The extraction of geothermal energy from hot dry rocks is received by circulating fluid through fractures, as reservoirs, created by a hydraulic fracturing technique. In the design of reservoirs, fracture behavior study is needed to simulate the fluid behavior in circulation system under in-situ stress condition. Experimental and numerical approach of this paper are concerned with the circulation volume, the fracture aperture distribution and the fluid velocity distribution. Some laboratory and field experiments were conducted under various flow rate and stress condition. The variation of the inlet pressure under steady flow state was measured against the inlet flow rate. By the comparison of the flow rate on laboratory experiment and numerical calculation, the fracture under stress condition was obtained to keep some aperture, numerically about 0.5 mm in Inada granite (Fig. 16 and 17). Simulations of fluid behavior by coupled stress and flow analysis were carried out for 4 types of typical circulation models. The fluid velocity distribution and the fracture aperture distribution were obtained for each model type. By the comparison of coupled stress-flow analysis and only flow analysis for rigid fracture, the fluid behavior in circulation model was recognized to be influenced by the fracture aperture distribution under in-situ stress condition (Fig. 24 and 25).
Comparison of mineral ages in some granitic bodies obtained by the K-Ar, Rb-Sr and fissiontrack methods with closure temperature estimates for the various isotopic systems has allowed thermal histories of several samples to be resolved. The discordant radiometric ages are obtained from the central parts of Rokko Nunobiki and Mikumo plutons, Tanakami stock and Kumano acidic rock body. These granitic plutons and stock have begun to cool slowly compared with Kumano acidic body. The granite porphyry facies of Kumano acidic body is cooled more rapidly than the other granitic bodies, but this body has begun to cool slowly at first as uplift and then progressively quicker as the surface is approached. Intrusion of the Kurobe granitic pluton 50 Ma ago caused the age of marginal facies (Nozawa, 1975). K-Ar ages for Kurobe granitic pluton were determined to resolve the cooling history of this pluton. Comparison of K-Ar ages with elevations of sampling sites for the cooling history has made the conclusion that the high temperatures in the tunnel near Sennin Dam along Kurobe River are caused by residual heat from the granitic body to be reached.
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