Two-dimensional numerical calculations are reported for steady state natural convection of a fluid in a horizontal porous layer with a permeable upper surface and with an impermeable lower surface. Numerical results are obtained for temperature and stream-function in the porous layer characterized by two heating conditions; one is with a constant temperature lower surface and the other with a constant heat flux lower surface locally. Relations among the pattern of convective flow in the porous layer, the aspect ratio of the heat source, and the discharges of the fluid and heat from the upper surface are discussed.

View full abstract

Geothermal steam contains a considerable amount of noncondensable gases. Consequently, the efficiency of the gas extracting system has a great influence on plant auxiliary power requirements and thereby the plant efficiency. We have developed and tested the new gas extraction system so called the E. R. R. system which consists of a steam ejector and a two stage radial blower. The steam ejector, having high efficiency at high vacuum pressures, and the radial blower, having high efficiency at low vacuum pressures, are combined to greatly increase overall efficiency. The steam ejectors in this system are driven by steam already used once in the turbine driving radial blower, so that steam consumption in this system decreases to about one hal f of that required for the system using only double-stage ejectors system. The characteristics of ejector driven by the low pressure steam were also analyzed in this test.

View full abstract

Various methods to describe quantitatively the cores and the cuttings from geothermal wells are proposed as summarized below. (1) Location of a well should be shown by the latitude, the longitude and altitude together with its place name. (2) Color of samples can be expressed by the Rock-Color Chart published by the Geological Society of America. (3) Hardness of cores is classified into the following five steps ; very soft below 1 kg/cm², soft 1-10kg/cm², medium hard 10-100kg/cm², hard 100-500kg/cm², and very hard above 500kg/cm² in uniaxial compression strength. (4) Crack Index proposed here is shown by the following equation.where d is the crack density coefficient (For every 10 cm interval crack, d is 10.), ΣLcr is the total length of crack zones, and Lob is the length of core observed. (5) The results of modal analysis of the representative rocks from a formation should be shown by the statistical method, that is, the mean value and the standard deviation of each constituent mineral. (6) The “alteration ratio” is classified into the five stages ; wholly altered, mostly altered, half-altered, partially altered, and unaltered. (7) The “alteration degree” is classified into five essential types (I-V) by the crystal chemical characteristics of alteration minerals, Type I Silica mineral type, Type II Hexagonal sulfate type, Type III Aluminum silicate type, Type N Sheet aluminosilicate type, Type V Framework silicate type, in addition to two subordinate types (VI and VII), Type VI Partially altered type, and Type VII Unaltered type. (8) The results of X-ray diffraction of altered rocks are shown by the Quartz Index (QI) as follows;where Im is the strongest X-ray intensity of a mineral in the examined sample and Iq is that of pure quartz. (9) The mass color of zircon in volcanic rocks changes with its formation age, and the representative colors by the Mansell Color System are shown in Table 3. (10) The homogenization temperature of liquid inclusions in alteration minerals is very useful for the temperature estimation of geothermal fluid and also for the understanding of the thermal history of a geothermal system.

View full abstract

The distribution and chemical compositions of the volcanic gases in Kusatsu-Shirane volcano district have been investigated since 1967. The volcanic gases in this district can be classified into fumarolic gases, hot and cold spring gases and “low temperature” fumarolic gases. The temperatures of most fumarolic gases lie in a range of 94-99°C. These gases contain H₂S, CO₂ and R gas (mainly N₂) as main components besides water vapor. In some cases SO₂ and HCl are detected as minor components. Those gases show the local characteristics and the chemical compositions of each gas lie in a certain range. The volcanic gases evolving from several places of the bottom of the crater lake Yugama were collected on the surface and analysed. There is a certain relationship between the chemical compositors of these collected gases and the depths of the gas-evolving sites and these facts may be explained by the differences of the solubility of each component into the lake water. The chemical variations of the hot spring gases can be explained also by considering the contacts of the ascending fumarolic gases and the subsurface water flow. The very high content of H₂S in the volcanic gases of Manza area are noteworthy and we should consider some secondary reasons. Starting from several initial chemical compositions of fumarolic gases we tried some calculations on the differentiations of these gases based on the differences of the solubility of each component and found fairly good agreement with the actually observed tendencies. Finally we offered the reason of the existence of the “low temperature” fumarolic gases.

View full abstract