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2018 AAPG International Conference and Exhibition

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Giant Discoveries in the Deep Offshore of the Gulf of Guinea: 1987-1997 and Beyond

Abstract

Past and present deep water exploration of West Africa offer an exceptionally successful and high-impact experience of combined geoscience and technical skills. The sudden downfall of oil prices of 1986 induced a slowdown of deep offshore exploration and development in the GOM, less significant however in Brazil whose domestic production was considered of vital interest for the country. Notwithstanding this discouraging context, Angola in 1989, followed by Nigeria in 1990, decided to open up deep offshore acreage. These offers were mainly for major international companies who had the technical expertise and economic strength to be potential candidates. In addition to Shell, Elf, Mobil, Eni, Gulf, Texaco and Total who were already present in West Africa, other companies like Exxon, BP and Amoco joined the party. Among the difficult decision-making conditions were some uncertainties about the contractual terms and scarce available seismic coverage in Nigeria, a loose 5kmX10km 2D grid in Angola, no 3D data at all and poor results of past exploration. 18 wells had been drilled in water depths exceeding 150m, (mostly in Albian reservoirs) with only one discovery, Nkossa drilled by Elf in Congo (1983) put on stream in 1996. Potential plays had to be defined and models could be Gulf of Mexico for Nigeria and Brazil for Angola. In summary the endeavour looked like a pretty risky business. The first licenses were granted in 1992 and 1993, with DHI-driven discoveries made in 1994: Bengo in Angola and in 1995: Bonga in Nigeria, both made by Shell, while Elf made a strike (Moho) on a former permit in Congo. In 1996 Elf drilled Girasol on Block 17 of Angola, setting the stage for a spectacular and fast sequence of many other discoveries in tertiary turbidites, while Exxon on Bloc 15, Chevron on Block 14 and Amoco on Block 18 were also successful. More discoveries were made during the 1987-1997 period in Nigeria: Ehra by Exxon, Agabami by Texaco, Usan-Ukot by Elf. The momentum was well established and despite new oil price bumps, but intensive use of 3D seismic, exploration successes continued later (like Akpo by Total) and were extended to other countries of West Africa like Ghana (Jubilee) and Equatorial Guinea (Ceiba), with a notable growing role of independent explorers (Triton, Anadarko, Tullow, Kosmos). Up to now at least 17 giants fields have been fond and total reserves could be around 18 Gboe, with more to come.