塔里木盆地台盆区古生界原油碳同位素组成及油源探讨

Carbon isotopic compositions and origin of Paleozoic crude oil in the platform region of Tarim Basin, NW China

基于塔里木盆地台盆区寒武系—奥陶系烃源岩干酪根样品以及古生界原油样品的碳同位素组成特征,探讨台盆区古生界原油的成因和来源。台盆区寒武系至少发育下寒武统以及中—上寒武统2套碳同位素组成具有明显差异的烃源岩,其中,下寒武统烃源岩干酪根碳同位素组成明显偏轻,中—上寒武统烃源岩干酪根碳同位素组成相对偏重,而奥陶系烃源岩则介于两者之间。台盆区古生界原油的碳同位素组成分布范围较大,其d^(13)C值为-35.2‰^-28.1‰,其中d^(13)C值为-34.0‰左右相对富集轻碳同位素的原油应主要来源于下寒武统烃源岩,d^(13)C值为-29.0‰左右相对富集重碳同位素的原油应主要来源于中—上寒武统烃源岩,碳同位素组成居中的原油不能排除寒武系烃源岩的贡献。分析认为,寒武系烃源岩具有主力烃源岩的条件,台盆区深层油气勘探潜力巨大。

Based on the carbon isotopic compositions of Cambrian-Ordovician source rocks Kerogen Samples and Paleozoic crude oil in the platform region of Tarim Basin, the origin and source of Paleozoic crude oil were investigated. There are at least two sets of source rocks with different carbon isotope compositions in the Cambrian, the Lower Cambrian source rock with lighter carbon isotope composition and Middle-Upper Cambrian source rock with heavier carbon isotope composition, while the Ordovician source rock is somewhere in between. The δ^13C values of Paleozoic crude oil samples are wide in distribution range, from-35.2‰ to-28.1‰. The crude oil with lighter carbon isotopic compositionsδ^13C-34.0‰） was mainly derived from Lower Cambrian source rock, and the crude oil with heavier carbon isotopic compositionδ^13C-29.0‰） was mainly derived from the Middle-Upper Cambrian source rocks, and the crude oil with δ^13C value in between may be derived from Cambrian source rocks. It is concluded through analysis that the Cambrian source rock could become the major source rock in the Tarim Basin and the platform region has huge potential oil and gas resources in the deep formations.