EXPLORATION GEOLOGY OF NORTHEASTERN AFRICA‐SEY CHELLES BASIN

Abstract

The basin of NE Africa‐Seychelles ranks with some of the largest in existence. Dimensions are: length 2,400 km (1,500 mi); average thickness 1.6 km (1.0 mi); and sedimentary volume 2,500,000 km3 (6,00,000 mi3). The early history of the basin in obscure until Late Carboniferous time. Thereafter a major continental cycle of Karroo deposition lasted until the Late Triassic or earliest Jurassic. The cycle that followed, mainly marine, continued with few major breaks until the Pliocene or Quaternary, and witnessed a broadening of the basin seaward of the present coast line. Maximum width of the basin may be related to granitic basement material that crops out on the Seychelles. A description of stratigraphy, thickness, and structure of known strata above basement provides background for an exploration analysis. Among the exploration parameters examined, and found to range from highly favorable to poor, are: sedimentary volume, drilling density, source rocks, reservoir rocks, structure, generation and migration, and hydrocarbon recovery. No commercial production has been established, despite the drilling of nearly 110 wells. This disappointing result could be due to some inherent defect in one or more of the exploration parameters, but also could be due in part to a failure of reflection seismometry to indicate the presence and nature of deep structure. If modern reflection‐seismic techniques can overcome previous inadequacies and provide precise locations, a new round of drilling might define more clearly the potential of the NE Africa‐Seychelles basin for commercial hydrocarbons.