RELATIONSHIP BETWEEN PERMEABILITY CHANGE AND NORMAL STRESS IN LARGE DISPLACEMENT SHEAR ZONE OF SAND

Permeability of sediments is important factors for production of natural gas from Methane-hydrate-bearing layers. There are many small faults near the seafloor observed in the horizontal compressive stress fields due to plate subduction around the forearc basin in the Nankai Trough, where methane-hydrate-bearing sediment is distributed in the seafloor. For a rational evaluation of permeability in the production field, it is important to understand properties of fault zone being a different condition from other layers due to large displacement shear. We investigate the permeability of a specimen experimental fault by ring-shear test under normal stresses of 0.5, 1.0 and 8.0 MPa. The grain size distribution in the shear zone of specimen after shearing at each normal stress level is analyzed by laser scattering type particle analyzer. In the relationship between permeability and porosity, the permeability reduction with decreasing porosity is relatively noted at the normal stress of 8.0 MPa, compared to the relationships at 0.5 and 1.0 MPa. The grain size reduction in shear zone of specimen due to grain breakage during large displacement shearing is clearly recognized at the normal stress of 8.0 MPa. In contrast, the grain breakages are not found at 0.5 MPa. This study is financially supported by METI and Research Consortium for Methane Hydrate Resources in Japan (the MH21 Research Consortium).