Petroleum Geology Features And Exploration Potential Analysis In The Coastal Basins Of West Africa

The coastal basins in West Africa are petroliferous basins in theworld; also they are one of the key areas of international oil and gasexploretion and production. In this paper, based on the data of 54 giantoil and gas fields, combining the tectonic-sedimentary evolution of thesebasins, applying the research clue and method of petroleum systems,closely analyzes the play elements, incloding the source rocks,reservoirs and seals, traps and the migration of oil and gas.Throughdissecting the typical giant oil or gas fields,finally classified andassessed the petroleum system in these Basins,and finally analyzed theexploring potentials of these basins.The research results are as follows:1) The coastal basins were divided into northern section, middlesection and southern section by St. Paul fault and Walvis Ridge. Thenorthern section basins experienced pre-rift stage, rift stage andpassive continental margin stage. The middle and southern section basinsexperienced pre-rift stage, rift stage, transition stage and passivecontinental margin stage.2) 4 sets of petroleum systems had been set up in the coastal basinsof West Africa: Akata-agbada petroleum system, Upper Cretaceous-Cenozoicpetroleum system, Lower Cretaceous- Upper Cretaceous petroleum system,Lower Cretaceous- Lower Cretaceous petroleum system.3) By the end of 2009, 54 giant oil and gas fields have been foundin the coastal basins in West Africa, with 52224.75MMBOE.The giant oiland gas fields are formed and distributed in the following rules:â‘ Thegiant oil and gas fields are abundantly distributed in Niger delta basinand Lower Congo basin along the coast. The reservoir racks are mainlysandstone and carbonate, the reservoir formation belong to Tertiary orCretaceous.â‘¡In the northern section,neither giant oilfield nor gas field had been found.In the middle section,such as such as Lower Congobasin and Gabon basin, only several giant oil fields had been found; Whilein Niger delta basin, 9 giant gas fields and 24 giant oil fields had beenfound; In the southern section,Only 2 giant gas fields had been found.4) In Niger delta basin, the reservoir traps are predominatelystructural traps, the forming of the giant oil and gas fields is mainlycontrolled by the rollover anticline. The deposition of salt rocks hasa crucial effect to the oil and gas generation, immigration, andaccumulation.In Lower Congo basin, the controlling factors for theunder-salt cretaceous reservoir is traps; For the upper-salt cretaceousreservoirs, the controlling factors are traps and reservoirs; For thetertiary reservoirs, the main controlling factors are traps and thematurity of the source rocks.5) The northern section although include several huge sedimentarybasins, it experienced low exploration activity and has little chance tofind giant fields. In the middle section, the basins have excellentreservoir-forming conditions. In the southern section, exploration canbe carry on in Orange Sub-basin.In the future,the exploration can focuson the middle section, especially on the turbidite reservoirs in deepwater zone.