Welcome to visit Geoscience!

Geoscience ›› 2017, Vol. 31 ›› Issue (03): 595-605.

• Energy Geology • Previous Articles     Next Articles

Pore Structures and Fractal Characteristics of High Rank Coals

LI Zhen1(), SHAO Longyi1(), HOU Haihai1, GUO Shuangqing2, ZHAO Sheng1, YAO Minglei1, YAN Chunzhong2   

  1. 1. College of Geoscience and Surveying Engineering, China University of Mining & Technology, Beijing 100083, China
    2. No.3 Team of Henan Coal Geological Bureau, Zhengzhou,Henan 450046, China
  • Received:2016-10-31 Revised:2017-03-26 Online:2017-06-10 Published:2017-06-27

Abstract:

Significant differences exist in pore structures between high rank coals and medium-low rank coals, and the principle of fractal geometry is an effective tool for quantitatively describing pore characteristics of high rank coal reservoirs. The experiments comprising scanning electron microscopy, mercury intrusion, porosity and permeability testing were performed on nine coal samples (Ro,max from 1.9% to 2.95%) from North China. The pore fractal dimensions of samples were calculated using the subsection regression method and the relationships between the pore fractal dimension and different parameters including pore volume percent, coal degree of metamorphism, porosity and permeability were discussed. The results show that coal samples are characterized by abundant micro-ascopores, relatively high semi-closed pore content, general pore connectivity and clearly piecewise fractal dimensions. For each sample, fractal dimensions of supermacropore (pore radius r>5 μm), macropore (0.5 μm<r<5 μm), mesopore (0.05 μm<r<0.5 μm) and micro-ascopore (r<0.05 μm) decrease in turn. In addition, fractal dimensions of these pores except micro-ascopores increase with the increasing Ro,max and decreasing pore volume percent for all samples. The correlations between coal porosity (or permeability) and fractal dimensions of supermacropore, macropore and mesopore, micro-ascopore present as quadratic,linearly positive and linearly negative curves, respectively. The skewness and kurtosis of fractal dimension distribution for each sample are positively and negatively associated with porosity or permeability respectively. Meanwhile, based on skewness and kurtosis, the prediction models of linear equations (y=ax+b)can be used to predict porosity and permeability of high rank coals.

Key words: high rank coal, pore structure, fractal dimension, mercury intrusion

CLC Number: