A Multi-1D modeling and hydrocarbon expulsion assessment of a sulfur-rich Thebes-S organofacies, Abu Rudeis-Sidri oil field, Eastern Egypt

Abstract

Most organic geochemical analyses focused on the source rock potentiality and ignored the contribution of numerical modeling to assess the generation potential of source rocks. The present study investigated the impact of the geologic evolution on thermal maturity, hydrocarbon generation potential of the Thebes-S organofacies to assess the hydrocarbon expulsion and exploration success of the Abu-Rudeis Sidri oil field. The Lower Eocene Limestone of the Thebes-S organofacies is considered as one of the most significant high sulfur-content source rocks within the central Gulf of Suez. The source rock intervals were depicted in five well locations using Passey et al.,1990 method (ΔlogR) and published geochemical data. Then, the results of one-dimensional petroleum system modeling performed at multiple well locations were evaluated using the petroleum system modeling approach. The gas ratio analysis and star plot of n-alkanes in the ARM-5 well of Thebes-S and the previously studied Duwi-S organofacies were also used for genetical comparisons. The uncertainty analysis of the key input parameters of the Thebes-S organofacies was applied. The results of well-calibrated 1D models show differences in maturation histories of source rocks, and hence, variations in oil generation potential. The Thebes-S organofacies generated hydrocarbon at a lower maturity, in which the oil generation windows were reached at depths from 2025 to 2404 m TVDSS, whereas the gas generation windows were reached at depths from 2652 m to 2775 m TVDSS. Tectonically the central Gulf of Suez is characterized by three major rift phases: the Oligo-Miocene (25-23 Ma), the Lower Miocene (21-19 Ma), and the Mio-Pliocene (6–5.2 Ma). The source rock approached the main oil window in Pliocene (∼4.42–1.95 Ma) and the thermogenic gas window at a later stage between 1.27 and 0.64 Ma. Besides the tectonic evolution, the burial depth was the major factor in the thermal maturation and hydrocarbon generation processes. Modeling results confirm insignificant hydrocarbon expulsion from the Thebes-S organofacies. This can be attributed to the following factors: (1) less overburden (2) low hydrocarbon saturation level; (3) late gas generation. These findings strengthen the idea that the oil was sourced from Duwi-S, rather than Thebes-S organofacies. This could suggest that the oil reservoirs from Thebes’ organofacies in the study area are self-sourced.