We examine crystallization conditions for saturated brines of calcium, potassium, and magnesium chlorides from the Angara‑Lena artesian basin, Siberian Platform. The study focuses on temperatures matching actual thermal conditions in wells of the “Lithium” site at the Kovykta gas‑condensate field. This critical type of lithium‑bearing raw material is classified as hard-to-recover reserves. In most wells (depths to 2.2 km), rock temperatures in the upper geological section remain below 20 °C. During well operation, various salts precipitate from saturated magnesium-calcium chloride brines within the production line. This leads to rapid wellbore clogging and eventual production shutdown. Thermodynamic analysis of phase diagrams reveals that crystallization yields antarcticite CaCl₂·6H₂O, tachhydrite Mg₂CaCl₆·12H₂O, minor amounts of carnallite KMgCl₃·6H₂O, bischofite MgCl₂·6H₂O, and several other chlorides, depending on temperature. At temperatures above 55 °C, salt precipitation becomes negligible. Thermohydrodynamic simulations of a single flowing well under hydrogeological conditions similar to those at the Kovykta area (southern Siberian Platform) demonstrate the feasibility of long-term (1 month to 1 year) exploitation of saturated sodium-chloride and calcium-chloride lithium-bearing brines. Such operations can yield lithium production rates of 31.2 to 4.2 t per well.

3D analysis of the magma transport and accumulation mechanism in the structure and basement of the Klyuchevskoy volcano preceding 11 eruptions in 2003-2021 has been performed. Using the Frac-Digger method and seismological data from the Kamchatka Branch Federal Research Center United Geophysical Survey Russia Academy of Sciences it has been shown that magma transport from the deep crustal magma chamber (−30 km) is carried out in the vertical fracturing (dykes) mode to the peripheral shallow magma chamber (+1 km). The feeding dykes orientation corresponds to geomechanical conditions of radial or N-NNE extension. This is followed by inclined dykes and sills of various orientations from the peripheral magmatic chamber. Magma accumulation in the peripheral magmatic chamber in the form of sills (in the horizontal fracturing mode at elevations of +0,3 to +2,3 km) contributes to the efficiency of magma degassing and heat exchange with meteoric waters, and to the formation of a high-pressure vapour-gas reservoir with subsequent venting of the volcano channel and its eruption. Three-dimensional analysis of the distribution of flank eruptions of the Klyuchevskoy volcano in 1932-2021 (16 cinder cones) shows their association with two main low-inclined structural surfaces. Changes in the drainage level of the magmatic system are reflected in the volumes and geochemical history of the 1932-2021 flank eruption products.

The temperature in the Valley of Geysers (Kamchatka) geothermal reservoir calculated using the feldspar Na-K-geothermometer has been steadily increasing over the past 10 years on average from 165 to 235 °C, which is close to the temperature values of a hydrothermal explosion of the steam and water mixture. For the analysis of chemical geothermometers, TOUGHREACT-simulation was used, with the help of which the previously known Na-K feldspar geothermometer was reproduced on a single-element model and new formulas were obtained for three Na-K geothermometers: zeolite, smectite, and based on volcanic glass. Data of chemical analysis for the period 1968-2018, in which the chloride ion is considered as an inert tracer of geofiltration processes, indicates that after 2007 a significant inflow of infiltration water (its mass fraction is estimated from 5 to 15 %) into the Geyser reservoir. It is assumed that the Na-K increased values of the feldspar geothermometer are not the result of the temperature increase in the Geyser reservoir, but the effect of smectite water dilution.

Numerical 3D model of Mutnovsky geothermal field (Dachny springs), which consist of 517 elements and partially takes into account double porosity, was developed in 1992-1993 using computer program TOUGH2. Calibration of the model was based on data from test yield of the wells and initial distribution of temperature and pressure in the reservoir. This model was used for techno-economic justification of power plant construction (Mutnovskaya GeoES, 2002). The model was recreated in the program PetraSim v.5.2, the calibration was carried out using additional data on production history before year 2006 and inversion iTOUGH2-EOS1 modeling. Comparison of reservoir parameters, estimated using inversion modeling, with previous parameter estimations (given in brackets) showed the following: upflow rate of heat-transfer agent in natural conditions 80.5 (54.1) kg/s, heat flux enthalpy 1430 (1390) kJ/kg, reservoir permeability 27∙10^–15-616∙10^–15 (3∙10^–15-90∙10^–15) m². Inversion modeling was also used to estimate reinjection rates, inflow of meteoric water in the central part of geothermal field and compressibility of reservoir rocks.

Data on fluid chemistry and rock mineralogy are evaluated for a number of geothermal fields located in the volcanic arc of Japan and Kamchatka (Russia). Common chemical characteristics are identified and used to define scenarios for detailed numerical simulations of coupled thermohydrodynamic-chemical (THC) processes. The following scenarios of upward flow of parental geothermal fluid were investigated: single-phase conditions, 260°C at the bottom, two-phase conditions 300C at the bottom, heat pipe conditions, 260°C at the bottom. According to the results of THC modeling for the single-phase upward flow scenario, the main secondary minerals in the productive zone are wairakite, quartz, K-feldspar and chlorite. THC modeling of the two-phase upward flow scenario shows quartz, K-feldspar (microcline), wairakite and calcite as the major secondary minerals in the productive zone in the model. THC modeling of heat pipe conditions shows no significant secondary mineral deposition. Secondary mineral deposition can lead to significant porosity reduction over a century time period under mass-flow conditions, and complete fracture sealing will occur within sufficient time under both single-phase and two-phase upward flow scenarios.

Geothermal energy is the driving force behind geothermal processes: volcanic, hydrothermal and seismic, and manifests itself in areas of modern volcanism in the form of active volcanoes, hydrothermal systems and earthquakes. Hydrothermal systems represent the "useful part" of geothermal energy, which can be used within geothermal fields to produce electrical and thermal energy, as illustrated by the examples of the Mutnovsky and Pauzhetsky geothermal fields. Active volcanoes have not found any application in the energy sector. However, the energy contained in them can be released in the form of hydrothermal explosions, as discussed in the example of the cone of Avacha volcano. Earthquakes are the most dangerous mode of geothermal energy release. The study of anomalous phenomena of hydrodynamic nature in active hydrothermal systems and on active volcanoes continues.

В конце 1966 г. на Паужетском геотермальном месторождении начала работать ГеоТЭС. Промышленная разработка этого месторождения показала, что тепловой режим эксплуатационного участка изменяется весьма существенно, хотя по результатам первого опытно-эксплуатационного выпуска можно было надеяться на стабилизацию геотемпературных условий во время длительной эксплуатации ...