--> Structural Evolution and Main Controlling Factors of Paleogene Hydrocarbon Accumulation in Termit basin, Eastern Niger

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Structural Evolution and Main Controlling Factors of Paleogene Hydrocarbon Accumulation in Termit basin, Eastern Niger


The Termit basin is a typical Mesozoic-Cenozoic continental rift basin of the Central and Western African rift system. Based on interpretations of seismic reflection data, this study analyzed the structural characteristics of the basin. It suggests that the basin is characterized by two distinct systems of normal faults in terms of timing of activation, which were formed in the early Cretaceous and Paleogene, respectively. The former are mainly rift-border faults trending NW-SE; whereas the latter developed in both basin margins and interior, striking parallel to the early Cretaceous faults on the basin margins and NNW-SSE in the interior of basin. An integrated study of regional structural background, depositional filling and comparison between fault architecture of the basin and analogue models of laboratory experiments reveals that oblique rifting(the Paleogene) superimposed earlier orthogonal(the early Cretaceous) rift structure in Termit basin. The structural characteristics and evolution are controlled by both the orthogonal and oblique rifting. During the first rift period, NW-SE trending faults sub-parallel to pre-Pan-African metamorphic belts were formed by orthogonal rifting. In the second rift period, the fault characteristics were mainly controlled by pre-existing structure and extension direction during oblique rifting. On both margins of the basin, greatly influenced by early Cretaceous faults, strikes of late faults are sub-parallel to pre-existing faults. However, within the basin and in the domains where early Cretaceous faults were not well developed, the extension direction played a major role in the development of late faults, with their strikes sub-perpendicular to the extension direction. Furthermore, this study proposed a spatial and temporal evolution model of Temit basin. Based on current exploration activity and understanding of structural evolution, this study illustrates petroleum geology and main controlling factors of Paleogene hydrocarbon accumulation. Principal source-reservoir-cap rock assemblage is the type of lower-generating and upper preserving with the upper Cretaceous marine Yogou Formation as source rock, lacustrine delta sandstone of the Paleogene Sokor1 formation as reservoir, thick mudstones of lower part of the Sokor2 formation as regional cap rock. The favorable traps are faulted horsts and antithetical faulted noses. Main controlling factors of Paleogene hydrocarbon accumulation includes: the vertical distribution of oil and gas is controlled by regional cap rock of Sokor2 formation; the efficiency of faulted blocks is determined by lithological lateral sealing of traps; the spatial distribution of hydrocarbon and oil-bearing strata are decided by fault activities in stage of Paleogene rifting. Paleogene hydrocarbon accumulation model was proposed on the basis of understanding main controlling factors.