塔北哈拉哈塘地区海相深层油气藏演化的Re-Os年代学约束

Quantitatively constraining key temporal aspect of petroleum evolution, for example the timing of oil generation, migration and the accumulation, are significant to our understanding of hydrocarbon evolution, as well as enhancing the success of exploration programs. This is particularly the case for Proterozoic – Paleozoic deep buried petroleum systems affected by complex tectonic events. Selecting the Halahatang oilfield in the northern Tarim Basin as the research object, this research plans to systematically conduct Re-Os isotope analysis on the crude oil and potential source rocks. Integrating the Re-Os analysis result with organic geochemistry analysis on oil and source rocks, reservoir fluid inclusion analysis and illite K-Ar dating, this research would try to quantitatively reconstruct the petroleum evolution process (generation to accumulation) of the Halahatang oilfield and trace the oil and source rock. This work would explore (1) the geological meaning of Re-Os dating on the crude oil which formed under deep buried and complicated structural conditions; (2) the applicability of the oil-source comparison through 187Os/188Os initial value of crude oil and source rocks from the deep buried marine reservoirs. In summary, this work would help the understanding the evolution and mechanism of the deep buried marine petroleum system.

油气生成、运移、聚集等油气演化过程中关键时刻的定量约束对了解整个油气演化过程、提高油气勘探的成功率都起着至关重要的作用。对于那些经历过复杂构造改造作用的古生代乃至更早期的深层油气系统，这些关键时刻的准确获取对于油气勘探显得更为重要。研究选择塔北哈拉哈塘地区奥陶系油气藏作为研究对象，系统开展原油及潜在烃源岩Re-Os同位素分析，将实验结果与烃源岩和原油有机地球化学，储层流体包裹体以及储层伊利石K-Ar同位素分析等结果综合分析，尝试定量解析哈拉哈塘油气藏的演化过程，示踪烃源岩。研究探索复杂构造地质条件下海相深层油气藏原油Re-Os等时线年龄在油藏演化过程中的地质意义，探索原油及烃源岩187Os/188Os初始值法在海相深层油气藏油-源对比中的适用性，为丰富和发展我国复杂地质条件下，海相深层碳酸盐岩油气成藏过程和成藏机理的研究服务。

油气生成、运移、聚集等油气演化过程关键时刻的准确约束对于了解整个油气演化过程、提高油气勘探成功率都起着至关重要的作用。对于经历了复杂构造作用的古生代乃至更古老的深层油气系统，这些关键时刻的准确厘定对于油气勘探更为重要。针对这一具有挑战性的科学问题，课题以塔里木盆地北缘哈拉哈塘凹陷海相深层油藏为研究对象，综合新颖的原油Re-Os同位素定年以及传统的有机地球化学、储层流体包裹体分析等多种测试手段，定量重建了奥陶系碳酸盐油藏的成藏过程。原油生物标志化合物(正构烷烃，萜烷，甾烷)结果指示哈拉哈塘凹陷原油主要来自寒武系泥岩，具有中-低成熟度并遭受一定程度生物降解的特征。虽然储层流体包裹体结果显示的烃类多种荧光、宽泛均一温度结果等特征指示油气藏经历了多期复杂演化过程。然而，与烃类共生包裹体相对稳定均一温度以及区域单井的埋藏历史结果共同指示哈拉哈塘油藏在二叠纪、100-110 ℃、39-59MPa条件下聚集成藏。除了个别样品(Ha15-2)偏离等时线，所有原油样品Re-Os定年结果指示早二叠世(285Ma)为烃类的重要生成时代，这一结果也与伊利石K-Ar同位素定年结果指示中晚二叠世为油藏重要的运移聚集时代相吻合。最终，综合区域地质背景和上述多项测试分析，研究重建了哈拉哈塘油藏演化过程：(1) 寒武系泥页岩在早二叠世进入生油窗开始生烃；(2) 生成的烃类在主要在中晚二叠世聚集成藏。这一针对哈拉哈塘凹陷油气成藏演化的研究证实了原油Re-Os同位素定年在限定油气生成时代方面的重要作用，同时对塔里木盆地北缘油气勘探具有现实指导意义。