塔中北斜坡原油轻烃组成及地球化学特征

Compositions and Geochemical Characteristics of Light Hydrocarbons in Northern Slope of Tazhong

塔中北斜坡原油为低硫、低蜡的典型腐泥型母质来源的原油,其苯含量低,正己烷和环己烷含量较高,正庚烷含量高,二甲基环戊烷含量极低,说明藻类和细菌是主要的烃源。该斜坡原油的Mango轻烃参数K1值主要分布在1左右,平均值为1.11,除个别井(塔中24井)K1值偏离较大之外,基本上与Mango所做结论一致;K2值普遍较低,平均值为0.21,为典型的海相油特征;原油庚烷值大于30%,异庚烷值也大于2.0,表明原油已处于高成熟阶段。

The crude oils in the northern slope of Tazhong generated from sapropel type organic materials are characterized by low sulfur and less wax. The contents of benzene and dimethylcyclopentane are low; and hexane, cyclohexane and normal heptane have a high content, which reflects that hydrocarbons are mainly from algae and bacteria. The ratio K1 is around 1, and its distribution is basically consistent with the conclusion reported by Mango about light hydrocarbons, but the K1 value of Tazhong 24 well is a bit high, deviating from the conclusion. Meanwhile, the ratio K2 is generally low, and the average value is 0.21, suggesting the oils present typical marine oils characteristics. Heptane value is more than 30% and isoheptane value is also greater than 2.0, which indicates that the oils are in the high mature stage. Noteworthy, the high Heptane and isoheptane values represent that the oils did not undergo intensive biological degradation.