Abstract: The gas injection pressure is the key technical parameter in the field of enhanced coalbed methane drainage engineering by gas injection. In order to study the effect of injection pressure on replacement effect for coal seam methane in different source gas injection, a laboratory gas injection simulation test method was adopted under the condition of vertical stress loading on coal particles containing methane, and a series of simulation experiments on replacement and driving methane in anthracite coal was carried out by use of helium, nitrogen and carbon dioxide injection under 1.25 MPa vertical load. Experimental results show that all the source gases are detained in the coal seam during the breakthrough time, and the breakthrough time of CO₂ can be as long as 440 min, that after the breakthrough, the injection source gases run out from exit gradually, and the retention rate decreases gradually, and only shows driving effect ultimately, that the breakthrough time of the injection source gases decreases with the increase of the gas injection pressure, and decreases with the increase of the source gas adsorption, and that the rate of replacement-driving is determined by the replacement action, driving action and its ratio, and it has no obvious relationship with the adsorption of the injection source gas, and the higher the injection pressure, the higher the efficiency.

Key words: gas pressure, replacement-driving action, breakthrough time, retention rate, replacement rate, anthracite