Seychelles

Areas A, B and C are located in the Seychelles micro-continent covering a combined area of approximately 14,964km² (3.7 million acres). Areas A and B are located in mainly shallow water in the northern half of the Seychelles plateau while Area C is in shallow water to the south. The operator is Black Marlin (75%); Avana has a 25% working interest. Black Marlin's net area under licence is 11,249km² (2.8 million acres).

The bulk of exploration activity occurred in 1977 when three separate PSCs were signed by a consortium led by Oxoco, Siebens and Burmah Oil (later acquired by Amoco). Between 1977 and 1979 this consortium acquired a total of 6,400 kilometers of seismic which revealed several structural and stratigraphic leads. Between 1980 and 1981 Amoco drilled three wells (Owen Bank A-1, Reith Bank-1 and Seagull Shoals-1); all were plugged and abandoned with indications of hydrocarbons shows. Amoco commissioned a further 27,900 kilometers of aeromagnetic survey and 7,100 kilometers of seismic as well as other gravity and geochemical surveys but relinquished the acreage in 1986 following the collapse of oil prices. In 1985, Enterprise Oil (later acquired by Shell) signed an Agreement for the South-Eastern Shelf plus Constant, Coetivy and Fortune Banks with an option to later include Platte Banks. It surveyed a total of 4,870 kilometers of seismic and in 1990 it drilled the Constant Bank-1 well which was plugged and abandoned. A further consortium of Texaco, Ultramar (now ENI) and Enterprise Oil conducted a group-shoot acquisition programme in 1991 but later relinquished their areas. The main exploration target is the Permo-Triassic Karoo interval which comprises nonmarine sands interbedded with shales. The Karoo formation contains both the source rock and the reservoir. Other potential reservoirs in the volcanic rocks and Jurassic clastic sediments may exist although further exploration work is needed.

The complexity of the tectonic evolution of the Seychelles plateau is due to the imposition of three phases of rifting and drifting that isolated the micro-continent from the centre of Gondwana. The first sedimentary rocks of Seychelles began forming during the Permo-Carboniferous time as part of the early Karoo section on the Gondwana paleo-continent. The western Seychelles margin can be reconstructed to a position adjacent to Somalia and as a northern extension of Madagascar prior to drifting from Africa in the Upper Jurassic. A second phase of rifting occurred during the mid Cretaceous when India and Seychelles separated from Madagascar. The Madagascar landmass acted as a major sediment source for the Seychelles micro-continent during this period. During this time a significant part of Seychelles was covered by basalts and volcanic rocks. The third and final rift phase occurred in the late Cretaceous with the drift between Seychelles and India initiating during the early Paleocene.