东濮凹陷CO2气源岩及地球化学特征

东濮凹陷在下古生界奥陶系风化壳与下第三系Es¹₃地层发现了高含CO₂气层(显示)。通过气源对比分析证实,该凹陷文留构造文33块、文269块Es¹₃中的有机气体是来源于下第三系碎屑岩地层生成的油型气,其CO₂则是石炭系—二叠系的煤在二次生烃中伴生的CO₂与下古生界奥陶系灰岩高温分解生成的无机CO₂混合而成。对东濮凹陷这2类CO₂气源岩进行高温模拟实验发现,石炭系—二叠系的煤生气能力是奥陶系灰岩的9倍,煤生成的气体70％~80%为甲烷,少量为CO₂；而灰岩所生气中95%以上为CO₂气；单位质量的煤与灰岩生成的气体中CO2体积相当,煤是东濮凹陷最重要的气源岩。

Carbon Dioxide Source Rock and Gas Geochemical Features, Dongpu Sag

Carbon dioxide layers have been encountered in the Ordovician weathering crust of Lower Paleozoic and in Es₁3 of Paleogene. Based on gas source correlation, it is considered that organic gas source in Es₁3 in Wenliu is from the oil\|type gas formed in the Paleogene clastic rock, while CO₂ is the mixture of the associated CO₂ formed in the secondary hydrocarbon generation of Carboniferous-Permian coal, and the non-organic CO₂ from Ordovician limestone decomposition under high temperatures in Lower Paleozoic. According to the high temperature simulation on the two types of CO2 gas source rock in the Dongpu sag, the gas generation capacity of the Carboniferous\|Permian coal is 9 times stronger than that of the Ordovician limestone. Seventy to eighty percent of the coal formed gas is methane, with little CO2, while ninety percent of the gas formed in limestone is CO2. Because ofthe gas formed from the same amount of coal and limestone, the contents of CO2 are similar. Coal is the most important gas source rock in the Dongpu sag.