哈拉哈塘凹陷奥陶系原油芳烃生物标志物特征及油源

Aromatic biomarkers and oil source of the Ordovician crude oil in the Halahatang Sag,Tarim Basin

哈拉哈塘凹陷是近些年的勘探热点地区,为了进一步明确其原油母源输入、沉积环境、成熟度和可能烃源层,对26个哈拉哈塘凹陷和塔河奥陶系原油样品、4个台盆区烃源岩样品进行了系统的芳烃生物标志物分析。研究结果表明,哈拉哈塘原油均具有高萘、高菲、低联苯、贫1,2,5-和1,2,7-三甲基萘而富1,3,6-三甲基萘、高4-MDBT/DBT和(2+3)-MDBT/DBT比值、轻芳烃碳同位素的特点,与塔河奥陶系原油非常相似,反映出其属于典型的海相成因,且以低等藻类和细菌占生源优势。高丰度的二苯并噻吩和较低的DBT/P、Pr/Ph比值,指示其源岩沉积于强还原的碳酸盐沉积环境。等效镜质体反射率Rc1和Rc2揭示哈拉哈塘原油成熟演化处于中等-较高范畴。甲基三芳甾烷异构体组成型式对比表明,中-上奥陶统烃源岩与哈拉哈塘和塔河奥陶系原油对比良好,推测其为本区奥陶系原油的烃源层。

Halahatang Sag has been one of the focuses for petroleum exploration in recent years. In order to confirm its oil source,depositional environment, thermal maturity and possible source rocks, systematic aromatic biomarkers analyses were performed on 26 oil samples from the Halahatang Sag and the Ordovician in Tahe oilfield as well as 4 potential source rock samples from the unmodified foreland region of the Tarim Basin. The results show that the Halahatang oil samples are characterized by high contents of naphthalenes and phenanthrenes,low content of biphenyl,low abundance of 1,2,5-TMN,high abundance of 1,3,6-TMN,high ratios of 4-MDBT/DBT and（2 ＋3）-MDBT/DBT,and light carbon isotope of aromatics,which are similar to those of oil samples from the Tahe oilfield,indicating typical marine origin with con-tribution of lower algae and bacteria in predominance. High relative content of dibenzothiophene and low values of DBT/P and Pr/Phinfer a strong reducing depositional environment and carbonate lithology for the source rock. The equivalent vitrinite re-flectances,i. e. Rc1 and Rc2,reveal a moderate to high maturity. Comparison of methyl triaromatic sterane isomeride shows that the Halahatang and Tahe oils correlate well with the Middle-Upper Ordovician source rocks,indicating a genetic affinity.