STRUCTURAL EVOLUTION OF THE ILLIZI BASIN AND ITS IMPACT ON THE GENERATION OF HYDROCARBONS. THE SAHARAN PLATFORM

Our present work is to examine the structural evolution of the Illizi basin and its impact on the generation of hydrocarbons.

Illizi basin is located in the South - West of the Algerian Sahara with an area of 108.424 Km2. This basin is subject of a huge exploration effort which began in 1956 with the discovery of the Edjeleh field. The Illizi basin is an intracratonic, consisted of different structural elements.

Basically, the sedimentary cover consists essentially of detritic deposits of a thickness varying from 2500 to 3000 m, between the Cambrian and the Paleogene times.

It was the a subject of a succession of tectonic phases which are the source of the current structural frame: of phase N040 (Viséan age), phase N120 of (hercynian- end Carboniferous age), phase N090 (Austrian- ante-Cretaceous medium) and phase N050-060 (Oligocene age).

During the lower Paleozoic movements, It existed a distention episode (rifting Cambro-Ordovician), with a continue implementation of sedimentary series, and the subsidence in the lower Devonian. Since the Devonian, the Tihemboka uplift become active regarding the rest of the basin.

On the basis of a structural analysis, two phases have been highlighted during the upper Paleozoic movements. It concerns the Hercynian movements that are assigned to early phase (N040) and Hercynian phase (N120) in a strict sense. Because of their compressive character, they were responsible for large number of strains and they had a very important role in the structuration of the Eastern Sahara. The majority of stand accidents have been reactivated and depreciated in carboniferous land, except the major trends crossing all series of Paleozoic and Mesozoic series. The influence of this reactivation is transmitted on sedimentation by the facial changes and the large variations of thickness.

The different phases of the Meso-Cenozoic have their importance in the current structuration basin. Although the influences by Hercynian and especially Pan-African heritage, they had well printed all the important structures.

The Illizi basin is the most studied oil province and one of the most productive of the Saharian platform. It contains mostly all favorable conditions to the Genesis, migration, and trapping of hydrocarbons.

The history of burring sources rocks shows a quick subsidence during the Paleozoic. The generation periods of hydrocarbon began in the Carboniferous and the expulsion of the oil began later.