塔东南坳陷侏罗系固体沥青成因及其成藏意义

The Southeast Depression of Tarim Basin develops the High-quality source rocks in the Jurassic, and is rich in oil and gas shows in the outcrop and drilled wells. However, there was no breakthrough in the oil and gas exploration, and some problems are not clear in the depression, for example, the possibility of hydrocarbon reservoir existence, hydrocarbon accumulation process. Based on the origin of solid bitumen, which was newly discovered, the bitumen genesis, forming period, and secondary changes will be studied in order to solve the problems of the possibility of hydrocarbon reservoir existence and hydrocarbon accumulation process. Firstly, researches on the combination methods of the initial 187Os/188Os ratio, which is obtained from the Jurassic source rocks and solid bitumen obtained from the QD-1 well (newly drilled in the depression), isotopic and organic geochemical characteristics of solid bitumen and source rocks from outcrop and drilling well, are used to determine the solid bitumen source (source rock) in order to answer the question of whether the oil and gas were accumulated in the study area. Secondly, combined with the conventional geochronology methods, the Re-Os isotopic dating is designed to determine the forming time of solid bitumen; Thirdly, the solid bitumen will be observed under the microscope; the differences between the source rock and solid bitumen, which are the main element, trace element, ratio of saturated hydrocarbons to aromatic hydrocarbons from the extracts, and the biomarker compounds, are compared to judge the secondary changes whether the solid bitumen was subjected to oxidation, washing, and biological degradation; Finally, according to the regional geological background, the forming time and secondary changes of solid bitumen, the hydrocarbon accumulation and accumulation process will be discussed in the Southeastern Depression of Tarim Basin. The research can provide theoretical guidance and reference for oil and gas exploration work in other regions under similar geological conditions.

塔东南坳陷在露头及钻井中均发育侏罗系优质的烃源岩，油气显示丰富，然而油气勘探一直没有突破，油气成藏与否及成藏过程并不清楚。项目聚焦于区域新发现固体沥青的成因，试图通过沥青的来源、形成时间及次生变化来阐明区域成藏及成藏过程这一关键科学问题。首先，利用区域新完钻且地1井烃源岩及固体沥青的锇同位素比值，结合露头、钻井烃源岩及固体沥青的同位素信息与地化特征，判断固体沥青来源，示踪烃源岩，回答研究区成藏的与否；其次，开展沥青Re-Os同位素测年，通过等时线斜率结合其它方法确定沥青形成时代；再次，在沥青镜下观察的基础上，结合烃源岩与沥青的主微量元素、抽提物饱芳比、生标化合物等差异，判断固体沥青是否经历过氧化、水洗及生物降解等次生变化；最后，根据区域地质背景、固体沥青形成时间及次生变化，探讨塔东南坳陷油气成藏及成藏过程。本项目的开展可为类似地质条件下其它地区的油气勘探工作提供理论指导和借鉴。

塔东南坳陷在露头及钻井中均发育侏罗系优质的烃源岩，油气显示丰富，然而油气勘探一直没有突破，油气成藏与否及成藏过程并不清楚。项目聚焦于区域新发现固体沥青的成因，试图通过沥青的来源与形成过程阐明区域成藏及成藏过程这一关键科学问题。本次研究通过野外及钻井烃源岩评价表明，康苏组及杨叶组均为区域优质烃源岩，杨叶组质量高于康苏组；且地1井岩心中发育很多固体沥青，在镜下可以观察到煤岩的相关显微组分；康苏组及杨叶组稀土元素球粒陨石配分曲线均为右倾轻稀土富集的特征，稀土元素和微量元素参数特征表明，固体沥青与康苏组煤层亲缘关系更为接近；母源类型上两套烃源岩生标化合物参数接近，杨叶组低等植物贡献更多一些；而从饱和烃成熟度生标指标来看，康苏组略高于杨叶组，固体沥青于康苏组较为接近；通过铼锇同位素测年确定固体沥青形成时间为192+30/-46Ma，这与康苏组地层（煤岩）的形成时间一致，判定固体沥青铼锇同位素等时线年龄应为源岩年龄，究其原因是固体沥青形成时间较晚，为喜马拉雅运动康苏组煤层早期成熟演化的渗出沥青体，与康苏组煤岩具有很近的亲缘关系；同时固体沥青在形成过程中并没有受到太多的氧化、生物降解等次生变化。本次研究认识与周边被阿尔金走滑错开的吐拉盆地侏罗系油砂和沥青、柴达木盆地侏罗系原油具有相似性，且其油源岩可能也是中下侏罗统，这无疑更加增添了塔东南地区侏罗系油气勘探的信心，建议区域上在远离阿尔金山前的地区部署钻井进行油气勘探。