Geochemical characteristics of crude oils, their asphaltene and related organic matter source inputs from Fula oilfields in the Muglad Basin, Sudan

Abstract

Bulk geochemical characteristics of crude oils, coupled with geochemical analyses of reservoir oil asphaltenes from Fula oilfields in the Muglad Basin, have provided information on source organic matter input, depositional environment and the correlation between these crude oils and their potential source rocks in the basin. Only one oil family is present within the Fula oilfields as indicated by biomarker and non-biomarker parameters. The Fula oils are characterized by moderate API gravity, low sulphur and moderate trace metal (Ni, V) contents, and high wax contents. This suggested that the oils were generated from source rock that was deposited in a principally lacustrine environment. This is supported by bulk geochemical characteristics and biomarker compositions. A variety of biomarker–specific parameters obtained from n-alkanes, regular isoprenoids, terpanes and steranes indicate that the Fula oils were generated predominantly from algae-derived organic matter that was deposited in a lacustrine environment which then experienced a slight seawater influence under suboxic to relatively anoxic conditions. These oils were generated from source rock with a wide range of thermal maturity ranging from early to peak oil window. The biomarker characteristics of these oils are consistent with those of the early Cretaceous Abu Gabra shales. The oil-source rock relationship is also demonstrated by similarities in the structural moieties of the Fula oil asphaltene and the Abu Gabra shale kerogens. The Pyrolysis GC of the analyzed Fula oil asphaltene indicates that the oils were derived from Type I-algal organic matter, consistent with paraffinic high wax oils.