塔中奥陶系原油的地球化学特征及其来源

Origin and Geochemical Characteristics of Ordovician Oils from Tazhong Uplift

塔中奥陶系的油气资源十分丰富,是塔里木盆地油气勘探的重点层系之一,但油源仍是困扰地质勘探家的重要问题。通过系统分析塔中奥陶系原油的地球化学特征,进行了原油族群划分和油源判识。原油以轻质油为主,轻烃分析表明,原油没有发生大量裂解,原油的生成温度介于115～129℃,表明其主体成分形成于生油窗阶段。运用特征性生物标志物系统分析表明,原油可分为三个族群,分别来源于中—上奥陶统源岩、寒武系源岩及混合来源。在"三芴"组成上,原油均以较低的氧芴含量和较高的硫芴含量为特征。原油中饱和烃的碳同位素比值均轻于-31.2‰,平均值为-32.8‰,芳烃的碳同位素比值均轻于-30.4‰,平均值为-31.7‰,这些特征明显与塔东2井和塔深1井的寒武系原油不同。分析认为,碳同位素明显偏重的原油应来源于寒武系源岩,但碳同位素较轻的原油可能来源于中—上奥陶统源岩,也可能来源于寒武系源岩。

Ordovician of Tazhong Uplift had abundant petroleum resources, and was main exploration Formation in the Tarim Basin. However, the origin of oils was the probleum which bothered the oil explorers all along. By systematic geochemical analysis of Ordovician oils in Tazhong Uplift, the paper discriminated oils into populations and determined their origins. Most of oils belong to light oils, light hydrocarbon shows that oils were generated in oil generating window and oils were not cracked in large amount. According to biomarker, the oil can be discriminated into three populations, one population originated from Middle-Upper Ordovician source rocks, the other population originated from Cambrian source rocks, and the third population had mixed origin. All the oils had higher content of dibenzothiophene and lower content of dibenzofuran in relative composition of Fluorine-dibenzofuran-dibenzothiophene. Carbon isotope of saturate and aromatics in oils were lighter than - 31.2‰ and - 30.4‰, separately, which were apparently lighter than Cambrian oils from wells of Tadong-2 and Tashen-1. It shows that oils with heavier carbon isotope came from Cambrian source rocks, but oils with lighter carbon isotope came from Cambrian source rocks or Middle-Upper Ordovician source rocks.