松辽盆地庆深气田天然气成因类型鉴别

通过对松辽盆地徐家围子烃源岩和原油热模拟实验、烷烃气碳同位素组成分析, 认为在高演化阶段单一热力作用可以引起重烃气(δ13C₂ > δ13C₃ > δ13C₄) 碳同位素组成倒转, 但CH₄与C₂H₆(δ13C₁ > δ13C₂) 却很难发生倒转.庆深气田天然气重甲烷碳同位素组成、烷烃气碳同位素完全倒转、高稀有气体同位素组成(R/Ra > 1.0), 说明该气田天然气来源具有多样性.利用R/Ra与CO₂/3He和R/Ra与CH₄/3He关系对庆深气田天然气成因类型进行识别, 认为该气田烷烃气中甲烷有部分为无机成因, 重烃气则为有机成因.该地区高地温梯度导致有机成因重烃气碳同位素组成发生倒转, 而CH₄与C₂H₆碳同位素组成倒转主要与重碳同位素的无机甲烷混入有关. 

Genetic Identification of Natural Gases in Qingshen Gas Field,Songliao Basin

According to measurement of carbon isotopes of gaseous alkanes thermally cracked from the hydrocarbon sources and oil under closed system pyrolysis, the results suggest that the reversal occurrence for carbon isotopes of heavy gaseous alkanses (δ13C₂ > δ13C₃ > δ13C₄) would be caused by single thermal dynamics, whereas the reversal trends of δ13C₁ and δ13C₂ (δ13C₁ > δ13C₂) could not be observed.The natural gases in the Qingshen gas field are characterized by the less negative δ13C₁ values, reversal series of carbon isotopes for gaseous alkanes and high R/Ra values (R/Ra > 1.0), indicating natural gases should have stemmed from multi-sources.Based on the correlation of R/Ra and CO₂/3He, R/Ra and CH₄/3He, the genesis of natural gases from the Qingshen gas field were identified.The hydrocarbon gases in the Qingshen gas field are a mixture of alkanes, in which the heavy gaseous alkanes were derived from the thermal decomposition of organic matters due to the high geothermal gradient, whereas mixing of inorganic methane into organic gas caused the reversal of the carbon isotopic trend of CH₄ and C₂H₆.