Development of a new high-temperature hydrothermal gas apparatus for studying deformation, fluid-flow and grain-boundary diffusion

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Deformation of rocks, and fluid flow and material transport via pore fluid in rocks at temperatures and pressures are significant in many problems such as understanding the mechanisms of earthquakes and their prediction, fluid circulation in the Earth, and Earth's environmental problems that are important both scientifically and socially. High-quality deformation and fluid-flow gas apparatus is needed for such studies, but gas apparatuses have not been developed in Japan. Thus the main task of the present research has been to design and make a conventional gas apparatus for studying deformation and fluid flow at temperatures to 1,000 degrees Centigrade and at pressures to 200 Mpa. Also, it has been important to establish an industrial foundation for producing and refining gas apparatuses domestically in the future. Although the maximum pressure was limited to 220 Mpa because of the government regulation on high-pressure gas, a high-temperature and high-pressure gas apparatus was develo … More ped successfully in the three-year period of this research. This apparatus cannot produce as high confining pressure (about 500 Mpa) as gas apparatuses used in other countries, but it is equipped with better servo-controlled actuators for the axial load and pore pressure than foreign apparatuses. Thus, the present apparatus is capable of measuring a very wide range of permeability using various methods such as the pore-pressure oscillation method and the pulse-decay technique. The apparatus will open ways for studying material properties under highly corrosive environments like supercritical water and has many industrial applications.The apparatus has been used to study permeability structures of fault zones of Nojima fault, Median Tectonic Line, Yanagase fault, a nappe-boundary fault in Chugoku district, and Kan-nawa fault at effective pressures to 180 Mpa and at room temperatures, using NィイD22ィエD2 gas as the pore fluid. The results have revealed large effects of effective-pressure cycling and quite variable permeability structures depending on the tectonic setting and the type of country rocks of faults. The work will be extended to fault constitutive properties and to more permeability measurements at temperatures and pressures. Less