Characteristics of Permeability Changes in Bituminous Coal Under Conditions of Stress Variation Due to Repeated Mining A
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Original Paper
Characteristics of Permeability Changes in Bituminous Coal Under Conditions of Stress Variation Due to Repeated Mining Activities Mengqian Huang,1 Lei Zhang ,1,2,4 Cun Zhang,3 and Shuai Chen1 Received 2 June 2019; accepted 12 August 2019
The factors affecting permeability change under repeated mining of coal seams are important study aspects that need to be explored. This study combined various stress variation characteristics of protective seam mining and simplified the stress path of repeated mining in protective seam mines. Based on the results from the bespoke gas flow and displacement testing apparatus, seepage tests for simulated repetitive mining were carried out. The results simulated the actual behavior very well. With any drastic increase in the mining influence, the axial deviation stress in the stress path increased, and the greater the difference in coal permeability during the unloading and stress recovery stage, the more substantial the increase in permeability. The change in coal permeability was significantly influenced by the severity of simulated repeated mining cycles. When the mining stress exceeded a critical value, the permeability of the coal sample increased with the increase in the number of loading and unloading cycles, but the reverse was true when the mining stress was lower than the critical value. The effective sensitivity of seepage to the applied stress decreased with an increase in the number of stress cycles. With a decrease in the deviation stress, that is, with lower severity of mining influence, the effective sensitivity of coal seepage to stress gradually decreased. KEY WORDS: The influence of repeated mining, Effective stress, Permeability, Stress sensitivity.
INTRODUCTION The reserves of recoverable coal in China are 47 billion m3. The recoverable reserves of gas 1
Jiangsu Engineering Laboratory of Mine Earthquake Monitoring and Prevention, School of Mines, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China. 2 A State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo 454000, Henan, China. 3 School of Resource and Safety Engineering, State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (Beijing), Beijing 100083, China. 4 To whom correspondence should be addressed; e-mail: [email protected]
buried at depths of 2000 m are 3.681 billion m3, equivalent to 5.2 9 l010 t of standard coal, which is second only to Russia and Canada, ranking third in the world, and accounts for 13% of the total coalbed methane resources in the worldÕs top 12 countries. Of the global reserves, the recoverable resources are 10.87 9 l012 m3, with huge development potential (Zhou et al. 2016). However, the permeability of most coal seams in China (such as Huainan) is 0.1 9 1018–1.0 9 1018 m2, which is four orders of magnitude lower than that in the USA and three orders lower than that in Australia. The permeability of the Shuicheng, Fengcheng, Hegang, Kailuan an
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