Thermal and permeability structure and recharge conditions of the low temperature Paratunsky geothermal reservoirs in Kamchatka, Russia

The Paratunsky low temperature geothermal field has been operating since 1964. During the period of exploitation from 1966 to 2014, 321 Mt of thermal water (Cl-Na, Cl-SO4-Na composition, M up to 2600 ppm) with temperatures of 70–100°С was extracted and used for district heating, balneology and greenhouses. The structure of the 40 km3 Paratunsky low temperature (80–110 °C) geothermal volcanogenic reservoir was geometrically characterized, hot water upflow regions and the 3D permeability distribution were identified with hydrogeological data, and the distribution of the feed zones and 3D temperatures were constrained by 3D spline approximation. Water isotope and gas (N2, 96–98%) data analysis indicated that the main recharge region of the Paratunsky geothermal reservoirs is the Viluychinsky Volcano (2173 masl) and adjacent highly elevated structures, located 25 km south from the geothermal field. Production zones coinciding with dip angle fractures occur in the condition of radial extension (possibly caused by magmatic origin heat sources below the reservoir) and hydraulic fracturing (possibly caused by the elevated position of the Viluychinsky Volcano’s recharge region). TOUGH2 modeling of the thermo-hydrodynamic natural state and the history of exploitation (involving pressure, temperature and chemical changes response to utilization) between 1965 and 2014 yield estimates of hot water upflow rates (190 kg/s), the production reservoir compressibility (up to 4 × 10−8 Pa−1) and permeability (up to 1.4 D). Modeling confirmed areal discharge of the thermal water from the production reservoir in the top groundwater aquifer (top Dirichlet boundary conditions). Modeling of the chemical (Cl-) history of exploitation provides an explanation of gradual Cl- accumulation due to the inflow of chloride-containing water through the eastern (open) boundary of the geothermal reservoirs. Modeling of the long-term exploitation until 2040 with an exploitation load of 256 kg/s merely shows a low pressure drop (0.7 bar) and an insignificant drop of temperatures in the production geothermal reservoir of the Paratunsky geothermal field.