Geochemical characteristics of silica scales precipitated from the geothermal water at the Onuma geothermal power plant.
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The geochemical characteristics of geothermically heated water can reveal deep geothermal processes, leading to a better understanding of geothermal system genesis and providing guidance for improved development and utilization of such resources. Hydrochemical and hydrogen oxygen isotope analysis of two geothermal field (district) hot springs based on regional geothermal conditions revealed that the thermal water in the Litang region is primarily of the HCO 3 Na type. The positive correlations found between F − , Li 2+ , As + , and Cl − indicated a common origin, and the relatively high Na + and metaboric acid concentrations suggested a relatively long groundwater recharge time and a slow flow rate. The values of δD and δ 18 O were well distributed along the local meteoric line, indicating a groundwater recharge essentially driven by precipitation. The thermal reservoir temperature (152°C–195°C) and thermal cycle depth (3156–4070 m) were calculated, and the cold water mixing ratio (60%–68%) was obtained using the silica-enthalpy model. Finally, hydrogeochemical pathway simulation was used to analyze the evolution of geothermal water in the region. The results were further supported by the high metasilicate content in the region. Of the geothermal fields in the region, it was found that the Kahui is primarily affected by albite, calcite precipitation, and silicate, while the Gezha field is primarily affected by calcite dissolution, dolomite precipitation, and silicate.
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The scale precipitation is a major issue at geothermal power plants as it reduces the production rate of geothermal energy. The scale precipitates at different physical and chemical conditions in each geothermal power plant as a result from a fluid–rock interaction for the specific conditions at each plant. Thus, it is important to understand the chemical characteristics and precipitation process of the scale from geothermal fluid. The information on the process of transportation of metals and its precipitation from hydrothermal fluid in general will be useful to understand the formation of hydrothermal ore deposit. In this study, we have examined the chemical characteristics of silica scaling from the Onuma geothermal power plant at Akita Prefecture, Japan. The scale consists of mainly amorphous silica and trace amounts of smectite, kaolinite, and euhedral pyrite. Chemical composition of silica scale indicates that Fe content scale shows positive correlation with Pb, Cu, and REE. These elements probably incorporate into pyrite in silica scale. The texture of pyrite suggests that pyrite is possible to crystalize prior to the growth of amorphous silica. Silica scale gradually changes its chemical composition from the production well toward the reinjection well. Concentrations of SiO2, Fe2O3, MgO, and MnO in silica scale significantly decrease toward to the reinjection well from the production well, and those of Al2O3, LOI, and alkali and alkali earth elements (Na2O, K2O, and CaO) increase toward to the reinjection well. Most of trace elements including REE in silica scale also significantly decrease toward to the reinjection well, and furthermore HREE decreases more extensively than LREE though alkali and alkali earth elements (Be, Rb, Sr, Cs, and Ba) increase toward to the reinjection well. The change of element concentration in silica scales can be utilized to understand the physical and chemical conditions in the pipes at the geothermal power plant.
Geothermal power
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Geothermal resources are abundantly available, low-cost, renewable, and clean. Therefore, the exploitation and utilization of geothermal resources would exert a great influence on society and economy. Fuzhou geothermal, which is on behalf of the medium and low temperature magmatite rock fissure type geothermal, is often with surface thermal manifestations and distributes zonally along the tectonic fissures. Aiming to investigate the origin of the Fuzhou geothermal field, this paper takes Fuzhou Guihu geothermal field as the research object, analyzing its geothermal background of regional tectonic characteristics. Special analyses of the geothermal water chemical and isotopic characteristics (including the formation and origin mode of ground water constants and trace elements, D/ 18 O isotopes) revealed that the underground hot water of Guihu was originated from precipitation and formed by the heating effect of the deep geothermal circulation. Based on isotopic fractionation, the calculated precipitation infiltration recharge elevation for the Guihu geothermal water is 536.3m. In the light of the surrounding topography, it is reasonably inferred that the Jialiang Mountain is the recharge source of the Guihu geothermal water.
Hot spring
Geothermal heating
Geothermal exploration
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The Pauzhetka geothermal production field in the southern part of the Kamchatka peninsula (Russia) supports an existing geothermal power plant. This geothermal field is a high-temperature, retrograde, low-sulfidation magmatic-hydrothermal system in an active island-arc volcanic setting. We present here a geochemical model for the magmatichydrothermal system, involving the following six main regions of the system: primary deep sodiumchloride waters, convective fissure, two-phase geothermal reservoir, aquifers, vadose zone, and surface. Moreover, the model takes fluxes between these regions and also mixing of cool underground water with geothermal fluid and condensed steam into account. The model has been verified using some analytical data of geothermal waters from a drill hole within the Pauzhetka geothermal field. Thermodynamic modeling using a Selektor-C program based upon the Gibbs free energy minimization provides the following results for the system: mineral composition, aqueous spiecies, Eh, pe, pH etc. In this study, quantity of aqueous species of the system under investigation at various temperatures and pressures and also in the presence/absence of atmospheric air has been estimated, implying that chemical analysis of samples from various drill depths is performed under the conditions of an analytical laboratory.
Carbonate minerals
Caldera
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