Permeability enhancement mechanism in coal beds fractured using high-voltage electrical pulse treatment: Cross-scale transportation of coalbed methane

In this study, to investigate the mechanism through which high-voltage electrical pulses (HVEPs) enhance coal permeability and improve coalbed methane (CBM) extraction efficiency, liquid nitrogen adsorption analysis, nuclear magnetic resonance, infrared spectroscopy, and scanning electron microscopy were performed on HVEP-treated coal samples. The mentioned techniques were used to analyze the crack structures, pore distribution patterns, and changes in the chemical functional groups in the coal samples. The permeability enhancement mechanism of HVEP in coal was explored from macroscopic, mesoscopic, and microscopic perspectives. The chemical modification of coal through the breakdown of its oxygen-containing functional groups reduced the gas adsorption capacity of the coal samples and enhanced their desorption abilities. Simultaneously, the number of pores within the bottleneck pore interval of the coal samples increased significantly. The closed pores transformed into semi-closed and open pores. The pore volume was 2.86 times the pore volume of the original coal, while the pore specific surface area growth rate was 48.67%. This pronounced pore expansion effect eliminated the bottleneck pore interval, which reduced CBM seepage efficiency and enabled cross-scale CBM transport. Extensive parallel fractures and fissures appeared throughout the coal body. The connectivity within the pore-fracture network was enhanced substantially. This improved connectivity provided efficient pathways for gas transport.