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Brittleness index analysis of coal samples

  • Research Article - Applied Geophysics
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Abstract

The brittleness index (BI), which serves as a key reference for reservoir fracturing, is also an important quantitative index for the evaluation of coal-bed methane (CBM) reservoirs. To address the lack of research regarding this application of the BI, we measured the ultrasonic wave velocity of 10 coal samples collected from the Qinshui Basin, China. We then calculated the BI in three test directions, i.e., BI(90°), BI(45°), and BI(0°), as well as the BI anisotropy value (ABI) using the dynamic elastic method. Analysis of the calculated results showed that BI(90°) generally had the highest values and that BI(45°) was close to BI(0°). The ABI showed a positive correlation with the dynamic Young’s modulus anisotropy value, dynamic Poisson’s ratio anisotropy value, S-wave velocity anisotropy value, and the ratio of P-wave and S-wave velocity anisotropy values. However, the ABI had an unclear correlation with the P-wave velocity anisotropy value. Further analysis of the correlation between the BI and two other reservoir parameters (coal structure type and fracture development) revealed that samples with high BI values generally corresponded to primary or fragmented types of coal and also had low Poisson’s ratios, which indicates undeveloped fractures, while samples with low BI values corresponded to granulated types of coal and had high Poisson’s ratios, which indicates developed fractures. We investigated these correlations in order to understand the multiparameter constraints and their combined application in brittleness evaluations, which could reduce risk and improve the precision of ideal brittleness identification in CBM reservoirs.

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Acknowledgements

We would like to thank the Anhui Key Research and Development Program (Grant No. 1804a0802203), the Natural Science Foundation of the Anhui Higher Education Institutions (Grant Nos. KJ2018A0071, KJ2016A192), and the Natural Science Foundation for Young Teachers in AUST (Grant No. QN2017202) for supporting this study. We also thank Li Donghui and Xue Haifei for their help with the coal sample testing. Finally, many thanks are due to the anonymous reviewers and the editor for their valuable suggestions.

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Authors and Affiliations

  1. School of Earth and Environment, Anhui University of Science and Technology, Huainan, 232001, People’s Republic of China

    Haibo Wu & Pingsong Zhang

  2. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou, 221116, People’s Republic of China

    Shouhua Dong & Yaping Huang

  3. Key Laboratory of Geotechnical Mechanics and Engineering of the Ministry of Water Resources, Changjiang River Scientific Research Institute, Wuhan, 430010, People’s Republic of China

    Min Zhang

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  1. Haibo Wu
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  2. Pingsong Zhang
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  3. Shouhua Dong
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  4. Yaping Huang
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  5. Min Zhang
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Correspondence to Haibo Wu.

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Wu, H., Zhang, P., Dong, S. et al. Brittleness index analysis of coal samples. Acta Geophys. 67, 789–797 (2019). https://doi.org/10.1007/s11600-019-00291-5

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