Organic geochemical characteristics of Zeit source rock from Red Sea Basin and their contribution to organic matter enrichment and hydrocarbon generation potential

Abstract

Organic-rich shale intervals in the Miocene Zeit Formation were collected from seven wells in the Red Sea basin for compilation of organic geochemical and petrological methods. The current study evaluated the paleo-oxygenation conditions regarding the preservation and the organic-rich sedimentation. The type of organic facies and their relation to hydrocarbon generation potential were also studied. Most of the Zeit shale samples are organically rich and include favorable source rocks, as indicated by the high TOC content of up to 1 wt%. The shale samples also have hydrogen index (HI) values between 58 and 595 mg HC/g TOC, resulting in two dominant organic facies of Types II-III, and III kerogen, with little Type II, and thereby contributing to generate both oil and gas. Biomarker fingerprints, including of n-alkanes, isoprenoids, terpanes, and steranes reveal that the Zeit shales contain mixed organic matter, with a high contribution of marine plankton/algal and microorganisms. The presence of the phytoplankton algae i.e. Chlorococcales and Tasmanites in the Zeit shales further suggests reducing conditions during deposition, thus, enhanced growth of algae and marine microorganisms owing to the presence of nutrients and contribute to good preservation of organic matter. According to maturity indicators of geochemical Tmax (≥430 °C) and vitrinite reflectance (VRo) values (0.52–0.98%), the analyzed Zeit shales are in a mature stage of oil window equivalent to early-mature and peak-mature. This implies that the Zeit shales were reached a sufficient maturity level for commercial oil generation.