Abstract
The permeability coefficient of coal seam is a key parameter for assessing the performance of underground coal bed methane extraction. First, compared with the widely accepted radial flow method, the related error range can be achieved by adapting the borehole pressure buildup method to calculate the permeability coefficient of coal seam at different positions of the same hard-soft composite coal seam. Second, the changing law shows that the permeability coefficient of coal seam varies in accordance with time and the different positions in hard-soft composite coal seam. The results indicate that the changing law is basically consistent in the permeability coefficient of coal seam, presenting a decreasing power function with time. The decay processes consist of three stages: rapid decay, slow decay, and stable process. At the early stage, the soft layer’s permeability coefficient is greater than that of the hard-soft interbedding, and the hard layer has the smallest coefficient. The decay rate of the permeability coefficient of the soft layer is greater than that of the hard layer and the hard-soft interbedding, which increases as time goes, resulting in the smallest permeability coefficient for the soft layer. It provides a new method for gas extraction in the hard-soft composite coal seam.
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The authors of this paper are very grateful to the reviewers for their valuable and pertinent suggestions for revising this article.
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Financial support for this work is provided by the State Key Laboratory of Deep Coal Mining Response and Disaster Prevention and Control Open Fund Project (SKLMRDPC19KF01), Hebei Province Ecological Wisdom Mine Joint Fund Project (E2020402036), and Outstanding Scholar of Yuezaki (800015Z1179).
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Wang, Y., Zhao, H., Wu, T. et al. Analytical solution and evolution process of gas permeability coefficient on typical hard-soft composite coal seam. Arab J Geosci 14, 1501 (2021). https://doi.org/10.1007/s12517-021-07774-0
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DOI: https://doi.org/10.1007/s12517-021-07774-0