柴达木盆地天然气气源对比

为了确定柴达木盆地不同地区的气源岩，在天然气组分、天然气甲烷至戊烷碳同位素、天然气轻烃组分与天然气轻烃碳同位素分析的基础上，挑选合适的气源对比指标，进行了天然气气源对比。分析总结出2套有效的气源对比指标：一套为盆地级气源对比指标，包括：甲烷碳同位素与甲乙烷碳同位素差交汇关系、天然气乙烷碳同位素与C₂⁺交汇关系、天然气轻烃组分与同位素交汇关系和天然气轻烃碳同位素交汇关系，用于鉴别柴东、柴北缘和柴西不同地区的天然气；另一套为精细级气源对比指标，包括：天然气轻烃庚烷值和天然气轻烃指纹特征，主要用于鉴别柴西或柴北缘不同层位的天然气。根据辨识出的天然气性质，结合气源岩的特征和分布，确定出的气岩对比结果为：柴西北部新近系天然气的主要烃源岩为N₂¹，柴西北部古近系烃源岩为N₁，柴西南部新近系烃源岩为E₃²，柴西南部古近系烃源岩为E₃¹，柴北缘天然气主要烃源岩为J_1＋2，柴东天然气主要烃源岩为Q_1＋2。

GAS-SOURCE CORRELATION IN THE QAIDAM BASIN

In order to determine the gas source rocks in different areas of the Qaidam Basin,several suitable indexes are selected for gas-source correlation based on analyses of natural gas components,carbon isotopes of hydrocarbons from methane to pentane,light hydrocarbon components and their carbon isotopes.Two sets of effective gas-source correlation indexes are presented.One is for basin-scale gas-source correlation,including methane carbon isotope vs.differential carbon isotope between methane and ethane,ethane carbon isotope vs.C2 ,and light hydrocarbon components vs.their carbon isotopes,and it has been used to identify the natural gases in the eastern part,northern edge and western part of the Qaidam Basin.The other is for trap-scale gas-source correlation,including the heptane value and fingerprint of light hydrocarbons,and it has been used to identify the natural gases in different horizons in the western and northern edge of the Qaidam Basin.Based on the recognized properties of natural gas and in combination with the characteristics and distribution of gas source rocks,the following conclusions are achieved from gas-source correlation:N21 is the major source rocks for the Neogene gas in the northwestern part of the Qaidam Basin,N1 for the Paleogene gas in the northwestern part of the basin,E32 for the Neogene gas in the southwestern part of the basin,E31 for the Paleogene gas in the southwestern part of the basin,J1 2 for gas on the northern edge of the basin,and Q1 2 for gas in the eastern part of the basin.