Source Rock Depositional Environment and Maturation Assessment Dependent C7 Light Hydrocarbons from Crude Oils in the Gulf of Suez, Egypt

Abstract

A collection of 14 crude oil samples representing 13 giant oil fields from the prerift and synrift reservoirs of the Gulf of Suez province were analyzed for C7 light hydrocarbons. The light hydrocarbon parameters C7 star plot diagrams in conjunction with the biomarker characteristics differences were used to distinguish the Gulf of Suez into two oil groups, the prerift and synrift oils, which are predominantly source related and maturity dependent. The biomarker properties indicate that the prerift oils exhibit oleanane index 23%, while the synrift oils are characterized by relatively higher oleanane index around 30% and low gammacerane index values <10%. The prerift oils are correlated with the Upper Cretaceous Brown Limestone and Sudr chalk formations, which are possibly representative of the carbonate-rich marine source rocks of type II kerogen. The synrift oils are correlated with Lower Miocene Rudeis siliciclastic source rocks of mixed types II-III kerogen. The prerift and synrift source rocks entered the oil generation window at vitrinite reflectance between 0.7 to 0.9 Ro%, equivalent to formation temperature at 110°C and 125°C, which permits the expulsion of mature crude oils to reservoir rocks according to their stratigraphic and structural relations. The higher sterane maturity parameters, i.e., diasterane index, C 29 ααα20S/(S + R), and C 29 αββ/(αββ + aaa), of the prerift oils imply a generation from carbonate rich marine source rocks at a very high maturity level in comparison with the relatively mature siliciclastic source rocks that generated the synrift oils in the Gulf of Suez rift basin.