| Co-Investigator(Kenkyū-buntansha) |
HAYASHI Kazuo Tohoku University, 高速力学研究所, 助教授 (30111256)
NIITSUMA Hiroaki Tohoku University, 工学部, 助教授 (90108473)
SEKINE Hideki Tohoku University, 工学部, 教授 (20005359)
NAKATSUKA Katsuto Tohoku University, 工学部, 教授 (60005345)
TAKAHASHI Hideaki Tohoku University, 工学部, 教授 (10005267)
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| Research Abstract |
The purpose of the project is for the development of the design methodology of artificial subsurface cracks for the extraction of geothermal energy from hot dry rocks. The basis of the approach is rock fracture mechanics. The project has three research areas; [T] evaluation of rock mechanical properties, [M] monitoring and mapping of subsurface cracks and [S] simulation of subsurface cracks. It consists of three phases, i.e., Phase I, II and III. In Phase I, the validation of rock fracture mechanics was made through hydraulic fracturings of rock cubic specimens with a variety of sizes from 0.5 m up to 10 m. In Phase II, a model field was set up at Higashihachimantai. A large subsurface crack was created by massive hydraulic fracturings nearly 350 m below the ground surface and two wells were successfully connected through the artificial crack. This subsurface circulation system is the first system in the world constructed as designed. In Phase III, effects of geothermal subsurface conditions, such as temperature and confining pressure, on rock fracture were investigated, including mechanochemical interactions berween water and rocks. Through these three phases, the design methodology for creating subsurface reservoir cracks was finally established. The main results of each research area can be listed as in the following. [T]: The process and the mechanism of crack growth in rocks and the size effect of rock fracture were clarified and new methods were developed for fracture toughness tests of rocks. [M]: Hardware and software of downhole AE measurement systems were developed. New methodologies utilizing the systems for monitoring of subsurface cracks were established. [S]: Simulators were developed for analyzing the crack behavior under a variety of geothermal subsurface conditions and an in-situ tectonic stress measurement method was successfully established for three-dimensional stress fields.
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