Types, characteristics, and implications on the exploration of far-source oil reservoirs in the north Melut Basin

The Melut Basin is an important petroliferous basin in African Continent. The northern part of the basin is characterized by far-source oil accumulation with the oil generation in the Lower Cretaceous and the oil accumulation in the Paleogene. Clarifying the formation conditions and controlling factors of the far-source oil accumulations is the key to improve the exploration success rate and seek new potential areas of far-source oil accumulations in the Melut Basin. Based on the study of regional petroleum geological conditions and the analysis of key oil accumulations, the formation conditions, types, characteristics and potential exploration areas of far-source oil accumulations in the Melut Basin have been systematically studied. The results show, ①The north Melut Basin develops two types of far-source oil accumulations with different hydrocarbon charging patterns and accumulation modes in the Paleogene Yabus Formation, the far-source fault-lithology combination oil accumulations within the oil kitchen and the far-source fault-block oil accumulations outside the oil kitchen; ②The formation of far-source oil accumulations of the Yabus Formation inside oil kitchen depends on the coupling of three geological conditions, that is, the "two strong and one weak" three-stage rifting cycles, creating conditions for the formation of the Paleogene Yabus-Adar far-source reservoir-caprock combination; the development of oil-rich sag, providing necessary oil supply for the Yabus far-source traps; and the multi-stage rifting activities, providing vertical migration pathways for hydrocarbon charging in the Yabus far-source traps; ③The far-source oil accumulations inside oil kitchen are mainly charged by the vertical hydrocarbon infilling through the oil-source faults, and the oil-source faults are the main controlling factor for the hydrocarbon accumulation. The identification of oil-source faults and the evaluation of the lateral sealing capability of trap-controlling faults are the key elements for the far-source fault-block traps inside oil kitchen; ④The far-source oil accumulations outside oil kitchen are mainly charged by lateral hydrocarbon infilling from the oil-rich sag. The transportation ridges formed by sand-rich strata, fault blocks and paleo-uplifts control the hydrocarbon accumulation of far-source traps outside oil kitchen. The identification of transportation ridges and the study on the hydrocarbon charging extent are the main evaluation focus of far-source traps outside oil kitchen. The research results successfully guided the exploration deployment and in-depth exploration of far-source oil accumulations in the Melut Basin, and have a great implication on the exploration of far-source oil accumulations in the other petroliferous basins.