塔里木盆地于奇西地区奥陶系原油特征及油气充注过程

塔里木盆地沙雅隆起北部于奇西地区奥陶系为重质油勘探区，但于奇西1井（YQX1）奥陶系钻遇中-轻质油.为探求其油气来源，通过沙雅隆起52件原油样品的金刚烷化合物分析，于奇西地区奥陶系131件岩心样品的岩石学观察、流体包裹体系统分析测试和同一期次油包裹体的气相色谱（GC）分析及色谱-质谱（GC-MS）分析，运用流体包裹体均一温度、单井埋藏史-热史图确定油气充注年龄，结合研究区断裂特征和盖层分布特征总结其油气成藏模式.结果表明，研究区原油普遍遭受生物降解作用并局部存在稠油与轻质油混合现象，同时奥陶系发育2~3期油气充注，分别为加里东晚期（452.5~420.5 Ma）、燕山期（150.2~100.6 Ma）和喜山期（20.1~2.1 Ma）；早期油气藏中原油因构造抬升发生生物降解而稠油化，晚期轻质油沿基底和寒武-奥陶系NW、NNE向走滑断裂垂向充注对早期油气藏进行混合改造，形成一定范围的中-轻质油藏. 

Geochemical Characteristics of Crude Oil and Hydrocarbon Accumulation in the Ordovician of Yuqixi Area,Tarim Basin

Medium-light oil was discovered in the Ordovician of Well YQX1, which is located in heavy oil exploration area, North Shaya Uplift in the Tarim Basin. In order to figure out the origin of medium-light oil, 52 crude oil samples from Shaya Uplift have been employed to test diamondoid compounds, and diagenetic observation and fluid inclusions analyses on 131 core samples have been made. Geochemical characteristics of trapped oil in petroleum inclusions have been analyzed by GC-MS method. Hydrocarbon charging periods have been obtained by the method of homogenization temperature (Th) of fluid inclusion projecting on burial history diagram with thermal curve. Combining faults characteristics and caprock distribution of study area, the pattern of hydrocarbon accumulation has been rebuilt. It is found that biodegradation of crude oil is common and mixing of heavy oil and light oil has occurred in some parts of the study area. Besides, three events of hydrocarbon accumulation occurred in the Ordovician of Yuqixi area, in the Late Caledonian (452.5-420.5 Ma), the Yanshanian (150.2-100.6 Ma), and the Late Himalaya (20.1-2.1 Ma), respectively. Biodegradation of crude oil resulted from tectonic uplift, which was followed by vertical migration of light oil along NW, NNE strike-slip faults in the Cambrian and Ordovician, resulting in the formation of oil mixing and current medium-light oil pools.