School of Resources and Geosciences, China University of Mining and Technology
School of Safety Engineering, China Universityof Mining and Technology
Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process under Ministryof Education, China University of Mining and Technology

Artificial improvement of coal seam permeability is the key to solve the low gas drainage efficiency and preventgas dynamic disaster. Plasma based on physical discharge is one of the effective means of coal seam antireflection.However, previous studies focus on the characterization of pore-fissure structure of single breakdown, ignore the polarization effect of plasma on coal, and lack of in-depth research on the electrical properties and the evolution characteristics ofpore-fissure structure under the action of cyclical plasma of loaded coal. In this paper, the cyclical plasma breakdown experimentsof coal samples were carried out. The voltage and current waveforms in the process of coal breakdown weremonitored thorough combining with high-voltage attenuation rod and the Roche coil, and the variation of electrical parameterssuch as pre-breakdown period, plasma breakdown period, number of wave peaks, peak voltage, peak current andenergy conversion efficiency were analyzed. The evolution of small pores, medium pores, large pores and micro cracksunder the conditions of 1, 5, 10, 15 and 20 times of breakdown was tested by NMR. The fractal dimension of seepage porewas also discussed through geometric fractal theory. The results show that the pre-breakdown period is at the level of thousandsof microseconds only for the first time, and then it will drop to tens of microseconds, while the plasma breakdownperiod shows a “ladder” growth with the increase of breakdown times. The energy conversion efficiency is maintained at28.7%−55.9%, showing a trend of rapid increase at first and then stable, indicating that the polarization effect of plasma onthe electrical properties of coal is limited. The growth rate of medium and large pores is the most obvious, and some microfracture structures will achieve a “0” breakthrough, indicating that plasma will significantly improve the seepage ofgas. The fractal dimension shows a decreasing trend after breakdown, which proves that the originally isolated pore structurewill be connected by the fracture from the perspective of pore fracture space dimension. The similarity between thechange trend of porosity and energy conversion efficiency shows that plasma has an impact on the electrical properties ofcoal, and the change of coal electrical properties will also have an impact on the distribution of plasma channels.

江苏省自然科学基金资助项目(BK20221122)；江苏省卓越博士后计划资助项目(2022ZB510)；华能集团总部科技资助项目(HNKJ20-H87)

张祥良，林柏泉，申建，等. 循环等离子体击穿受载煤体电学响应及孔隙结构演化规律[J]. 煤炭学报，2023，48(4)：1567−1583

ZHANG Xiangliang，LIN Baiquan，SHEN Jian，et al. Electrical response and pore structure evolution affected by cyclical plasma breakdown[J]. Journal of China Coal Society，2023，48(4)：1567−1583