珠江口盆地白云凹陷珠海组南部物源及其油气勘探意义

Southern provenance supply of Zhuhai Formation and its significance on oil and gas accumulation in Baiyun Sag,Pearl River Mouth Basin

珠海组是珠江口盆地白云凹陷重要的油气储层与区域性疏导层,对其物源的认识是研究优质油气储层发育与有效疏导砂体分布的重要基础。基于大量的三维地震数据和钻井资料分析,提出珠海组沉积期白云凹陷发育北部古珠江(主)、南部隆起(次)、东沙隆起(贡献有限)3个物源区。利用详细的地震相分析、钻井岩心岩石组构分析、泥岩黏土矿物分析及碎屑锆石U—Pb年代学分析,重点对关注度较低的南部隆起物源开展研究。结果表明,白云凹陷西南部云开低凸起上普遍发育由南向北的叠瓦状前积地震相及向北东、东方向延伸的下切河道,指示了由南向北及由西向东的碎屑沉积物的搬运过程;云开低凸起及周缘钻井中的珠海组具有较粗的岩石粒度、泥岩中较高的高岭石含量、碎屑锆石以中生代岩浆锆石为主的特征,这与凹陷北部古珠江物源控制下的细—极细岩石粒度、泥岩中较高的伊利石黏土矿物含量、碎屑锆石以前寒武纪—古生代变质锆石为主的特征截然不同。综合分析认为,南部隆起物源为云开低凸起珠海组提供了充足的沉积碎屑物质,并推进至白云主洼,该物源的发育对云开低凸起的油气运移及成藏具有重要的意义。

The Zhuhai Formation is an important oil-gas reservoir and migration layer in Baiyun Sag,and the provenance analysis of Zhuhai Formation is a key basis for the studies of reservoir development and oil-gas migration conduits.Based on large amounts of 3 Dseismic and well data analyses,this paper proposed that there were three provenance areas which could offered clastic materials for Baiyun Sag during the process of Zhuhai Formation deposition,and Paleo Pearl River,which situated in north of Baiyun Sag,carried most of the deposits,then the South Uplift,the clastic originated from the Dongsha Uplift were relatively limited.We focused on the study of South Uplift provenance in this paper utilizing seismic facies,petrologic fabrics of cores in wells,X-ray analysis of clay materials and the ages of clastic zircons.Imbricate foresets of Zhuhai Formation prograded northward and the incised river channels elongated eastward or northeastward in Yunkai Lower Uplift implying the transportation processes of clastic materials from south to north.Also,the apparent differences between granularity in sandstones,content of kaolinite in mudstones and ages of clastic zircons in the wells situated in northern and southern parts of Baiyun Sag indicate the clastic materials in Zhuhai Formation originated from different areas and different mother rocks.After comprehensive analysis,it was realized that southern provenance provided so abundant clastic materials,and these materials covered the Yunkai Lower Uplift from south to north and arrived southern parts of Baiyun Sag during deposition of Zhuhai Formation,and the widely distributed sandstones originated from South Uplift also provided effective reservoirs and benefited the oil-gas migration from Baiyun Sag to Yunkai Lower Uplift.