Early mature sulfur-rich oils from the Central Gulf of Suez province: bulk property and geochemical investigations of maltene and asphaltene show source related-type

This study analyzed the bulk properties and geochemical characteristics of four crude oils from the Central Gulf of Suez province (NE Egypt). Such oils were derived from high sulfur Type II kerogen, as demonstrated by their API gravity and sulfur content (S) of more than 2.45 wt. %. The result agrees with their asphaltene structures, derived using open pyrolysis-gas chromatography (Py–GC), which further suggests that the analyzed oils were primarily paraffinic and produced from Type II kerogen. The high S content combined with the vanadium (V) and nickel (Ni) metals ratios also indicates that the examined oils were scoured from carbonate-rich rocks that were deposited in a highly reducing marine environment. The occurrence of reduced oxygen with enhanced stratified conditions during deposition is further supported by the existence of gammacerane, low Pr/Ph ratio, Pr/C17, and Ph/C18 ratios, and high homohopane ratios of C3122R/ C30 and C35/C34. The tricyclic terpane distribution and homologous sequence of normal steranes C27-C29 suggest that the oils were derived from mainly phytoplankton algae and microbial mats. The existence of low quantities of 18α (H)-oleanane also indicates a source age that is not older than Late Cretaceous. In addition, the biomarker maturity ratios show that the investigated oils were obtained from low maturity source rocks. The geochemical results also suggest that the oils under study are genetically consistent with the organic-rich intervals in the Upper Cretaceous Brown Limestone Formation.