Effect of Mesozoic and Tertiary Deformations on Hydrocarbon Exploration in Northern Western Desert, Egypt

By

Ahmed El Awdan¹, Fekry Youssef¹, Adel R. Moustafa²

(1) Khalda Petroleum Company, Cairo, Egypt (2) Ain Shams University, Cairo, Egypt

 A detailed structural study of a segment of the northern Western Desert (Khalda concession areas) reveals the effect of Mesozoic and Tertiary deformations on hydrocarbon exploration there. An early rifting phase in the Jurassic and Early Cretaceous formed several half graben-like basins with intervening platforms having basin and range geometry. Thick wedges of Jurassic and Lower Cretaceous sections were deposited in these basins and include potential source rocks. Rift-bounding faults are oriented E-W, ENE-WSW, and WNW-ESE. NNE-SSW oriented faults locally bounded some basins as well.

Late Cretaceous (Maastrichtian) dextral wrenching on the E-W to ENE-WSW oriented faults deformed the syn-rift and post-rift sediments. This led to the development of NE-SW oriented folds, NW-SE oriented normal faults, WNW-ESE oriented dextral-slip faults, and a few NE-SW oriented reverse faults. Wrenching also led to positive inversion of old NNE-SSW oriented normal faults bounding some early rift basins.

A late phase of post-Cretaceous extension mildly affected this area and rejuvenated a few of the old faults by normal slip. Structural traps in the northern Western Desert include NE-SW and NNE-SSW oriented folds formed by Late Cretaceous wrenching and inversion as well as tilted fault blocks formed by Jurassic and Early Cretaceous rifting. Drilling has not tested the latter. Fault related stratigraphic traps also exist. These traps have never been explored either. En echelon faulting formed by Late Cretaceous wrenching most likely increases the sealing capacity of faults bounding hydrocarbon fields.