1591 Figure 4 – Experiment facilities of field injection trial 3.2 Change in permeability of the goaf BFS slurry injected into the goaf was expected to reduce permeability by blocking fractures through solidification in the subsurface. To evaluate the post-injection permeability of the goaf, injection tests were conducted immediately after the injection trials with CO₂ MNB water and BFS slurry, and again two months later. The results of the injection tests are shown in Figures 5(a) and (b). As shown in Figure 5(a), prior to the experiments, the injection flow rate under an injection pressure of 1.0 MPa was approximately 100 L/min. Immediately after the experiments, the flow rate decreased to 24 L/min, and two months after the experiments, it further decreased to 12 L/min. The permeability coefficient calculated under the 1.0 MPa injection pressure condition indicated that the permeability of the goaf had decreased after the experiments as shown in Figure 5(b). This reduction is attributed to the blockage of fractures caused by the solidification of the BFS slurry. These results suggest that the solidification reactions of the injected BFS slurry progressed over time, decreasing the permeability of the goaf. Accordingly, this also indicates the possibility that CO₂ was mineralized in the goaf through solidification reactions with the injected CO₂ MNB water and BFS slurry.
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