Spatial distribution of coalbed methane migration pathways and selection of optimal target areas for coalbed methane extraction for abandoned mines

Authors

LIU Qinjie, School of Mining Engineering, Anhui University of Science and Technology, Huainan 232001, China; Anhui Engineering Research Center of Exploitation and Utilization of Closed/Abandoned Mine Resources, Huainan 232001, ChinaFollow
YANG Youxing, School of Mining Engineering, Anhui University of Science and Technology, Huainan 232001, ChinaFollow
WU Benniu, School of Mining Engineering, Anhui University of Science and Technology, Huainan 232001, China; Anhui Engineering Research Center of Exploitation and Utilization of Closed/Abandoned Mine Resources, Huainan 232001, China
DUAN Minke, School of Mining Engineering, Anhui University of Science and Technology, Huainan 232001, China; Anhui Engineering Research Center of Exploitation and Utilization of Closed/Abandoned Mine Resources, Huainan 232001, China
DENG Zhuoyue, School of Mining Engineering, Anhui University of Science and Technology, Huainan 232001, China
GUO Chenye, Southwest Branch, China National Coal Group Corporation, Chongqing 400023, China; Chongqing Energy Investment Group Company Limited, Chongqing 400060, China
SUN Qiang, China Coal (Tianjin) Underground Engineering Intelligent Research Institute Co., Ltd., Tianjin 300120, China

Abstract

Objective and Methods The spatial distribution and long-term evolution of effective migration pathways determine the migration pathways of residual coalbed methane (CBM) in abandoned mines. Furthermore, they provide an important basis for selecting the optimal target areas for CBM extraction drilling in abandoned mines and maximizing extraction efficiency. This study investigated the first mining area at the first horizontal elevation of the Songzao Coal Mine in Chongqing. Using a comprehensive approach that integrated theoretical analysis, numerical simulations, and physical simulation experiments using similar materials, this study systematically examined the distribution patterns of effective CBM migration pathways in abandoned mines under the mining of multiple inclined coal seams. Furthermore, it proposed a scheme for selecting the optimal target areas for CBM extraction.Results and conclusions Theoretical calculations, numerical simulations, and physical simulation experiments using similar materials revealed that the fracture zones after the repeated mining of coal seams K2b, K1, and K3b exhibited maximum heights of 72.89 m, 76.4 m, and 77.3 m, respectively, suggesting a high consistency. The stress fields in the overburden underwent three stages of evolution: formation of arch-shaped pressure relief zones, asymmetric stress transfer, and dynamic stress equilibrium. This process culminated in the formation of a three-dimensional asymmetric structure consisting of a pressure relief dome of the roof and lateral stress shells. The fracture development in the overburden followed a coevolutionary pattern characterized by mining predominance, spatial differentiation, and temporal accumulation sequentially. Specifically, in the initial stage, the mining-induced rapid migration of the overburden led to the formation of a basic fracture network. In the middle stage, fractures experienced superimposition and propagation under the influence of repeated mining. In the late stage, three-dimensional O-shaped fracture traps were finally formed after over 10 years of consolidation and recovery. As a result, the fracture network entered a relatively stable stage, providing effective pathways for CBM migration and forming a CBM enrichment area under the sealing of the overlying thick and hard limestones. After long-term compaction, the fracture heights decreased to 67.97 m and the fractures presented a differentiated framework featuring a symmetric trapezoidal shape along strikes and an inclined trapezoidal shape in the dip directions. In combination with the CBM migration patterns, it is recommended that the optimal target area for CBM extraction should be the upper corner within burial depths ranging from 6.41 m to 36.70 m above the goaf floor of coal seam K3b.

Keywords

abandoned mines, residual coalbed methane (CBM), migration pathway, selection of optimal target area for CBM extraction

DOI

10.12363/issn.1001-1986.25.03.0157

Recommended Citation

LIU Qinjie, YANG Youxing, WU Benniu, et al. (2025) "Spatial distribution of coalbed methane migration pathways and selection of optimal target areas for coalbed methane extraction for abandoned mines," Coal Geology & Exploration: Vol. 53: Iss. 8, Article 8.
DOI: 10.12363/issn.1001-1986.25.03.0157
Available at: https://cge.researchcommons.org/journal/vol53/iss8/8

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