The Contrast Experimental Study of displacing Coalbed Methane by Injecting Carbon Dioxide or Nitrogen

n accordance to Coalbed Methane(CBM) low productivity and environment problem in China, the experiments of displacing CBM by injecting carbon dioxide and nitrogen were researched respectively. The adsoption/desorption disciplines of Carbon Dioxide(CO2), Methane(CH4) and Nitrogen(N-2) in coalbed were studied with experiment; the mechanism of CBM displacing by CO2 and N-2 injection and enhancing recovery were also researched. The results show that gases with higher critical temperature have stronger adsorption under the same pressure and desorption lag occurs during desorption process. Under the same volume and pressure condition, CO2 has stronger adsorption ability,thus enhancing the CH4 productivity in the pore surface of coalbed; N-2 mainly enters into macro-pore and decrease the pressure of CH4 in the constant pressure condition, the effect of methane adsorption decreases, then CH4 is displaced. With the injection flow of CO2 increasing, the productivity is enhanced correspondingly. However, the productivity could not be enhanced anymore after a certain amount of gas injection