原油单萜烃的分布及地球化学意义

应用全二维气相色谱-飞行时间质谱(GC×GC-TOFMS)对采集自塔里木、北部湾、准噶尔、琼东南及江汉盆地的共45件原油样品进行分析。借助标准样品对原油中18个C₁₀化合物进行定性定量,其中包括2,6-二甲基辛烷(2,6-DMO)、2-甲基-3-乙基庚烷(2-M-3-EH)、1,1,2,3-四甲基环己烷、反-1-甲基-4-异丙基环己烷、1-甲基-3-异丙基苯和1-甲基-4-异丙基苯6种单萜烃化合物。研究表明,原油样品中均存在丰度不等的6种单萜化合物。高等植物精油催化加氢产物中检测到丰富的单萜烃,表明陆生高等植物为单萜烃的可能来源之一。新分子标志物参数2-M-3-EH/2,6-DMO(MTR)与Pristane/Phytane(Pr/Ph)相结合可以有效区分源自不同沉积环境源岩的原油样品:源于偏还原沉积环境源岩的原油具有较高的MTR和较低的Pr/Ph值,而源于偏氧化沉积环境源岩的原油则具有较低的MTR和较高的Pr/Ph值。定量数据表明,两类原油中MTR和Pr/Ph值的差异源于原油中2-M-3-EH及Phytane含量的差异,即两类原油样品中2,6-DMO和Pristane的含量范围十分相似,而2-M-3-EH及Phytane的含量范围则差异明显。偏还原环境下沉积的源岩所生成的原油中2-M-3-EH和Phytane的含量相对较高,而偏氧化条件下沉积的源岩所生成的原油中两者含量则相对较低。MTR可以与Pr/Ph一起用于判断源岩沉积环境的氧化还原程度,其对于生标含量很低或匮乏的轻质油及凝析油十分重要。

Occurrence and geochemical significance of monoterpenoid hydrocarbons in crude oils

A total of 45 crude oil samples collected from Tarim, Beibuwan, Junggar, Qiongdongnan and Jianghan Basins were analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS). Standard samples were used for qualitative and quantitative analysis of eighteen C₁₀ compounds in crude oil, including six monoterpenoid hydrocarbons, i.e., 2, 6-dimethyloctane (2, 6-DMO), 2-methyl-3-ethylheptane (2-M-3-EH), 1, 1, 2, 3-tetramethyl cyclohexane, t-1-methyl-4-isopropylcyclohexane, 1-methyl-3-isopropylbenzene and 1-methyl-4-isopropylbenzene.The results show that there are six monoterpenoids with different abundances in crude oil samples. Abundant monoterpenoid hydrocarbons were detected out in catalytic hydrogenation products of higher plant essential oil, suggesting terrestrial higher plant is a possible source of monoterpenoid hydrocarbon. The assemblage of new molecular marker parameter 2-M-3-EH/2, 6-DMO(MTR) and pristine/phytane (Pr/Ph) can be used to effectively distinguish crude oil samples derived from source rocks under different sedimentary environments. The crude oil from source rocks under reducing sedimentary environment has higher MTR and lower Pr/Ph values, whereas the crude oil derived from source rocks under oxidative sedimentary environments possesses lower MTR and higher Pr/Ph values. The quantitative data prove that the differences in MTR and Pr/Ph values are due to the variations in 2-M-3-EH and Ph contents of crude oil, i.e., for two kinds of crude oil, the content ranges of 2, 6-DMO and Pristane are very similar, while those of 2-M-3-EH and Phytane are quite different. The contents of 2-M-3-EH and Phytane are higher for crude oil derived from source rocks under reducing sedimentary environment, while lower for crude oil derived from source rocks under oxidative sedimentary environment. Both MTR and Pr/Ph can be used to identify the redox degree of sedimentary environment for source rocks, which is of great significance to light oil and condensate oil with very low or insufficient bio-marker content.