Original Article

Petroleum Geology & Experiment

, 37:18

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Pore structure of two organic-rich shales in southeastern Chongqing area:

Insight from Focused Ion Beam Scanning Electron Microscope (FIB-SEM)
  • Yong MaAffiliated withKey Laboratory of Shale Gas Resource Exploration of Ministry of Land and Resources of the People’s Republic of China, Chongqing Institute of Geology & Mineral ResourcesState Key Laboratory of Petroleum Resources & Prospecting, China University of Petroleum
  • , Ningning ZhongAffiliated withState Key Laboratory of Petroleum Resources & Prospecting, China University of Petroleum
  • , Lijun ChengAffiliated withKey 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
  • , Zhejun PanAffiliated withCSIRO Earth Science and Resource Engineering
  • , Hongying LiAffiliated withKey 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
  • , Qingming XieAffiliated withKey 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
  • , Chao LiAffiliated withKey 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

Abstract

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.

Key words:

FIB-SEM organic-matter pores three-dimensional reconstruction Niutitang Formation Wufeng- Longmaxi formations southeastern Chongqing area

渝东南两套富有机质页岩的孔隙结构特征