Abstract: To evaluate the feasibility of geological CO2 storage in saline aquifer and overlying coal mining in Ordos Basin, the safety risk study of coal mining with CO2 injection was carried out. Based on the finite element numerical simulation software, the two-dimensional fluid-structure coupling numerical simulation of CO2 injection cooperation in coal mining is realized, and the effects of different CO2 injection rates, injection times and coal mining degrees on CO2 migration, formation pore pressure and vertical deformation are studied. Considering the CO2 injection rate of 100 000−700 000 tons per year and the half and complete excavation of coal, the numerical simulations of 9 different conditions are carried out according to the control variable method. The results show that the injection rate is the main factor affecting the variation of pore pressure, displacement and the migration range of CO2, and the migration range of CO2 is less affected by the overlying load, while the pore pressure and deformation increase with the decrease of the overlying load. The study shows that when injecting CO2 at an annual rate of 200 000 tons for 20 years: (1) The impact on the stability of the formation is relatively small. The change in pore pressure during the injection process in the upper formation is 3.4 MPa, and the change in effective stress is relatively small compared to the in-situ stress. (2) The degree of ground uplift is relatively small. The maximum deformation is 10 mm, located at the top of the injection well, and the deformation in the coal mining area is 7 mm. (3) The range of CO2 migration is relatively small. The migration distance is 540 m, which is far from the mining area and has a relatively small impact on the coal mining area. The study shows that the rate of CO2 injection is the main factor affecting the changes in pore pressure, deformation, and the range of CO2 migration. An increase in the injection rate will increase the pore pressure, deformation, and the range of CO2 migration. The degree of coal mining is relatively small compared to the impact of CO2 injection, the range of CO2 migration is almost unaffected by coal mining, and pore pressure and deformation show a slight increasing trend with the increase in the degree of coal mining. The research findings provide a reference basis for assessing the safety risks associated with the synergistic operation of CO2 injection and coal mining.

Key words: geological CO2 storage, coal mining, finite element analysis, fluid-structure coupling, pore pressure, deformation, risk assessment