Optimization Effects of Ionic Solutions on Coal Fracturing Using High-Voltage Electric Pulse

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High-voltage electric pulse (HVEP) technology holds significant potential in enhancing the permeability for coalbed methane extraction, and the introduction of ionic solutions greatly amplifies its fracturing effectiveness. To elucidate the optimization effects of different ionic solutions in HVEP technology, this study systematically compared the improvement in coal samples conductivity after treatment with KCl, MgCl₂, and FeCl₃ solutions. Physical experiments on HVEP-induced coal fracturing were conducted to reveal the evolution of pore and fracture structures in coal and the associated permeability changes. The results demonstrate that: (1) ionic solution soaking significantly improves the conductivity of coal samples, reduces the difficulty of electrical breakdown, and enhances energy utilization efficiency. The improvement effects vary among solutions, with FeCl₃ showing the best performance for XT anthracite and MgCl₂ being more effective for SSP bituminous coal. (2) Compared to distilled water, ionic solution-treated coal samples exhibit significantly increased porosity and average pore size after breakdown, with an enhanced internal fracture network. The number of macropores and mesopores increases, while micropores and nanopores decrease, resulting in improved pore-throat connectivity. (3) In terms of permeability enhancement, the effects of the three ionic solutions surpass those of distilled water. Consistent with the conductivity improvement trend, FeCl₃ and MgCl₂ solutions demonstrated optimal permeability enhancement for XT and SSP coal samples, respectively. Therefore, when combining ionic solution treatment with HVEP technology for coal seam fracturing and permeability enhancement, it is crucial to consider the specific characteristics of the coal to select the most suitable ionic solution and achieve higher efficiency in permeability improvement.