Well group carbon dioxide injection for enhanced coalbed methane recovery and key parameter of the numerical simulation and application in deep coalbed methane

CO2 -ECBM technology in deep coal seam is that CO2 can replace more CH4 and be buried in a long-term because of its strong adsorption effect. Experimental analysis in northern Shizhuang shows that the CO2 adsorption ca- pacity is two times of CH4 . With desorption pressure decrease,CH4 has higher desorption speed than CO2 so that it can be displaced effectively. CO2 injection causes the change of the physical property of coal reservoir,mainly refers to per- meability variation caused by matrix shrinkage and swelling during CO2 adsorption and desorption,and the permeability decreases at first and increases rapidly with the decrease of pressure. By applying the permeability change rule,the ge- ological model and numerical model were established. The influences of CO2 injection quantity,frequency and injection mode on the yield,recovery ratio and CO2 burial of the well group or single well were analyzed. The simulation results show that the gas recovery increases after two years CO2 injection with the injection rules such as the injection rate of 10 -15 tons per day,continuous injection for 90 days,closing well for 90 days. Field test indicates that the CO2 adsorp- tion capacity of No. 3 coal seam is 8 tons / day. The group well burial potential is about 12 616 t.