Purpose.In this paper we present and validate an analytical model of water inflow and rising level in a flooded mine and examine the model robustness and sensitivity to variations of input data considering the examples of three closed hard-coal mines in Germany. Methods. We used the analytical solution to a boundary value problem of radial ground water flow to the shaft, treated as a big well, and water balance relations for the series of successive stationary positions of a depression cone to simulate a mine water rebound in the mine taking into account vertical distribution of hydraulic conductivity, residual volume of underground workings, and natural pores. Findings. The modeling demonstrated very good agreement with the measured data for all the studied mines. The maximum relative deviation for the mine water level during the measurement period did not exceed 2.1%; the deviation for the inflow rate to a mine before its flooding did not exceed 0.8%. Sensitivity analysis revealed the higher significance of the residual working volume and hydraulic conductivity for mine water rebound in the case of thick overburden and the growing significance of the infiltration rate and the flooded area size in the case of lower overburden thickness. Originality.The developed analytical model allows realistic prediction of transient mine water rebound and inflow into a mine with layered heterogeneity of rocks, irregular form of the drained area, and with the inflow/outflow to a neighboring mine and the volume of voids as a distributed parameter without gridding the flow domain performed in numerical models. Practical implications.The study demonstrated the advantages of analytical modeling as a tool for preliminary evaluation and prediction of flooding indicators and parameters of mined out disturbed rocks. In case of uncertain input data, modeling can be considered as an attractive alternative to usually applied numerical methods of modeling ground and mine water flow.

Purpose. Evaluation of the efficiency of open geothermal systems in flooded and drained mines of the Donetsk basin for heat supply of buildings with maintaining a safe mine water level. Methods. Both circulation and non-return geothermal systems for the mine water heat recovery are analyzed. We proposed the energy and cost criteria for evaluating the effectiveness of open geothermal systems based on a comparison of the produced thermal energy with the energy costs for its production. The criteria use the relationships of thermodynamics, hydraulics, analytical formulas for calculation of ground water flow and methods to calculate the heat demand of indoor spaces. Findings. The estimated ranges of thermal capacity from a few tens kW to a few MW and a coefficient of performance (COP) conversion factor of 3.5-6.8 achievable by geothermal systems for the studied closed mines of Donbas correlate well with the values of these indicators at open geothermal systems operated in different countries, which shows the technical and economic feasibility of the installation to cover local heat demands. The possibility to fully cover the needs for thermal energy is shown on the example of buildings with office spaces for staying of a few hundred people. We demonstrate how to preliminary calculate the parameters of mine water circulation with maintaining the safe level in terms of keeping the ground water quality in the areas adjacent to the mine. Originality. The developed criteria and calculation methodology allow to realistically evaluate the parameters of the efficiency of operation for open non-return and circulation geothermal systems, taking into account mining, geological and technology conditions, to prioritize the exploration of geothermal resources in mines and to evaluate the parameters of mine water circulation with maintaining the safe mine water level. Practical implications. The study showed the feasibility of installation and effective operation of open geothermal systems at the mines of the Donetsk basin for heat supply of buildings located in the adjacent areas with maintaining a safe mine water level.

The study aims to develop a method of effectiveness evaluation for geothermal heat recovery in closed mines of Donbas using relations of heat transfer theory in rocks and fluids. Geothermal heat is proposed to recover using coaxial geothermal probes to be installed in flooded closed mines. As a result of evaluation and ranking, five top promising sites with the highest expected performance indicators among 27 closed mines located in Donbas have been identified. The evaluation method takes into account geological settings, mine condition, and heat exchange parameters of the probe with mine water. The locations of the most promising sites were found to correlate with the areas of higher geothermal flux and the deeper mines. The results obtained can be used in feasibility studies on installation and operation of geothermal probes in closed mines.