Underground CO2 storage and technical problems in coal mining area under the “dual carbon” target

As the main energy source in China, the status of coal is difficult to change in the short term, but the development of coal industry is facing a new challenge in meeting the goal of“carbon peaking and carbon neutrality”. Actively promoting the green mining and low-carbon utilization of coal resources and fully playing the bottom role of coal security supply are major practical needs to ensure national energy security. Among them, the CO2 emission is the biggest constraint for the sustainable development of the coal industry. The development of large scale and low-cost CO2 storage technology is a problem that must be faced and solved in the low-carbon utilization of coal resources. Based on the study of natural CO2 storage in coal seams and geological conditions for CO2 gas reservoir storage, this paper discusses and prospects the technical methods of CO2 underground storage using the disturbedareaformed by coal mining, underground gasification and in situ pyrolysis.Also,it clarifies the necessary conditions for the CO2 underground efficient storage: ① the existence of a geologically confined layer in the upper part of the coal seam that is not affected by mining disturbances is a prerequisite for achieving CO2 storage in the disturbed space of the coal mine. ② Building functional filling space is the core work of CO2 underground storage.③ The physical characteristics of storage carriers such as fractured rock mass, gasification coal ash and pyrolysis semi coke confined by functional filling body are important factors affecting CO2 storage capacity and storage effect. Accordingly, the technical problems to be solved for the CO2 underground storage are analyzedincluding ① geological conditions and evaluation methods of the CO2 underground storage; ② materials and engineering technology for constructing CO2 storage space;③ detection of disturbance range of coal mining, gasification and pyrolysis and evaluation of CO2 storage potential; and ④ monitoring and evaluation of CO2 filling and storage effect. On this basis, according to the characteristics of disturbance space formed in the process of coal mining, underground gasification and in situ pyrolysis, the realization ways of CO2 underground storage in coal mined out area, coal underground gasification ash and crushed rock, and coal in situ pyrolysis char are proposed respectively.