A wide geothermal field, consisting of six basins, around Mt. Waita in central Kyushu contains a large number of steaming grounds and hotsprings. Two geothermal power plants are also located in this area. Since FY 1978, a national project was started to survey deep geothermal resources in this field. As a part of the project, 81 bore holes (80m-depth) were drilled. The mean heat conductivity of the mostly andesitic cores from these bore holes is 3.90×10-3 cal sec-1 cm-1 deg-1. The distributions of subsurface temperature and heat flow observed in these bore holes indicate five anomalous areas with high heat flow. Formulae providing the standard temperature at 20m-, 50m- and 80m-depth with respect to the height above the mean sea level were developed using the temperature data obtained from 39 bore holes located in the normal-heat-flow areas. Geothermal gradient in lowland areas is larger than in the highlands around Mt. Waita. In order to discuss the geothermal condition of the field, the heat discharges from the six basins are estimated. Their total is about 143, 500 kcal sec-1, of which 5, 030 kcal sec-1 by conduction, 9, 690 kcal sec-1 by hotsprings, 27, 550 kcal sec-1 by fumaroles and the remaining 101, 200 kcal sec-1 by steaming wells including the two power plants. A half of the total water discharge (1, 980 thr-1) is attributed to hotsprings. Comparing the convective heat discharge from the field, except Kuju-Iwoyama and the two power plants, with the two nearby geothermal fields, Beppu and Yufuin, the field has 22% of the total discharge of Beppu and is about 1.7 times larger than Yufuin.
Hot Dry Rock technology requires detailed information on the dependences of the thermal properties of rocks on temperature, pressure, moisture and mineralogy up to the depth of the order of five kilometers. Thermal conductivities were measured by the needle probe method at atmospheric pressure. Temperature dependences of the thermal conductivity of 40 dried core samples from HSV-1 Well having 1000 m depth at the field test site for HDR technology in the Yakedake geothermal area, Gifu prefecture were presented in the temperature range from 30 to 500°C. The thermal conductivity of the dry core samples, λea, exhibited a θ+b, -aθ+b and cdθ< dependences on temperature, θ, macroscopically (where, a, b, c and d>0 and are constants). In situ conduction heat flows at the depths from 40 to 1000m were estimated by the above thermal conductivity data and the temperature logging data. The estimated results offered useful informations on the fracture zones of the HSV-1 Well.
This paper describes effects of permeability distribution on flow and heat transfer in a geothermal reservoir. In order to evaluate the effects generally, a low permeability layer is assumed to be placed in the reservoir model. The theoretical results are as follows; 1) When thermal convective flow exists in a geothermal reservoir, the permeability distribution takes effect on flow pattern. In result, it has influence on the change of average temperature with time at the outlet. 2) If the permeability distribution takes no effect on the pressure at the inlet, the heterogeneity should be considered. 3) If the permeability distribution takes effect on the pressure at the inlet, the reservoir can be treated as a homigeneous model.
The Shizukuishi No. 2 tunnel is a hot tunnel penetrating through a shallow hot dry rock. In the tunnel, after completion, construction of a pipeline is scheduled to transport geothermal water produced from wells in the Kakkonda Geothermal Power Plant to the heat-exchanger-site for a demonstration project on direct use of geothermal energy. On 20 and 21 April 1983, just after the hot tunnel of a total length of 940 m has been dug through, temperatures and heat flow on the wall surface of the tunnel, some thermal properties of the rock samples, the temperature profiles in slender, short pitholes drilled in the rock matrix, the dry- and wet-bulb air temperatures and wind speed in the tunnel and the mass and temperature of the discharged water from the tunnel were measured in all-round. Based upon the results summarized in several figures and tables, heat budget is computed on the fluid passing through the tunnel. The heat losses by air and water are 38.6 and 45.5 kcal sec-1, respectively. The total heat loss of 84.1 kcal sec-1 is compared with heat-exchange between fluid and rock matrix. Finally, heat transfer coefficient or Newtonian cooling factor determined from the measurement is discussed by means of Taylor-Prandtl analogy on turbulent-forced convection.
Self potential surveys were carried out in the Kakkonda geothermal area, Shizukuishi-cho, Iwate prefecture, from 1979 to 1981. The effects of artificial structures and activity of fumaroles on the self potential were investigated and the extent of geothermal reservoir was discussed by the results of self-potential method and the other geophysical prospecting data. The following results are obtained.(1) The self-potential profiles were obtained three times along a traverse in the area. Despite the almost one year gap in the time of data collection, the profiles are sufficiently similar to demonstrate that the self-potential data obtained by the proper field procedure are reproducible.(2) Self-potential anomalies ranging in amplitude from 100mV to 400mV were observed arround the ferroconcrete structures. This implies that data correction is needed if the self-potential survey is conducted near artificial structures.(3) There are no significant anomalies associated with the activities of fumaroles and hot spring in the area investigated.(4) The area of negative anomalies at the northern part of Takinoue tunnel and at the northeastern part of Kakkonda river, coincide roughly with the areas of low resistivity, high temperature and high radiometry. This result may give us an index to determine the extent of geothermal reservoir.
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