Experimental Study On Strengthening Cracking And Increasing Permeability Of Coal By High Voltage Electric Pulse Based On Sodium Chloride Solution Medium

Because coal seams in China are generally rich in gas and have low permeability,scholars’ research on pressure relief and permeability enhancement of coal has always been the important content of safe coal mining.In order to improve the permeability of coal and realize the efficient co-mining of coal and gas,high-voltage pulse technology is an effective method.This method has gradually matured since the introduction of oil into coal mines,and has been applied to coal mine site from laboratory research.In order to further improve the cracking and anti-reflection effect of coal,based on the high-voltage pulse anti-reflection technology,this paper replaces the water usually added in the highvoltage pulse liquid with different concentrations of sodium chloride solution,studies the influence law of different concentrations of sodium chloride solution on the peak pressure of high-voltage pulse discharge,then,the effect of high-voltage electric pulse based on sodium chloride solution discharge medium on strengthening cracking and increasing permeability of coal is explored.The main research results are as follows:1.After the high-voltage electric pulse is discharged in 0,0.5mol/L,0.8mol/L,1.0mol/L,1.2mol/L,1.5mol/L,2.2MPa/L,2.5mol/L sodium chloride solution,at a distance of 30 cm from the discharge electrode,with the increase of the concentration of sodium chloride solution,the voltage of the high-voltage electric pulse The peak pressure of high voltage pulse in tap water is 1.25 MPa,which indicates that the peak discharge pressure can be increased after high voltage pulse is discharged in sodium chloride solution.2.COMSOL is used to simulate the stress distribution of the primary crack in the coal borehole under the impact load of high-voltage electric pulse electrohydraulic effect.From the simulation results,although the length of the primary crack in the coal borehole is different,after the impact load is applied to the borehole,a large amount of stress is distributed at the end of the primary crack,while the stress in other parts of the crack is low.According to the stress concentration phenomenon of the primary cracks in the coal drill hole,the analysis shows that the mode of high-voltage electric pulse for increasing permeability of coal block is as follows: under the impact load of the high-voltage electric pulse,when the stress at the end of the primary cracks in the coal drill hole reaches the yield strength of coal,these cracks will extend or produce new cracks,and the cracks inside the coal will increase in scale and quantity,and the cracks will be interconnected in the coal space.3.After tap water and 1.2mol/L sodium chloride solution were added into two identical coal blocks 1# and 2# respectively,the high-voltage pulse discharge was carried out for 8 times.The results showed that the cracks on the surface of 2# coal block appeared earlier and developed faster.After 8 times of high-voltage pulse discharge,the cracks on the surface of 2# coal block were longer than those of 1# coal block.There are many cracks in the 2# coal block,and the high-voltage pulse can improve the cracks in the 2# coal block.This experiment shows that sodium chloride solution can improve the anti-permeability of coal by high voltage pulse technology.Figure 39 table 10 reference 71...