The optical detection of fission tracks (FT) in dielectrics in the early 1960s was subsequently utilized in dating geological materials and events. Fission track dating (FTD) has had a rapid growth from a fact of Solid State Nuclear Track Detectors into a successful thermotectonic analytical tool in the realm of geochronology. Recent fission-track length studies have shown that thermal overprints can also be detected and dated by this technique. In this review paper the formation, factors affecting the chemical etching, a comparison of different dating procedures and the annealing behavior of fission tracks as well as the determination, meaning and error statistics of FT ages are discussed high-lighting the recent issues and trends, particularly in 1980s, of fission-track geothermochronometry. The problem of λf has led to the concept of FT age standardization. Some case histories illustrating the applications of FTD are cited.
Reinjection of hot water is carried out in most geothermal power plants in Japan. The evaluation of the reinjection is important because the reinjection affects geothermal reservoir performance during heat extraction. Many studies have been made on this subject by considering the rock mass in a geothermal reservoir as a homogeneous porous medium. In this paper, a geothermal reservoir is modeled as a finite permeable medium including large natural fractures connecting production and reinjection wells. The analysis is applied to the Takinoue geothermal area in Japan, and the evaluation of reservoir volume and the variation of production fluid temperature are discussed.
A geochemical survey of soil gases (He, H2, Rn, CO2 and its δ13C) was carried out in the North Kirishima geothermal field, Japan. As a result, three anomalous zones were identified. All three Zones (A, B and C) have a high Rn content. Furthermore, the CO2 content in Zone A and H2 content in Zone C are also high. The carbon isotopic ratios (δ13C) of CO2 are : -23 to -22‰from Zone A, -18 to -17‰ from Zone B and -16 to -11‰ from Zone C. The low δ13 C values of CO2 from Zone A suggest its organic origin probably from the 200-300 m thick lacustrine sediments underlying the area. On the other hand, the values from Zone C are higher and seem to be affected by volcanic CO2 (∼ -7 to -2‰). The significant concentrations of H2 (∼ 410 ppm) and the high δ13C values of CO2 from Zone C suggest the existence of a high temperature geothermal fluid underneath the zone. This is supported by the fact that high temperature geothermal fluid was discharged from Well KT-4 in this zone. It is inferred that soil gases in the geothermal area contain some components derived from a deeply underlying geothermal system, and can be very useful in geothermal prospecting.
An analysis on the heat transfer problem associated with a new energy extraction scheme from hydrothermal systems is presented. The proposed scheme uses ultralarge heat pipes as the energy transfer device. In the second report we intended to evaluate the rate of heat transfer to the heat pipe evapolator when it is subject to transverse flows in geothermal reservoirs. First an integral solution based on the boundary layer approximation was obtained. The validity of the integral solution was then confirmed by extensive numerical experiments. The analysis was extended further to cases where the flow direction forms an arbitrary angle with the heat pipe axis. According to the present analysis it is found that the presence of transverse flows of 0.01 mm/sec increases the rate of heat transfer five times as much as one without flows.
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