东濮凹陷CO_2气源岩及地球化学特征

Carbon Dioxide Source Rock and Gas Geochemical Features,Dongpu Sag

在东濮凹陷在下古生界奥陶系风化壳与下第三系Es31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CO2体积相当,煤是东濮凹陷最重要的气源岩。

Carbon dioxide layers have been encountered in the Ordovician weathering crust of Lower Paleozoic and in Es3^1 of Paleogene. Based on gas source correlation, it is considered that organic gas source in Es3^1 in Wenliu is from the oil-type gas formed in the Paleogene clastie rock, while CO2 is the mixture of the associated CO2 formed in the secondary hydrocarbon generation of Carboniferous-Permian coal, and the nonorganic CO2 from Ordovician limestone decomposition under high temperatures in Lower Paleozoic. According to the high temperature simulation on the two types of CO2 gas source rock in the Dongpu sag, the gas generation capacity of the Carboniferous-Permian coal is 9 times stronger than that of the Ordovieian limestone. Seventy to eighty percent of the coal formed gas is methane, with little CO2, while ninety percent of the gas formed in limestone is CO2. Because ofthe gas formed from the same amount of coal and limestone, the contents of CO2 are similar. Coal is the most important gas source rock in the Dongpu sag.