In this paper, the use of a zero-mass extraction device has been simulated in the volcanic area of CampiFlegrei (Italy),one of the most promising geothermal districts of Italy.The sustainability of the heat extraction has been studied with a coupled model of the geothermal reservoir and the deep borehole heat exchanger. The reservoir model has been built using the SHEMAT software, the heat transfer in the deep borehole heat exchanger has been simulated using GEOPIPE, a pure conductive semi-analytical model. An iterative approach has been used to couple the two simulators. The work has demonstrated that the area of CampiFlegrei is a promising candidate to produce sustainable geothermal energy with a zero-mass extraction device. It is also demonstrated that the coupled model of reservoir and deep borehole heat exchanger is the best modelling approach when convective structures are present in the geothermal system, which can generate heat recovery effects.