--> --> Lacustrine Deltas in the Fula Sub-Basin – Mrphology, Type and Significance in the Oil Exploration of Sudan

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Lacustrine Deltas in the Fula Sub-Basin – Mrphology, Type and Significance in the Oil Exploration of Sudan

Abstract

Lacustrine deposits in rift basin environments have become major petroleum exploration targets in many parts of the world. Here, in particular, river deltas, facies of permeable strata within thick sections of impermeable mud rocks characteristic of lacustrine deposits, may be important hydrocarbon reservoirs. The evolution of deltas is strongly influenced by lake water level changes. A water level rise may cause the generation of steepened delta fronts composed of coarse-grained sediment, while lowering of the water level may cause the entrenchment of the delta plain and lobes into the marginal muds, which are in turn redispersed away from the delta by shoreline currents and other wave activities. The Fula Sub-basin (∼100 km2) forms a major part in the NNE of the Muglad Basin, the largest of the NW-SE oriented rift basins in the Sudan. The Muglad Basin extends from western and southern Kordofan in south-central Sudan to the southern part of Sudan, covering an area of roughly 160,000 km2. It represents one of the major rifting systems in the world and forms one of the main components of the West and Central African Rift System that started to develop during late Jurassic to early Cretaceous time. The sedimentary sequences of the Fula Sub-basin predominantly consist of non-marine cyclic sequences of lacustrine and fluvial/alluvial facies of early Cretaceous to late Tertiary age, directly resting upon Precambrian Basement. Furthermore, the Fula Basin forms one of the most important oil fields of Sudan. Therefore, a detailed study on its depositional sequences was carried out. The lacustrine delta morphologies of the Fula Sub-basin are partially destroyed by erosion or subsequent structural readjustments. By studying the morphology of its fan-like, elongated and lobate deltas, and the grain size distributions, the channel types and transport velocities were interpreted. Our preliminary results show that, in the Fula Sub-basin, the amalgamated sand units, developing in the lacustrine deltas, together with the channel sands of the fluvial system are the main reservoirs in the basin. Further studies will help in a better reservoir evaluation, providing a greater degree of confidence for deltaic exploration.