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

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 (R-o) between 0.77 and 1.07% is in reasonably good agreement with pyrolysis T-max (temperature at maximum of S-2 peak) data (438-459 degrees C). 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 C-14-C-24 alkanes, a pristane/phytane ratio of less than 2, abundant C-27 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 C-32 22S/(22S + 22R) homohopane and C-29 20S/(20S + 20R) and beta beta/(beta beta + alpha alpha) sterane ratios reveal that the Khatatba samples are thermally mature and have reached the peak oil-window maturity supporting the R-o data.