Continental Slopes of the West Africa Region: A Unique Treasure of Hydrocarbons

Abstract

The West African region embraces a number of coastal sedimentary basins, which continued in deep-water areas of the Atlantic Ocean. It includes the following oil-and-gas-bearing basins: the Gulf of Guinea, the Kwanza–Cameroonian, and the Namibian. The sedimentary cover of the basins of this passive margin is represented by Mesozoic–Cenozoic deposits. The composition of sediments accumulated in them is quite specific and surprisingly units over the vast areas. The tectonic structure of the majority of the continental margins of West Africa makes possible to refer them to the margins of epiplatform orogenic belts. The existence of two systems of linear troughs—internal and external—on the passive margins at the early stages of continent–ocean transition zones relates deep-water hydrocarbon deposits to internal troughs filled by younger sediments: the alluvial fans of submarine rivers and landslide fronts with prograde formations (turbidites, debris flows, etc.). Late Cretaceous and Middle Paleogene clay formations played the role of source beds in the region, so-called “black clays.” An analysis of over 200 hydrocarbon fields, mainly petroleum, discovered in the past 10–15 years in the region revealed a clear tendency of these fields occurring in a productive zone of oil pools extending in a sea depth interval of 400–3000 m on the continental slope and possibly to 4000 m at the continental rise. Moreover, all discovered fields have been estimated in terms of reserves from large to giant. It is also noteworthy that within the shallow of this region, which includes the shelf and the coastal plain, only a number of small, insignificant oil and gas pays have been discovered. The main of oil and gas bearing potential prospects are related to deposits in the middle and lower parts of the continental slope and possibly adjacent areas of the continental rise. In the long term, the drilling objectives will be both postsalt and presalt deep-water oil-and-gas fields.