as late Ordovician glacial erosional relict buried hills, potentially forming suitable structural and stratigraphic traps. The presence of hot shale in the Kufra Basin is evidenced by typical seismic onlaps of strong amplitude reflectors at base Silurian levels, shallow drilling results and outcrop spectral gamma-ray evidence. A spore colouration study of A1-NC198 cuttings indicates a deep oil window maturity for the Silurian, implying potential oil generation in the basin if suitable Silurian source rocks exist. The stratigraphy of the A1-NC198 succession was analysed by means of biostratigraphy and chemostratigraphy, which form the basis for improved well correlations within the basin.

Abstract Proven Infracambrian hydrocarbon plays occur in various parts of the world, including Oman, the former Soviet Union, India, Pakistan and Australia. Organic-rich strata also occur in NW Africa, and gas shows originating from Infracambrian hydrocarbon source rocks are known from well Abolag-1 in the Mauritanian part of the Taoudenni Basin. The distribution of Infracambrian source rocks in North Africa is patchy and deposition commonly occurred in half-graben and pull-apart basins. In these intra-shelf basins, marine, organic-rich shales and limestones were deposited beneath the turbulent wave zone, away from the coarse siliciclastic Pan-African molasse detritus. On the West African Craton (including the Taoudenni Basin) organic-rich horizons were also deposited earlier, in pre- and syn-Pan-African times between 0.5 and 2 Ga (Ga is 10 9 years). The long-lasting sedimentation history in this area contrasts with that of the Pan-African regions, such as Oman, which lies in the Pan-African province of the East African Orogen, where preserved sediments are rarely older than 640 Ma. Infracambrian black phyllites in the Anti-Atlas region of Morocco were deposited on a continental slope of a short-lived ocean lying to the north of the West African Craton. Hydrocarbons generated during Infracambrian times from these deposits, however, have a low preservation potential. Infracambrian organic-rich and/or black-pyritic deposits in North Africa are proven in the Taoudenni Basin, the Anti-Atlas and the Ahnet Basin. Thick carbonate successions exist in the Taoudenni Basin, indicating deposition in areas some distance from contaminating coarse siliciclastic hinterland influx. Infracambrian strata may also occur in the Tindouf Basin. However, their deep burial and consequent early maturation history may be unfavourable for the preservation of Infracambrian-sourced hydrocarbons in this area. Local development of Infracambrian source facies may also occur in the Reggane, Ahnet, Mouydir and Iullemeden basins, as indicated by black shales in wells MKRN-1 and MKRS-1 in the Ahnet Basin. Generally, however, these basins appear to be close to the active Pan-African orogenic belt and, consequently, probably received large quantities of coarse siliciclastic sediment, largely of continental facies, which may have diluted any significant hydrocarbon source potential.

Abstract During the Frasnian, organic-rich shales were deposited across much of North African, most notably in parts of Morocco, Algeria, southern Tunisia, western Libya and the Western Desert of Egypt. They are estimated to be the origin of about 10% of all Palaeozoic-sourced hydrocarbons in North Africa. The depositional, palaeoecological and geochemical characteristics of this black shale unit can be best studied in the eastern Algerian Berkine (i.e. western Ghadames) Basin where the thickest and organically richest ‘hot shales’ occur. In wireline logs, the Frasnian hot shales are marked by high gamma-ray values, often in excess of 300–400 API, which, according to gamma-ray spectrometry, almost exclusively originate from an elevated uranium content. Comparison with total organic carbon (TOC) data shows that the gamma-ray curve can be used as a proxy for the TOC content of the Frasnian shales, with 150 API correlating approximately with TOCs of about 3% in eastern Algeria. The hot shale unit usually consists of high-frequency, high-amplitude, metre-scale gamma-ray cycles; however, especially in the thicker hot shale units, the lower frequency envelope curve of the high-frequency gamma-ray cycles has a gradual, bell-shaped form. The gradual increase and subsequent decrease in organic richness over time may be interpreted as evidence for a gradual rise and subsequent fall of the oxygen minimum zone (OMZ), with invasion of oxygen-depleted waters onto the North African shelf. The rise of the OMZ may have been triggered by the Early Frasnian transgression, which has been described in detail from Morocco, where it is now well-dated by conodonts and is associated with characteristic black shales and carbonates. Additional high-resolution biostratigraphic data are still needed in order to better correlate the Frasnian hot shales of Algeria, Tunisia and western Libya with other Late Devonian dysaerobic/anaerobic facies in Morocco, western Egypt, Europe, South and North America.