The deep well SN-7D is located in the Sumikawa geothermal System, Sengan area, Northeast Honshu, and is one of the most productive wells in Japan. It produced 161 t/h of steam and 318 t/h of hot water during the flow test in the fall of 1988. The geothermal fluids originate mainly from fracture zones in the deepest part of the well, where many secondary inclusions are observed in healed fracture planes in the tonalitic intrusives. The Sumikawa geothermal system is located on the northern flank of the andesitic stratovolcano of Akita-Yakeyama which has had several historical eruptions. Lacustrine deposits of siltstone and tuff alternations of Pleistocene ages are distributed beneath Akita-Yakeyama. Tertiary formations are composed of mainly dacite, andesite and black shale, underlying the lacustrine deposits. They are intruded by the tonalite at the deepest level of the well. The fluid inclusions occur mainly along fracture trails, clearly denoting their secondary origin in igneous quartz crystals of the tonalite and volcanic rocks as well as in late hydrothermal veins of calcite, anhydrite and wairakite. The calcite and wairakite also host a few primary inclusions. Four core samples from 1505, 1921, 2292, and 2484 m depth and two samples of cuttings, with wairakite from 1045 m and anhydrite from 1435 m, have fluid inclusions suitable for microthermometric measurements. The widespread coexistence of liquid-rich and vapor-rich inclusions indicates extensive boiling in the host-water dominated system. The Th and Tm characteristics of fluid inclusions in wairakite and some calcite in veins is consistent with the measured temperature and salinity of geothermal fluids from SN-7D. High and intermediate salinity inclusions are found exclusively in healed fracture planes in the igneous quartz of the tonalite. Their higher temperature range suggests that they might be related to previous thermal events.
For soil gases from the Doroyu-Kawarage geothermal field in northern Japan, the concentrations of Rn, H2, CH4, CO2 and rare gases (He and Ne) together with isotopic ratios of CO2 and He (δ 13C of C02 and 3He/4He) were measured. In presently developing geothermal field to the northern part of Doroyu fault, Rn concentrations of soil gases are clearly higher than those to the southern part. On the other hand, the distribution of low δ 13C values (-20∼-24‰) corresponds to that of Sanzugawaformation.This formation contains the organic matter underlying only to the northern part of the fault. However, higher δ 13C values to the northern part, coexist with high concentration of H2. Soil gas samples from Kawarage and Doroyu geothermal manifestations contain high concentrations of Rn, H2 and CO2, and the δ 13C values also are extremely high. Therefore, it is inferred that CO2 derived from a deep-seated geothermal system are added to those originated from organic matter in the Sanzugawa formation. These data indicate that the δ 13C values of CO2 can be useful in geothermal prospecting in addition to information provided by H2 measurement. Soil gases from Kawarage and the vicinity do not give the high Rn concentrations, in spite of the high Hg concentrations. Such a fact may give the information on the alteration by the secondary hydrothermal water without U and Th, which is originated from the vaporization of deep-seated geothermal water. Furthermore, the 3He/4He and 4He/20Ne ratios of Kawarage fumarolic gas are 9.5×10-6 and 180, respectively, indicating that the He is originated from magmatic gas. This fact is consistent with a consideration that the heat source of this geothermal field is the magma of the neighboring Quaternary volcanos such as Mt. Takamatsudake and Mt. Kabuto.
This paper describes a tracer response analysis for water-steam flow through a porous medium. The experiments are carried out by using a packed, glass beads bed submerged horizontally in a thermostat at a temperature of more than 373K. Water is injected continuously into the bed under a constant pressure gradient and is heated from the surrounding, and a part of the water vaporizes in the bed. When the temperature and the flow rates of steam and hot water attain to be steady, 0.5 cm3 of ammonia water solution (about five volume percent of NH3) is injected into the bed as a tracer by using a syringe for a few seconds. The tracer vaporizes in the bed, and ammonia gas flows out of the bed with steam. Then, the NH3 content in the exit gas is measured by a gas chromatography every a few minutes. The experimental results of tracer response are analyzed by a onedimensional, mathematical model which describes mass transfer in water-steam flow under the boiling condition. The conclusions are as follows: (1) The mathematical model proposed in this paper describes experimental tracer response in gas phase of water-steam flow accompanied by boiling. (2) The analysis of the tracer response gives the leading edge of boiling (the position at which water starts to boil in a porous medium). (3) The theoretical value of the leading edge of boiling is consistent with the experimental one.
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