渝东南两套富有机质页岩的孔隙结构特征——来自FIB－SEM的新启示

Pore structure of two organic-rich shales in southeastern Chongqing area: Insight from Focused Ion Beam Scanning Electron Microscope (FIB-SEM)

马勇 钟宁宁 程礼军 潘哲君 李红英 谢庆明 李超

Ma Yong Zhong Ningning Cheng Lijun Pan Zhejun Li Hongying Xie Qingming Li Chao

国土资源部页岩气资源勘查重点实验室(重庆地质矿产研究院), 重庆 400042 2. 中国石油大学(北京) 油气资源 与探测国家重点实验室, 北京 102249 3. CSIRO Earth Science and Resource Engineering, 澳大利亚 墨尔本 Vic 3169

Key Laboratory of Shale Gas Resource Exploration of Ministry of Land and Resources of the People's Republic of China (Chongqing Institute of Geology & Mineral Resources), Chongqing 400042, China 2. State Key Laboratory of Petroleum Resources & Prospecting, China University of Petroleum, Beijing 102249, China 3. CSIRO Earth Science and Resource Engineering, Melbourne Vic 3169, Australia

使用聚焦离子束扫描电镜(FIB-SEM)对渝东南地区下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组2套富有机质页岩的孔隙结构进行了系统观察,并对页岩纳米级有机质孔隙进行了三维重构和孔隙结构参数定量分析.研究发现,五峰组—龙马溪组页岩内层间微裂隙、矿物粒内孔、矿物粒间孔和有机质孔隙均较为发育.其中,有机质孔隙呈蜂窝状均匀发育,孔隙半径集中在3~100 nm,孔隙连通性较好,FIB-SEM三维重构计算有机质孔隙度在9.13%~18.42%之间,岩石总孔隙度中有机质孔隙度的贡献受控于TOC含量;牛蹄塘组页岩内溶蚀孔和粒间孔较为发育,有机质孔隙发育不均匀,孔隙呈扁平状或针孔状,孔隙半径集中在3~25 nm,孔隙连通性较差,有机质孔隙度在1.59%以下,有机质孔隙度对岩石总孔隙度的贡献与TOC含量关系较小,页岩的总孔隙度主要来自于矿物基质孔.FIB-SEM揭示了2套页岩有机质孔隙结构存在较大差异.

We used a Focused Ion Beam Scanning Electron Microscope (FIB-SEM) to observe the pore structures of the Lower Cambrian Niutitang shale and the Upper Ordovician Wufeng to Lower Silurian Longmaxi shale, sampled in the southeast of Chongqing.Three-dimensional distributions of the nanometer-sized organic-matter pores were reconstructed and their pore structure parameters were analyzed quantitatively. Our work indicated that microfractures between strata, interparticle and intraparticle pores in the mineral matrix, and organic-matter pores were well-developed in the Wufeng-Longmaxi formations. Pores within organic matter form a well-distributed honeycomb like structure with good connectivity, and the pore radius is between 3 and 100 nm. Porosity of organic matter calculated using the FIB-SEM 3-D reconstruction is between 9.13% and 18.42%,and the contribution of organic-matter pores in the total porosity is correlated with the total organic carbon (TOC) content. Dissolution pores and interparticle pores are developed in the Niutitang Formation while organic-matter pores are unevenly distributed. The organic-matter pores are tabular or pinhole with the pore radius between 3 and 25 nm and have poor connectivity. The calculated organic-matter porosity is below 1.59% and has little relationship with the TOC content. So the total porosity in the Niutitang shale mainly comes from the mineral matrix pores. The FIB-SEM results have shown significant differences in the pore structure of the two shales.

重庆市国土资源和房屋管理局科技计划项目(CQGT-KJ-2012-1).

https://doi.org/10.11781/sysydz201501109