The present study analyses the possibility to implement a WellBore Heat exchanger (WBHX) on one of the largest European oil fields: the Villafortuna Trecate oilfield. The research is focused on the optimization of the WBHX to maximize the extracted heat. Hence, a numerical model of a WBHX has been setup. The simulations have considered the use of two different heat transfer fluids: water and diathermic oil. It was also tried different internal diameters of the pipes in order to optimize the geometrical configuration for the specific case study. To assess the energy conversion by an ORC plant a model has been build. The goal was to evaluate the possible working fluid as well as validate the MIT correlation. The R-C318 has been selected and a good agreement between MIT correlation and the ORC plant model has been highlighted. The simulations demonstrated the importance to consider the change of fluid properties inside the exchanger. With a water flowrate of 15 m(3)/h the optimum condition is obtained; under such condition, the thermal power is 1.5 MW and the net electrical power is 134 kW for single well. The results lead also to conclude that the water is the best heat transfer fluid. (C) 2015 Elsevier Ltd. All rights reserved.