South Kavala Gas Field - Taphrogenetic Prinos Basin

Résumé

The South Kavala gas field located at the southwest edge of the Prinos basin was discovered at the turn of 1972 -73. The basin formation started in the middle Miocene with continental deposits. Later on the sea transgressed all over the basin until the south Kavala ridge at the southern limit lifted up and transformed it to a lagoon, leading to the formation of Evaporites in upper Miocene time. At Pliocene the sea dominated again covering even the previous mentioned ridge. An unconformity exists between Miocene and Pliocene visible mainly on the basin flanks. The trapping mechanism is a combination of a roll-over anticline in front of a northeast - southwest syngenetic fault and a pinch - out of the sediment deposits to the southwest towards the South Kavala ridge. The basement itself forms an erosional high. The gas reservoir is found between two evaporitic horizons and consists mainly of sandstone, microconglomeratic alternating with shale and marl. It is of turbiditic origin forming sedimentological cycles. Individual facies A4/B2, C and E representative of the turbidite facies classification of Walker and Mutti (1973) have been recognised. The net pay thickness is small and amounts up to eleven meters. The gas consists 83% of methan, 7.5% of ethan, 1.5% of propan and around 1.5% of butan. It is free of H2S and contains condensate. As source rocks are considered the under continental and marine conditions deposited preevaporitic shales. The coal beds are also considered to be potential source rocks. The gas is of low maturity and its generation started during latest Miocene and continued through the Pliocene. The main migrations paths apparently were along the faults that cross the basin. The in place reserves are close to 1.109m3 αερίου. The field is on production from 1981 and 80% of the recoverable reserves have been already produced.