Study on the effect of CO2-alkaline water two phase displacing gas and wetting coal

To solve the deficiencies in the techniques of coal seam water injection and gas displacement, the new measure of CO2-alkaline water two-phase displacing gas and wetting coal was developed. A variety of corresponding experiments were conducted to investigate the effects and action mechanism of this method. The results showed that in comparison to the conventional coal seam water injection, after adopting this new measure, the fluid pressure in coal samples increased obviously and the pressure hysteresis phenomenon appeared. The water injection effects were improved distinctly. The water injection volume of DL, ZX, and XT coal samples increased 262%, 204%, and 356%, respectively. The increments of moisture content at 60 mm in three coal samples were 394%, 532%, and 461%, respectively. The wetting radius in three coal samples increased all more than 50%. The ground stress restrained the effect of water injection, while increasing the diameter of water injection borehole can effectively improve the water injection effect. Hence, this measure can significantly enhance the effects of water injection and better prevent the risk of gas outburst.