Journal de géologie et géophysique
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Geochemical Study for Evaluating the Source Rock and their Hydrocarbons Generation Potentiality in Zeit Formation, Sudanese Red Sea Coastal Plain

Sadam HMA Eltayib*

The study area lies in NE Sudan along the Eastern coast of the Sudanese red sea. The coastal plain is geologically characterized by Cenozoic siliciclastices and shallow marine rift related sedimentary sequences. The main subsurface stratigraphic units in the study area from bottom to top are: Basement Complex (Cambrian), Kareem Formation (Oligocene), Belayim Formation (Late Oligocene), Dungunab Formation (Miocene), Zeit Formation (Late Miocene), Wardan Formation (Late Pliocene) and Shagara Formation (Pleistocene-Holocene). The Total Organic Carbon (TOC%) and pyrolysis data are used to determine the source rock quality and quantity as organic richness, source rock generating capability and kerogen types of the source rock. The source rock characterization graph shows that Zeit Formation includes shale intervals of poor to very good TOC contents with average values ranging from 0.16% recorded in well Digna-1 to 2.76% in well Suakin-1 which was drilled in the Western periphery part of the East Tokar Basin. The average of S2 values in wells ranges from 0.26 to 2.1 reflecting the same wide range from poor to excellent generating potential. The relationships between the TOC values and each of the S1 and S2 values also indicate the direct relation between the organic carbon content (TOC) and the generation potential (S2) of shales in the area as the TOC increases with increasing of S2 values, which confirm the promising potential of the TOC-rich shale intervals of Zeit Formation as a potential and effective source rock. The different geochemical data obtained indicate that the organic matter of Zeit Formation source rocks is rich in type III (gas prone) kerogens mixed with markedly less type II (oil and gas prone) as proved by the conventional van Krevelen diagram using the elemental composition of kerogens (H/C and O/C atomic ratios). These results could be attributed to the marked terrestrial source of the organic matter which could be lacustrine, fluvial, estuary and deltaic sedimentary environments of the Zeit sediments.