Method for improving coal bed methane recovery efficiency and coal mine safety protection

The invention discloses a method for improving the coal bed methane recovery efficiency by injecting CO2 into a coal bed in the coal bed methane production stage and meanwhile avoiding later-period coal mine protection explosion accidents by controlling the CH4 concentration of the coal bed. The method includes the steps of determining the coal bed CO2 critical injection concentration for coal mine safety production, establishing a CO2 critical injection amount calculating model for coal mine safety production, and determining and obtaining the CO2 injection speed at the optimal coal bed methane production degree through a numerical simulation method according to the CO2 critical injection amount. The coal bed methane recovery efficiency can be effectively improved through the effect of replacing the coal bed methane with CO2, and on the basis of energy conservation, it is avoided to the maximum extent that the unexploited methane is directly dispersed into the atmosphere during coal production. 本发明公开了一种在煤层气开