Evaluation and research progress of CO2 sequestration in deep coal seams

BackgroundWith increasing pressure for global carbon emission reduction, geologic CO2 sequestration has emerged as a critical technical approach to achieving the goals of peak carbon dioxide emissions and carbon neutrality. Owing to their high CO2 adsorption capacity and favorable sealing conditions, deep coal seams are considered one of the most promising media for CO2 sequestration, following saline aquifers and depleted hydrocarbon reservoirs. Therefore, the exploitation and utilization of deep coal seams hold significant strategic importance for the green, low-carbon transformation of the coal industry. MethodsBased on literature analysis and a review of outcomes from cutting-edge research, this study systematically elucidates the global research progress in CO2 sequestration in deep coal seams and summarizes the underlying mechanisms and application status. Focusing on evaluation indicators and research methodologies, this study further identifies key challenges in current research and proposes future development directions.Progresses and ProspectsCO2 sequestration in deep coal seams primarily involves the synergistic effects of multiple mechanisms, including adsorption, solubility trapping, and mineral trapping. Under multi-field coupling conditions, the core indicators for evaluating CO2 sequestration in deep coal seams include sequestration potential, CO2 injectability, sequestration efficiency, and sequestration safety. Representative methods, such as numerical simulation of CO2 sequestration evolution, the development of thermo-hydro-mechanical-chemical (THMC) coupling models, and multi-scale analysis, have emerged as key approaches to elucidating sequestration mechanisms and enabling quantitative evaluation. Furthermore, relatively systematic evaluation method frameworks have been developed. Presently, research on CO2 sequestration in deep coal seams has gradually progressed from the exploration of fundamental mechanisms to multi-field coupling-based evaluation and engineering validation. However, such research still faces several challenges, including the incomplete fine-scale characterization of sequestration potential, limited optimization of parameters for adsorption capacity, unclear mechanisms underlying the long-term evolution of sequestration efficiency, and the immaturity of technical systems for long-term safety monitoring. In the future, it is necessary to gradually establish theoretical and technical frameworks applicable to engineering practices by closely integrating multi-scale geological conditions with engineering requirements, strengthening dynamic monitoring throughout the sequestration process, and promoting the transition of evaluation methods from qualitative to quantitative and from static to dynamic. In addition, there is a need to. All these efforts will provide support for the large-scale application and industrial development of CO2 sequestration in deep coal seams.