Effect of cethyltrimethylammonium bromide (CTAB) on the precipitation of silica from geothermal water was examined. CTAB did not react with monosilicic acid and only polysilicic acid was precipitated by CTAB. There was an optimum pH for the precipitation of silica. Polysilicic acid was precipitated more easily with increasing their particle size. In the concentration range of 10-7 -10-4 mol dm-3 of CTAB, the amount of precipitated silica inreased with increasing concentration of CTAB and most of polysilicic acid was precipitated at CTAB concentration of 10-4 mol dm-3 within 5 min. It is suggested that the decrease in the negative charge on polysilicic acids due to the electrostatic adsorption of cethyltrimethylammonium (CTA+) ions on the surface of polysilicic acids and the hydrophobic interaction between CTA+ ions adsorbed on different polysilicic acids accelerate polymerization reaction between polysilicic acids to cause precipitation of silica.
Exploratory well DY-1 in the Hohi geothermal field (Kyushu, Japan) is drilled to a depth of 2618 meters into a liquid-dominated reservoir with maximum temperature in the uncased region around 185°C. During 6 months in 1982, the well was continuously discharged at rates between 16 kg/s and 60 kg/s with the average rate being about 25 kg/s. Wellhead pressure and separator water/steam discharge rates were measured throughout the interval. Based upon these measurements, calculations of the flow within the wellbore have been performed with a two-phase wellbore simulator. It is shown that excellent agreement between calculations and measurements can be obtained using the Dukler frictional model and the Hughmark liquid-holdup correlation. Further calculations using the wellbore simulator have been performed for the purpose of investigating the effects of changing the well design upon the performance of well DY-1 and analyzing the catastrophic decline in performance of well DY-1 caused by calcite deposition.
Measurements of seismic noise have been made in the Takenoyu geothermal area, central Kyushu, Japan in order to study the nature of waves originated from geothermal activities. Spatial variation of the average amplitude shows high levels of seismic noise extending over the hot ground. We consider such seismic noise is caused by geothermal activities. The geothermal seismic noise mainly consists of body wave and the depth of the origin is estimated to be about 10 to 30 m below the surface. Considering the distribution of the underground temperature of this area, the origin of the geothermal seismic noise may be boiling of hot water in the upper part of the geothermal reservoir.
ELF-MT survey was carried out in a study of geothermal structure of the Noya geothermal area, Oita Prefecture. ELF-MT method uses natural electomagnetic field in Schumann resonant frequency band from 8 to 20 Hz (3 frequencies). Resistivity maps were compiled from 37 sites at approximately 0.5 km spacing. Major low resistivity zones extended NE-SW direction along the Noya-Mizuwake fault. The lowest apparent resistivity zone, less than 25 ohm-m, is associated with the Noya hot springs and alteration zones. This zone (A-zone) is the most active geothermal zone in this studied area. Temperature log in the test hole 51-WT-2, drilled near the lowest resistivity zone, shows 110°C at 60m depth and 112°C at 700m depth. This indicates that hot water was stored within very shallow formation in this low resistivity zone. The extensive alteration zone (B-zone) is located in 1 or 2 kilo-meters distant from the Noya hot springs, in the direction of Kodairadani. A high resistivity zone of more than 250 ohm-m is found in the center of B zone, and is surrounded by low resistivity zones. The temperature log in the test hole 51-WT-1, drilled near this high resistivity zone, shows maximum temperature of 177°C at 700m depth (the bottom of the hole). High resistivity in the B-zone may be caused by presence of dike rock or silicification. The apparent resistivity mapping by ELF-MT technique, thus, indicated clearly the two different typ of the geothermal zone in this area.
A seisminc survey was carried out from 1980 to 1983 in Takinoue (Kakkonda) geothermal area, Iwate prefecture. Effects of steam supply system, activity of fumaroles and stream of river on seismic noise were investigated. The instruments used for in-situ measurements consist of three-component seismometers, amplifier and tape recorder. The system has flat response to ground velocity in the frequency range of 1 to 40Hz. The data was analyzed in the laboratory with microcomputer. The original analog data were digitized at 100/sec. Fourier spectra of 2048 selected samples were computed using the fast Fourier transform. The results are summarized as follows. 1) The seismic waves produced by the stream of the Kakkonda river have spectral characteristics of high frequency above 15 Hz, and the noise amplitude drops to background level within a distance of about 40 m from the riverside. 2) The seismic waves generated by the activities of the steam supply system, mainly production well, re-injection well and separator, have spectral characteristics of high frequency above 20Hz. The radius of influence is about 150m for the production wells and about lOm for the steam gathering pipeline. 3) Fumaroles and hot springs seem to be the source of high frequency seismic noise which may locally have high amplitude. The seismic noise in the frequency band 5-15 Hz is dominant in the wide area around fumaroles and hot springs. It may be assumed that low frequency waves are generated by deeper convection of steam and hot water.
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