Investigation of the petroleum geology and sequence stratigraphy in Melut Basin, South Sudan: a case study using well logs and basin modeling

We investigated the sequence stratigraphy and the total petroleum system elements in the Adar oil field, Melut Basin. Also, we used the wireline logs to define the petrophysical parameters for the potential reservoirs and simulate the burial history and thermal maturity. Moreover, we calculated the TOC using the Passey “ΔLogR” technique and got preliminary evaluations of the total organic carbon in the basin. Based on analyzed sequence stratigraphy, three supercycle sets occurred in the Melut Basin; Upper ZUNI A, TEJAS A, and TEJAS B. The log-derived TOC values are 0.02–4.7wt.% (average 2.70 wt.%) for the Cretaceous dark shale of Melut Formation, while it ranges between 0.03 and 5.07 wt.% (average 3.42 wt.%) for the Upper Cretaceous Galhak Formation. The measured TOC for the thick shale interval (~ 3000 m) of the Lower Cretaceous Al-Gayger Formation is 2.08 wt.%. Meanwhile, the thermal model and R o curve indicate that only the Lower Cretaceous Al-Gayger Formation and the Lower part of Galhak entered the oil peak generation. The expelled oil migrated up through the faults and has accumulated in the Paleogene reservoirs. The Paleogene Samma sandstones exhibit a net pay thickness of 31.05 m, characterized by average porosity of 13.5%, average permeability of 2525mD, and hydrocarbon saturation is 55.2%. While the net pay thickness of the Paleogene Yabus sandstones is 30.1 m, characterized by 14.7% average effective porosity, average permeability of 3546.1mD, and hydrocarbon saturation is 63.7%. This study provides a better understanding of the petroleum geology and sequence stratigraphy in Melut Basin.