摘要:
测试并分析了柴北缘各油气田的14个天然气样品的氦、氩稀有气体同位素比值,并进行了气源对比。研究发现,柴北缘天然气40Ar/36Ar值分布在951～1712,平均1098,多数样品40Ar/36Ar较通常认为源于侏罗系的天然气40Ar/36Ar明显偏高,研究认为本区不存在幔源高40Ar/36Ar流体的介入,储层年代效应也不可能造成天然气40Ar/36Ar明显偏高,因此柴北缘天然气40Ar/36Ar明显偏高,主要是由于源岩年代积累效应引起的。据估算,气源岩年龄分布范围为164.7～460.8Ma,平均为345.1Ma,可能多数来源于石炭系。这一认识得到了柴北缘广泛分布有石炭系源岩和已发现源于石炭系原油的支持。柴北缘石炭系天然气的发现预示了柴北缘石炭系是一个新的油气勘探层系,从而拓展了柴北缘天然气勘探领域。
Abstract:
He and Ar isotopic compositions of fourteen natural gas samples from the north margin of Qaidam Basin were analyzed. The relation of gas and source was also correlated using 40Ar/36Ar ratio. It is found that the 40Ar/36Ar values of natural gases in the area distribute in the range from 951 to 1 712, averaging 1098, with most values higher than 40Ar/36Ar values of the Jurassic natural gases from other Chinese basins. The research shows that there were not mantle derived fluid with high 40Ar/36Ar values in the region, and an aging effect of reservoirs could not result in the phenomena. Therefore, the higher 40Ar/36Ar values are mainly caused by the aging effect of source rocks. By calculation, the age of gas source rocks distributes between 164.7 and 460.8 Ma, averaging 345.1 Ma, showing that the most might be from Carboniferous. This conclusion is in agreement with the fact that there are widely distributed Carboniferous source rocks and crude oils derived from the Carboniferous. The discovery of the Carboniferous gases in the area indicates that Carboniferous is a new exploration target, developing a new exploring area in the north margin of Qaidam Basin.
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