下扬子地区下寒武统深水陆棚相富有机质泥页岩差异性成岩演化过程及其对孔隙发育的控制作用

With huge resource potential, shale gas is an important unconventional gas resource. Digenetic evolution and pore system characteristics of organic-rich shales have been considered as key elements of shale gas exploration and evaluation. However, the related research is very weak and restricts further understanding of the characteristics of shale gas reservoirs. The project intends to focus on deepwater shelf organic-rich shale of the Lower Cambrian Formation in the Lower Yangtze Platform, South China. Various methods such as thin section, field emission scanning electron microscope, cathodoluminescence, X-ray diffraction and gas adsorption have been added in this study. Shale lithofacies, digenetic evolution and its control on pore system characteristics constitute the research focus. The relationship among lithofacies classification, diagenetic evolution and pore development characteristics is analyzed synthetically. The most favorable type of shale lithofacies is thus determined under the framework of shale lithofacies and diagenetic evolution pathway. The research results not only have important scientific significance for the understanding of the mechanism of shale gas enrichment and the improvement of shale gas accumulation theory, but also provide a theoretical basis for the lower Cambrian marine shale gas exploration and evaluation in South China, especially in in the Lower Yangtze Platform.

页岩气资源潜力巨大，是重要的非常规油气能源。富有机质泥页岩成岩演化与孔隙发育特征是页岩气勘探评价的核心要素之一，但目前相关的研究十分薄弱，制约了对页岩气储层特征的深入认识。本项目拟以下扬子地区下寒武统深水陆棚相富有机质泥页岩作为研究对象，采用铸体薄片、场发射扫描电镜、阴极发光、X射线衍射和气体吸附等多种实验分析手段，重点研究不同泥页岩岩相类型所对应的成岩演化过程及其对孔隙发育的控制作用等内容，综合分析岩相、成岩演化以及孔隙发育特征之间的内在联系，优选有利的泥页岩岩相类型。研究成果对于深化页岩气富集机理的认识和成藏理论的完善具有重要的科学意义，同时对于南方特别是下扬子地区下寒武统海相页岩气的勘探评价具有现实意义。

页岩油气和致密砂岩油气是目前我国最主要的两类非常规油气资源，其中储集特征的认识仍较为薄弱，储层发育的影响因素有待深入探究。本项目先后以塔里木盆地西北缘下寒武统富有机质泥页岩、加拿大魁北克地区奥陶系Utica页岩、松辽盆地南部下白垩统登楼库组致密砂岩和鄂尔多斯盆地中部上三叠统延长组致密砂岩作为研究对象，采用铸体薄片、场发射扫描电镜、能谱分析、X射线衍射、气体吸附及微纳米CT等多种实验分析手段，重点研究不同泥页岩和致密砂岩所对应的成岩演化过程及其对储层发育的影响。研究表明，受沉积环境和热液作用的影响，塔里木西北缘下寒武统黑色泥页岩在纵向上具有显著的岩性组合差异，进一步导致了成岩时空演化的差异性，表现为各成岩矿物组合、分布及形成顺序上存在显著的差异，同时泥页岩成岩序列的研究进一步证实了在低孔低渗的泥页岩中仍存在一定程度的内部和外部来源的矿物元素迁移，可形成多种广泛分布的中成岩阶段成岩产物；致密砂岩孔喉发育在不同的成岩演化路径框架下具有差异性，不同的成因演化形成的储层其储集性能也存在差异性规律，其中辫状三角洲河口沙坝和分流河道等微相砂体粒度较粗且绿泥石膜粒表覆盖率较高，相较其它砂体具有更为显著的有效孔隙空间，易形成优质储层。