番禺4洼文昌组烃源岩生物标志化合物特征与油源判识

Biomarker characteristics and oil-source discrimination of source rocks in Wenchang Formation of Panyu 4 sag

在三级层序格架下分析了珠江口盆地番禺4洼文昌组烃源岩生物标志化合物纵向演化特征及影响因素,优选出T/C30藿烷、Ts/Tm及C304-甲基甾烷/C29甾烷等参数作为原油族群划分和油源对比的主要指标,厘清了该洼陷区已发现原油的来源和分布规律。研究认为,以高丰度C304-甲基甾烷、极低丰度双杜松烷T构型化合物和Ts与Tm相对含量均势为主要特征的第1类原油来自文四段半深湖—深湖相烃源岩,以高丰度C304-甲基甾烷、明显检出双杜松烷T构型化合物和Ts与Tm相对含量均势为主要特征的第2类原油来自文三段半深湖—深湖相烃源岩,以较高丰度C304-甲基甾烷和双杜松烷T构型化合物以及Ts较Tm显著优势为主要特征的第3类原油来自沉积环境相对偏氧化的文二段烃源岩。番禺4洼文昌组烃源岩中双杜松烷T构型化合物相对含量很可能受沉积时代和沉积环境的双重控制,上、下文昌组烃源岩中双杜松烷T构型化合物丰度变化可能与陆源区龙脑香科植物的逐步繁盛有关,较高丰度双杜松烷T构型化合物与高丰度C304-甲基甾烷的共存反映了在以低等水生生物来源有机质为主的宏观背景下具有一定丰度陆源树脂类有机质的输入。

The vertical evolution characteristics and influencing factors of biomarkers of source rocks in Wenchang Formation in Panyu 4 sag, Pearl River Mouth basin were analyzed under the three-order sequence framework, and T/C30 hopane, Ts/Tm and C304-methyl sterane/C29 sterane were selected as the key indicators for oil population division and oil-source correlation. The source and distribution pattern of the crude oil discovered in this sag have been clarified. Study shows that the first type of crude oil characterized by high abundance of C304-methyl steranes, ultra-low abundance of "T" compound of bicadinanes and relative content equilibrium of Ts and Tm were derived from the semi-deep and deep lacustrine source rocks in Wen-4 member, the second type of crude oil characterized by high abundance of C304-methyl steranes, obvious presence of "T" compound of bicadinanes and relative content equilibrium of Ts and Tm were sourced from semi-deep and deep lacustrine source rocks in Wen-3 member, and the third type of crude oil characterized by relatively high abundance of C304-methyl steranes, high abundance of "T" compound of bicadinanes and significant advantage of Ts over Tm were originated from source rocks in Wen-2 member with relatively oxidized depositional environment. The relative content of T compound of bicadinane in Wenchang source rocks of Panyu 4 sag is very likely to be controlled by both sedimentary time and depositional environment, and the change in abundance of T compound of bicadinane between the upper and lower Wenchang source rocks is likely to be related to the gradually flourishing dipterocarpaceae plants in terrigenous region. The coexistence of relatively high abundance of T compound of bicadinanes and high abundance of C304-methyl steranes reflects the input of a certain abundance of terrigenous resin organic matters under the macro-background dominated by organic matters from lower aquatic organisms.