Thermal evolution characteristics of source rocks in the Northern depression of the Melut Basin, South Sudan, and their petroleum geological significance

doi:10.3969/j.issn.1672-7703.2020.06.008

Abstract

Abstract: Study of the thermal evolution characteristics of source rocks in the Melut Basin in South Sudan is of great significance for oil and gas exploration in the basin. Following the restoration of thermal history of the Northern depression, the maturity history of source rocks in the Renk Formation was simulated using the “Easy% Ro” dynamic simulation method combined with the analysis of geological and geochemical data, and petroleum system modeling. Also, the hydrocarbon generation and expulsion history of the source rocks was studied by “Ro - hydrocarbon expulsion rate” model. The results show that there are some differences in the thermal evolution degrees of Renk Formation source rocks between the three sags in the Northern depression. The source rocks in the Jamous sag were the earliest to enter the mature, high mature, and over mature stages, followed by those in the Ruman sag. Source rocks in the Moleeta sag were the most recent. Due to these differences in thermal evolution history, there are also some differences in hydrocarbon generation and expulsion times between the three sags. Source rocks in the Jamous sag began to expel hydrocarbon in the late Cretaceous (88 Ma) and entered the large-scale hydrocarbon expulsion stage in the Paleocene. In the Ruman and Moleeta sags, large-scale hydrocarbon expulsion occurred in the Eocene. Overall, the hydrocarbon generation and expulsion times of source rocks in the Northern depression have a good matching relationship with the formation times of the traps and cap rocks of the Yabus/Samma Formation, Galhak Formation, and Gayger Formation. The main controlling factor for hydrocarbon accumulation in the Yabus/Samma Formation is oil-source connecting faults, while in the Gayger and Galhak Formations it is reservoir physical properties. The source rocks in the Renk Formation, with a high degree of thermal evolution and continuously expelling hydrocarbon, provide a rich material basis for oil and gas charging into stratigraphic-lithologic reservoirs in the Northern depression. Therefore, stratigraphic-lithologic reservoirs should be an important replacement area for future exploration in the Northern depression and deserving of further research and exploration.

CLC Number:

Xue Luo, Shi Zhongsheng, Ma Lun, Chen Bintao, Wang Lei, Ma Fengliang, Shi Jianglong. Thermal evolution characteristics of source rocks in the Northern depression of the Melut Basin, South Sudan, and their petroleum geological significance[J]. China Petroleum Exploration, 2020, 25(6): 79-86.

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