GEOCHEMICAL CHARACTERISTICS OF THE CRUDE OILS IN THE SOUTHEASTERN OFFSHORE MARGIN OF THE MEDITERRANEAN BASIN, NORTH SINAI, EGYPT

doi:10.21608/aunj.2020.221178

GEOCHEMICAL CHARACTERISTICS OF THE CRUDE OILS IN THE SOUTHEASTERN OFFSHORE MARGIN OF THE MEDITERRANEAN BASIN, NORTH SINAI, EGYPT

Document Type : Novel Research Articles

10.21608/aunj.2020.221178

Abstract

Source rock characterization in the southeastern offshore margin of the Mediterranean basin was accomplished using five crude oil samples. Two samples were recovered from the Early Cretaceous Malha Formation reservoir in the Mango Basin. Three samples were recovered from the sand bodies within the Late Oligocene Tineh Formation in the Tineh Basin. Little is known about the geochemical characteristics of the organic matter in offshore North Sinai. These samples were tested for API gravity, sulphur content, and gas chromatography in order to infer the origin of organic matter, depositional environments, composition and thermal maturity of the source rock. The results showed that all the studied crude oil samples are characterized by low sulphur content ranging between 0.06 % and 0.24 %. Samples from the Mango-1 well (S4 & S5) shows high specific gravity (36 & 38 API), while S3 from the Tineh-1 well has moderate specific gravity (28.4 API). These results suggest the presence of two different types of oil families. Nickel and vanadium contents revealed that the studied crude oil types from the Mango-1 (S4 & S5) and S2 from Tineh-1 wells are grouped together and differ from S3 in the Tineh-1 well pinpointing to two different genetic oil families. Based on the carbon isotope composition, two main types of the studied crude oils were distinguished: waxy oils in the Tineh-1 well (S2) and the Mango-1 well (S4 and S5) and non-waxy oil in the Tineh-1 well (S3). The n-alkanes/isoprenoids ratios in S4 from the Mango-1 well revealed the highest contribution from the terrestrial organic matter during deposition, whereas the comparative ratios in S1, S2, and S5 showed a mixed source, and S3 showed the highest contribution from marine organic matter. This indicates that the source of the organic matter in the Mango-1 well was deposited under oxic to sub-oxic conditions, while in the Tineh-1 well; the organic matter was deposited under dysoxic to anoxic conditions. These results suggest the presence of two source rocks in the offshore North Sinai. All the samples (S1-S5) from the Mango-1 well and the Tineh-1 well are derived from a mature source rock with variation in thermal maturity level from early mature in the Tineh-1 well (S1, S2, and S3) to the mature (oil-window) in the Mango-1 well (S4 and S5).

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