Abstract:

When the CO₂ is sealed in the unmined coal seam, the injected CO₂ will be in a supercritical state due to the influence of high temperature and high pressure, which will reduce the stability of the coal seam. In order to study the energy dissipation and failure characteristics of coal body caused by disturbance after supercritical CO₂ immersion corrosion, based on the self-developed high-pressure gas adsorption/desorption experimental system, we conducted adsorption experiments on the coal with different supercritical CO₂ immersion corrosion time (0, 2, 4, and 6 days), and impact compression tests were carried out on the coal after the action of supercritical CO₂ by using split Hopkinson pressure bar experimental system, and combined with high-speed videotape camera to film the impact process, to analyze the energy dissipation rules of the impact coal, and to elucidate the destructive cracking evolution and crushing fractal characteristics of the coal. The results show that: the stress-strain curves of coal samples after different supercritical CO₂ immersion corrosion time have similar trends under the same impact load, which can be divided into three stages: elastic energy dissipation, plastic energy dissipation, and post-peak energy dissipation. With the increased of supercritical CO₂ immersion corrosion time, the energy absorption capacity of coal samples decreased, the number of cracks on the surface of impact coal samples increased, the crack network and propagation direction became more complex, the crushing of coal samples became more intense, the crushing particle size decreased, and the crushing morphology became more complex. Finally, the linear correlation between fractal dimension and energy consumption density of coal samples after different corrosion time was determined. The results of the study have certain theoretical significance for carrying out the exploration of CO₂ injection to strengthen the deep coalbed methane extraction project.

Key words: CO₂ geological storage, supercritical CO₂, impact loading, energy dissipation, crushing fractal