Abstract:

This paper simulated the thermal evolution of source rocks in the northern and southern continental marginal sedimentary basins in the South China Sea on the basis of two profiles crossing from the north to the south of the South China Sea, and compared the thermal evolution differences of these basins. The result reveals that the hydrocarbon generation threshold of the southern continental marginal basins is lower than that of the northern continental marginal basins. The hydrocarbon generation threshold of the southern continental marginal basins is between 2,200 m and 2,300 m, and the source rock in Miocene has attained the threshold. The hydrocarbon generation threshold of the northern continental marginal basins is between 2,500 m and 2,600 m, and the source rock in and below Oligocene has attained the threshold. This regular pattern of the source rocks in the southern and northern continental marginal basins is accordance with the nowadays changing law of heat flow which is high in the south and low in the north,and high in the west and low in the east; the high heat-flow value is beneficial to source rock to become mature and to generate hydrocarbon, thereby, where the heat-flow value is high, the hydrocarbon generation threshold is low. It is revealed that the expanding of the South China Sea and the underthrusting of the Old South China Sea causes the changing of the geothermal field of this area，resulting the difference of source rocks- thermal evolution between the southern and northern continental marginal basins in the South China Sea.

Key words: hydrocarbon accumulation condition, thermal evolution, geothermal field, northern continental marginal basin, the South China Sea