北部湾盆地流沙港组湖相烃源岩的差异

Differences in lacustrine source rocks of Liushagang Formation in the Beibuwan Basin

北部湾盆地是中国近海重要的富油盆地,油气发现主要集中于涠西南凹陷、乌石凹陷和福山凹陷,探明原油地质储量约为4.05×108t,但各个主要凹陷的探明油气地质储量存在显著差异。北部湾盆地各凹陷的油气富集程度与其湖相烃源岩的差异密切相关,从涠西南凹陷到乌石凹陷,再到迈陈凹陷和福山凹陷,古近系流沙港组烃源岩的品质总体下降,烃源岩的有机质丰度降低,有机质类型从以腐泥型为主变成以混合型占优势,烃源岩的生烃潜力下降。分析表明,尽管北部湾盆地流沙港组烃源岩在形成期各凹陷普遍具有较高的古湖泊有机质生产力,但各凹陷的有机质来源仍然存在差异,有机质保存条件也存在差异,从涠西南凹陷到乌石凹陷,再到迈陈凹陷、福山凹陷和海中凹陷,湖相藻类来源的有机质减少,陆生高等植物来源的有机质增加,有机质保存条件具有变差的趋势。

The Beibuwan Basin is an important oil-rich basin in the offshore area of China.The oil and gas resources are mainly distributed in Weixi'nan sag,Wushi sag and Fushan sag.The proved oil reserves are about 4.05 X 1081,but the proved oil and gas reserves of each sag are significantly different.The enrichment degree of hydrocarbon in each sag of the Beibuwan Basin is closely related to the difference in lacustrine source rocks.From Weixi9 nan sag to Wushi sag,Maichen sag and Fushan sag,the quality of source rocks in the Paleogene Liushagang Formation overall declines,the organic matter abundance of source rocks decreases»the dominant organic matter type changes from the sapropelic type to the mixed type,and the hydrocarbon generation potential of source rocks decreases.The analysis shows that although in the formation period of source rocks in Liushagang Formation,each sag in the Beibuwan Basin generally had high organic matter productivity in ancient lakes,there is still a certain difference in the organic matter sources of each sag,as well as the preservation conditions of organic matters.From Weixi'nan sag to Wushi sag,Maichen sag,Fushan sag and Haizhong sag,the organic matters from lacustrine algae are reduced,the organic matters from terrestrial higher plants are increased,and the preservation conditions of organic matters tend to be worse.