Thermal Evolution Of Organic Matter In The Oued Saret Region (Western Border Of The Gourara Basin, Algerian Sahara)

The Oued Saret region is located in the Western border of the Gourara Basin towards the North West of the Saharan Platform. This basin shows a succession of Palaeozoic clastic deposits of Cambrian to Carboniferous age. These are unconformably overlain by the Mesozoic sediments. The structural and sedimentary elements of this basin have been affected by tectonics movements and orogenic phases related to the Pan-African; Caledonian; Hercynian and Alpine phases. The present sedimentary and structural picture of the Gourara Basin has been acquired during the Hercynian phase (faults, anticlines structures, erosions of high zones...), then rebounded during the Meso - Cenozoic. From the geochemical point of view, the main source rock horizon is represented by the Silurian, essentially the Silurian hot shales which constitute the potential source rock having a good richness in organic matter and high maturity. The initial COT was probably much higher. The organic matter is of type II. With regard to maturity, the Silurian has undergone a very strong subsidence during the Palaeozoic. This allowed the restrained organic matter in the Silurian source rock to reach a high transformation ratio (about 98%) before the Hercynian structuration. The geochemical modelling shows that oil generation began toward 360 My (Upper Carboniferous) with a maximum toward 320 My. At 300 My (Late Carboniferous), the Silurian source rock reached the gas phase. From these results, we can say that oil generated from the Silurian source rock at the end Palaeozoic has been expelled towards permeable levels, then accumulated in the local traps and dismigrated during the Hercynian event. Only the gas generated after the Hercynian compressionnal event would be trapped. These assumptions could constitute a response to the absence of liquid hydrocarbons in the Oued Saret region and could guide the exploration for gas research toward the neighbouring zones