Method for removing coal seam gas and residual gas through CO2 and modified water

The invention discloses a method for removing coal seam gas and residual gas through CO2 and modified water. Three stages are adopted for removing the gas and the residual gas and include the conventional gas extraction stage, the gaseous phase displacement stage and the hydraulic power displacement stage. The gas extraction stage is conducted firstly, then the gaseous phase displacement stage is conducted, and finally the hydraulic power displacement stage is conducted. In the manner, the coal seam gas extraction efficiency can be effectively improved, the displacement range of the coal seam gas is enlarged through carbon dioxide gas, the permeability of a coal seam is improved, and convenience conditions are supplied to hydraulic power displacement; and the modified water is injected into the coal seam, the redundant carbon dioxide gas in the coal seam is absorbed, the modified water can deeply enter a coal body, and the water content of the coal seam is increased.