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Abstract

AAPG Bulletin, V. 96, No. 11 (November 2012), P. 20192036.

Copyright copy2012. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/04181211178

Organic geochemical characteristics and interpreted depositional environment of the Khatatba Formation, northern Western Desert, Egypt

Mohamed Ragab Shalaby,1 Mohammed Hail Hakimi,2 Wan Hasiah Abdullah3

1Petroleum Geoscience Department, Faculty of Science, University of Brunei Darussalam, Brunei; [email protected]
2Geology Department, University of Malaya, Kuala Lumpur, Malaysia; present address: Geology Department, Faculty of Applied Science, Taiz University, Taiz, Yemen; [email protected]
3Geology Department, University of Malaya, Kuala Lumpur, Malaysia; [email protected]

ABSTRACT

The Middle Jurassic Khatatba Formation in the northern Western Desert of Egypt was evaluated in terms of organic matter abundance, type and thermal maturity, as well as for some organic petrographic characteristics. Depositional environments were interpreted based on organic geochemical (Rock-Eval pyrolysis, extract analysis, and biomarker distributions) and organic petrological methods. Organic carbon contents range between 1.0 and 32.5 wt. %. The Khatatba shale and coaly shale samples have hydrogen index values in the range of 63 to 261 mg hydrocarbon (HC)/g total organic carbon, with mixed types 2–3 and 3 kerogens. Mean vitrinite reflectance (Ro) between 0.77 and 1.07% is in reasonably good agreement with pyrolysis Tmax (temperature at maximum of S2 peak) data (438–459degC). Organic-rich sediments of the Middle Jurassic Khatatba Formation have very good source rock generative potential and have obtained thermal maturity levels equivalent to the oil window. The main generation products are gas with very limited liquid HCs (oil or condensate). Seven shale and coaly shale samples from Khatatba Formation were characterized using gas chromatography (GC) and GC–mass spectrometry techniques. The Khatatba samples are characterized by the predominance of C14-C24 alkanes, a pristane/phytane ratio of less than 2, abundant C27 regular steranes, and the presence of tricyclic terpanes. These are consistent with the suboxic marine-environment conditions for the Khatatba source rock. Biomarker parameters for these samples generally indicate a mixture of land- as well as marine-derived organic-matter input. The maturity indicators based on C32 22S/(22S + 22R) homohopane and C29 20S/(20S + 20R) and betabeta/(betabeta + alphaalpha) sterane ratios reveal that the Khatatba samples are thermally mature and have reached the peak oil-window maturity supporting the Ro data.

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