Тип бассейна: Платформ
Подтип бассейна: Внутриплатформенный (интракратонный)
Класс бассейна: Рифтовый (Внутриплатформенный)
Возраст бассейна: Молодой - Кайнозойский
Тип полезных ископаемых:
Геологический возраст начало:
Геологический возраст конец:
Площадь: 323819.2 км²
Muglad basin is bounded approximately by the longitudes 26°00´ and 30°00´ E and latitudes 8° 00´and 12° 00´ N (Fig. 1). It extends from its northern part at the Southern Darfur Province, passes southwards through the Southern Kordofan, the Upper Nile and the Equatorial Provinces to link with the Anza Trough in northwestern Kenya. The Muglad Basin Complex is the main petroliferous sedimentry basin in the Sudan and represents the western flank of its interior rift basins, which are parts of the Central African rift system (Fairhead, 1988). The Muglad Basin Complex, which is about 300 km wide and more than 1200 km long, is predominantly trending NW–SE. Geophysical studies indicate a sedimentary section up to 13,720 m (45276 ft) thick in the deepest part of the Muglad Basin, which is Kaikang Trough. However, the maximum drilled thickness of sediments in the Muglad Basin does not exceed 15,000 ft. Neem field is a part of the Muglad basin. Different phases of rifting of the Muglad basin were under the control of distinct tectonic regimes since Early Cretaceous. In general, three basin forming mechanisms were evolved to explain subsidence of the Muglad basin at different stages. Depositional elements during different phase of the rift formation and its development. They might vary from basin to basin depending on the local tectonics and climate and sedimentation but overall predictability is still the same.
Figure 1. Location map of the Neem oilfield, Muglad Basin, Sudan.
Geological and tectonic settings
Sudan’s geological study was focused on the surface geology mainly for surface mapping and limited shallow mining activities. With the recent discovery of commercial hydrocarbon, extensive subsurface data have been acquired both offshore and onshore. These data revealed existence of several sedimentary basins offshore in the Red Sea and onshore in interior Sudan. These basins are all rift basins, owing their existence to the rifting activities of the Western, Central and East African Rift Systems.
Figure 2, shows the geological and lithological rock units distribution of southwestern part of Sudan including Muglad basin. Acquired data from these basins such as surface geology, regional gravity and magnetics show that the basins were deep and filled with continental sediments during Paleozoic and Mesozoic times. Basin depth in the central Sudan reaches to more than 10,000 m of clastic sediments. Lithofacies changes primarily reflect the variations in the subsidence rates and depositional environments of various sub-basins. This chapter, concisely, reviews some regional aspects of rifting processes, structural style, sedimentary processes and stratigraphy of the study area.
Figure 2. Geological map of the southwestern part of the Sudan
Lithostratigraphic Units of Muglad Rift Basin
All sedimentary rocks in Muglad basin are of non-marine origin. Correlations and age assignments have been established by palynomorph assemblages of fossils. Different environmental conditions have been concluded from lithological, mineralogical and paleontological information. The depositional environments, (Figure 3), can be grouped as alluvial fan, fluvial-braided stream, fluvial floodplain, and lacustrine determined from integrating data from wells, seismic facies mapping, and basin geometry.
Figure 3 Generalized depositional model depicting the environments operative during the filling of the southern Sudan rift basin
Based on the stratigraphic column, (Fig.4), the main stratigraphic units in the Muglad area are:
(1) The Precambrian - Jurassic Basement Complex.
(2) The Cretaceous strata.
(3) The Tertiary Strata.
(4) Quaternary sediments.
The Precambrian – Jurassic Basement Complex The Basement Complex term is generally stratigraphically used in Sudan to include all the Precambrian and Cambrian crystalline rocks. In the study area the Basement Complex is cropping out at the SW, NW, and NE edges of the Muglad basin, (Figure 2). At these localities granitic as well as granodioritic gneisses were encountered and have been dated as 540 ±40 Ma.
The Cretaceous Strata
A few Nubian sandstone outcrops neighboring to the Muglad block, in which the rocks are non-marine, massively bedded, highly weathered, medium to coarse-grained sandstones.
In the subsurface, a thick sequence of Cretaceous sediment has been recorded. Cretaceous-Paleocene sediments reflect two cycles of deposition, each represented by a coarsening-upward sequence. These cycles are correlatable basin-wide and are directly related to rifting and basin infilling. The first cycle is represented by the Sharaf, Abu Gabra, and Bentiu Formations. The second cycle is present in the Cretaceous Darfur Group and the Paleocene Amal Formation.
Figure 4. Generalized Stratigraphic column of Muglad Basin, Sudan (Idris, 2002)
The Quaternary Strata
Quaternary Strata represent the latest cover of the study area, which consists of UmmRawaba and Zaraf formations composed of unconsolidated to semi-consolidated continental gravels, sands, clayey sands and clays of fluvial and lacustrine environments.
Tectonic Evolution of the Muglad Rift Basin
Rift related basins in Sudan developed in the late Jurassic as a result of separation of west and east Gondwana. These rift basins are regionally linked to the Central African Shear Zone (CASZ) which began in late Jurassic (?) and consists of Benue trough in Nigeria, Chad basin in Chad and Muglad basin in Sudan. Muglad basin is part of the trend of Cretaceous sedimentary basins of apparent rift origin related to the global phenomenon of plate tectonics, Figure (5).The southern Sudan interior rift basins are defined by extensive NW–SE, NNW–SSE, N–S, NE–SW, and E–W rifts that started to develop during the late Jurassic to Early Cretaceous time (Schull, 1988). The split-up of the supercontinent Pangea resulted in the formation of the Central African Shear Zone (CASZ), which controlled the orientation of the faults within the basin. The majority of the faults are deep-seated normal faults trending in a NNW-SSE direction perpendicular to the CASZ.
Browne and Fairhead suggested three periods of rifting which occurred in response to crustal extension, this provided the isostatic mechanisms of subsidence accomplished by normal faulting parallel and sub-parallel to the basinal axes and margins. Schull (1988) suggested from the drilled wells that the initial strongest rifting phase have begun in the Jurassic (?) - Early Cretaceous (130-160 Ma) and lasted until near the end of the Albian.
According to Schull the tectonic evolution of Muglad basin can be divided into a pre-rifting phase, three rifting phases, and a sag phase which are well documented by geophysical data, well information, and regional geology as follows:
Figure 5. Schematic map showing the relationship between the Central African Shear Zone, the Muglad Rift Basin, Sudan and associated rift basins
Petroleum System
The hydrocarbon system has an ideal combination of source, reservoir and top seal rocks which are all Cretaceous in age. In Fula depression the source rock is the lower part of Abu Gabra Formation which is characterized by deep lacustrine shale of early Cretaceous. The reservoir rock belongs to the first rifting phase characterized by braidedstream sandstones of the Bentiu Formation. The top seal is the mudstone of Darfur Group in the Upper Cretaceous. The combination of source, reservoir and top seal with the tectonics created different patterns of structural hydrocarbon traps such as Y-shaped, fanshaped as well as step-wise patterns giving rise to good oil-trapping tilted blocks. The main types of hydrocarbon traps according to Gibbs are reverse faulted blocks, reverse faulted anticlines, and reverse faulted noses.
The source rock (lacustrine shale) is characteristic only in the first rifting phase sequence which took place in early Cretaceous while the reservoir sandstones are characteristic in all rift sequences, but the productive zones were found in Bentiu and Aradeiba Formations.
Oil in Aradeiba Formation is mainly in Aradeiba-D Member. Aradeiba-D Member was deposited in lacustrine-fluvial environment, but the sand ranges and grain size is generally smaller than that of Bentiu. Heterogeneity and dimensions of sandstone bodies and the siltstone/mudstone barrier/baffle units vary more greatly within Aradeiba-D than that in Bentiu.
Source: Seismic attributes and petrophysical modelling of the aradeiba-d member, Mugland rift basin, Sudan. Migdad El-Kheir Shuaib, 2013
Sedimentologic and petrophysical assessment of the lower cretaceous Abu‑Gabra tight reservoir formation, Laloba oilfeld, Bamboo sub‑basin, Muglad Rift basin, Sudan. Abdaseed Bokhari, Osman Abdullatif, Olugbenga Ehinola, Olugbenga Boboye, 2024
Следующий Бассейн: Atbara Rift