This paper presents a quasi-three-dimensional simulation study to show some fluid behaviours under production and reinjection. The developed simulator is applied to simplified geothermal systems in the single phase zone and in the two phase zone. Compared with the calculated result of three dimensional calculation, itis confirmed that results from both models demonstrate similar behavior for the reservoir.
Since 1966 a geothermal-snow-melting-system for roads has been operated at Jozankei Spa, Sapporo, Japan, to cover 1, 628 m (11, 880m2) as of May of 1982. The snow melting system consists of polybuthene pipes embedded in pavement. The inlet and outlet temperatures of geothermal water which is forced by pumps to circulatethrough the piping system are about 80°C and 30°C, respectively. A couple of years ago, shallow and narrow crackings were found over several parts of the road surface below which polybuthene pipes were buried. Although the polybuthene pipes of relatively low heat-resistivity were embedded in low temperature aggregates or the dense grade asphalt concrete, enfeeblement of the pipes are expected. Also, for advancing the heating effect on road surface the depth ofthose pipes were shallowed to 5cm. To avoid the danger of destruction the embedded pipes under those conditions, conventional macadam rollers (10 to 12 ton) and tirerollers (8 to 15 ton) were not used but 5-ton-vibrating rollers. Then the cause of cracking may be considered lack of compaction. Some laboratory experiments were carried out to determine the preferable structure of pavement and to examine strength of pavement for vehicles travelling in order to prevent occurrence of the crackings.
In order to get more correct informations from the data obtained by electrical methods such as surface electrical survey, well logging or other applications ingeothermal fields, it is desired to know the relationship between the electricalresistivity of rocks and temperature under the condition of water saturation. Inthis paper, the results of laboratory measurements conducted on tipical igneous rocks, sedimentary rocks and altered rocks are described together with those about rocks cored from a geothermal well. The rock samples with rod shape were cut out from original rocks and saturated with water, and then set in a teflon cylindrical electrode cell which was designed so that the electrical leakage between electrodes of sample ends might not occur along outer solution. A teflon vessel was used as a container of the electrode cell, and was put into an autoclave equipped with outer lead terminals. The electrical resistance of rock samples was measured under water saturated condition (vapour free) as a function of temperature by Kohlrausch bridge method in the range of temperature from 10°C to 180°C. The dependency of electrical resistivity on temperature was approximately similar to that of aqueous solution, when the logarithm of the resistivity was plotted versus a reciprocal of Kelvin temperature. Thus the temperature dependency of electrical resistivity of water saturated rocks is understood by introducing Stokes' formula for ionic conduction of aqueous solution, Andrade's formula for temperature dependency of ionic mobility (viscosity) and Archie's formula expressing rock resistivity in terms of pore fluid. According to the results mentioned above, the resistivity formation factors of rocks and chemical characteristics of underground water in geothermal fields arevery important for predicting subsurface temperature profile from electrical methods, and since the ionic concentration of pore fluid strongly depends on the kind of rock minerals, an accumulation of statistical data of resistivity formation factor for rocks in geothermal field is desired for further development of underground iexploration.
Mineralogical and isotopic studies have been made on rocks and minerals from the exploratory drillhole 54-NK-1 (Depth: 700m) in the Nakao geothermal area, Gifu, Japan. The rocks, mainly composed of welded tuff, have been afftected to varying degrees by hydrothermal alteration. Sericite and chlorite are common in the altered rocks. Kaolinite and calcite also occur as hydrothermal alteration products. The δD values for kaolinites indicate that the hydrothermal water involved was derived from the local meteoric water. Assuming that calcites are in equilibrium with the water at present-day temperatures (up to 200°C), the δ18O values for calcites indicate that the water has undergone oxygen isotopic exchange with surrounding rocks, resulting in an 18O-enrichment of about 2 permil at a depth of 550-700m. This is interpreted to mean that a greater reservoir of hot water may exist at depth, and that the minimum water-rock weight ratio is about 2:1in the reservoir.
Hydraulic fracturing experiments of the Hot Dry Rock have been conducted at a site near Yakedake volcano (active volcano), central Japan, as one of the Sunshine project-New energy project by the Japanese Government since 1979. Making use of this opportunity, we made seismic and geomagnetic observations on the ground surface near the injection wells from 1980 to 1982. The following results were obtained: 1) Any change of microseismic activity around the test site was not detected from the daily frequency of the observed near microearthquakes. 2) Only a few seismic signals, which were presumably occurred beneath the test site, were detected during the injection of water. 3) The seismic waves passing through the newly formed fractured zone attenuate much more than those passing through the other paths. This shows a possibility to detect the newly formed fractured zone by the observation of seismic wave attenuation. 4) Q values of rock samples obtained from beneath the site were measured in the laboratory by the pulse transmission technique. As a result, the relation between Q value and porosity was obtained. 5) Any special geomagnetic variation near the injection well was not detected during the injection of water.
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