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Keywords:

  • Marine oils;
  • oleanane;
  • biomarkers;
  • gammacerane;
  • Miocene source rocks;
  • Gulf of Suez;
  • Egypt;
  • Brown Limestone;
  • Rudeis Formation

The results of geochemical analyses were used to classify ten oil samples from six fields in the central and southern sectors of the Gulf of Suez, Egypt. The samples were collected from sandstone pay-zones ranging in age from Early Palaeozoic (Nubia-C) to Miocene (Kareem Formation) at various present-day depths. Molecular and stable isotope analyses indicate the presence of two genetic oil families (Families I and II) and suggest their probable source rocks.

The biomarker characteristics of Family 1 oils include low Pr/Ph ratio, CPI < 1.0, depleted rearranged steranes, very low diahopane concentrations, high sulphur content, high metal content and V/Ni ratio, low oleanane index, abundance of gammacerane and C27 steranes, and high relative abundance of homohopanes and C30 24-n-propylcholestanes. Source rock deposition took place under anoxic marine-carbonate and hypersaline conditions. The NCR and NDR 24-norcholestane ratios together with the presence of highly-branched isoprenoids in this oil family are consistent with Upper Cretaceous – Lower Paleogene source rocks. These characteristics suggest that the Upper Cretaceous Duwi Formation/Brown Limestone or Lower Eocene Thebes Formation are the source rocks for the oils in this family, which occur in the central sector of the Gulf of Suez.

Family II oils have geochemical characteristics that point to a mature source rock deposited in a weakly reducing or suboxic setting under normal salinity conditions. Abundant oleananes, high 24- to 27-norcholestane ratios and abundant C25 highly-branched isoprenoids suggest a Paleogene source rock. The Lower Miocene Rudeis Formation is the best candidate to have generated these oils which occur in the southern sector of the Gulf of Suez.