惠州凹陷文昌组烃源岩及相关原油中的2-甲基藿烷系列

2-Methylhopane series in the source rocks and the related crude oils from Wenchang Fomation in Huizhou Sag

首次报道了在惠州凹陷文昌组优质烃源岩及相关原油中普遍存在丰富的2-甲基藿烷系列生物标志物,而在恩平组烃源岩中则几乎缺乏这类生物标志物,其分布具有明显的专一性。这类特殊生物标志物在该地区沉积地层中分布特征的专一性是由不同时期沉积水体的水化学条件决定的。生物化学的研究结果表明,蓝细菌中富含2-甲基藿烷多醇,它们是2-甲基藿烷系列的前身物,因此蓝细菌是这类生物标志物的主要生物来源。依据现有的文献资料,发现较丰富的2-甲基藿烷系列大多出现在碳酸盐岩沉积中,显然这是一种偏碱性的水介质条件,可能暗示着这样的环境有利于蓝细菌的大量发育,这也可能是控制惠州凹陷文昌组和恩平组烃源岩中2-甲基藿烷系列分布规律的主要因素。2-甲基藿烷系列在不同层位烃源岩中分布的专一性可以作为确定原油的成因类型和追溯原油的来源可靠的指标。

2-methylhopane series have been identified for the first time in the source rocks of Wenchang Formation and the related crude oils, but absent in the source rocks of Enping Formation in Huizhou Sag. This phenomena could be related to the water chemistry of depositional environment in different periods. The analytical results of biological chemistry have been showed that there are abundant 2-methylbacteriohopanepolyols in cyanobacteria, which are the precursors of 2-methylhopane series. Therefore, 2-methylhopane series are a kind of biomarker, indicating the contribution of cyanobacteria. Based on the data in literatures, abundant 2-methylhopanes seem to be related to carbonate rocks in Jiyang Depression indicating that the depositional environment was alkaline, and implying that cyanobacteria could be lived and developed very well under such an environment. It may be the main reason that abundant 2-methylhopanes have been found only in the source rocks of the Wenchang Formation, not the Enping Formation in the Huizhou Sag. In addition, the specific distributions of 2-methylhopanes in different source rocks in the Zhujiangkou Basin make them reliable indicators for the correlation and the genetic determination of crude oils.