Effect of liquid CO2 phase change fracturing on effective gas extraction radius - an experimental study

This paper presents the results of an experimental study of effect of liquid CO2 phase change fracturing on effective gas extraction radius. The effective gas extraction radius before and after CO2 phase change fracturing was measured during the experiment to evaluate its effect. The results show that the gas migration rate increases, resulting in an accelerating reducing of gas pressure in the coal seam,after the application of liquid CO2 phase transition fracturing. The effective gas extraction radius after CO2 phase change fracturing increases by about 1 m under the same extraction time. The estimated extraction time after CO2 phase change fracturing is reduced by 15, 29 and 47 days when the effective extraction radius is 1, 2 and 3 m respectively, and the average gas extraction rate increases by 43%. The results also show that the gas extraction rate increases dramatically at the beginning of CO2 phase change fracturing, following by a decelerating increase, and then remaining stable eventually as the coal permeability increase caused by CO2 phase change fracturing reaches the maximum value.