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2018 AAPG International Conference and Exhibition

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Structural Evolution and its Control on Hydrocarbon Accumulation of the Southern Depression in Melut Basin, South Sudan

Abstract

The southern depression of Melut basin in South Sudan was developed in the background of right-lateral strike slip tectonic stress field of Central African shear zone, which is a part of the meso-cenozoic intracontinental rift basin. The structural evolution history of the southern depression and its influence on hydrocarbon accumulation remains unclear. Therefore, this paper selects the typical seismic section that perpendicular to main structural trend of the southern depression to restore the structural evolution by using balanced cross section technique. The strata denudation was restored by acoustic time difference and stratigraphic thickness trend, the fold was restored by inclined shear algorithm and trishear algorithm, and the fault was restored by inclined shear algorithm and fault parallel flow algorithm. The structural evolution section and its stretching rate were obtained by methods mentioned above and decompaction correction. Analysis indicates that the southern depression experienced a strong rifting period in Cretaceous. The structural inversion occurred in Paleogene and lasted until the end of Paleogene when the strata compressed. The strata stretching rate was up to -1.32% in Adar Group, which is the most compressive period in the southern depression. The history of structural evolution shows that southern depression has experienced three stages of structural evolution, including strong rifting stage in Cretaceous, and structural inversion stages in Paleogene and Neogene. The rifting activity was stable and sustained in Cretaceous. The structural inversion occurred in Early Paleogene and is continued until Neogene, forming the Ghanam uplift. At the same time, hydrocarbon generated and migrated in large-scale, and the structural evolution history matched the hydrocarbon accumulation history well, benefiting for the hydrocarbon accumulation in Cretaceous and Paleogene. Enhanced structural inversion in Late Paleogene led to the strata denudation of Paleogene in uplift zone at different levels, among which the cap rock of Adar Group had been eroded in the top of uplift zone, damaging the hydrocarbon accumulation in Paleogene. This study further specified the key exploration formation in southern depression of Melut basin, that is, Cretaceous reservoir-cap rock assemblage in strong inversion area is the main exploration target, and both Cretaceous and Paleogene in weak inversion area are the main exploration targets.