A new parameter as an indicator of the degree of deformation of coals
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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 WordsWei’s parameter (ε) deformation degree of coals quantitative index vitrinite reflectance ellipsoid
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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.
- Cao, D. Y., 1990. The Vitrinite Reflectance Anisotropy in the Nappe Structure in the Huaibei Coalfield, Anhui Province. Geology Review, 36(4): 334–340 (in Chinese with English Abstract).Google Scholar
- Cao, D. Y., 1991. Deformation Indicators for Study of Tectonic Stresses Field in Coalfield. Journal of China Coal Society, 16(1): 73–80 (in Chinese with English Abstract)Google Scholar
- Cao, D. Y., Wang, W. X., 1990. Analysis Technique of Heterogeneous Vitrinite Reflectance and Its Application on Structural Studies. Coal Geology of China, 2(1): 1–8 (in Chinese)Google Scholar
- Jiang, B., Jin, F. L., Zhou, Q., et al., 1997. Experimental Research on Deformation of Optical Fabric of Coal Vitrinite Reflectance. Coal Geology & Exploration, 25(2): 11–15 (in Chinese with English Abstract)Google Scholar
- Jiang, B., Qin, Y., 1999. Geocheminal Mechanism of Evolution of Vitrinite Reflectance of Deformed Coals and Its Geological Significance. Coal Geology & Exploration, 27(5): 19–22 (in Chinese with English Abstract)Google Scholar
- Ju, Y. W., Wei, M. M., Hou, Q. L., et al., 2010. The Tectonic Differentiation of the Coal Basins and the Emplacement Models of the Deep Coal in North China. Journal of China Coal Society, 35(9): 1501–1505 (in Chinese with English Abstract)Google Scholar
- Ju, Y. W., Wei, M. M., Xue, C. D., 2011. Control of Basin-Mountain Evolution on the Occurrence of Deep Coal and Coalbed Methane in North China. Journal of China University of Mining & Technology, 40(3): 390–398 (in Chinese with English Abstract)Google Scholar
- Levine, J. R., Davis, A., 1989. Reflectance Anisotropy of Upper Carboniferous Coals in the Appalachian Foreland, Pennsylvania, U.S.A. International Journal of Coal Geology, 13(1–4): 314–373. doi: 10.1016/0166-5162(89)90099-2Google Scholar
- Stach, E., Mackowsky, M. T., Techmuller, M. E. A., 1982. Stach’s Textbook of Coal Petrology. Gebruder Borntraeger, Berlin.Google Scholar
- Wang, G. L., Cao, D. Y., Jiang, B., et al., 1992. Thrust Nappe, Extensional Gliding Nappe and Gravity Gliding Structures in the Southern Part of North China, in Addition on the Research Methods of Decollement. China University of Ming and Technology Press, Xuzhou (in Chinese)Google Scholar
- Wei, M. M., 2011. Structural Deformation of High Rank Coal and Its Effect on Permeability of Coalbed Methane Enrichment Area in the Southern Section of Qinshui Basin: [Dissertation]. Kunming University of Science and Technology, Kunming. (in Chinese with English Abstract)Google Scholar
- Wu, Y. D., 2010. Study on Characteristics of Tectono-Thermal Modeling and Regularities of Coalbed Gas’s Distribution and Enrichment, Huaibei-Huainan Coalfields, China: [Dissertation]. Graduate University of Chinese Academy of Sciences, Hefei. (in Chinese with English Abstract)Google Scholar