The paper deals with the possible use of existing oil wells for geothermal energy production. A mathematical model., describing the process of exploitation of a borehole heat exchanger has been worked out. It was used for determining energy efficiency, employing the main parameter, i.e., flow of produced heat energy. The results of simulation of borehole heat exchanger operation in deep conditions of Iwonicz Zdroj field's depleted deposits (Polish Carpathians) are presented. A considerable part of oil deposits in the Carpathian region-a cradle of the worlds oil industry-are to be decommissioned. Owing to the high density of population, the wells are planned to be adapted for borehole heat exchangers for clean energy production for local purposes. The decommissioning costs will be avoided.