Geology and hydrocarbon occurrences in the Ghadames Basin, Algeria, Tunisia, Libya

Abstract

Abstract The Ghadames Basin is a large intra-cratonic basin, covering portions of Algeria, Tunisia and Libya. The three countries are independently conducting petroleum exploration in their portions of the basin, using different play concepts and consequently obtaining different exploration results. This paper presents the first published basin-wide view of petroleum stratigraphy and play types. Some 700 exploratory wells have been drilled in the basin, resulting in the discovery of at least 150 oil pools with 9500 MMBO (million barrels of oil) in place. Most wells were located in the structurally higher parts of the basin, with deeper portions being less explored because of shifting dune conditions and an expectation of reservoir thinning into the basin centre. Silurian and Devonian source rocks occur across large parts of the basin and have generated volumes of hydrocarbon orders of magnitude above those discovered. The numerous structural phases (Taconic, Caledonian, Hercynian and Austrian) that have affected the basin have had important implications for depocentre migration, structural style, and for patterns of trap formation, alteration and destruction. The erosion pattern and topography developed on the Hercynian unconformity is a key control on petroleum systems within the basin, controlling the preservation of Palaeozoic hydrocarbons, communication between source and higher reservoirs and patterns of long-distance migration in the Triassic reservoir. For each of the producing plays, an analysis is presented of the geological factors controlling the habitat of hydrocarbons (e.g. the effect of various tectonic phases, the influence of basin-scale facies variations on reservoir quality, and the source rock-reservoir relationship), and is related to the variations that have been observed in exploration success rate and producibility. It is believed that a substantial volume of hydrocarbons still remains undiscovered in a range of trap and play types.