Oil and gas wells at the end of their life span, are generally plugged, the landscape is restored and abandoned. Thus, all further possibilities to convert the wells for alternative use is lost. One possibility to re- or further use the wells is to re-complete and use the wells for geothermal energy production. The conversion of not economic oil and gas wells to produce renewable energy seems to be a valid business opportunity considering that not only geothermal energy is produced but also a positive impact on CO2 emission reduction is given. The thesis studies the potential geothermal energy production from typical oil and gas wells in the Vienna basin, its use and applications. The energy, which can be produced by a borehole heat exchanger in reverse circulation was calculated, for wells at different depth, different thermal rock conductivities, various circulating flowrates, and several out- and inflow temperatures. The results are presented in plots within this thesis. The diagrams allow a quick evaluation of the energy potential the individual well can produce and estimate the opportunity level of the anticipated business application. Applications for geothermal energy produced from oil and gas wells at the end of their lifespan were investigated. Common business applications were chosen to explain the use of the calculated general information and demonstrate its value at a first glance to understand the business opportunity. Finally, because not only the well itself, but also the adjacent reservoir can be used as thermal storage, a literature review on the Neubrandenburg aquifer thermal energy storage was examined. Its efficiency and reliability as well as the problems of this project are discussed.