Mesozoic-Cenozoic basin evolution in the northern Western Desert of Egypt

Abstract

Borehole and seismic data indicate that hydrocarbon fields of the northern Western Desert occupy Mesozoic inverted basins lying mostly to the north of latitude 29N. These basins were formed as north and northeastward tilted half grabens in the Jurassic and Early Cretaceous in response to opening of the Neotethys and Atlantic Ocean respectively. NW-SE extension direction during the Jurassic changed to NE-SW direction during the Early Cretaceous. The main basin-bounding faults are oriented NE-SW, ENE-WSW, NNE-SSW, and WNW-ESE and seem to be locally controlled by old structural fabrics. Basin inversion started in the Late Cretaceous due to the WNW-ESE convergence between Afro-Arabia and Eurasia. Faults aligned parallel to the convergence direction continued normal slip and basin subsidence without inversion. Basin inversion started in the Senonian and took place in several pulses, the strongest of which was during the Santonian. Mild inversion continued in the Early Tertiary and completely ended at the Early Miocene. Basin inversion reactivated early rift faults of NE-SW, ENE-WSW, and NNE-SSW orientation by reverse slip and formed several NE-SW and NNE-SSW oriented folds in their hanging walls. Inversion folds are compartmentalized by transverse (NW-oriented) normal faults. These folds and tilted fault blocks of the Jurassic/Cretaceous rifting form the main structural traps of the northern Western Desert. Several stratigraphic and combination traps are yet to be discovered. Jurassic and Cretaceous source rocks in the rift basins with TOC values up to 10% and 5% respectively form the main source rocks that contributed hydrocarbons trapped in Jurassic and Cretaceous reservoir rocks. The discovered hydrocarbons are 1.15 billion bbl of oil and condensate and 12.6 tcf of gas (3.2 BBOE). Recent discoveries indicate that the actual number is indeed much higher. Paleozoic rocks still remain an interesting target for future exploration in the north Western Desert.