1590 (b) Figure 3 – Results of the injection test; (a) pressure and temperature variations, (b) injection pressure and injection rate Table 1 – Evaluation of permeability Injection pressure Injection rate Permeability (MPa) (m3/s) (cm/s) 0.1 4.08×10-4 2.53×10-4 0.2 5.65×10-4 1.75×10-4 0.3 6.01×10-4 1.24×10-4 0.4 6.55×10-4 1.02×10-4 0.5 6.43×10-4 7.98×10-5 0.6 8.56×10-4 8.86×10-5 0.7 1.09×10-3 9.71×10-5 0.8 1.26×10-3 9.74×10-5 0.9 1.50×10-3 1.03×10-4 1.0 1.68×10-3 1.04×10-4 1.2 1.79×10-3 9.24×10-5 3. FIELD INJECTION TRIAL In this study, injection trials were conducted in the goaf with the aim of CO₂ injection and mineralization, using CO₂ MNB water and BFS slurry. Furthermore, to evaluate the effectiveness of the reactions of the injected BFS slurry, the permeability of the goaf was assessed through post-injection injection tests, and the solidified slurry recovered two years after the injection trials was analyzed. 3.1 Injection trials with CO₂ MNB water and BFS slurry The injection trials were conducted using the equipment configuration illustrated schematically in Figure 4. CO₂ MNB water was prepared by installing a fine-bubble generator (TH-10; Taisei Kogyo Co., Ltd.) in a 3 m³ water tank and circulating the water in the tank for more than 3 hours. The CO₂ supply rate was 45 L/min. BFS slurry was prepared by adjusting the mixture ratio of water, BFS, and admixtures to a W/B ratio of 1.0–2.0 prior to injection. The overall injection volumes for the experiments are summarized in Table 2. In total, 84 m³ of water, 23 m³ of CO₂ MNB water, and 78 m³ of BFS slurry were injected, confirming that the injectability into the goaf was adequate.
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