中国典型海相富有机质页岩的生气机理

Mechanisms of Shale Gas Generation from Typically Organic-Rich Marine Shales

目前页岩生烃的评价体系主要停留在静态条件下,忽略了成烃的动态过程,不能正确评价页岩原始的生烃潜力.采用生烃动力学模拟实验方法,分别对一个相对低成熟的典型海相富有机质页岩及其干酪根样品开展封闭体系和半开放体系下的人工熟化,并对熟化后的两个系列样品进行黄金管生气动力学模拟实验.对裂解产物中气态烃化合物、轻烃类化合物以及碳同位素开展了定量分析,结果表明,甲烷生成过程被划分为4个阶段,即生油(小于1.0%EasyRo)、凝析油生成(1.0%~1.5%EasyRo)、湿气生成(1.5%~2.2%EasyRo)和干气生成阶段(大于2.2%EasyRo);页岩中甲烷的最大产率主要来自干酪根的初次裂解(占22.7%)、可排沥青(占57.6%)和残余沥青(占19.6%)的二次裂解;经过早期排烃作用的页岩样品仍有大量的可溶沥青,在高-过成熟阶段其可以与干酪根、不可溶沥青相互作用,成为晚期主要的页岩生气母质.

The evaluation system of shale hydrocarbon generation is mainly addressed in the static condition at present,ignoring the dynamic process of hydrocarbon generation.Consequently,the original hydrocarbon generation potential of the shale cannot be properly evaluated.In this study,a typically marine shale sample with relatively low maturity and its kerogen were artificially matured by a half closed pyrolysis system and a closed pyrolysis system.Samples with different maturity levels obtained from the two systems were then pyrolyzed for gas generation in sealed gold tubes（i.e.,pyrolysis experiment in sealed gold tubes）.The quantitative analysis based on the products of C1-C5 gases,C6-C12 light hydrocarbons and carbon isotopes of gases from the simulation experiments indicates that the generation process of methane in kerogen can be divided into four stages：oil-generation（〈1.0% EasyRo）,condensate-generation（1.0%-1.5% EasyRo）,wet-gas-generation（1.5%-2.2% EasyRo）and dry-gas-stage（〉2.2% EasyRo）.Kerogen,expelled bitumen and residue bitumen contributes 22.7%,57.6% and 19.6% of maximum yield of methane in shale,respectively.Abundant soluble bitumen still exists in the shale matrix after the hydrocarbon expulsion,which becomes the major source of shale gas by interacting with kerogen and insoluble bitumen at high maturity levels.