Petroleum geochemistry and geology of the Midyan and Al Wajah basins, Northern Red Sea, Saudi Arabia

The purpose of this study is to define the petroleum geochemistry of the Midyan and the Al Wajah petroleum basins located in the northern Red Sea. The rift basins consist of Neogene rocks resting nonconformably on Proterozoic and Upper Cretaceous basement. Using Rock Eval 6, we analyzed cutting samples from three wells located in the Midyan basin and one well in the Al Wajah basin for their source rock quality. The key source rocks in the Midyan and Al Wajah basins are the Maqna Group and the Mansiyah Formation. Although the source rocks in the Al Wajah basin are rich in organics, none of them has generated a significant amount of hydrocarbon. In the Midyan basin, the Jabal Kibrit Formation and the Yuba and Sidr Members of the Kial Formation, of the Maqna Group, attained sufficient maturity to generate oil. However, the Mansiyah Formation has not generated oil because of its low maturity. The maturity and the marine organic contents increase from south central wells to southwestern wells. The Rock Eval 6 data were supported by gas chromatography - flame ionization detector (GC-FID), biomarker and stable carbon isotope analyses of oil and gas condensates collected from seven wells in the Midyan basin and two wells in the Al Wajah basin. The results suggest three hydrocarbon types in the Midyan basin and two types in the Al Wajah basin. In the south central Midyan basin, the oil is characterized by low maturity and source rock was deposited in a hypersaline environment. However, in southwestern Midyan, the oil is characterized by higher thermal maturity and by source rock that was deposited in a normal salinity environment. The third type, which includes the Midyan condensate, is characterized by low maturity, and shale source rock contains Kerogen type-II. In the Al Wajah basin, the two gas condensate types have low maturity but distinctive biomarker composition from each other. Burial and thermal models suggest that the oil generation in the Midyan basin started at ~ 8 Ma. The oil and gas was then trapped in normal fault traps beneath the Mansiyah Formation prior to the trap formations.