Impact of basin inversion on hydrocarbon habitat in the Qarun Concession, Western Desert, Egypt

Abstract

Detailed study of seismic and borehole data of the Qarun concession indicates that three structural deformations affected this area. The first deformation led to the development of a northwestward dipping half graben that was filled by Jurassic sediments unconformably overlain by Cretaceous sediments. The depocenter of this Jurassic basin was at the present-day Kattaniya High. The second deformation inverted the Jurassic basin and formed the Kattaniya High. Detailed surface and subsurface structural studies indicate that right-lateral wrenching also played a major role during basin inversion. Cretaceous and older rocks lying south of the highly inverted zone were dragged leading to decrease in the NW dip of the Jurassic and older rocks as well as reversal of the dip of Cretaceous rocks. Due to this dip reversal, another (post-inversion) basin was formed south of the Kattaniya High. This basin (El-Gindi Basin), therefore, inherited a synformal geometry between the Kattaniya High and the NW dipping Wadi El-Rayan platform. The third deformation rejuvenated old NW-SE oriented normal faults in post-Eocene time. Basin inversion had both negative and positive effects on hydrocarbon accumulation. Inversion of the Jurassic basin uplifted the depocenter in the Kattaniya High and, therefore, stopped maturation of Jurassic source rocks and led to their severe erosion. Due to these factors, hydrocarbon exploration in the Kattaniya High is very risky. Positive effect of basin inversion is manifested by the creation of El-Gindi Basin and deposition of a thick Apollonia section which accelerated the maturation of the underlying Cretaceous source sediments. Oil migrated updip from these Cretaceous source rocks toward the NW (toward Qarun oil fields) and SE (toward Wadi El-Rayan platform). Oil also migrated updip (southeastward) from the Jurassic kitchen and along major faults toward the Qarun oil fields.