Abstract:

The petroleum systems and their reservoirforming factors of the major sedimentary basins in the Nansha sea waters (South China Sea) were controlled by tectonic evolution and characterized by the basins of different types having similar basinfilling features, which means that the sedimentary features of contemporary strata are alike, and that the main unconformities formed almost at the same time. The major basins had undergone the synrift stage from the Paleogene to the Early Miocene and postrift stage since the Middle Miocene, so four various petroleum systems developed in the Nansha sea waters: (1) the lacustrine petroleum system of the earlyrift period has been developed in the western Nam Con Son Basin; (2) the transgressive delta petroleum systems of the laterift period have been developed in the eastern Nam Con Son Basin, the Balingian area in the Zengmu Basin, the Reed Bank Basin and the Northwest Palawan Basin; (3) the marine petroleum systems of the early postrift period have been developed in the Central, West Luconia and the East Natuna area of the Zengmu Basin; and (4) the regressive delta petroleum system of the late postrift period has been developed in the BruneiSabah Basin. The source rocks within these sedimentary basins are mainly the Miocene mudstone, and the coal strata only contribute to gasfield; the sedimentary facies of the source rock are dominated by the transitional facies, and nearly half of the oilgenerating are from the marine source rock, whereas the terrestrial source rock has little contribution to the hydrocarbon. The reservoir rocks are dominated by the Upper Miocene sandstone and the MiddleUpper Miocene limestone, and the former gathered oil, while the latter accumulated gas. The trap types of the oil reservoirs are dominated by the structural trap, and the stratigraphicstructural trap also has a considerable amount. The trap types of the gas reservoirs consist of the stratigraphic trap, stratigraphicstructural trap and the structural trap. The fractured igneous rock and/or metamorphic rock developed in the prerift period usually formed bedrock reservoirs.

Key words: petroleum system, sedimentary basin, Cenozoic, Nansha sea waters, South China Sea