 This study investigated the potential of underground biomethanation as a way to achieve carbon neutrality and promote carbon circular utilization through methanating CO2 and hydrogen-rich industrial waste gas and depleted natural gas reservoirs, MECHIC. It found that the concept could be economically viable if certain parameters were met, such as a high methanation efficiency, low facility site investment, and low hydrogen content in waste gas. Furthermore, it was determined that the variation in natural gas prices had the greatest effect on the project's net present value, while the variation in other factors had less of an impact. Finally, the study identified acceptable ranges for these parameters, within which the MECHIC concept would remain economically viable.