轮南油田原油中三甲基苯基类异戊二烯化合物的检出及其意义

Occurrences and Implications of Aryl Isoprenoids Detected in the Crude Oils from Lunnan Oilfield,Tarim Basin,NW China

轮南油田不同时代储层原油中检出了丰富的三甲基苯基类异戊二烯化合物。该类化合物被普遍认为是来自于高盐度和强还原水体沉积环境中绿硫菌体内的类胡萝卜素的特征性生物标志化合物。该类化合物的检出对轮南油田烃源岩研究具有重要的指示意义 ,暗示了具有分层水体或高盐度的强还原环境下发育的优势烃源岩 ,对该区烃类的主力生烃贡献不容忽视。基于C15 3,4 ,5 三甲基苯基类异戊二烯异构体在轮南油田原油中的分布规律 ,及C15 3,4 ,5 /C13 2 ,3,6比值与Pr/Ph ,Ga/C31H和Ts/Tm等常规地球化学参数的对比 ,说明具有生源意义、能够指示沉积相特征的三甲基苯基类异戊二烯化合物分布 ,在一定程度上也受烃类热演化程度的影响。

Abundant 1-alkyl-2,3,6-trimethyl aryl isoprenoids were detected in the aromatic fraction of the Paleozoic crude oil samples from Lunnan Oilfield,Tarim Basin,NW China. These compounds were considered to be derived from β-cleavage of diaromatic carotenoid moieties mainly found in the chlorobiaceae family of photosynthetic sulfur bacteria and regarded as a biomarker that indicates a saline and strongly reducing sedimentary environment. It can be inferred that these biomarkers indicate prolific bacteria growth in a stratified water column at and below the oxic-anoxic boundary layer in depositional environment,which implied that contributions of first-class source rocks in a stratified water column and highly reducing sedimentary environment were underestimated in present exploration strategy in the Tarim Basin. Especially,the distribution of C_ 15 -3,4,5-isomer was surveyed in these oil samples to pursue its geochemical significance or application. Furthermore,the ratio of C_ 15 -3,4,5 isomer to C_ 13 -2,3,6 isomer (C_ 15 -3,4,5/C_ 13 -2,3,6) was proposed and correlated with some typical geochemical parameters (such as Pr/Ph,Ga/C31H,Ts/Tm). The results in this paper show that the ratios of C_ 15 -3,4,5/C_ 13 -2,3,6 have a systematic increase with these increasing parameter values. This indicates that,apart from being a biomarker of having a specific precursor and indicating hypersaline and highly reducing sedimentary facies,1-alkyl-trimethyl aryl isoprenoids can also have a significance in the determination of organic matter maturity. The above-mentioned discussion can help us better understand their distribnution,thermal maturity effect, diagenetic and catagenetic transformation of isorenieratene.