Review of African petroleum and gas deposits

Abstract

The sedimentary basins of Africa are reviewed by basin type and by sedimentary sequences for basins with polycyclic histories. Estimated remaining recoverable reverses, as of 31 December 1984, are 55 billion bbls oil and 187, 000 billion CF gas. These account for 8% of the world's oil reserves and 6% of the world's gas reserves. Cumulative oil production to the end of 1984 was 38, 800 million bbls. Cumulative net gas production figures for the continent are not available. Twenty-three basins have commercial hydrocarbon production and are examined on the basis of exploration success. Little exploration has taken place in the other basins. By analogy with well explored basins of the same type, new targets and potentially prospective areas are outlined. The deltaic basins have the highest exploration intensity and are the richest basin type (MMBOE/10, 000 km 2). However, they contain 27% of ultimate recoverable reserves (MMBOE) in Eocene to recent sediments, including more than a third of Africa's gas reserves. Approximately 34% of the reserves occur in rift basins in sediments ranging in age from Cambrian to Miocene. Large areas of the rift basins remain unexplored. About 34% of the reserves are found in the continental multicycle and interior basins of north Africa. These occur mainly in Paleozoic reservoirs capped by Triassic evaporites but also in Mesozoic reservoirs. More than half the ultimate recoverable gas reserves occur in these basins, mainly in Triassic sediments. Small reserves are found in the downwarp, pull-apart and median basins, for the most part in Mesozoic reservoirs. Many producing provinces are still not fully explored and the potential for new discoveries exists. Although exploration has resulted in some success in the non-producing basins large areas remain untested and are attractive targets for future exploration. Petroconsultant's world basin study indicates that success rates in large basins are significantly greater than in small basins, irrespective of basin type. This, coupled with the use of improved exploration tools would suggest favourable hydrocarbon potential, especially in large relatively unexplored basins.