Tectonic Dynamics of Cenozoic Sedimentary Basins and Hydrocarbon Resources in the South China Sea

This paper discusses the distributing characteristics of petroleum in the South China Sea by comparing on the tectonic environments, the assemble of reservoirs, source and cap rocks between the southern and northern South China Sea in order to demonstrate the exploration guide of the petroleum. Petroleum potential in the southern margin of the South China Sea is better than that in the northern margin according to present petroleum exploration. Possible reasons causing such a difference may be grouped into the following aspects. Firstly, the southern South China margin belongs to an extruding environment in Cenozoic time, where the volume of source rocks is bigger than that in the northern margin belonging to a passive environment. Secondly, heat flow and geothermal gradient in the southern margin are higher than those in the northern margin, for example, heat flow in the Pearl River Mouth basin on the shelf of northern margin is 53-87 mW/m² with an average value of 67 mW/m²; but in the Zengmu basin in the southern margin, an average heat flow is 97 mW/m² with a maximum value of 130 mW/m². This fact indicates that the maturation of source rocks in the southern margin is higher than that in the northern margin. Thirdly, many large scale oil-bearing structures in the southern margin are formed due to the extruding environments in Cenozoic time, but trap structures in the northern margin are relatively little in quantity and small in scale in extension environments. Finally, the coordination between the formation time of trap structures and hydrocarbon-generating time in the southern margin is also better than that in the northern margin. Present hydrocarbon exploration also shows that a number of big oil and gas fields exist in the southern margin, only medium-little oil and gas fields occur in the northern margin. Therefore, petroleum potential in the southern margin is richer than that in the northern margin of the South China Sea.