南海海域新生代沉积盆地构造演化的动力学特征及其油气资源

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

通过对构造环境、地球物理场特征、盆地生储盖层发育等方面对比研究 ,讨论南海南北部沉积盆地的油气资源分布特征 ,为在南海进行油气勘查指明方向 .目前油气勘探实践证明 ,南海南部的油气资源比北部丰富 ,究其原因 ,南海北部为被动大陆边缘 ,张性沉积盆地的烃源岩体积较小 ,而南部挤压环境下形成的沉积盆地的烃源岩体积大 ;北部的地热流较南部小 ,因此地温梯度也较小 ,如北部陆架上的珠江口盆地的热流值在 5 3～ 87mW /m2 之间 ,平均 6 7mW /m2 ,而南海南部大曾母盆地平均热流值达 97mW /m2 ,最大值达 130mW /m2 ,故南部边缘烃源岩的成熟度比北部高 ;由于南部边缘处于挤压构造环境 ,因此在沉积盆地中形成了许多挤压构造 ,而北部边缘一直处于张性构造环境 ,形成的构造较少且较小 ;同时 ,南部边缘沉积盆地中 ,烃源岩生烃与构造形成在时间上搭配较好 .因此 ,在南海南部边缘沉积盆地中形成了许多大型油气田 ,而南海北部边缘沉积盆地中 ,大型油气田较少 ,中小型油气田较多 .

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/m^2 with an average value of 67 mW/m^2; but in the Zengmu basin in the southern margin,an average heat flow is 97 mW/m^2 with a maximum value of 130 mW/m^2. 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.