Analysis on the difference of breakthrough time for different injection gases to replace-displace methane in coal seams
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Abstract:
Coal gas injection is an intensive extraction technology which is gradually developed in recent years, and the breakthrough time of gas injection is one of the important parameters of the technology. The breakthrough time is the required time of injection gas goes from one end of the coal seam to the other end, and it is closely related to the adsorption and the permeability of the source gas. In order to study the laws of permeability and adsorption on the breakthrough time, the laboratory simulation experiment is carried out with injecting He, N2 and CO2 in coal seams to replace-displace CH4. The results show that the breakthrough time on pure seepage of N2 and CO2 is very short, only 5.93% and 0.28% of the total breakthrough time, which indicates that gas adsorption performance is the main factor that causes the difference of breakthrough time. The breakthrough time increases as the gas adsorption performace of injection gas increases, and the breakthrough time of He, N2 and CO2 is 0.92 min, 14 min and 246 min, respectively. According to the laboratory experiment and theoretical model analysis, it can be concluded that the stronger the adsorption performance of injection gas is, the longer the breakthrough time and the more obvious the replacement effect in the initial stage of gas injection is, but the displacement effect gradually increases as the adsorption of the injection gas tends to be saturated.
