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根据天然气地球化学基本理论,对柴达木盆地西部(柴西)地区天然气的地球化学特征进行分析。测试和收集该地区18个油气田及含油气构造的83个天然气样品,分析其组分和C同位素数据,结果显示,该区天然气以烃类气体为主,烃类含量介于79.24%~99.81%之间,天然气比重介于0.72~1.36之间,天然气干燥系数(C_1/C_2~+)介于1.04~617.8之间,甲烷C同位素值介于-51.4‰~-24.2‰之间,乙烷C同位素值介于-34.2‰~-17.4‰之间。在此基础上,对该区不同构造带的天然气成因类型进行研究。研究结果表明,柴达木盆地西部地区天然气类型可划分为腐泥型气、腐殖型气、混合气3类,柴西北部天然气主要为腐泥型气和混合气,少量腐殖型气;柴西南部主要为腐泥型气,少量混合气。同时,建立了天然气成因类型的判识指标,对该区的天然气地球化学特征有了较为深入的认识,对今后的天然气勘探具有指导意义。
According to the basic theory of natural gas geochemistry, the geochemical characteristics of natural gas in western Qaidam basin are analyzed. Tested and collected 83 natural gas samples from 18 oil and gas fields and petroleum-bearing structures in the area, analyzed their composition and C isotope data. The results show that the natural gas in this area is mainly hydrocarbon gas with hydrocarbon content ranging from 79.24% to 99.81% , The specific gravity of natural gas ranges from 0.72 to 1.36, the natural gas drying coefficient (C 1 / C 2 ~ +) ranges from 1.04 to 617.8, the C isotopic values of methane range from -51.4 ‰ to -24.2 ‰, ethane C Isotope values ranged from -34.2 ‰ to -17.4 ‰. On this basis, the types of gas genesis in different tectonic belts in this area are studied. The results show that the natural gas types in western Qaidam Basin can be divided into three types: sapropel gas, humus gas and gas mixture. The natural gas in the northwestern part of Qaidam Basin is mainly sapropel gas and mixed gas with a few humic gases. Southwest of the main sap-type gas, a small amount of gas mixture. At the same time, the identification index of natural gas genetic type has been established and the gas geochemical characteristics of this area have been further understood, which is of guiding significance to the future natural gas exploration.