Žemės gelmių šiluma Lietuvoje: ekologiška, atsinaujinanti energijos rūšis
ENIn the context of geothermal field of Middle Europe of average intensity of heat flow density 30–60 mW/m2 Lithuania (especially its western part) is notable for a particularly high potential of geothermal energy (heat flow reaching up to 80–100 mW/m2). Resources of geothermal energy of Lithuania are accumulated in two stages: 1) magmatic– metamorphic rocks (mostly granitoids) of crystalline basement of temperature over 100˚C and 2) terrigenous rocks of sedimentary cover (thickness of cover reaching 2 300 m). There are three geothermal aquifers: a) Cambrian (thickness up to 200 m and temperature 70–95˚C), b) Lower-Middle Devonian (~250 m, 35–50˚C), c) Middle-Upper Devonian (up to 200 m, 20–30˚C). Reservoirs are sandstones, sands, siltstones, silts, which porosity reaches from 6–20% (in Cambrian) to 20–30% (in Devonian) and permeability accordingly 5–380 mD to 15–7.000 mD. Mineralization of pore water varies between 15 and 200 g/l. The evaluated petrogeothermal resources up to the depth of 6 km in the western Lithuania are 298.5·109. Most of these resources are accumulated in West Lithuania. The operating Klaipėda demonstration geothermal plant with looped circulation system is the only of this type in the Baltic Region. Deep-mounted pumps supply 38˚C saline (93 g/l) water from two production wells about 1 km deep. The temperature of water in heat pumps is raised to 70˚C and the heat is then transmitted to district heating network of Klaipėda city. The used geothermal water is pumped back to the layer through two injection wells. The overall capacity of the plant is 35 MW (13.6 – geothermal and 21.4 from subsidiary peak boiler). Heat costs are 0.0544 Lt/kWh. There also exist geothermal heat pump systems coupled with boilers for private houses of capacities up to 45 kW. Heat pump supplies heat for space heating, hot water production, warming up pool water or cooling in some cases.Expenses for heating during the season are about 1.2 Lt/m2. The guidelines for further utilization of geothermal resources in Lithuania sould emphasize: 1. Cambrian, lower–middle Devonian and middle-upper Devonian aquifers of geothermal water for heating, balneology, etc. in western Lithuania. 2. Shallow geothermal water utilization in the whole country for private space heating. 3. In more distant future, accomplishment of explorations in some bigger Lithuanian cities (Klaipėda, Palanga) or geologically favorable areas designed to elaborate petrogeothermal energy utilization projects for heating and power generation.
