| Abstract |
Our research group is conducting a new scientific program on Science and Technology for Frontier of Geothermal Energy. Deep-seated and high temperature geothermal reservoirs are a dream-inspiring target as an advanced EGS, and future geothermal reservoirs are under supercritical and superheated conditions in and around ductile rock bodies. The ductile regime which is estimated to exist beyond the brittle zone is the target region for future geothermal development due to high enthalpy fluids and relatively weak water-rock interaction. It is very difficult to determine the strict depth of the Brittle-Ductile boundary due to strong dependence of temperature (geotherm) and strain rate, however, the ductile zone is considered to be developed above 400ºC and below 3 km around active volcanic fronts in Tohoku District, Japan. Additionally, caldera structures which formed in Plio-Pleistocene are also candidates for deep-seated geothermal reservoirs. In this case, the depth of the reservoir will be greater than 3 km, and geofluids whose origin is considered to be slab melting fluids will be reserved. Hydrothermal experiments associated with additional advanced technology are being conducting to understand the ‘Beyond Brittle World’ and to develop deeper and hotter geothermal reservoirs. We are expecting the following advantages: (a) simpler design and control of the reservoir, (b) full heat mining and/or injected water, (c) sustainable production, (d) cost reduction by development of the relatively shallower ductile zone in compression tectonic zones, (e) large quantity of energy extraction from widely distributed ductile zones, (f) establishment of universal and conceptual design/development methodology, and (g) suppression of felt earthquakes from/around the reservoirs. In the ductile regime, a mesh-like fracture cloud has great potential for heat extraction between injection and production wells in comparison with a single and simple mega-fracture. Based on field observation and high performance hydrothermal experiments, our research goals are: 1) Analysis and understanding of geothermal structure and geofluids in ductile condition of the Japanese Island arc, 2) Fundamental technologies of drilling under ductile region for geothermal reservoir, 3) Development of geothermal reservoir simulator for two-phase and multiphase flow including supercritical state through rock fracture, 4) Lab scale support for ICDP-JBBP (International Continental Drilling Project, Japan Beyond Brittle Project), 5) Application of new EGS technologies to conventional geothermal fields as recovery from the 2011 Great East Japan Earthquake and energy crisis in Japan. |