南羌塘扎仁地区白云岩油苗芳烃地球化学特征

Aromatic geochemistry characteristics of dolomite oil seepage in Zaring Area of South Qiangtang Basin

南羌塘发现了大规模的白云岩古油藏带,这对该区油气勘探意义重大。采用GC-MS分析技术探讨了南羌塘盆地扎仁地区白云岩油苗芳烃化合物地球化学特征,分析结果表明:研究的样品中萘系列化合物质量分数低,总体上具有三甲基萘大于二甲基萘大于甲基萘大于萘的分布规律,MNR值变化于0.96～1.97,说明白云岩油苗经受了一定热演化,是甲基重排的结果;菲系列化合物质量分数较高,且甲基菲的分布模式为9-甲基菲大于2-甲基菲大于1-甲基菲大于3-甲基菲,反映了白云岩油苗生烃母质主要为低等水生生物,甲基菲成熟度指标MPI1为0.44～0.61,由此算出其成熟度Ro值为0.67%～0.77%,表明油苗的热演化大致为低—中成熟阶段;三芴系列在芳烃中质量分数较高,并且氧芴和芴的质量分数很低,而硫芴的质量分数很高,DBT/P值介于1.04～2.58,表明白云岩油苗生烃母质形成于海相偏还原环境;三芳甾烷质量分数很低,其与沉积环境有关的C26(20S)/C28(20S)值为0.29～0.37,表明白云岩油苗生烃母质形成于淡水、微咸水沉积环境,其与成熟度有关的C20/[C20+C26(20S)]值介于0.61～0.77,表明扎仁地区白云岩油苗处于成熟阶段。

Large scale dolomite paleo-oil pool zones have been found out in South Qiangtang Basin,which has a significant sense for the exploration activity in this area.Aromatic geochemistry characteristics have been discussed on the basis of GC-MS analysis for the dolomite oil seepage in Zaring Area of South Qiangtang Basin.The analysis results show that the content of naphthalene series of compounds is low and the distribution model form high to low is trimethylnaphthalene,dimethylnaphthalene,methylnaphthalene,naphthalene.MNR values is 0.96-1.97,showing that the dolomite oil seepage was subjected to a certain degree thermal evolution because of methyl rearrangement.The compound content of phenanthrene series is high,and the distribution model of the methylphenanthrene form high to low is 9-methylphenanthrene,2-methylphenanthrene,1-methylphenanthrene,3-methylphenanthrene,indicating the hydrocarbon-generating parent material of dolomite oil seepage is mainly low aquatic organisms.The MPI values are 0.44-0.61,and the calculated maturity Ro values are 0.67%-0.77%,showing that the thermal evolution of dolomite oil seepage is at low-middle maturity stage.The content of the fluorene series in aromatic hydricarbon is high,and the content of dibenzofuran and fluorene are very low.The content of dibenzothiophene is very high.DBT/P values are 1.04-2.58,indicating that the parent material of dolomite oil seepage was formed in the partial reduction of marine environment.The triaromatic steroid content is very low and the C26（20S） / C28（20S） values associated with the depositional environment are 0.29-0.37,indicating that the parent material of dolomite oil seepage was formed in fresh water and brackish water depositional environment.The C20/ [C20＋ C26（20S）] values related to maturity are 0.61-0.77,indicating that the dolomite oil seepage is at mature stage.