Gas extraction enhancement technology with hydraulic flushing and gas-injection displacement

QU Huarong

doi:10.11799/ce202506014

Abstract：In order to improve the effect of pressure-relief gas extraction by hydraulic flushing drilling in low-permeability coal seams and eliminate the negative effect of flushing-induced concentrated stress on gas flow,a gas extraction enhancement technology with hydraulic flushing and coordinated gas injection displacement was proposed.In order to explore the factors affecting the effect of the technology,a coupled flow-solid model of multi-component gas storage and transportation process was established,and the effects of different flushing hole equivalent diameters,gas injection pressures,and drilling spacings on increasing gas flow and eliminating coal and gas outburst were analyzed.The results show that the larger the equivalent diameter of the flushing hole,the more significant the flow increase effect at the initial stage of gas injection.The effect of the equivalent diameter of the flushing hole on the flow increase effect decreases gradually in the later period of gas injection.When the gas injection time is less than 25 days,the gas extraction purity under the condition of an equivalent diameter of 2.4 m is significantly higher than that under the condition of an equivalent diameter of 1.6 m.When the gas injection time is greater than 25 days,the pure gas extraction flow under the two conditions is gradually approaching,and the pure gas extraction flow under the condition of an equivalent diameter of 2.4 m is less than 1.6 m in the later stage.The initial gas injection pressure has little effect on the flow increase effect.As the gas injection time increases,the influence of gas injection pressure on the flow increase effect decreases gradually.The spacing of boreholes has no significant effect on gas flow increase and gas outburst control,but the lag of production increase may occur when the spacing of boreholes is large.Therefore,although the larger equivalent diameter of the flushing hole and gas injection pressure conditions can effectively shorten the outburst period,the effect of gas injection is not significant in the later stage of displacement.The field engineering test results show that the maximum gas extraction flow is increased to 0.0325 m3/min and the flow increase is 44%～85%by using the technology of hydraulic flushing and gas injection displacement in low-permeability coal seam.Meanwhile,the maximum concentration of gas extraction in the borehole was increased to 79.3%,and the concentration was increased by 103%～167%.