Permeability evolution in fine-grained Aji granite during triaxial compression experiments

Triaxial compression experiments were carried out on samples of fine-grained Aji granite to measure the evolution of permeability during deformation prior to failure under confining pressures of 20 and 40 MPa. During the initial stages of deformation, a small decrease in permeability was observed, due to the closure of pre-existing microcracks; permeability then increased with increasing differential stress. During deformation, permeability varied by up to two orders of magnitude, and we observed a small pressure dependence, with a larger variation observed at 20 MPa than at 40 MPa. This suggests that more cracks developed during brittle deformation under the lower confining pressure. The observed increase in permeability during our experiments was approximately proportional to inelastic volumetric strain, which corresponded to the volume of dilatant cracks. On the other hand, prior to brittle failure, we observed a further increase in permeability that was greater than the inelastic volumetric strain, suggesting crack aperture opening accelerated at this stress level (>& SIM;80%). The permeability enhancement resulting from the crack dilation affects the gas-sealing capacity of the fluid-saturated caprock. Our experimental findings would be beneficial for the safety assessment in applications such as the long-term storage of various gaseous wastes.

Automated summary

Triaxial compression experiments were conducted on fine-grained Aji granite samples to study the evolution of permeability during deformation before failure under confining pressures of 20 and 40 MPa. The permeability initially decreased slightly due to the closure of existing microcracks during deformation, but then increased with increasing differential stress. The permeability varied significantly during deformation and showed a pressure dependence, with a larger variation observed at 20 MPa compared to 40 MPa. These findings have important implications for applications such as long-term storage of gaseous wastes, as the permeability enhancement resulting from crack dilation affects the gas-sealing capacity of the fluid-saturated caprock.