Progress and application of key technologies for CO2 enhancing coalbed methane

The industrial application of CO2 enhancing coalbed methane ( CO2 - ECBM ) is an important way promote the clean and efficient utilization of coal，accelerate the development of natural gas，and achieve the goals of “carbon peaking” and “carbon neutrality”. In view of the current lack of monitoring and control technology for the whole process of CO2 injection，migration，storage and production，this paper systematically carried out key technology exploration，and formed CO2 -ECBM technology system suitable for well groups with geological adaptability.The results show that the construction of a multi⁃scale experimental system for the occurrence and flow of CO2，CH4 and H2O in “ molecular，micro⁃nano，core，near⁃engineering，and engineering” scales is the basis to reveal the CO2 -ECBM mecha⁃ nism and its technical application. To promote CO2 -ECBM，it is necessary to comprehensively consider CO2 inject⁃ ability，CH4 stimulation and CO2 sequestration，and combine high⁃precision 3D geological and numerical models to se⁃ lect favorable well areas. The effect of CH4 stimulation is affected by CO2 injection mode，injection pressure，injection speed and bottom⁃hole flow pressure. A 6⁃stage technology sequence including“stepped injection and pressure boos⁃ ting，pressure⁃limiting injection displacement，gas flooding water productivity suppression，gas production well stimula⁃ tion，intermittent drainage，and gas production well site reclamation” is promoted. To monitor CO2 transport and stor⁃ age，a three⁃dimensional monitoring network covering CO2“injection⁃displacement⁃storage” based on “underground⁃ well⁃surface” technical system is built，which can monitor CO2 migration path by remote sensing monitoring of sur⁃ face micro⁃deformation and environmental changes， near⁃surface passive seismic fracture tomography， dynamic multi⁃directional and multi⁃component VSP monitoring technology，and deep well real⁃time temperature and pres⁃ sure monitoring devices. Based on the above technology， CO2 injection was realized in the TS - 634 well area of Shizhuang in Qinshui Basin by 2 001.04 t，and the CO2 migration direction and production enhancement effect were ef⁃ fectively monitored. It is concluded that the above technologies can serve CO2 -ECBM，and promoting the industrializa⁃ tion process of CO2 -ECBM needs to comprehensively optimization in terms of policy formulation，market mechanism and demand⁃driven. Thus，the technology can serve energy structure transition and “dual carbon” strategy realization.