Oil-source correlation in the West Esh El Mellaha, southwestern margin of the Gulf of Suez rift, Egypt

Abstract There are several source rock units in the Gulf of Suez graben, but the Upper Cretaceous–Miocene sequence has probably produced most of the commercial hydrocarbons in this petroleum province. One hundred and nine shale, marl and marly shale samples collected from five wells in the West Esh El Mellaha Concession and surrounding area were studied by petrographic and organic geochemical methods to determine organic facies, depositional paleoenvironment, and thermal maturity. We also investigated the molecular and stable carbon isotopic compositions of nine oil samples to establish genetic relationships with the source rock samples. Pyrolysis data for samples from the Cenomanian–Santonian Matulla, Paleocene Esna, Eocene Thebes, Oligo-Miocene Nukhul and Lower–Middle Miocene Rudeis formations contain hydrogen-poor terrigenous Type-III to II/III kerogen. However, the Campanian–Maastrichtian Brown Limestone samples contain Type-II and Type-II/III kerogens indicating very good to excellent generation potential. The acyclic isoprenoids and normal alkane distributions and biomarkers in the source rock extracts indicate derivation from bacteria and algae, with varying contributions from land plants, deposited under suboxic to anoxic conditions in normal marine to higher salinity waters. The oil samples have high sulfur content and low to moderately high API gravity, typical of mature oils from pre-rift marine carbonate or calcareous shale lithofacies. Hierarchical cluster analysis (HCA) of 18 source-related biomarker ratios revealed four genetic families of oil samples. The two South Malak-1 oils (Family-4) are substantially different from the Rabeh E−8 and Rabeh E−10 (Family-1), Rabeh-1 and Hurghada-1 (Family-2) and Abu Marwa-1 and Wadi El Sahl-1 (Family-3) oil families, which are more closely related. Principal component analysis (PCA) and HCA based on the 18 ratios for the total data from extracts and oils indicate three groups. The South Malak-1 oils seem to be most closely related to the two Brown Limestone extracts. Group-1 oils appear to represent mixtures with one end member consisting of the South Malak-1 oils and the Brown Limestone source rock, but the other end member is not in the dataset.