Experimental Study on Improving Coalbed Methane Recovery by Gas Injection

Through the contrast experiments of single component N₂, CO₂ and different ratio of mixture flooding, the displacement laws of coalbed methane under different gas and different proportion are explored. The results show that, with the increase of N₂ displacement pressure, the displacement efficiency increases first and then decreases, the replacing efficiency gets worse, the coal permeability gets lower and lower, but still higher than the original permeability; with the increase of CO₂ displacement pressure, the displacement efficiency increases all the time, the replacing efficiency changes little, the permeability decreases first and then increases, the whole permeability is lower than the original permeability; the laws of mixture （CO₂∶N₂=1∶4） and mixture （CO₂∶N₂=1∶9） are similar to N₂, and the law of mixture （CO₂∶N₂=1∶1） is similar to CO₂. N₂ constant displacement is better than intermittent displacement; CO₂ intermittent displacement is better than constant displacement.