Petroleum systems in rift basins – a collective approach inSoutheast Asian basins

This paper synthesizes some of the main conclusions reached in a recent regional review of the Tertiary basins of Southeast Asia, carried out by Shell. Four distinctive types of petroleum systems, correlating with the four main stages of basin evolution (early to late syn-rift and early to late post-rift), are developed widely in the basins. These petroleum system types have characteristic interbedded environmentally controlled source, reservoir and seal lithofacies which, in combination with the structural trap style, determine the hydrocarbon habitat. Variations in the tectonostratigraphic evolution consequent on differences in, for example, basin palaeogeographical position and proximity to late Tertiary collision events, are reflected in differences in the representation of the four petroleum system types. In turn, this is reflected in the overall hydrocarbon volumes found, the average field sizes and the ratio of oil to gas. The recognition of analogous petroleum systems (‘petroleum system types’) and reservoir lithofacies play types in well-explored basins can facilitate prediction of hydrocarbon prospectivity in less well-known rift/post-rift basins and plays, and thereby contribute to future exploration evaluation in these provinces.