The depositional environment and maturity of source rocks in the southern Gulf of Suez were evaluated using biomarker and isotope data from crude oils derived from a variety of source rock types of different geological ages. Two oils families were identified and are referred to as types A and B. Type A oils are characterized by a predominance of oleanane and relatively low gammacerane concentrations, suggesting that they were derived from a terrigenous source rock with a significant input of angiosperm material inferred to occur within the marginally‐mature syn‐rift Lower Miocene Rudeis Shale. By contrast, type B oils are distinguished by a predominance of gammacerane and relatively low oleanane concentrations, suggesting that they were generated from mature marine carbonate source rocks inferred to occur within the Upper Cretaceous Brown Limestone and Middle Eocene Thebes Formation. Maturity parameters including the sterane isomerisation ratios C29αββ/(αββ+ααα), C29ααα20S/(S+R) and TAS/(TAS+MAS), together with aromatic sulphur compound ratios (4‐MDBT / I‐MDBT; 4,6‐ / 1,4‐DMDBT; 2,4–/ 1,4‐DMDBT; and DBT / phenanthrenes), support the higher thermal maturity of type B oils relative to type A oils.
The biomarker variablility reflects the occurrence of two distinct source rocks in the southern Gulf of Suez and suggests that two independent petroleum systems are present here. These appear to be confined to the pre‐rift (pre‐Miocene) and syn‐rift megasequences respectively.
Active oil seepages in the Gebel El‐Zeit area (southern Gulf of Suez, Egypt) occur in fault zones on the western flank of the East Zeit Basin. Gas chromatography‐mass spectrometry indicates that these oils are rich in tricyclic terpanes and extended hopanes with few diasteranes. These characteristics are typical of oils derived from marine siliciclastic source rocks; an input of terrestrial angiosperms material is indicated by the very high oleanane index of 32.65% and the low gammacerane index of 6.28%. The molecular maturity parameter C29ααα cholestane [20S/(20S+20R)] is < 0.5 indicating that these oils were generated at relatively low thermal maturities. The seepage oils resemble Miocene crude oils in the East Zeit Basin which are believed to be generated from the Lower Miocene Rudeis Shale. Burial history modelling indicates that oil generation from this unit began at around 3–4 Ma at vitrinite reflectance levels of Ro%=0.60–0.85. This implies extensive lateral and vertical migration has taken place for the generated oil to reach the surface. Alternatively, the seepage oils may be sourced by leakage from preexisting accumulations.
The offshore Nile Delta basin is considered as one of the most promising province in Egypt which has an excellent potential gas and condensate reserves for future exploration. This study aimed to characterize the origin of natural gas and to determine whether it is biogenic, thermogenic or mixed processes which are considered the dominant generation pathways. Regional geochemical studies were conducted on test gas samples produced from the Miocene and Plio-Pleistocene reservoirs of Abu Qir, N. Abu Qir, Temsah, Wakkar and Port Fouad fields representing the western and the eastern Nile Delta province. The geochemical analyses revealed that the main constituents of the natural gases are methane . %-. % with minor contribution from ethane and propane. Methane carbon isotopic composition ranges between _ . ‰ and _ . ‰ PDB displaying a strong indication for gas mixing of thermogenic and early microbial methane. The gas chromatography_mass spectrometry carried out on the produced natural gases exhibits high oleanane index that ranges between % and %, the medium concentration of moretane index between % and % and the absence of gammacerane index indicating that the natural gases were derived from siliciclastic source rocks containing type III kerogen of terrestrial origin and higher land plants input of Tertiary age. The calculated maturity parameters of the studied natural gas proportions based on various sterane isomerisation distributions, i.e. C αßß/ αßß+ααα _and C ααα S/ S+R reached . and . respectively indicating a medium stage of thermal maturation equivalent to the main peak of oil generation window . Ro% . The sterane isomerization ratios may reflect the rapid rate of subsidence and sedimentation in the Nile Delta and appear to have been generated during the early stage of source rock maturation.
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