柴西地区南翼山构造天然气来源及成藏模式

Origin and accumulation model of natural gas in Nanyishan structure of western Qaidam Basin

以现今南翼山构造古近系和新近系天然气藏及其共生油藏的特征为研究基础,利用已发现气藏中天然气碳同位素特征及其共生原油的地球化学特征,进行了气源分析和油源对比,通过天然气成藏史恢复,对南翼山构造古近系和新近系气藏的成藏过程进行了系统分析。研究认为:1南翼山构造古近系和新近系气藏中高成熟度的天然气是以中生界煤系烃源岩演化生成的煤型气为主,古近系和新近系烃源岩演化生成的天然气量相对较少;2南翼山构造长期活动的基底断裂是古近系和新近系天然气藏形成的主控因素。通过对天然气来源分析,并结合构造演化,总结出了南翼山构造多源混合供烃、断裂-裂缝输导体系输导、晚期构造混合聚集成藏模式,以此为依据预测了柴达木盆地中生界煤系烃源岩新的沉积范围,可以成为下一步煤型气勘探的有利方向。

Based on the characteristics of Paleogene and Neogene natural gas reservoirs as well as their symbiotic reservoirs of Nanyishan structure,carbon isotope characteristics of natural gas and geochemical characteristics of symbiotic crude oil in the existing gas reservoirs were used for gas source analysis and oil source correlation.Through the restoration of natural gas accumulation history,a systematical analysis was conducted on the accumulation process of Paleogene and Neogene gas reservoirs in Nanyishan Structure.Studies have shown that：1） in Nanyishan structure,the high-maturity natural gas in the Paleogene and Neogene gas reservoirs are dominated by coal related gas evolving from Mesozoic coal measure source rocks with less amount of natural gas evolving from Paleogene and Neogene source rocks;2） the basement faults with long-term activities are the main control factor for the formation of Paleogene and Neogene natural gas reservoirs.Through an analysis on natural gas sources in combination with tectonic evolution,the accumulation model of Nanyishan structure was obtained including the multi-source hybrid hydrocarbon supply,transportation of fault-fissure transport system and late tectonic hybrid aggregation.Accordingly,the new sedimentary scope of Mesozoic coal-measure source rocks in Qaidam Basin was predicted,providing a favorable direction for the next step of coal-related gas exploration.