Laboratory measurements on coal matrix swelling were carried out during CO_2 injection, by monitoring strain and P-wave velocity changes. Coal samples were drilled from the large blocks collected from Kushiro Coal Mine, Northeast Hokkaido. Fractured and intact cylindrical samples were used respectively, to investigate swelling behaviors and its impact on coal permeability. Swelling strains are much larger due to the CO_2 adsorption than the N_2 adsorption in the same sample. Results of the intact coal sample show that the permeability decreased by about 50% associated with CO_2 adsorption. Both P-wave velocity and amplitude increased significantly due to the coal matrix swelling. Our results suggest that coal matrix swelling caused the cleat closure and the cleat closure reduced the coal permeability.
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