Study on the improvement of permeability of loaded bituminous coal after plasma breakdown

To quantitatively evaluate the effect of plasma on the permeability of coal, and to fill the gap in the research on the effect of plasma on the permeability of loaded coal by electrical breakdown, this study investigates the variations of the permeability of plasma-breakdown coal under different gas pressures, axial pressures and confining pressures with the aid of an established integrated experimental system for permeability enhancement by plasma. The following results are concluded: (1) The plasma breakdown based on the principle of electrical breakdown can raise the permeability of loaded coal. (2) When the gas pressure increases in the range of 1–2 MPa, the permeability of original coal corresponds to a V-shaped variation while that of the breakdown coal declines gradually. (3) The interconnected fracture network formed in breakdown coal can raise the coal permeability by tens to hundreds of times. (4) Due to the existence of the fracture structure, the permeability of the breakdown coal is more sensitive to the variation of external stress; (5) The flow state in coal changes from “Darcy” flow to “non-Darcy” flow, and the fracture structure formed after breakdown conduces to fluid migration. The above results suggest that the plasma technology based on the principle of electrical breakdown can effectively improve coal permeability and promote the application of plasma technology in coal mining.