Abstract
The organic-rich claystone and shale sediments of Lower Cretaceous Abu Gabra Formation are considered an important regional source rock in the Muglad Basin, Sudan. A total of 20 cutting samples from these organic-rich sediments were collected from six wells drilled at oilfields in the Fula sub-basin, Muglad Basin, in order to geochemically assess the type of organic matter, thermal maturity, and palaeoenvironmental conditions. Results reveal that Abu Gabra organic-rich sediments contain high organic matter more than 2.0 wt% TOC and have a very good to excellent oil-generation potential. This is supported by high bitumen extractions and hydrocarbon yields with values exceeding 5,000 and 3,000 ppm, respectively. The investigated biomarkers indicated that the Abu Gabra sediments contain a mixture of algal and amorphous organic matter that were deposited in a lacustrine environment setting. This has been identified from kerogen microscopy and normal alkane distributions, which are characterized by dominance of types I/II kerogen and low-medium molecular weight n-alkane compounds, respectively. This is also supported by high abundance of C27 regular sterane concentrations, high C27/C29 regular sterane ratios and relatively low value of the biomarker sterane/hopane ratio as well as the presence of tricyclic terpanes. A mainly suboxic to relatively anoxic preservation conditions is inferred from Pr/Ph ratios (1.01–2.51). This is further supported by lower amounts of acyclic isoprenoids compared to n-alkanes (e.g., pristane/n-C17 and phytane/n-C18 ratios). Based on the analyzed biomarker thermal maturity indicators, it may be deduced that the Abu Gabra sediments have entered an early mature stage for oil generation. This is also supported by vitrinite reflectance values of 0.58–0.72 % Ro indicative that these sediments have reached oil window maturity.
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