| West Africa coastal basins are nowadays the hotspots of deepwater hydrocarbon exploration around the world.Controlled by Africa plate evolution and the Atlantic Ocean rifting,the evolution of West Africa coastal basins can be divided
into pre-rifting, syn-rifting, and post-rifting stages. And 15 coastal basins can be subdivided into 5 regional sections from
north to south, i.e. the salt basins in the north section, the basins in the middle one, the Niger delta section,the salt basins in
the middle-south section, and the basins in the south one. Deepwater fields in these basins,most of which are oil fields, develop in post-rifting Tertiary and Upper Cretaceous regressive sequences. The fields that have been discovered are, in amount and
commercial reserves, major in the Niger delta section and the Lower Congo Basin (in the middle-south section), which respectively occupy 55% and 29% of the total field amount and 48% and 41% of total commercial reserves in West Africa.
Source rocks include the Lower Cretaceous lacustrine shales (deposited during syn-rifting stage) and the Upper Cretaceous and
Tertiary marine shales (during post-rifting stage). The most significant deepwater reservoirs are turbidite sandstone, and primary
reservoir facies are channel reservoirs,followed by sheet sands and sandy debris flow sediments. The types of deepwater traps
are stratigraphic-structural combination traps in majority, and the next are structural traps and stratigraphic traps in minority.
Most of the combination traps and structural traps are connected to salt structures or mud-diapirs. |
