Underground oil shale mining has been applied for ninety years in Estonian deposit in the middle-north part of Baltic oil shale deposit. The underground mining method of oil shale creates underground free space and the mine workings are filled with water after closure, which makes issues of land stability topical.
Underground water pools or technogenic water bodies with all-the-year-round stable temperature are formed in the filled underground of oil shale mines. These water bodies have a potential for use as a source of heat for heat pumps and reduction of wintertime heating costs. The aim of this research is to calculate the amount of mine water in closed or abandoned oil shale mines in the central part of Estonian oil shale deposit and offer solutions for usage of undermined areas.
Using mine water as a source of heat for heat pump stations means the possibility of using geothermal energy. The first pilot pump in Estonia was launched in Kiikla settlement in 2011. The best solution for such systems is a heat pump complex near Ahtme thermal power plant. The optimal size for the heat pump at Ahtme is 10 MW heat production. Different methods of heat collection for heat pump plants can be applied when other mines will be closed in the future.
A 3D-model of the mined underground area has been created using geometric data of mine plans, acts of closed mines, as well as borehole and land survey data. The main tools chosen for spatial modelling were spreadsheets and Microsoft Access databases for systemising and querying data, MapInfo Professional for georeferencing, Vertical Mapper for interpolating and grid calculations and MODFLOW for pumping simulation. Each step of model creation involved analysis and decision on which values should be used to obtain modelling results. Layer thicknesses and required properties of water body were calculated using interpolated grids and surface elevations.
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