Petroleum generation and accumulation in the Berkine basin, eastern Algeria

Abstract

The Berkine (Ghadames) basin is regarded as an important hydrocarbon play in eastern Algeria. An evaluation of organic source facies, the application of petroleum geochemistry, and an extensive basin modeling study were carried out to improve the understanding of the petroleum charge of the basin. Geochemical data indicate that the Llandoverian-Wenlockian and the Frasnian hot shales are the most important oil-prone source rocks for the known hydrocarbon accumulations in the basin. Maturity data reflect the Late Cretaceous-Tertiary burial and are consistent with a 60-63 mW/m2 heat flow in the vicinity of the anticlines and 50 mW/m2 heat flow farther away from the folded area. A two-dimensional basin modeling study revealed the importance of poorly constrained parameters, such as the amount and rate of Hercynian erosion, on hydrocarbon generation and trapping efficiencies. The model shows that a Cretaceous-Tertiary petroleum generation and emplacement for both source rocks can better explain the different gas and oil fields than can an earlier, Hercynian event. The faults related to the Triassic-Jurassic rifting are most certainly permeable and can be considered as major migration pathways for petroleum. In contrast, the overpressure that developed along the El Biod-Hassi Messaoud axis in the Ordovician reservoirs was probably caused by the low permeability of the faults bounding the anticlines that therefore prohibited any lateral or vertical fluid movements. The model also indicates two petroleum systems that have Triassic reservoirs: (1) a Frasnian-sourced system that is confined to the central part of the basin and (2) a Llandoverian-Wenlockian-sourced system in the western part of the basin. Migration into Paleozoic reservoirs was followed by dismigration into overlying Triassic traps after the Cretaceous compressive movements.