In order to discuss the interferences between an existing geothermal reservoir and reservoir to be developed, reservoir evaluations for a complex model were carried out, changing some of the parameters of the reservoir and the aquifer, and the conditions of production and reinjection. From the results, it is fairly clear that the interference increases as the flow rate of production increases and the reservoir porosity decreases. Larger coefficients of permeability of the aquifers and shorter aquifers seem to increase the interference during the early production stages. However, under the same conditions, the interference is reduced in the later stages of production.

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Four hot spring areas, located at Ban Nam Ron, Ban Pu Toei, Ban Pu Kham and Ban Wang Kham, are to be found in Phetchabun province, approximately 350km northeast of Bangkok, Thailand. The surface temperatures range from 35 to 47°C; the discharges are generally small. Systematic studies were carried out to select for further exploration drilling the geothermal energy system showing the highest potential. These studies included geologic, geophysic (resistivity) and geochemical work. The geological work included field mapping, petrographic studies and fracture analysis, as well as the compilation of a 1:15, 000 geologic map and cross-section. Schlumberger profiling and depth sounding resistivity surveys, covering a distance of 105km, were carried out and the results are shown in isoresistivity contour maps. Water samples, in the form of both groundwater and hot spring water, were collected and analysed. The Phetchabun geothermal system is principally a fracture-controlled system and is classified as a low-enthalpy system with subsurface temperatures of around 120°C. The potential uses are therefore restriced to direct uses. The Pu Kham hot spring, the most easily accessible, densely populated, and with agricultural products easy available, is considered to be the most viable for exploration drilling to a proposed maximum depth of 100m. The proposed exploration well should encounter hot water upflowing along fracture zones at a depth of not more than 100m. The potential uses will depend on the temperature and quantity of the hot water flow (discharge). This work is part of a contracted research project supported by a grant from the National Energy Administration (NEA) of Thailand.

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The performance characteristics of a small-size screw expander for the energy conversion of hot spring water are described in this report. Recently, the screw expander has been recognized as an effective machine for low temperature energy conversion, i.e. hot spring water. Usually in the low temperature energy conversion cycle, organic working mediums such as NH₃ or fron are used. With the organic working mediums, the performance tests of screw expander under the same conditions of a practical conversion cycle are very difficult. On the other hand, usually small-size screw expanders may be produced by adapting the massproduced screw compressors. We therefore made compression tests with air using small-size screw expanders. For a small-size screw expander, the compression tests with air are rather easy than the expansion tests with air or organic working mediums. If the performance of the expansion with organic working mediums could be estimated by the compression tests with air, it might be an effective technique for the design of the low temperature energy conversion cycle using the small-size screw expander. In this paper, we report the experimental results of the compression tests with air, of the expansion tests with air or RI 1, and comprise the results. The principal specifications of the two testing screw expanders are the built-in volume ratios are 2.0 and 2.4, and the exit displacement, 0.816m³/1000 rev., which is the same for both expanders.

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Kuju-iwoyama, the most active fumarolic area in central Kyushu, Japan is situated in an explosive crater of Kuju Volcano. The natural heat discharge is estimated as about 100 MW and most of it (more than 95%) are from steaming grounds and fumaroles. The temperature of the fumaroles exceeds 200°C and the maximum temperature is 480°C. A temporary seismic observation system was installed around the fumarolic area in order to investigate the relation between seismic activity and the thermal process beneath it. As a result, high microearthquake activities were detected just beneath the fumarolic area down to about 1.5 km below the surface. Lower P wave velocity and lower Poisson's ratio were also obtained just beneath the fumarolic area. The origin of such high microearthquake activity just beneath the fumarolic area is considered to be high pore fluid pressure in the two-phase reservoir. Microseismic observation is a useful technique to delineate geothermal reservoirs with high reservoir pressure.

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After the first report (Nishimura et al., 1986), deep wells, having about 1000m depth, were drilled at Kami-Cho, Tojyo-Cho, Mikata-Cho, Hidaka-Cho, Toyooka City (Hyogo Pref.), Nodagawa-Cho, Amino-Cho (Kyoto Pref.) and Otsu City (Shiga Pref.) and their terrestrial heat flows are determined as 60, 56, 163, 82, 79, 79, 105 and 62 (mW/m²), respectively.

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We carried out a gamma-ray spectra survey to discuss the relation between geothermal manifestations and gamma-ray intensities for three radioactive elements, ¹⁰K, ²¹⁴Bi and ²⁰⁸Tl, in the Komatsu geothermal area, near Hatchoubaru geothermal power station in Oita prefecture, where a typical hydrothermal fractured type reservoir was developed. A data analysis method, based on Covell (1959) method, including the error estimation of observed data was used in this study Using detection limits of gamma-ray from each element, based on Currie (1966) method, was also proposed in this data processing. The results of field survey showed high gamma-ray intensity areas for Bi well correspond to high lm-depth temperature areas. This means that ²²²Ra, the parent element of Bi, comes up to the surface together with circulating thermal water. High intensity areas for Tl correspond to the locations of fumaroles distributed around high lm-depth temperature areas. This fact is interpreted that Tl is accumulated in places where the thermal water comes up to the surface rapidly, because ²²²Rn, the parent element of Tl, has a very short half-life. We can conclude the high gamma-ray intensities of Bi and Tl to be potential indicators for the existence of upflows of thermal water.

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