塔中Ⅰ号坡折带高熟油气地球化学特征及其意义

Geochemical characteristics and implication of high thermal maturity oils in Tazhong-Ⅰ faulted slope break zone

李素梅 庞雄奇 杨海军 顾乔元 李玉江

Li Sumei Pang Xiongqi Yang Haijun Gu Qiaoyuan Li Yujiang

塔中Ⅰ号坡折带45个原油样品的地球化学分析表明,原油富含轻烃组分、贫重质组分,反映源岩较高的热成熟度.原油中发育异常高丰度的含硫芳烃-二苯并噻吩,反映了海相成因特征.伽马蜡烷/C藿烷、规则甾烷与C甾烷相对分布等多项指标与生物标志物指纹反映区内至少有两种油源.双金刚烷系列与链烷烃分布指示塔中Ⅰ号坡折带东端存在一强气侵注入点.观察到邻井原油、不同层系原油烃类化学成分显著的差异,指示油气成因与成藏条件的差异.塔中Ⅰ号坡折带油气的地球化学特征反映了叠合盆地海相成因油气的普遍特征,包括高过成熟性、多源与多期成藏、油气化学成分的非均一性及油气藏的相对分隔性.本研究为区内寻找多种成因类型油气与油源确认提供了依据,指示塔中低凸起油气勘探潜力巨大.

Considerable quantity of oils and gas with diverse characteristics and origins has been discovered in the Tazhong-Ⅰ faulted slope break zone,Tarim basin.Totally 45 oil samples were gathered and analyzed with conventional geochemical approaches.The results show that the oils are characterized by significant predominance of light fractions and lack of heavy fractions,suggesting high thermal maturity of source rocks and/or thermal cracking of the oils.High absolute abundance of dibenzothiophene was detected in the oils,indicating a marine source.Several indexes(including relative distribution of gammacerane/C hopane,C-to C-steranes,and C-steranes) and biomarker fingerprints indicate that the oils in the area were generated from at least two kinds of primary source rocks.It was suggested that there is a strong gas invasion point at the eastern end of Tazhong-Ⅰ faulted slope break zone according to the abnormal distributions of diamondoid hydrocarbons and n-alkanes.There are evident differences among those oils even from closely adjacent wells,inferring different hydrocarbon generation and accumulation processes.All the features for the oil samples analyzed indicate the common characteristics of the oils in the superimposed basins in western China,i.e.,high thermal maturity,multiple sources and multiphase pooling,heterogeneity of chemical composition,and relative compartmentalization.This study is helpful for investigating the origin and accumulation mechanisms of the oils.It was suggested that great petroleum potential could be expected in the Tazhong-Ⅰ faulted slope break zone.

10.11743/ogg20080209