Palynological and organic geochemical studies of the Upper Jurassic-Lower Cretaceous successions, Western Desert, Egypt: Implications for paleoenvironment and hydrocarbon source rock potential

Abstract

Abstract The Upper Jurassic-Lower Cretaceous successions in the north Western Desert of Egypt are one of the most prolific hydrocarbon plays in North Africa. However, the source rock characteristics and depositional environments are still poorly understood. The current work assesses these sedimentary sections utilizing an integrated palynofacies and organic geochemical approach for a comprehensive source rock characterization. The investigation was carried out on 70 samples from the OBA. 3-1/1A (interval: 2540 to 3650\u202fm) and OBA. S-C (interval: 2705 to 3782\u202fm) wells. The results obtained are sufficient to categorically establish two types of organofacies linked to depositional environments and kerogen types, namely palynofacies PF I and PF II. The first facies (PF I) is characterized by kerogen type II and III and occurs in the Alamein and Alam El Bueib members of the Lower Cretaceous Burg El Arab Formation. This is further confirmed by pyrolysis results that revealed fair organic richness and gas generation potential in the Alamein Member with TOC ranges from 1.0 to 2.5\u202fwt% and HI from 64 to 112\u202fmg\u202fHC/gTOC). The Alam El Bueib Member illustrated better organic richness and quality with TOC ranges from 1.6 to 3.1\u202fwt% and HI from 121 to 318\u202fmg\u202fHC/gTOC. The thermal maturity assessment indicates that the Alamein Member is immature and the Alam El Bueib Member is early to oil-mature. PF II occurs in the Jurassic Masajid Formation, which is a transitional mature to overmature, fair to good source rock with mixed kerogen type II and III (TOC 1.3 to 2.4\u202fwt% and HI 148 to 238\u202fmg\u202fHC/gTOC). The paleoenvironmental conditions were deduced mainly from the APP ternary plot. The Alamein and Alam El Bueib members were deposited in a suboxic to anoxic basin, whereas the Masajid Formation was deposited under distal, dysoxic to anoxic basinal or proximal, suboxic to anoxic shelf conditions. In summary, it is concluded that the Late Jurassic and Early Cretaceous witnessed deposition of gas-prone source rocks similar to those found in the southern onshore Nile Delta Basin. The results have significant implications for the understanding of the source rock types in the northern onshore and offshore Egyptian basins and the future of the gas exploration.