Mechanisms behind permeability enhancement of coal reservoirs induced by electro-chemical composite energy pulse fracturing

Authors

MENG Bingbing, School of Civil Engineering, Sun Yat-sen University, Zhuhai 519000, China; State Key Laboratory for Tunnel Engineering, Sun Yat-sen University, Guangzhou 510275, China; Henan International Joint Laboratory of Unconventional Energy Geology and Development, Jiaozuo 454003, ChinaFollow
CAO Yunxing, Henan International Joint Laboratory of Unconventional Energy Geology and Development, Jiaozuo 454003, China
DUAN Hongfei, School of Civil Engineering, Sun Yat-sen University, Zhuhai 519000, China; State Key Laboratory for Tunnel Engineering, Sun Yat-sen University, Guangzhou 510275, ChinaFollow
ZHANG XinSheng, Henan International Joint Laboratory of Unconventional Energy Geology and Development, Jiaozuo 454003, China
ZHAO Lijuan, School of Civil Engineering, Sun Yat-sen University, Zhuhai 519000, China; State Key Laboratory for Tunnel Engineering, Sun Yat-sen University, Guangzhou 510275, China
SHI Bin, Henan International Joint Laboratory of Unconventional Energy Geology and Development, Jiaozuo 454003, China
YU Guofeng, State Key Laboratory for Mining of Deep Coal Resources and Environment Protection, Huainan Mining Group Co., Ltd., Huainan 232000, China

Abstract

Background Electro-chemical composite energy pulse fracturing (ECCE-PF) technology (i.e., the electrical explosion of metal wires igniting energetic materials) can effectively change the pore structure of coal reservoirs and enhance coal seam permeability. Elucidating the mechanisms behind the influence of this technology on both the scales of modified coal pores/fractures and methane desorption pattern can provide a theoretical basis for the wide application of this technology to coal seam permeability enhancement. Methods This study investigated coal samples from the Zhangcun Coal Mine in the Lu’an coal mining area, Shanxi Province. Using a self-developed ECCE-PF experimental platform, an experimental study was conducted on the pulse fracturing of coals. Specifically, the pore structures of coals pre- and post-fracturing were quantitatively analyzed and characterized using mercury injection capillary pressure (MICP), liquid nitrogen adsorption, and CO₂ adsorption methods, which enable the characterization of macropores (> 50 nm), mesopores (2–50 nm), and micropores (<2 nm), respectively. Furthermore, this study systematically investigated the variation patterns of methane desorption behavior of coals pre- and post-fracturing using methane adsorption-desorption experiments, followed by a comparative analysis of the morphologies and spatial distribution of fractures within the coal matrix pre- and post-fracturing using scanning electron microscopy (SEM). Results Post-fracturing coal samples exhibited a pronounced increase in macropore volume within specific pore-size ranges, with a 29.7% increase observed in the pore volume of macropores with sizes of approximately 140 000 nm. For mesopores in coal samples, their average pore sizes generally showed an upward trend, while their pore volume and specific surface area decreased by 34.8% and 16.94%, respectively. Similarly, the pore volume of micropores in coal samples also declined slightly. These changes were primarily attributed to the enlargement of mesopores and their transformation into macropores post-fracturing. Under adsorption pressures of 0.5 MPa, 1.5 MPa, and 2.5 MPa, coal samples showed significantly enhanced cumulative methane desorption capacity and desorption rate within 120 min post-fracturing. SEM observations further revealed typical erosional damage characteristics of coals post-fracturing, as predominantly manifested by coal matrix stripping and the development of pores and fractures in adjacent zones, accompanied by both the formation of new serrated fractures and markedly enhanced pore-fracture connectivity. Conclusions The application of ECCE-PF technology to coal reservoirs triggers progressive transformation processes in coals, where micropores evolve into mesopores and mesopores transition to macropores and then to fractures. These processes significantly enhance the connectivity of the pore-fracture system, providing effective pathways for methane desorption, diffusion, and migration and, thereby, significantly enhancing both the methane desorption rate and cumulative desorption capacity. The insights of this study elucidate the permeability enhancement mechanisms of ECCE-PF from the perspective of pore structure evolution and methane desorption behavior, providing a robust theoretical basis for the engineering application and wide promotion of this technology in coal seam permeability enhancement.

Keywords

electro-chemical composite energy, pulse fracturing, coal, pore structure, desorption, mechanism behind permeability enhancement

DOI

10.12363/issn.1001-1986.25.12.0923

Recommended Citation

MENG Bingbing, CAO Yunxing, DUAN Hongfei, et al. (2026) "Mechanisms behind permeability enhancement of coal reservoirs induced by electro-chemical composite energy pulse fracturing," Coal Geology & Exploration: Vol. 54: Iss. 2, Article 6.
DOI: 10.12363/issn.1001-1986.25.12.0923
Available at: https://cge.researchcommons.org/journal/vol54/iss2/6

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