Nanopore Characteristics of Late Paleozoic Transitional Facies Coal-Bearing Shale in Ningwu Basin, China Investigated by Nuclear Magnetic Resonance and Low-Pressure Nitrogen Adsorption

作者：Sun, Cairong; Tang, Shuheng^*; Zhang, Songhang; Wei, Jianguang; Hou, Yunchao; Zhang, Tingqiang

来源：Journal of Nanoscience and Nanotechnology, 2017, 17(9): 6433-6444.

DOI：10.1166/jnn.2017.14477

• Ningwu Basin
• Nanopore Structure
• Coal-Bearing Shale
• NMR
• Low-Temperature N-2 Adsorption
• Transitional Facies

Transitional facies coal-bearing shales are different from marine shales. In transitional facies coal-bearing shales, nanopores offer the main storage space for gas. Thus, studying the characteristics of the nanopore structures is essential. This paper takes Late Paleozoic transitional facies coal-bearing shale in the Ningwu Basin as an example to investigate the nanopore structures in transitional facies coal-bearing. Using both nuclear magnetic resonance (NMR) and low-temperature N-2 adsorption methods, we have found that the T-2 spectra are bimodal at T-2 = 0.8-1 ms, T-2 = 50-100 ms, separately and the low-temperature N-2 adsorption isotherms of the samples can be assigned to Type IV isotherm according to classification of IUPAC. Fractal analysis by low-temperature N-2 adsorption isotherms (D-N1) and NMR (D-NMR1) shows pores are of relatively strong anisotropy. Generally, smaller pores are the major contributor to pore fractal dimensions, whereas larger pores increase the porous complexity. NMR fractal methods offer a new insight into featuring the meso-macropores and even fractures. Additionally, low-temperature N-2 adsorption methods are regarded as an effective tool to describe pore structure, especially micro-mesopores. Combining the two methods bring more comprehensive understanding on the pore structure of shale. The evolution of the nanoporosity in coal-bearing shale is a function of many factors, among which TOC and maturity (R-o) are vital. The pore surface area increases with increasing TOC content. Some organic matter is present as bitumen. Bitumen forms at a lower maturity, reducing the porosity, while bitumen degrades at a higher maturity, increasing the pores. In addition, samples of Type II kerogen are likely to possess larger pore specific surface areas when other factors are similar. However, there are no evident relationships between the pores and the contents of clay minerals and quartz. Overall, Late Paleozoic transitional facies coal-bearing shale in the Ningwu Basin develops organic nanopores and nanopores show stronger anisotropy. The evolution of nanopores is a complicated process, which attribute to multiple factors.

• 出版日期2017-9
• 单位中国地质大学（北京）