南海珠江深水扇系统及其油气勘探前景

Petroleum prospect in deep-water fan system of the Pearl River in the South China Sea

依据浅水陆架区大量的探井资料和二维地震资料,应用层序地层学方法对珠江口盆地距今21～10.5Ma地层段的研究表明,该段地层可划分为6个三级层序,在各层序相应的体系域内均发育深水扇沉积,并且各层序的深水扇都叠置在白云凹陷之上.对盆地内近60口探井的微体古生物定量分析表明,该地层段存在6期三级海平面变化,并与全球三级海平面变化相一致.周期性海平面下降、古珠江大河充足的沉积物供应和白云凹陷长期热沉降作用所形成并保持的陆坡深水条件是南海珠江深水扇系统发育的主要控制因素.南海北部深水陆坡沉积系统与大西洋两岸勘探热点地区的深水沉积系统有许多共同点,如都位于被动大陆边缘、长期的热沉降和大型古河流提供丰富的物源.白云凹陷北坡大型天然气田的发现也证实了白云凹陷下第三系巨厚湖相烃源岩的资源潜力.垂向叠置在烃源岩之上的多期深水扇必将成为重要的油气勘探领域.

Plenty of well data and 2D seismic data obtained from the shallow-water shelf region were used to identify six tertiary sequences from 21million to 10.5 million years before present with the sequence stratigraphic analysis. The deep-water fans were figured out in corresponding lowstand system tracts. The deep-water fan of every sequence was overlapped in Baiyun Depression. Micropaleontologic quantitative analysis for 60 exploration wells demonstrated that there were six times of tertiary sea level change from 21 million to 10. 5 million years before present, which is consistent with the regulation of global tertiary sea level change. Periodic sea level falling, abundant sediment supply from the Paleo-Pearl River and long-term thermal subsidence of Baiyun Depression in Pearl River Mouth Basin resulted in the slope deep-water environment, which is the key factor for development of deep-water fan system of the Pearl River in the South China Sea. The deep-water slope deposition system in the northern South China Sea is similar to the deep-water deposition systems in the Atlantic deep-water petroleum exploration hotspots. They are both located in the passive continental margin and own long-term thermal subsidence and abundant supply from large paleo-river. Recent discovery of a large natural gas field in the northern slope of Baiyun Depression demonstrates its great resource potential in the huge lacustrine source kitchen in the Eogene of Baiyun Depression. The multi-period deep-water fans vertically superposed on the source rock will become the key fields for petroleum exploration.