Influence of alkaline solution injection for wettability and permeability of coal with CO2 injection

The technology for combining CO2 injection with alkaline solution injection into coal bodies is proposed and investigated to address the disadvantages of traditional CO2 injection technologies, such as the production of dangerous amounts of excess residual gas and prevention of water injection into the deeper coal seams. After the CO2 injection, the wettability of coal sample is greatly improved, especially the alkaline solution. CO2 injection can effectively displace methane in coal, while alkaline solution can dissolve CO2 molecules adsorbed in coal and improve the wetting effect of coal. The increase of moisture will lead to the decrease of coal permeability, which can reduce gas emission. The permeability loss ratios for coal samples injected with CO2 were more than 90% much higher than those for coal samples not injected with CO2. After alkaline injection, the moisture content of coal into which CO2 had been injected increased 6.13 times compared to raw coal. Therefore, this technology may consume excess CO2 gas from the coal body and improve the effect of water injection into deeper coal seams.