Application of existing wells as ground heat source for heat pumps in Poland

Lots of exploited deep wells in Poland are liquidated after drilling. Employment of these wells for district-heating requires the use of heat pumps for the improvement of the harnessed geothermal heat enthalpy. The Podkarpacie region in the south-eastern part of Poland is where the oil and gas industry was born. There are plenty of old wells (often over 100 years old) drilled by a precursive technique. Due to the depletion of hydrocarbon resources, these wells could be either liquidated, which is expensive, or used as borehole heat-exchangers, which may turn out to be profitable. In the latter case, the captured heat can be sold and liquidation delayed. A preliminary calculation of the energy resource from decommissioned wells in Poland and a simulation of the heat exchange achievable from depleted oil wells are presented in this paper. An economic analysis of systems with heat pumps and deep wells as borehole heat-exchangers follows. Conditions determining the profitability of geothermal heat-pumps in district-heating systems (including heat exchangers) are established. The unit cost of heat is defined, based on the mode of heat utilization. The unit price strongly depends on the operation characteristic of a heat pump and consequently on the parameters of a heating system. The results of the simulation and economic analysis show that the viability of borehole heat-exchangers is only weakly influenced by geological conditions and well parameters, and strongly influenced by the customers and cost of traditional energy carriers. Another important factor is how the heat exchanger is equipped and designed. The matching of wells to heat exchangers affects both the heat exchange during exploitation and the investment costs. Economic profitability is vital for the discussed solution. Among other advantages is the positive environmental aspect of the use of old wells for geothermal-heat harnessing. Moreover, this option creates the possibility of using heat sources locally and achieves partial independence of price trends for traditional fuels. Geothermal energy is often classified as renewable. By using the potential of the many wells across Poland (via heat exchangers), it should be possible to increase the share of the renewables in the energy balance of Poland.