The mise-à-la-masse survey has been used mostly for the ore prospecting in the mining industry. In 1984, the mise-à-la-masse survey was carried out using a casing pipe of HT-8 well in Hatchobaru geothermal area in order to map geothermal reservoirs. The measurement gave rise to the sharply contoured residual anomalies due to high contrasts of resistivities among the geothermal fluid, hydrothermaly altered zones and surrounding formations. The residual maps derived from the data processing clearly indicated several promissing low resistivity zones including the present production zone where the almost all of productive wells located inside. It was confirmed that the strike of faults which regulated the upstream of the geothermal fluid and lateral distribution of geothermal reservoirs showed a good correlation with those determined by the Schlumberger resistivity and magnetotelluric surveys in this area.
Deep wells, having about 1, 000 m depth, were drilled at Takarazuka City, Ichinomiya-Cho, and Yabu-Cho, Hyogo-Prefecture, Omachi City, Nagano Prefecture and around Tango Peninsula, Kyoto Prefecture. Terrestrial heat flow determined at Takarazuka and Yabu is less than 2.0 HFU (84 mW/m2), that around Tango Peninsula and Ichinomiya more than 2.0 HFU, and that at Omachi more than 2.7 HFU (113 mW/m2). From these results, it is concluded as follows: (i) the heat flow of the northern part of Kinki District is higher than that of the southern part. This has already been pointed out by Uyeda and Horai (1964), and (ii) the heat flow determined at the western part of Omachi City, of which rock body is Ariake granitic body, is more than 2.7 HFU. Nishimura and Mogi (1986) showed that the thermal origin of the Kurobe hot dry rocks was the residual heat of the granitic body and the seismic wave was attenuated in this region (Fukao and Yamaoka, 1983). These facts indicate that the temperature of this granitic body is high and has residual heat in the central part of this body.
In March and April 1984, West Japan Engineering Consultants (WJEC) was contracted by Kyushu Electric Power Company (KEPCO) to conduct field survey for a proposed mise-à-la-masse method. The survey was carried out using an exploratory well HT-8 located in the vicinity of the present production area of the Hatchobaru geothermal field in north central Kyushu, Japan. The apparent resistivity and potential maps derived from the data processing clearly indicated several promising zones of low resistivity including the present production zones where the almost all of productive wells located inside and indicated two-dimensional structure across the strike of the Komatsuike sub-fault. Two-dimensional mise-à-la-masse modeling of surface potential and apparent resistivity profiles has been developed over various bodies for multiple electrode configurations. The surface responses are obtained by the finite difference method for a horizontal body with the contrast in conductivity between the body and subsurface is 10:1, but different locations of a line sources of current electrode. A two-dimensional model has been derived to simulate results as close to observed field data across the present production zone as possible. The similarities between the observed data and the best fitted model are striking, in particular of the data for the surface potential distribution.
The impermeable basement inferred from gravity anomaly affects hydrothermal convection system. Several convenction models are numerically computed incorporating simplified basement structures. It is shown that the four factors of localized heat source, basement relief, topography, and permeability of overburden, control hydrothermal system, and determine temperature distribution. The same numerical method is applied to simulate temperature profiles of the three geothermal wells at the Hohi geothermal area, central Kyushu. These wells are located on an elongated topography and basement relief, and two dimensional modeling can be applied to them. Good matchings are achieved for these models. It is concluded that the basement relief derived from gravity anomaly is accurate enough to be used in constructing regional hydrothermal models, and can be used in assessing geothermal potential.
In designing a geothermal hot water supply system, we have to consider how to correct the unbalance between hot water demand and supply. This unbalance is caused by various random and/or cyclic demand variations. There are two methods to correct this unbalance. One is the control of supply and another is the installation of a buffer tank. The former is used to correct the large and long-term unbalance, and the latter is used to correct the small and short-term unbalance during a period when total demand is nearly balanced with total supply. In this paper we consider a basic system with one demand area and three systems with two demand areas; which have different types of buffer tanks, and present the mathematical models of the system behaviors. The systems are as follows:System I: one supply, one demand and one buffer tank, System II: one supply, two demands and two independent buffer tanks, System III: one supply, two demands and one co-used buffer tank, System IV: one supply, two demands, one co-used buffer tank and two independent buffer tanks.Furthermore, we analyze the effect of buffer capacity on the shortage of hot water supply by a simulation method under the condition that supply is constant and demand has random and/or cyclic variations, and compare System II, III and IV. From the simulation analysis, we have reached the following conclusions, where the random variation is given by the normal distribution with the standard deviation σh and the mean of shortage of hot water supply per day is denoted by UD/d:(1) For random variations in System I the decrease of UD/d per unit buffer capacity is large when buffer capacity is small, but it becomes smaller as buffer cap acity increases. When (buffer capacity)/σh is constant, UD/d/σh is constant.(2) For random variations System III is more economical and effective than System II. Especially whenthe co-used buffer capacity M is large, UD/d/(the number of demand areas) is close to the value which isobtained by installing independent buffer capacity M in each demand area (System II).(3) When buffer tanks are installed in some places, UD/d decreases if it is possible that the surplus hot waterin one area is diverted to another area where the hot water supply is insufficient . When total buffer capacityin System IV is constant and large, the distribution method of buffer capacity has little effect on UD/d .
Recently, geothermal resources or hot springs have been developed in granitic bodies at some areas. A wide alteration zone occurred in these areas. To make clear the thermal history of the body, it is important to examine how the alteration effects on thermal properties of the rock. In order to investigate a thermal conductivity variation with the alteration of granitic rocks, we carried out mode mineral analyses and thermal conductivity measurements for 16 rock samples. These samples consisted of 8 samples collected from outcrops on the middle reaches of the Kurobe River in the Northern Japan Alps, and 8 samples from borehole cores at the Western part of Omachi City near the Northern Japan Alps, and at Kumihama in Kyoto Prefecture. 10 samples include alteration minerals such as Chlorite, Sericite, Calcite and some other clay minerals. Bulk density was measured for all samples, but thermal conductivity did not depend on density. The Hashin-Strickman's Formula was adoped on the calculation for thermal conductivity of rocks using that of rock-forming minerals to describe the relation between thermal conductivity of rocks and mode of minerals. These results showed that the Quartz content dominates thermal conductivity of granitic rocks, because Quartz has very high thermal conductivity. And also showed that as contents of alteration minerals, such as Chlorite and Calcite, altered from Feldspar and Mica increased, thermal conductivity of the rock increased, because the thermal conductivity of Chlorite and Calcite are higher than that of Feldspar and Mica.
It is possible to apply the stereography with optical angles from 6.5°to 8.5°to the area where was taken pictures of a couple of neighboring LANDSAT MSS imageries. In Japan, the stereographic coverage of LANDSAT 2-3 is 65 % on the northern part and 45% on the southern part, while that of LANDSAT 4-5 is 45 % and 30%, respectively. The other areas can be also viewed stereographically by a pair of LANDSAT 2-3 and LANDSAT 4-5 MSS imageries. In this case, optical angles vary from 0.8°to 5.6°in accordance with a mode of covering. The stereography of LANDSAT scenes has been applied to the stratigraphic analysis of Kirishima volcanoes, where the exploration for geothermal resources is being carried out actively. The result indicates that the stereography of LANDSAT MSS imageries is very useful to understand the surface geology, which is important, though not main, for the exploration.
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