Permeability and meso-structure evolution of coking coal subjected to long-term exposure of triaxial stresses and high-p
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ORIGINAL ARTICLE
Permeability and meso-structure evolution of coking coal subjected to long-term exposure of triaxial stresses and high-pressure nitrogen Zijun Feng . Yifan Yang . Wenxing Niu . Yangsheng Zhao . Zhijun Wan . Yanbin Yao
Received: 1 April 2020 / Accepted: 18 June 2020 Ó Springer Nature Switzerland AG 2020
Abstract Permeability and meso-structure evolution of coal are crucially important to the profound understanding of coal–gas interactions in the enhanced coalbed methane recovery and in controlling gas outburst. Very few studies focus on the effect time has on these interactions We performed a series of experiments on the permeability evolution of coking coal subjected to the long-term exposure of triaxial stresses and nitrogen pore pressure. The coking coal seam belongs to a low permeability reservoir with an initial permeability of 10-16 m2. The change tendency of the permeability was divided into types I and II. In Z. Feng (&) Y. Yang W. Niu Y. Zhao Department of Mining Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China e-mail: [email protected] Z. Feng Z. Wan State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China Z. Feng Y. Yang W. Niu Y. Zhao Key Laboratory of In-Situ Properties-Modified Mining of Ministry of Education, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China
type I, coal permeability increased at first then decreased and stabilized at a lower level while only decreasing and stabilization were present in type II. There existed a threshold value (2.0 9 10-19 m2) about the initial permeability to control the tendency transition from type I to type II. The natural logarithm of both the maximum permeability in the increasing phase and the stable permeability in the stabilization phase were closely linear to the natural logarithm of initial permeability. The tendency corresponded to a change of coal structure, which was broken into many small-sized grains by the integrative action of longterm stresses, gas pressure, and gas adsorption. A simple elastic–plastic model was established to explain the destroyed mechanism of the coal macromolecular structure. The results will be helpful in understanding the mechanism of gas outburst in coal mines and gas-coal interactions in enhanced coalbed methane recovery. Keywords Enhanced coalbed methane recovery Gas outburst permeability Scanning electronmicroscope Structure variation
Z. Wan School of Mines, China University of Mining and Technology, Xuzhou 221116, China
1 Introduction
Y. Yao School of Energy Resources, China University of Geosciences, Beijing 100083, China
As a natural gas trapped in coal seams, coalbed methane (CBM) is one of several clean unconventional geological resources. According to incomplete
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Geomech. Geophys. Geo-energ. Geo-resour.
statistics, worldwide CBM resources are estimated to total more than 256
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