南海琼东南盆地东区天然气成因类型与烃源探讨

Genesis and sources of natural gas in eastern Qiongdongnan Basin,South China Sea

根据钻井测试、地震等资料,运用天然气地球化学、成藏综合研究方法,分析了琼东南盆地东部松东凹陷和宝岛凹陷天然气成因及来源。研究表明,研究区天然气主要为油型气,其中松东凹陷北坡的BF13和SF24区中新统天然气为成熟的油型气;宝岛凹陷北缘二号断裂带BF19-2-3井区上渐新统陵水组天然气为高成熟—过成熟油型气,可能混入少量煤型气。该认识有别于以往莺琼盆地报道的典型煤型气。已发现的油型气主要来源于始新统湖相烃源岩,可能部分有崖城组煤系源岩的贡献,推断琼东南盆地除崖城组煤系气源岩之外存在另一套重要的气源岩。松东凹陷和宝岛凹陷下一步重点天然气勘探方向为松东凹陷西北坡和宝岛凹陷北缘二号断裂带。

The genesis and sources of natural gas in the Songdong and Baodao sags in the eastern Qiongdongnan Basin were analyzed through gas geochemistry and pool-forming research methods based on sample tests and seis-mic data. The natural gas in the study area is mainly the oil type. In the BF13 and SF24 regions on the northern slope of the Songdong Sag, mature natural gas of the oil type was found in the Miocene. In the BF19-2-3 region in the fault belt no. 2 in the northern Baodao Sag, high-maturity and over-mature natural gas of the oil type （ sometimes mixed with coal gas） was found in the Upper Oligocene Lingshui Formation. The findings differed from former reports about the coal-type gas in the Yinggehai and Qiongdongnan basins. The discovered oil type natural gas mainly was sourced from lacustrine deposits in the Eocene, and partially from the coal formations in the Yacheng Formation. It was deduced that there was another set of important gas source rocks besides the coal formations in the Yacheng Formation. The northwestern slope of the Songdong Sag and the fault belt no. 2 in the northern Baodao Sag are important exploration targets for natural gas.