高过成熟页岩中小分子烃类降解对页岩气组成及其储集的影响

The shale gas currently exploited in China is mainly featured by high thermal maturity level, reservoired in great depth and with a high dryness index concerning its hydrocarbon compositions. Among the hydrocarbon molecules the methane concentration is generally more than 95% while depleted in C2-C5 hydrocarbon molecules, which may have been degraded in the shale rocks during their geological/geochemical evolution processes. Up to date it is not very clear with respect to the geochemical/physiochemical mechanisms of this kind degradation processes occurred inside shale rocks, particularly the associated role and significance of minerals, residual kerogens and water in the rocks should be probed during the degradation processes of small hydrocarbon molecules.. In this work series of thermal simulation experiments will be performed, combined with the shale gas reserve in China, to probe the geochemical/physiochemical mechanisms of small hydrocarbon molecule degradation inside shale rocks. Experimental work will be carried out to investigate the catalysis effect of transition metals, residual kerogens, and their composites to the degradation of C2-C5 molecules occurred inside shale rocks, especially to study the role and significance of water in this kind degradation processes, its constraints to the gas compositions and the storage capacity of shale rocks. The concurrent evolution features will be discussed including the minerals, residual kerogens and water associated with the small hydrocarbon molecule degradation during the geochemical thermal processes inside the shale rocks. After all the planned work performed in this application project, it is hopefully to clarify the geochemical evolution mechanisms for the high dryness index of shale gas, to understand the role and significance of water in the degradation processes. And all the research outcomes from this work will be helpful for the properly geochemical appraisal of the shale gas reserves in our country.

我国目前勘探开发的页岩气资源具有成熟度高、埋深大，其组成干燥系数高的特点，其中甲烷在烃类气体中含量基本大于95%、而C2-C5烃类贫乏。C2-C5小分子烃类在页岩中发生了降解，而其降解的微观地球化学过程目前并不十分清楚，其中页岩矿物、残余干酪根、水等在小分子烃类降解中的作用值得深入探讨。本工作利用模拟实验、结合我国实际页岩气资源，探讨高过成熟页岩中小分子烃类降解的微观地球化学机制，研究页岩中黏土矿物、残余干酪根及二者组成的复合物对小分子烃类降解的催化作用；重点研究水在小分子烃类降解中具有的贡献，小分子烃类降解对高过成熟页岩气组成、以及水相中降解产物对其储集性能的影响制约；探讨高过成熟页岩中矿物类型转化、残余干酪根演化、以及小分子烃类降解的协同演化特征。研究成果可以探明高过成熟页岩气具有高干燥系数的地球化学机制、明晰水在小分子烃类降解中扮演的角色，为我国高过成熟页岩气资源的准确评价提供支持。

我国重点勘探开发的页岩气资源具有成熟度高、干燥系数高的特点，其中甲烷在烃类气体中含量基本大于95%、而C2~C5烃类贫乏。这些小分子烃类可能在页岩中发生了降解，而其降解的微观地球化学过程目前并不十分清楚，本项目在表征页岩中微量元素和矿物组成特征以及评价页岩中残余干酪根生烃潜力的基础上，选取小分子烃类开展不同系列黄金管限定体系热模拟实验，探讨了不同沉积环境页岩中微量元素富集演化过程、小分子烃类的降解特征、降解机制以及粘土矿物、水对小分子烃类降解的影响，分析高过成熟页岩中小分子烃类降解对页岩气组成及其储集的影响。. 本项目主要获得以下几点成果：（1）我国主要页岩气勘探生产目标层段牛蹄塘组和龙马溪组干酪根中含有丰富的微量元素，与干酪根紧密赋存的微量金属元素能为高过成熟阶段页岩气的生成提供催化作用、有利于页岩气资源的富集；（2）利用丙烷、丁烷和戊烷等小分子烃类开展热解模拟实验，总体上页岩中小分子烃类的降解对页岩气干燥系数及资源量有积极的贡献，页岩中粘土矿物和水对小分子烃类的降解有积极影响，尤其是水存在条件下，小分子烃类能够通过离子反应机理发生降解，降解过程中生成的有机酸对页岩储集性能的改善也有一定作用；（3）高过成熟度页岩中小分子烃类裂解过程中释放的有机酸与长石和碳酸盐矿物发生溶蚀反应，可以在矿物表面形成溶蚀孔；除矿物溶蚀孔以外，页岩还发育收缩有机孔、有机质孔、矿物粒间孔和粒内孔等等储集空间，有利于页岩气资源的富集；（4）在该项目资助下培养两名博士研究生（其中已毕业1名、在读1名），发表研究论文（标注该项目资助）11篇。