Oil-oil and oil-source rock correlations in the Muglad Basin, Sudan and South Sudan: New insights from molecular markers analyses

Abstract

Abstract Oil-oil and oil-source rock correlations for nineteen crude oils and eight mudstone extracts from four sub-basins in the Muglad Basin were achieved by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Based on the characteristics of biomarker compositions and hierarchical cluster analysis, an outlier crude oil has been discovered in the Muglad Basin. The majority of discovered oils have similar geochemical characteristics and belong to an established oil family. This oil family has relatively higher (C19+C20)/C23TT and C24TeT/C26TT ratios, small amounts of long-chain tricyclic terpanes with a dominance of C21TT among C19 C23TT homologues, a lower abundance of C28 regular steranes with abundant C30 4α-methylsteranes, an unusually higher content of diasteranes and diahopanes. These biomarker ratios indicate the mixed inputs of aquatic plankton and terrigenous organic matter deposited under oxic to sub-oxic, and fresh to brackish water sedimentary environments. This oil family belongs to source rocks of the Abu Gabra Formation as proven by oil-source rock correlation. In contrast, the distribution characteristics of tricyclic and tetracyclic terpanes, C28 regular steranes, C30 4α-methylsteranes, diasteranes and diahopanes are all significantly different than those of the established oil family in the well Kela-1 oil (2563 m) within the Darfur Group reservoir. The geochemical signatures indicate that their related source rock is an algal dominated organic matter input, deposited in sub-oxic condition, and brackish to saline sedimentary environment. Moreover, the composition and characteristics of molecular markers of the well Kela-1 oil are highly consistent with those of the two mudstone samples from the Darfur Group. This clearly demonstrates that the Darfur Group mudstones are the potential source rocks for the outlier crude oil. Identification of the outlier crude oil shows that the Darfur Group mudstones have a certain potential regarding hydrocarbons resources that could provide petroleum companies an impetus to enhance their exploration efforts.