Permeability and porosity are important hydraulic properties to understand fluid flow in underground. In this study, we focused on fluid flow in sediments and fault rocks, and measured gas permeability and porosity under isotropic high pressure. The samples were collected from the Quaternary deposits Uonuma Formation and Katakai fault zone in Ojiya city, Niigata. The Uonuma Formation in our study area consists of several different layers which are sand gravel, coarseto fine-sand and silt. The Katakai fault zone is composed of dark brownish gouge and deformed sand with many fractures.Gas permeability and porosity were measured using the constant pressure method and the gas expansion method, respectively. The measurements were conducted at confining pressures up to MPa. At low confining pressure, gas permeability of sand samples showed at MPa, sand samples were maximum .smaller than silt at MPa. The porosity of the fault gouge was sensitively affected by change of confining pressure and dramatically decreased with pressurization . at MPa .We also compared our data with reference data and the Kozeny-Carman equation to confirm the accuracy. As a result, porosity data approximately corresponded to reference data which were measured using drilling core from Niigata Basin. Permeability data did not conform to the value obtained from the Kozeny-Carman equation because of heterogeneity of grain size composed sample.
Abstract