Journal of Earth Science

, Volume 28, Issue 2, pp 358–366 | Cite as

A new parameter as an indicator of the degree of deformation of coals

  • Mingming Wei
  • Yiwen Ju
  • Quanlin Hou
  • Guochang Wang
  • Liye Yu
  • Wenjing Zhang
  • Xiaoshi Li
Natural Gas and Coal Geology
  • 70 Downloads

Abstract

The deformation of coal is effected by thermal effect, pressures and tectonic stress, and the tectonic stress is the principal influence factor. However, the proposition of a useful quantitative index that responds to the degree of deformation of coals quantitatively or semi-quantitatively has been a long-debated issue. The vitrinite reflectance ellipsoid, that is, the reflectance indication surface (RIS) ellipsoid is considered to be a strain ellipsoid that reflects the sum of the strain increment caused by stress in the process of coalification. It has been used to describe the degree of deformation of the coal, but the effect of the anisotropy on the RIS ellipsoid has not yet been considered with regards to non-structural factors. In this paper, Wei’s parameter (ε) is proposed to express the deformation degree of the strain ellipsoid based on considering the combined influence of thermal effect, pressure and tectonic stress. The equation is as follows: ε=√[(ε 1-ε 0)2+(ε 2-ε 0)2+(ε 3-ε 0)2]/3, where ε 1=ln R max, ε 2=ln R int, ε 3=ln R min, and ε 0=(ε 1+ε 2+ε 3)/3. Wei’s parameter represents the distance from the surface to the spindle of the RIS logarithm ellipsoid; thus, the degree of deformation of the strain ellipsoid is indicated quantitatively. The formula itself, meanwhile, represents the absolute value of the degree of relative deformation and is consequently suitable for any type of deformation of the strain ellipsoid. Wei’s parameter makes it possible to compare degrees of deformation among different deformation types of the strain ellipsoid. This equation has been tested in four types of coal: highly metamorphic but weakly deformed coal of the southern Qinshui Basin, highly metamorphic and strongly deformed coal from the Tianhushan coal mining area of Fujian, and medium metamorphic and weakly or strongly deformed coal from the Huaibei Coalfield. The results of Wei’s parameters are consistent with the actual deformation degrees of the coal reservoirs determined by other methods, which supports the effectiveness of this method. In addition, Wei’s parameter is an important complement to the indicators of the degrees of deformation of coals, which possess certain theoretical significance and practical values.

Key Words

Wei’s parameter (εdeformation degree of coals quantitative index vitrinite reflectance ellipsoid 

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Notes

Acknowledgments

The authors would like to acknowledge Prof. Fali Jin (China University of Mining and Technology) for his help during vitrinite reflectance tests. The authors would also like to acknowledge the reviewers and editors for the detailed discussions. And this research was financial supported by National Natural Science Foundation of China (Nos. 41372213, 41030422) and Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA05030100). The final publication is available at Springer via http://dx.doi.org/10.1007/s12583-015-0576-1.

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Copyright information

© China University of Geosciences and Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  • Mingming Wei
    • 1
    • 2
  • Yiwen Ju
    • 1
  • Quanlin Hou
    • 1
  • Guochang Wang
    • 1
  • Liye Yu
    • 1
  • Wenjing Zhang
    • 1
  • Xiaoshi Li
    • 1
  1. 1.Key Laboratory of Computational Geodynamics of CAS, College of Earth ScienceUniversity of Chinese Academy of SciencesBeijingChina
  2. 2.State Key Laboratory of Organic GeochemistryGuangzhou Institute of Geochemistry of CASGuangzhouChina

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