四川盆地不同区块龙马溪组页岩气地球化学特征对比

摘要

基于龙马溪组页岩气样品的气体组分、稳定碳氢同位素资料分析,对比研究了四川盆地不同区块(威远、长宁和涪陵区块)龙马溪组页岩气地球化学特征,探讨了页岩气成因和碳同位素倒转原因.结果表明:①威远、长宁和涪陵3个区块龙马溪组页岩气甲烷含量高(95.52%~99.45%),非烃含量低(主要为CO2、N2,各占0.01%~1.07%、0.01%~2.95%),均属于典型的干气;甲烷、乙烷碳同位素(δ13C1、δ13C2)值分别为-37.3‰~-26.7‰、-42.8‰~-31.6‰,且烷烃气(C1-C3)碳同位素呈现完全倒转现象.②威远区块龙马溪组页岩气主要为油型裂解气,长宁和涪陵区块龙马溪组页岩气主要是由油型裂解气和干酪根裂解气的混合气;四川盆地龙马溪组页岩气碳同位素倒转的原因主要是同源不同期气体的混合、原油裂解气和干酪根裂解气的混合.%On the basis of Longmaxi Formation shale gas samples gas composition, stable carbon and hydrogen isotopic data analyses, comparatively studied the Sichuan Basin different blocks (herein Weiyuan, Changning and Fuling blocks) Longmaxi Formation shale gas geochemical features, discussed shale gas genesis and carbon isotopic reversal causation. The result has shown that:①Methane content is high in the 3 blocks Longmaxi Formation shale gas (95.52%~99.45%), non-hydrocarbon content low (mainly CO2, N2 each 0.01%~1.07%, 0.01%~2.95%), belongs to typical dry gas. Methane, ethane carbon isotopes (δ13C1、δ13C2) are-37.3‰~-26.7‰,-42.8‰~-31.6‰respectively, and alkane gas (C1-C3) carbon isotope presents complete reversal.②Longmaxi Formation shale gas in Weiyu?an block is mainly petroleum pyrolysis gas;while in Changning and Fuling blocks is mainly mixed petroleum pyrolysis gas and kerogen pyrolysis gas. Sichuan Basin Longmaxi Formation shale gas carbon isotopic reversal causation is mainly mix of homologous different pe?riod gases, mix of petroleum pyrolysis gas and kerogen pyrolysis gas.