Research on gas injection to increase coalbed methane production based on thermo-hydro-mechanical coupling

•The thermo-hydro-mechanical flow (THM) model of water-bearing coal seam is established.•Coal seam water can hinder gas migration, thus reducing CH4 production and CO2/N2 storage.•Different migration rates of CO2 and N2 lead to different breakthrough times of CO2/N2-ECBM.•The injection ratio of mixed gases (CO2, N2)will impact parameter of coal seam, including reservoir permeability, CH4 production, and CO2/N2 storage capacity.•CO2 displacement mainly utilizes competitive adsorption characteristics, while N2 displacement utilizes “high-speed scouring” effect and “ dredging, expanding ” effect onfractures.