华南下寒武统、下志留统富硅质页岩成因模式比较研究

The Early Cambrian and Early Silurian shales are the important prospecting target layers for marine shale gases in South China. These two shale formations contain high abundance of both TOC (Total Organic Carbon) and Silicon. As principal components of brittle minerals, the silicon is the controlling factor in the forming of natural fractures and the fracturing measures for the shale gas exploitation. While, most of the previous studies mainly focused on the organic matter enrichment and the hydrocarbon generation potential of the two shale formations, the distribution of the silicon component in the shales and its origin as well as genesis models are rarely studied. It is greatly hindered to compare and to evaluate the shale gas potential objectively and correctly in these two shale strata. Therefore, the comparative study of the genesis models for Silicon-rich shales from Early Cambrian and Early Silurian in South China should be strengthened. The results of this study are very significant in the exploration and exploitation of shale gases theoretically and practically.

华南下古生界海相页岩是我国页岩气勘探开发的重要领域，其中的下寒武统、下志留统是海相页岩气勘探开发的重要层位。该两套页岩均具有高有机碳、高硅质的特点。其中硅质作为页岩中脆性矿物的主要成分，对页岩气成藏时天然裂缝的形成、开发时后期压裂改造的实施起着决定性作用。但以往的基础油气地质研究多聚焦于页岩中有机质的富集机理、生烃潜力等方面，而对页岩中硅质的来源、成因类型等关注不够。同时，对硅质在下寒武统、下志留统这两套页岩中分布特征与成因模式的差异性，亦缺乏足够的认识，这极大阻碍了对这两套页岩的页岩气潜力的客观比较与正确评价。因此，开展华南下寒武统、下志留统富硅质页岩成因模式的比较研究，揭示此两套页岩中硅质的分布规律、成因类型及两套页岩的成因模式，具有重要的理论和实践意义。

华南下古生界的下寒武统、下志留统页岩是我国海相页岩气勘探开发的重要层位。目前，针对该两套页岩层系的高频层序格架划分、页岩中硅质成分的来源成因、以及硅质页岩岩相在层序格架中的分布规律等方面的认识非常薄弱。本课题通过对华南多口钻遇下寒武、下志留统页岩层系的钻井开展了系统的高精度层序地层学研究；在等时地层格架内，进一步开展了两套页岩的岩相分析，揭示了其富硅质岩相在各自层序格架内的分布规律。在此基础上，选取两套页岩中具代表性的钻井岩心样品，开展了系统地元素、同位素地球化学分析，在初步揭示硅质成因类型及分布的基础上，借助扫描电镜、阴极发光等手段，在下寒武统牛蹄塘组、下志留统龙马溪组硅质页岩中确定出4种石英类型，即碎屑石英颗粒、生物成因石英、自生石英加大边、粘土矿物转化石英。并进而对各类石英对页岩储层特征及含气性的关系开展了进一步分析。该研究成果将深化对华南古生代两套典型页岩沉积演化过程的认识，为我国海相页岩下一步深层页岩气勘探部署提供理论支撑，同时对早寒武、早志留时期的古海洋演化背景及相应时期的地质事件提供约束和重要参考。