Effect of N2 on CH4 replacement in water-bearing coal under high pressure injection
In order to reveal the effect of N2 on CH4 displacement in coal with different water contents under high-pressure injection conditions,high-pressure injection N2 displacement experiments were conducted on three coal samples with water contents of 0.75％,1.5％,and 3％.The experimental results show that with the increase of coal moisture content,the ability of coal to adsorb CH4 and N2 shows a gradual weakening trend.The adsorption amount of N2 is always smaller than that of CH4,and the ability of N2 to replace CH4 gradually decreases;Under the pressure conditions of this experiment,the larger the pre adsorption equilibrium pressure of CH4 exceeds 0.75MPa,the lower its N2 utilization rate.At the same time,with the increase of coal moisture content,the CH4 replacement rate and N2 injection ratio show a gradually decreasing trend.Therefore,it can be concluded that the CH4 replacement rate and N2 injection ratio are negatively correlated with the coal moisture content.The experimental water containing coal sample can better restore the raw coal in a humid environment underground.Through feedback on the CH4 replacement rate and N2 injection ratio,it is found that excessive injection pressure cannot achieve good gas injection effect,but instead reduces the utilization rate of the replacement source gas.Therefore,for the engineering technology of replacing coal seam CH4 with N2 injection underground,in order to avoid the phenomenon of blindly increasing the injection pressure and causing a decrease in N2 replacement efficiency,It is recommended to control the equilibrium pressure of CH4 adsorption at 0.75 MPa when injecting N2 into underground coal seams to replace CH4.
High pressure injectionMoisture content of coalCH4 preadsorption equilibrium pressureCH4 replacement rateN2 injection ratio
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